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1
Sardo, Rachel. "Anomalous effects while cooling liquid water." Diss., Online access via UMI:, 2007.
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Tan, Junyi, and 譚軍毅. "Investigation of novel liquid desiccant cooling system." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2009. http://hub.hku.hk/bib/B42664251.
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Tan, Junyi. "Investigation of novel liquid desiccant cooling system." Click to view the E-thesis via HKUTO, 2009. http://sunzi.lib.hku.hk/hkuto/record/B42664251.
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Hausgen, Paul E. "An analysis of mono-dispersed liquid droplet cooling." Thesis, Georgia Institute of Technology, 1994. http://hdl.handle.net/1853/16746.
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Hublitz, Astrid. "Efficient energy storage in liquid desiccant cooling systems." kostenfrei, 2008. http://mediatum2.ub.tum.de/node?id=637243.
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Boysan, Mustafa Emre. "Analysis Of Regenerative Cooling In Liquid Propellant Rocket Engines." Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/12610190/index.pdf.
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High combustion temperatures and long operation durations require the use of cooling techniques in liquid propellant rocket engines. For high-pressure and high-thrust rocket engines, regenerative cooling is the most preferred cooling method. In regenerative cooling, a coolant flows through passages formed either by constructing the chamber liner from tubes or by milling channels in a solid liner. Traditionally, approximately square cross sectional channels have been used. However, recent studies have shown that by increasing the coolant channel height-to-width aspect ratio and changing the cross sectional area in non-critical regions for heat flux, the rocket combustion chamber gas side wall temperature can be reduced significantly without an increase in the coolant pressure drop.
In this study, the regenerative cooling of a liquid propellant rocket engine has been numerically simulated. The engine has been modeled to operate on a LOX/Kerosene mixture at a chamber pressure of 60 bar with 300 kN thrust and kerosene is considered as the coolant. A numerical investigation was performed to determine the effect of different aspect ratio cooling channels and different number of cooling channels on gas-side wall and coolant temperature and pressure drop in cooling channel.
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Omer, Muhammad. "Impingement Cooling: Heat Transfer Measurement by Liquid Crystal Thermography." Thesis, Linköping University, Applied Thermodynamics and Fluid Mechanics, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-52859.
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In modern gas turbines parts of combustion chamber and turbine section are under heavy heat load, for example, the rotor inlet temperature is far higher than the melting point of the rotor blade material. These high temperatures causes thermal stresses in the material, therefore it is very important to cool the components for safe operation and to achieve desired component life. But on the other hand the cooling reduces the turbine efficiency, for that reason it is vital to understand and optimize the cooling technique.
In this project Thermochromic Liquid Crystals (TLCs) are used to measure distribution of heat transfer coefficient over a scaled up combustor liner section. TLCs change their color with the variation of temperature in a particular temperature range. The color-temperature change relation of a TLC is sharp and precise; therefore TLCs are used to measure surface temperature by painting the TLC over a test surface. This method is called Liquid Crystal Thermography (LCT). LCT is getting popular in industry due to its high-resolution results, repeatability and ease of use.
Test model in present study consists of two plates, target plate and impingement plate. Cooling of the target plate is achieved by impingement of air coming through holes in the impingement plate. The downstream surface of the impingement plate is then cooled by cross flow and re-impingement of the coolant air.
Heat transfer on the target plate is not uniform; areas under the jet which are called stagnation points have high heat transfer as compare to the areas away from the center of jet. It is almost the same situation for the impingement plate but the location of stagnation point is different. A transient technique is used to measure this non-uniform heat transfer distribution. It is assumed that the plates are semi-infinitely thick and there is no lateral heat transfer in the plates. To fulfill the assumptions a calculated time limit is followed and the test plates are made of Plexiglas which has very low thermal conductivity.
The transient technique requires a step-change in the mainstream temperature of the test section. However, in practical a delayed increase in mainstream temperature is attained. This issue is dealt by applying Duhamel’s theorem on the step-change heat transfer equation. MATLAB is used to get the Hue data of the recorded video frames and calculate the time taken for each pixel to reach a predefined surface temperature. Having all temperatures and time values the heat transfer equation is iteratively solved to get the value of heat transfer coefficient of each and every pixel of the test surface.
In total fifteen tests are conducted with different Reynolds number and different jet-to-target plate distances. It is concluded that for both the target and impingement plates, a high Reynolds number provides better overall heat transfer and increase in jet-to-target distance
decreases the overall heat transfer.
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Zhou, Zhipeng (Joe Zoe). "Performance analysis of hybrid liquid desiccant solar cooling system." Thesis, Queensland University of Technology, 2009. https://eprints.qut.edu.au/40088/1/Zhipeng_Zhou_Thesis.pdf.
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This thesis investigates the coefficient of performance (COP) of a hybrid liquid desiccant solar cooling system. This hybrid cooling system includes three sections: 1) conventional air-conditioning section; 2) liquid desiccant dehumidification section and 3) air mixture section. The air handling unit (AHU) with mixture variable air volume design is included in the hybrid cooling system to control humidity. In the combined system, the air is first dehumidified in the dehumidifier and then mixed with ambient air by AHU before entering the evaporator. Experiments using lithium chloride as the liquid desiccant have been carried out for the performance evaluation of the dehumidifier and regenerator. Based on the air mixture (AHU) design, the electrical coefficient of performance (ECOP), thermal coefficient of performance (TCOP) and whole system coefficient of performance (COPsys) models used in the hybrid liquid desiccant solar cooing system were developed to evaluate this system performance. These mathematical models can be used to describe the coefficient of performance trend under different ambient conditions, while also providing a convenient comparison with conventional air conditioning systems. These models provide good explanations about the relationship between the performance predictions of models and ambient air parameters. The simulation results have revealed the coefficient of performance in hybrid liquid desiccant solar cooling systems substantially depends on ambient air and dehumidifier parameters. Also, the liquid desiccant experiments prove that the latent component of the total cooling load requirements can be easily fulfilled by using the liquid desiccant dehumidifier. While cooling requirements can be met, the liquid desiccant system is however still subject to the hysteresis problems.
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Crafton, Elyssa Farah. "Measurements of the evaporation rates of heated liquid droplets." Thesis, Georgia Institute of Technology, 2001. http://hdl.handle.net/1853/17589.
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King, Calvin R. Jr. "Thermal management of three-dimensional integrated circuits using inter-layer liquid cooling." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/44759.
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Heat removal technologies are among the most critical needs for three-dimensional (3D) stacking of high-performance microprocessors. This research reports a 3D integration platform that can support the heat removal requirements for 3D integrated circuits that contain high-performance microprocessors in the 3D stack.
This work shows the use of wafer-level batch fabrication to develop advanced electrical and fluidic three-dimensional interconnect networks in a 3D stack. Fabrication results are shown for the integration of microchannels and electrical through-silicon vias (TSVs). A compact physical model is developed to determine the design trade-offs for microchannel heat sink and electrical TSV integration. An experimental thermal measurement test-bed for evaluating a 3D inter-layer liquid cooling platform is developed. Experimental thermal testing results for an air-cooled chip and a liquid-cooled chip are compared. Microchannel heat sink cooling shows a significant junction temperature and heat sink thermal resistance reduction compared to air-cooling. The on-chip integrated microchannel heat sink, which has a thermal resistance of 0.229 °C/W, enables cooling of >100W/cm² of each high-power density chip, while maintaining an average junction temperature of less than 50°C. Cooling liquid is circulated through the 3D stack (two layers) at flow rates of up to 100 ml/min.
The ability to assemble chips with integrated electrical and fluidic I/Os and seal fluidic interconnections at each strata interface is demonstrated using three assembly and fluidic sealing techniques. Assembly results show the stacking of up to four chips that contain integrated electrical and fluidic I/O interconnects, with an electrical I/O density of ~1600/cm².
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Wei, Xiaojin. "Stacked Microchannel Heat Sinks for Liquid Cooling of Microelectronics Devices." Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/4873.
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A stacked microchannel heat sink was developed to provide efficient cooling for microelectronics devices at a relatively low pressure drop while maintaining chip temperature uniformity. Microfabrication techniques were employed to fabricate the stacked microchannel structure, and experiments were conducted to study its thermal performance. A total thermal resistance of less than 0.1 K/W was demonstrated for both counter flow and parallel flow configurations. The effects of flow direction and interlayer flow rate ratio were investigated. It was found that for the low flow rate range the parallel flow arrangement results in a better overall thermal performance than the counter flow arrangement; whereas, for the large flow rate range, the total thermal resistances for both the counter flow and parallel flow configurations are indistinguishable. On the other hand, the counter flow arrangement provides better temperature uniformity for the entire flow rate range tested. The effects of localized heating on the overall thermal performance were examined by selectively applying electrical power to the heaters. Numerical simulations were conducted to study the conjugate heat transfer inside the stacked microchannels. Negative heat flux conditions were found near the outlets of the microchannels for the counter flow arrangement. This is particularly evident for small flow rates. The numerical results clearly explain why the total thermal resistance for counter flow arrangement is larger than that for the parallel flow at low flow rates.
In addition, laminar flow inside the microchannels were characterized using Micro-PIV techniques. Microchannels of different width were fabricated in silicon, the smallest channel measuring 34 mm in width. Measurements were conducted at various channel depths. Measured velocity profiles at these depths were found to be in reasonable agreement with laminar flow theory. Micro-PIV measurement found that the maximum velocity is shifted significantly towards the top of the microchannels due to the sidewall slope, a common issue faced with DRIE etching. Numerical simulations were conducted to investigate the effects of the sidewall slope on the flow and heat transfer. The results show that the effects of large sidewall slope on heat transfer are significant; whereas, the effects on pressure drop are not as pronounced.
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Hui, Sam S. B. Massachusetts Institute of Technology. "Design and implementation of liquid cooling system for ArchiMITes vehicle." Thesis, Massachusetts Institute of Technology, 2011. http://hdl.handle.net/1721.1/69512.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 27).
MIT Vehicle Design Summit is building ArchiMITes, a lightweight hybrid vehicle with a modular auxiliary power unit. For testing purposes, the vehicle platform will first be built as an all-electric vehicle. It will be powered by five lithium ion batteries that generate a total of 700 W of heat. Without a cooling system, the batteries will quickly rise above 50 'C and become damaged. This project seeks to design and put together a liquid cooling system to remove the heat from the batteries. Calculations indicate that the battery cell temperature will be 17.39 'C above the ambient temperature. This temperature difference incorporates a factor of safety of 2. Further studies on battery placement, working fluid fill methods, and fan and pump control are recommended.
by Sam Hui.
S.B.
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Al-Neama, Ahmed Fouad Mahmood. "Serpentine minichannel liquid-cooled heat sinks for electronics cooling applications." Thesis, University of Leeds, 2018. http://etheses.whiterose.ac.uk/20318/.
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The increasing density of transistors in electronic components is leading to an inexorable rise in the heat dissipation that must be achieved in order to preserve reliability and performance. Hence, improving the thermal management of electronic devices is a crucial goal for future generations of electronic systems. Therefore, a complementary experimental and numerical investigation of single-phase water flow and heat transfer characteristics of the benefits of employing three different configurations of serpentine minichannel heat sink (MCHS) designs has been performed, to assess their suitability for the thermal management of electronic devices. These heat sinks are termed single (SPSMs), double (DPSMs) and triple path serpentine rectangular minichannels (TPSMs), and their performance is compared, both experimentally and numerically, with that of a design based on an array of straight rectangular minichannels (SRMs) in terms of pressure drop (ΔP), average Nusselt number (Nuavg) and total thermal resistance (Rth). The results showed that the serpentine channel bends are very influential in improving heat transfer by preventing both the hydrodynamic and thermal boundary layers from attaining a fully-developed state. The SPSM design provides the most effective heat transfer, followed by the DPSM and TPSM ones, both of which out-performed the SRM heat sink. The SPSM heat sink produced a 35% enhancement in Nuavg and a 19% reduction in Rth at a volumetric flow rate (Qin) of 0.5 l/min compared to the conventional SRM heat sink. These improvements in the heat transfer are, however, achieved at the expense of significantly larger ΔP. It was found that the incorporation of serpentine minichannels into heat sinks will significantly increase the heat-removal ability, but this must be balanced with the pressure drop requirement. Therefore, an experimental and numerical investigation of the benefit of introducing chevron fins has been carried out to examine the potential of decreasing pressure drop along with further thermal enhancement. This novel design is found to significantly reduce both the ΔP across the heat sink and the Rth by up to 60% and 10%, respectively, and to enhance the Nuavg by 15%, compared with the SPSM heat sink without chevron fins. Consequently, the design of the SPSM with and without chevron fins was then optimised in terms of the minichannel width (Wch) number of minichannels (Nch) and chevron oblique angle (θ). The optimisation process uses a 30 (without chevron fins) and 50 (with chevron fins) point Optimal Latin Hypercubes Design of Experiment, generated from a permutation genetic algorithm, and accurate metamodels built using a Moving Least Square (MLS) method. A Pareto front is then constructed to enable the compromises available between designs with a low pressure drop and those with low thermal resistance to be explored and appropriate design parameters to be chosen. These techniques have then been used to explore the feasibility of using serpentine MCHS and heat spreaders to cool GaN HEMTs.
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Lamont, Justin Andrew. "Heat Transfer in Stationary and Rotating Coolant Channels Using a Transient Liquid Crystal Technique." Diss., Virginia Tech, 2012. http://hdl.handle.net/10919/19192.
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Heat transfer inside rotating coolant channels have a significant impact in design of gas turbine airfoils and other rotating components such as generator windings. The effects of the Coriolis acceleration and centrifugal buoyancy have a significant impact on heat transfer behavior inside such rotating coolant channels due to the complex flow patterns of coolant. Detailed heat transfer knowledge greatly enhances the designers\' ability to validate numerical models of newly designed channels. A rotating experimental rig was designed and built to model scaled up coolant channels at speeds up to 750 rotations per minute (rpm). A camera is mounted onto the rotating test section and a transient liquid crystal technique is used to measure detailed heat transfer coefficients on a surface of interest. The experimental set-up is innovative, as it involves no surface heating of the test section, very little instrumentation beyond a few thermocouples and a spray coating of thermochromic liquid crystals on the test surface. To validate the test rig and the experimental method, multipass coolant channels with rib turbulators, large diameter radially outward channels with rib turbulators, and jet impingement cooling schemes are studied during rotation. 90deg, W, and M-shaped rib enhancements are studied and detailed heat transfer measurements clearly capture the heat transfer enhancement mechanisms with and without rotation. Jet impingement schemes with single and double rows, normal and off-angle jets, and a cross flow outlet condition are all studied under rotation. Non-rotating studies are also performed for baseline comparisons to rotating conditions. Large aspect ratio, diverging channels with dimple and rib turbulators are studied in a stationary condition. Results for all different test geometries show good comparisons with published studies indicating that the rotating rig and experimental method are valid. Jet impingement schemes produce higher heat transfer compared to the two-pass channels with ribs, however pressure losses are significantly higher. The fewer the jets and H/d=1 produces the highest pressure losses with no significant gain in heat transfer. Off angle jets at H/d=1 produces very high pressure losses with no heat transfer advantage. A final study with radially outward coolant channels is performed with the highest rotation speeds. The structure, test section, and camera are thoroughly designed to withstand the exceptional g-forces. Heat transfer in the radial channels with and without rotation show very little effect of rotation due to the small rotation number.Ph. D.
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Kane, Stephen James. "Two-phase flow of water and steam in a liquid metal fast breeder reactor pipe." Thesis, University of Southampton, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261438.
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Gajcowski, Edward J. "Transient model for liquid droplets evaporating from heated solid surfaces." Thesis, Georgia Institute of Technology, 1996. http://hdl.handle.net/1853/17383.
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Novak, Vladimir. "Experimental and Numerical Studies of Mist Cooling with Thin Evaporating Subcooled Liquid Films." Diss., Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/10528.
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An experimental and numerical investigation has been conducted to examine steady, internal, nozzle-generated, gas/liquid mist cooling in vertical channels with ultra-thin, evaporating subcooled liquid films. Interest in this research has been motivated by the need for a highly efficient cooling mechanism in high-power lasers for inertial fusion reactor applications. The aim is to quantify the effects of various operating and design parameters, viz. liquid atomization nozzle design (i.e. spray geometry, droplet size distribution, etc.), heat flux, liquid mass fraction, film thickness, carrier gas velocity, temperature, and humidity, injected liquid temperature, gas/liquid combinations, channel geometry, length, and wettability, and flow direction, on mist cooling effectiveness.
A fully-instrumented experimental test facility has been designed and constructed. The facility includes three cylindrical and two rectangular electrically-heated test sections with different unheated entry lengths. Water is used as the mist liquid with air, or helium, as the carrier gas. Three types of mist generating nozzles with significantly different spray characteristics are used. Numerous experiments have been conducted; local heat transfer coefficients along the channels are obtained for a wide range of operating conditions. The data indicate that mist cooling can increase the heat transfer coefficient by more than an order of magnitude compared to forced convection using only the carrier gas. The data obtained in this investigation will allow designers of mist-cooled high heat flux engineering systems to predict their performance over a wide range of design and operating parameters.
Comparison has been made between the data and predictions of a modified version of the KIVA-3V code, a mechanistic, three-dimensional computer program for internal, transient, dispersed two-phase flow applications. Good agreement has been obtained for downward mist flow at moderate heat fluxes; at high heat fluxes, the code underpredicts the local heat transfer coefficients and does not predict the onset of film rupture. For upward mist flow, the code underpredicts the local heat transfer coefficients and, contrary to experimental observations, predicts early dryout at the test section exit.
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Ryley, Joshua Claydon. "Turbine blade mid-chord internal cooling." Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:14469a51-517c-400c-b477-4fb432c8b648.
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Modern gas turbine engines operate at temperatures well above the melting point of the metal components. This has driven manufactures to develop sophisticated cooling methods which minimise the use of coolant to maximise engine efficiency by enabling further increases in operating temperature. This thesis investigates the cooling performance of engine representative mid-chord internal cooling passages for turbine blades. The work forms part of a larger E.C. FP7 project ERICKA (Engine Representative Internal Cooling Knowledge Applications).This thesis provides detailed maps of heat transfer coefficient (HTC) under a number of conditions, new experimental techniques, and has lead to a better understanding of the impact HTC distributions have on the thermal performance of a turbine blade at engine conditions. Transient liquid crystal experiments have been conducted on a large scale model of an engine representative internal cooling passage at three aspect ratios (width:height (chord length:spanwise length), 1:2, 1:3 and 1:4). Spatially resolved maps of Nusselt number have been produced for the full surface of the internal cooling passages. Little information exists in the literature for more engine representative geometries, and it is rare for spatial measurements to be presented over the full surface. The detailed maps provide validation data for CFD within the ERICKA programme. A novel method which produces spatially resolved maps in areas with highly non-one-dimensional heat transfer has been developed and validated. This method couples transient finite element analysis and data from transient liquid crystal experiments. Applied to the ribbed passage geometry, this produced spatially resolved maps of HTC over the rib surface. To the author’s best knowledge this is the first time spatial HTC maps have been presented for an engine representative rib. Industry best practice methods for internal cooling passage design typically apply averaged values of HTC, in part due to lack of spatially resolved data. To determine the significance of this approximation on blade design and life, experimental measurements have been applied to finite element (FEA) models at typical engine conditions. Application of a 3D HTC distribution to a FEA model of a section of ribbed wall demonstrated a significant under prediction (up to 58%) of localised thermal gradients when an average value is applied compared to a spatially resolved profile. This work demonstrated good agreement between distributions taken from experimental data and CFD predictions, indicating that CFD distributions may be more appropriate than bulk values in the design process. A 2D FEA study was undertaken to quantify the impact of HTC distribution approximations and aspect ratio on cooling of a generic turbine section. This study considered multiple adjacent internal cooling passages. It was confirmed that multi-pass arrangements offer greater heat removal for a given mass flow rate. Also a symmetric heat transfer profile with a higher HTC on the ribbed wall is the most desirable distribution. Use of average values significantly impacted the metal temperature, causing an underprediction up to 13◦C and 8◦C in the maximum and average values respectively. Based on the experimental HTC data, the 1:3 aspect ratio passage offered the lowest metal temperatures. Applying HTC distributions from CFD data (calculated with using the centreline temperature) showed, in general, good agreement, with the lowest metal temperatures (by up to 8◦C) in the 1:4 aspect ratio passage. Use of and HTC distribution provided by CFD prediction based on the mixed bulk temperature, produced average and peak metal temperatures 16◦C and 17◦C, respectively, lower in the 1:4 aspect ratio passage than the next best design. This highlights the need for appropriate and consistent method to be used in the analysis. As expected, reducing the passage aspect ratio led to increases in both thermal gradient and total pressure loss.
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Youssef, Rageey M. "Modeling the effect of a spray on a liquid film on a heated surface." Morgantown, W. Va. : [West Virginia University Libraries], 2007. https://eidr.wvu.edu/etd/documentdata.eTD?documentid=5074.
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Thesis (Ph. D.)--West Virginia University, 2007.Title from document title page. Document formatted into pages; contains xv, 136 p. : ill. (some col.). Vita. Includes abstract. Includes bibliographical references (p. 100-105).
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Pyrtle, Frank III. "Vibration Induced Droplet Generation from a Liquid Layer for Evaporative Cooling in a Heat Transfer Cell." Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7487.
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During this investigation, vibration induced droplet generation from a liquid layer was examined as a means for achieving high heat flux evaporative cooling. Experiments were performed in which droplets were generated from a liquid layer using a submerged vibrating piezoelectric driver. Parameters determined during this investigation of droplet generation were droplet mass flow rate, droplet size, driver frequency, driver voltage, and liquid layer thickness. The results showed that as the liquid layer thickness was increased, the frequencies and frequency ranges at which droplet generation occurred decreased. Droplet mass flow rates were varied by adjustment of the liquid layer thickness, driver frequency, and driver voltage. The dependence of the drivers displacement, velocity, and acceleration on frequency and voltage was determined, and the drivers frequency response was related to the occurrence of droplet generation. As a result, a frequency-dependent dimensionless parameter was proposed as a method for predicting droplet generation from the surface of the liquid layer. The dimensionless parameter is a combination of the Froude number and the dimensionless driver acceleration. The measurements have shown that droplet generation occurs when the parameter is between distinct upper and lower bounds.
An analytical heat transfer model of a droplet cooling heat transfer cell was developed to simulate the performance of such a cell for thermal management applications. Using droplet flow rates determined as functions of driver voltage, driver frequency, liquid layer thickness, and interception distance, the heat transfer rate of a droplet cooling heat transfer cell was predicted for varied heat source temperatures and cell conditions. The heat transfer model was formulated in such a way as to accommodate a number of parameter variations that can be used for the design of a simple heat transfer cell. The model was used to determine the effect of droplet cooling on the heat transfer rate from a heated surface, but it can also be used to determine the influence of any of the other embodied parameters that may be of interest for thermal management applications.
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Sellers, Sally M. "Heat transfer resulting from the evaporation of liquid droplets on a horizontal heated surface." Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/17993.
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Charboneau, Bryan Charles. "Double-Sided Liquid Cooling for Power Semiconductor Devices Using Embedded Power Technology." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/31907.
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Power electronics is a constantly growing and demanding technical field. Consumer demand and developing technologies have made the improvement of power density a primary emphasis of research for this area. Power semiconductors present some of the major challenges for increasing system level power density due to high loss density and interconnection requirements. Advanced cooling schemes, such as double-sided, forced liquid convection or multi-phase flow, can be implemented with non-wire bond packaging to improve thermal management while maintaining proper electrical performance. Embedded power is one such packaging technology, which provides a compact structure for interface of power semiconductor to fluid flow.
The objective of this work was to identify the potential of implementing embedded power packaging with double-sided forced liquid convection. Physics based, electro-thermal models were first used to predict the improvement in heat transfer of double-sided, forced liquid convection with embedded power packaging over single-sided liquid cooled wire bond based packaging. A liquid module test bed was designed and constructed based on the electro-thermal models, which could be interfaced with high power MOSFET based samples implementing various packaging technologies. Experiments were used to verify the model predictions and identify practical limitations of high flow rate, double-sided liquid cooling with embedded power. An improvement of 45% to 60% in total junction to case thermal resistance is shown for embedded power packaging with double-sided liquid cooling for water flow rates between 0.25 and 4.5 gal/min.
Master of Science
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Wang, Zuolan. "The application of thermochromic liquid crystals to detailed turbine blade cooling measurements." Thesis, University of Oxford, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303677.
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Lychnos, Georgios. "Feasibility of a solar panel-powered liquid desiccant cooling system for greenhouses." Thesis, Aston University, 2010. http://publications.aston.ac.uk/15254/.
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To investigate the technical feasibility of a novel cooling system for commercial greenhouses, knowledge of the state of the art in greenhouse cooling is required. An extensive literature review was carried out that highlighted the physical processes of greenhouse cooling and showed the limitations of the conventional technology. The proposed cooling system utilises liquid desiccant technology; hence knowledge of liquid desiccant cooling is also a prerequisite before designing such a system. Extensive literature reviews on solar liquid desiccant regenerators and desiccators, which are essential parts of liquid desiccant cooling systems, were carried out to identify their advantages and disadvantages. In response to the findings, a regenerator and a desiccator were designed and constructed in lab. An important factor of liquid desiccant cooling is the choice of liquid desiccant itself. The hygroscopicity of the liquid desiccant affects the performance of the system. Bitterns, which are magnesium-rich brines derived from seawater, are proposed as an alternative liquid desiccant for cooling greenhouses. A thorough experimental and theoretical study was carried out in order to determine the properties of concentrated bitterns. It was concluded that their properties resemble pure magnesium chloride solutions. Therefore, magnesium chloride solution was used in laboratory experiments to assess the performance of the regenerator and the desiccator. To predict the whole system performance, the physical processes of heat and mass transfer were modelled using gPROMS® advanced process modelling software. The model was validated against the experimental results. Consequently it was used to model a commercials-scale greenhouse in several hot coastal areas in the tropics and sub-tropics. These case studies show that the system, when compared to evaporative cooling, achieves 3oC-5.6oC temperature drop inside the greenhouse in hot and humid places (RH>70%) and 2oC-4oC temperature drop in hot and dry places (50%
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Chen, Xiuping. "Embedded active and passive methods to reduce the junction temperature of power and RF electronics." Thesis, Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/51901.
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AlGaN/GaN high electron mobility transistors (HEMTs) have been widely used for high power and high frequency RF communications due to their fast switching and large current handling capabilities. The reliability of such devices is strongly affected by the junction temperature where the highest magnitude occurs in a local region on the drain side edge of the gate called the hotspot. Thus, thermal management of these devices remains a major concern in the design and reliability of systems employing AlGaN/GaN HEMTs. Due to the large power densities induced in these devices locally near the drain side edge of the gate, it is clear that moving thermal management solutions closer to the heat generation region is critical in order to reduce the overall junction temperature of the device. In this work, we explore the use of embedded microchannel cooling in the substrate of AlGaN/GaN HEMTs made on Si and SiC substrates and compare them to passive cooling techniques using Si, SiC, and diamond substrates. In addition, the impact of cooling fluids and harsh environmental conditions were considered. The study was performed using a combination of CFD and finite volume analysis on packaged AlGaN/GaN HEMTs. Active cooling using embedded microchannels were shown to have a significant impact on the heat dissipation over the passive cooling methods, approaching or exceeding that of diamond cooled devices. For vertical power devices (IGBT), embedded microchannels in the power electronics substrates were explored. In both the power devices and lateral AlGaN/GaN HEMTs, the use of embedded microchannels with nonlinear channel geometries was shown to be the most effective in terms of reducing the device junction temperature while minimizing the pumping power required.
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Tyagi, Kartikeya. "Detailed Experimental Measurements of Heat Transfer Augmentation in Internal Channels Using a Thermochromic Liquid Crystal Technique." Thesis, Virginia Tech, 2015. http://hdl.handle.net/10919/52990.
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Design of internal cooling channels for gas turbine blade is critical to system performance. To achieve maximum efficiency, i.e. maximum cooling with minimum coolant usage, intensive research is required to optimize heat transfer enhancement features. The present study aims at experimental and numerical investigation of two heat transfer augmentation techniques for internal cooling, viz. dimple and swirl induced jet impingement. Dimples are suitable candidates for high performance enhancement as they impose a low pressure drop penalty. The present study aims at experimentally measuring heat transfer on all the walls of diamond, triangular, square and cylindrical shaped dimples in a staggered configuration at three flow conditions in a high aspect ratio channel. A thermal-hydraulic performance factor was evaluated to characterize each dimple shape. Numerical simulations were conducted to visualize flow patterns which was correlated with heat transfer distribution. The results were in good agreement with previous studies. Triangular dimples showed the highest overall performance due to lowest pressure drop penalty, but heat transfer was low inside the dimples. In rotating channels, Coriolis Effect and centrifugal buoyancy significantly affect heat transfer distribution. There is a need to develop a cooling geometry that benefits from rotation and provides consistent cooling. A new geometry was derived from a past study, consisting of two channels divided by a wall with angled holes to provide jet impingement from inlet to outlet channel. Liquid crystal technique was used for heat transfer measurements. It was found that at high rotational speeds, heat transfer increased in the inlet channel, while it decreased in the outlet channel. Additional testing at even higher speeds may provide insight into replacing a traditional U-bend channel in a turbine blade.Master of Science
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Wilson, Scott E. "Investigation of Copper Foam Coldplates as a High Heat Flux Electronics Cooling Solution." Thesis, Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/6944.
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Compact heat exchangers such as porous foam coldplates have great potential as a high heat flux cooling solution for electronics due to their large surface area to volume ratio and tortuous coolant path. The focus of this work was the development of unit cell modeling techniques for predicting the performance of coldplates with porous foam in the coolant path.
Multiple computational fluid dynamics (CFD) models which predict porous foam coldplate pressure drop and heat transfer performance were constructed and compared to gain insight into how to best translate the foam microstructure into unit cell model geometry. Unit cell modeling in this study was realized by applying periodic boundary conditions to the coolant entrance and exit faces of a representative unit cell. A parametric study was also undertaken which evaluated dissimilar geometry translation recommendations from the literature. The use of an effective thermal conductivity for a representative orthogonal lattice of rectangular ligaments was compared to a porosity-matching technique of a similar lattice. Model accuracy was evaluated using experimental test data collected from a porous copper foam coldplate using deionized water as coolant. The compact heat exchanger testing facility which was designed and constructed for this investigation was shown to be capable of performing tests with coolant flow rates up to 300 mL/min and heat fluxes up to 290 W/cm2. The greatest technical challenge of the testing facility design proved to be the method of applying the heat flux across a 1 cm2 contact area. Based on the computational modeling results and experimental test data, porous foam modeling recommendations and porous foam coldplate design suggestions were generated.
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Schlesinger, Daniel. "Molecular structure and dynamics of liquid water : Simulations complementing experiments." Doctoral thesis, Stockholms universitet, Fysikum, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-120808.
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Water is abundant on earth and in the atmosphere and the most crucial liquid for life as we know it. It has been subject to rather intense research since more than a century and still holds secrets about its molecular structure and dynamics, particularly in the supercooled state, i. e. the metastable liquid below its melting point. This thesis is concerned with different aspects of water and is written from a theoretical perspective. Simulation techniques are used to study structures and processes on the molecular level and to interpret experimental results. The evaporation kinetics of tiny water droplets is investigated in simulations with focus on the cooling process associated with evaporation. The temperature evolution of nanometer-sized droplets evaporating in vacuum is well described by the Knudsen theory of evaporation. The principle of evaporative cooling is used in experiments to rapidly cool water droplets to extremely low temperatures where water transforms into a highly structured low-density liquid in a continuous and accelerated fashion. For water at ambient conditions, a structural standard is established in form of a high precision radial distribution function as a result of x-ray diffraction experiments and simulations. Recent data even reveal intermediate range molecular correlations to distances of up to 17 Å in the bulk liquid. The barium fluoride (111) crystal surface has been suggested to be a template for ice formation because its surface lattice parameter almost coincides with that of the basal plane of hexagonal ice. Instead, water at the interface shows structural signatures of a high-density liquid at ambient and even at supercooled conditions. Inelastic neutron scattering experiments have shown a feature in the vibrational spectra of supercooled confined and protein hydration water which is connected to the so-called Boson peak of amorphous materials. We find a similar feature in simulations of bulk supercooled water and its emergence is associated with the transformation into a low-density liquid upon cooling.At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 4: Manuscript.
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Golden, Daniel Lee. "Simulation and comparison of vapor-compression driven, liquid- and air-coupled cooling systems." Thesis, Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/37297.
Full textAbstract:
Industrial and military vehicles, including trucks, tanks and others, employ cooling systems that address passenger cooling and auxiliary cooling loads ranging from a few Watts to 50 kW or more. Such systems are typically powered using vapor-compression cooling systems that either directly supply cold air to the various locations, or cool an intermediate single-phase coolant closed loop, which in turn serves as the coolant for the passenger cabins and auxiliary loads such as electronics modules. Efforts are underway to enhance the performance of such systems, and also to develop more light weight and compact systems that would remove high heat fluxes. The distributed cooling configuration offers the advantage of a smaller refrigerant system package. The heat transfer between the intermediate fluid and air or with the auxiliary heat loads can be fine tuned through the control of flow rates and component sizes and controls to maintain tight tolerances on the cooling performance. Because of the additional loop involved in such a configuration, there is a temperature penalty between the refrigerant and the ultimate heat sink or source, but in some configurations, this may be counteracted through judicious design of the phase change-to-liquid coupled heat exchangers. Such heat exchangers are inherently smaller due to the high heat transfer coefficients in phase change and single-phase liquid flow compared to air flow. The additional loop also requires a pump to circulate the fluid, which adds pumping power requirements. However, a direct refrigerant-to-heat load coupling system might in fact be suboptimal if the heat loads are distributed across large distances. This is because of the significantly higher pressure drops (and saturation temperature drops) incurred in transporting vapor or two-phase fluids through refrigerant lines across long plumbing elements. An optimal system can be developed for any candidate application by assessing the tradeoffs in cooling capacity, heat exchanger sizes and configurations, and compression, pumping and fan power. In this study, a versatile simulation platform for a wide variety of direct and indirectly coupled cooling systems was developed to enable comparison of different component geometries and system configurations based on operating requirements and applicable design constraints. Components are modeled at increasing levels of complexity ranging from specified closest approach temperatures for key components to models based on detailed heat transfer and pressure drop models. These components of varying complexity can be incorporated into the system model as desired and trade-off analyses on system configurations performed. Employing this platform as a screening, comparison, and optimization tool, a number of conventional vapor-compression and distributed cooling systems were analyzed to determine the efficacy of the distributed cooling scheme in mobile cooling applications. Four systems serving approximately a 6 kW cooling duty, two with air-coupled evaporators and two with liquid-coupled evaporators, were analyzed for ambient conditions of 37.78°C and 40% relative humidity. Though the condensers and evaporators are smaller in liquid-coupled systems, the total mass of the heat exchangers in the liquid-coupled systems is larger due to the additional air-to-liquid heat exchangers that the configuration requires. Additionally, for the cooling applications considered, the additional compressor power necessitated by the liquid-coupled configuration and the additional power consumed by the liquid-loop pumps result in the coefficient of performance being lower for liquid-coupled systems than for air-coupled systems. However, the use of liquid-coupling in a system does meet the primary goal of decreasing the system refrigerant inventory by enabling the use of smaller condensers and evaporators and by eliminating long refrigerant carrying hoses.
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Tran, Lucky. "Development of Full Surface Transient Thermochromic Liquid Crystal Technique for Internal Cooling Channels." Master's thesis, University of Central Florida, 2014. http://digital.library.ucf.edu/cdm/ref/collection/ETD/id/6371.
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Proper design of high performance industrial heat transfer equipment relies on accurate knowledge and prediction of the thermal boundary conditions. In order to enhance the overall gas turbine efficiency, advancements in cooling technology for gas turbines and related applications are continuously investigated to increase the turbine inlet temperature without compromising the durability of the materials used.
For detailed design, local distributions are needed in addition to bulk quantities. Detailed local distributions require advanced experimental techniques whereas they are readily available using numerical tools. Numerical predictions using a computational fluid dynamics approach with popular turbulence models are benchmarked against a semi-empirical correlation for the friction in a circular channel with repeated-rib roughness to demonstrate some shortcomings of the models used. Numerical predictions varied widely depending on the turbulence modelling approach used. The need for a compatible experimental dataset to accompany numerical simulations was discussed.
An exact, closed-form analytical solution to the enhanced lumped capacitance model is derived. The temperature evolution in a representative 2D turbulated surface is simulated using Fluent to validate the model and its exact solution. A case including an interface contact resistance was included as well as various rib sizes to test the validity of the model over a range of conditions. The analysis was extended to the inter-rib region to investigate the extent and magnitude of the influence of the metallic rib features on the apparent heat transfer coefficients in the inter-rib region. It was found that the thermal contamination is limited only to the regions closest to the base of the rib feature.
An experimental setup was developed, capable of measuring the local heat transfer distributions on all four channel walls of a rectangular channel (with aspect ratios between 1 and 5) at Reynolds numbers up to 150,000. The setup utilizes a transient thermochromic liquid crystals technique using narrow band crystals and a four camera setup. The setup is used to test a square channel with ribs applied to one wall. Using the transient thermochromic liquid crystals technique and applying it underneath high conductivity, metallic surface features, it is possible to calculate the heat transfer coefficient using a lumped heat capacitance approach. The enhanced lumped capacitance model is used to account for heat conduction into the substrate material. Rohacell and aluminum ribs adhered to the surface were used to tandem to validate the hybrid technique against the standard technique. Local data was also used to investigate the effect of thermal contamination. Thermal contamination observed empirically was more optimistic than numerical predictions.
Traditional transient thermochromic liquid crystals technique utilizes the time-to-arrival of the peak intensity of the green color signal. The technique has been extended to utilize both the red and green color signals, increasing the throughput by recovering unused data while also allowing for a reduction in the experimental uncertainty of the calculated heat transfer coefficient. The over-determined system was solved using an un-weighted least squares approach. Uncertainty analysis of the multi-color technique demonstrated its superior performance over the single-color technique. The multi-color technique has the advantage of improved experimental uncertainty while being easy to implement.M.S.M.E.
Masters
Mechanical and Aerospace Engineering
Engineering and Computer Science
Mechanical Engineering; Thermo-Fluids Track
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Gdhaidh, Farouq Ali S. "Heat transfer characteristics of natural convection within an enclosure using liquid cooling system." Thesis, University of Bradford, 2015. http://hdl.handle.net/10454/7824.
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In this investigation, a single phase fluid is used to study the coupling between natural convection heat transfer within an enclosure and forced convection through computer covering case to cool the electronic chip. Two working fluids are used (water and air) within a rectangular enclosure and the air flow through the computer case is created by an exhaust fan installed at the back of the computer case. The optimum enclosure size configuration that keeps a maximum temperature of the heat source at a safe temperature level (85°C) is determined. The cooling system is tested for varying values of applied power in the range of 15-40W. The study is based on both numerical models and experimental observations. The numerical work was developed using the commercial software (ANSYS-Icepak) to simulate the flow and temperature fields for the desktop computer and the cooling system. The numerical simulation has the same physical geometry as those used in the experimental investigations. The experimental work was aimed to gather the details for temperature field and use them in the validation of the numerical prediction. The results showed that, the cavity size variations influence both the heat transfer process and the maximum temperature. Furthermore, the experimental results ii compared favourably with those obtained numerically, where the maximum deviation in terms of the maximum system temperature, is within 3.5%. Moreover, it is seen that using water as the working fluid within the enclosure is capable of keeping the maximum temperature under 77°C for a heat source of 40W, which is below the recommended electronic chips temperature of not exceeding 85°C. As a result, the noise and vibration level is reduced. In addition, the proposed cooling system saved about 65% of the CPU fan power.
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Nyberg, Karen LuJean. "Design and evaluation of automatic control for human/liquid cooling garment thermal interaction /." Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
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Gdhaidh, Farouq A. S. "Heat Transfer Characteristics of Natural Convection within an Enclosure Using Liquid Cooling System." Thesis, University of Bradford, 2015. http://hdl.handle.net/10454/7824.
Full textAbstract:
In this investigation, a single phase fluid is used to study the coupling between natural convection heat transfer within an enclosure and forced convection through computer covering case to cool the electronic chip. Two working fluids are used (water and air) within a rectangular enclosure and the air flow through the computer case is created by an exhaust fan installed at the back of the computer case. The optimum enclosure size configuration that keeps a maximum temperature of the heat source at a safe temperature level (85℃) is determined. The cooling system is tested for varying values of applied power in the range of 15−40𝑊.
The study is based on both numerical models and experimental observations. The numerical work was developed using the commercial software (ANSYS-Icepak) to simulate the flow and temperature fields for the desktop computer and the cooling system. The numerical simulation has the same physical geometry as those used in the experimental investigations. The experimental work was aimed to gather the details for temperature field and use them in the validation of the numerical prediction.
The results showed that, the cavity size variations influence both the heat transfer process and the maximum temperature. Furthermore, the experimental results
ii
compared favourably with those obtained numerically, where the maximum deviation in terms of the maximum system temperature, is within 3.5%. Moreover, it is seen that using water as the working fluid within the enclosure is capable of keeping the maximum temperature under 77℃ for a heat source of 40𝑊, which is below the recommended electronic chips temperature of not exceeding 85℃. As a result, the noise and vibration level is reduced. In addition, the proposed cooling system saved about 65% of the CPU fan power.
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Peacock, Graham. "Enhanced cold-side cooling techniques for lean burn combustor liners." Thesis, Loughborough University, 2013. https://dspace.lboro.ac.uk/2134/12329.
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In order to meet the increasingly strict emissions targets required in modern civil aviation, lean burn combustors are being pursued as a means to reduce the environmental impact of gas-turbine engines. By adopting a lean air/fuel mixture NOx production may be reduced. The increase in proportional amount of high pressure air entering directly into the combustor reduces the amount available for cooling of the combustor liner tiles. A reduced mass of air places restrictions on the porosity of cooling arrays, requiring a departure from applications of pedestal and slotted film cooling typically used to cool double skin combustor liners. An alternative approach applied to lean burn combustors places impingement and effusion arrays on the cold and hot skins respectively for cooling of both sides of the hot liner skin. Although impingement cooling is well established as a means of promoting forced convection cooling, there are many areas on a liner tile where cooling behaviour is not well characterised. Additionally, film cooling reduces combustive efficiency and increases the production of NOx and CO, prompting interest in reducing its use in combustor cooling. The research for this thesis has focussed on investigations into current and proposed geometries to identify methods to enhance cold side cooling in lean burn applications. A fully modelled combustor liner tile has been used for investigation into the impact of structural and pressure blockages on cold side cooling performance of an impingementeffusion array using a transient liquid crystal technique to measure heat transfer performance. Research has found structural blockages can reduce heat transfer performance to ~60% of typical values, with crossflow development due to pressure blockage producing similar reductions in Nusselt values to ~70% of typical. A second investigation explored enhanced cooling geometries combining a distributed impingement feed over roughened channels of pedestals at variable height (H/D) and pitch (P/D). A newly proposed 'Shielded Impingement' concept combines full height pedestals, to protect impingement jets from developing crossflow, with quarter height pedestals for turbulence enhancement of crossflow cooling. The research has found that Shielded Impingement geometries displayed the strongest cooling performance of all tested designs due primarily to increased downstream Nusselt numbers. Pressure losses were comparable to short pedestal geometries, with little apparent effect of full height pedestals. Low pressure losses mean that application to extended channels in line with the full tile geometry is possible.
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Glover, Garrett A. "The Next Generation Router System Cooling Design." DigitalCommons@CalPoly, 2009. https://digitalcommons.calpoly.edu/theses/191.
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Advancements in the networking and routing industry have created higher power electronic systems which dissipate large amounts of heat while cooling technology for these electronic systems has remained relatively unchanged. This report illustrates the development and testing of a hybrid liquid-air cooling system prototype implemented on Cisco’s 7609s router. Water was the working fluid through cold plates removing heat from line card components. The water was cooled by a compact liquid-air heat exchanger and circulated by two pumps. The testing results show that junction temperatures were maintained well below the 105°C limit for ambient conditions around 30°C at sea level. The estimated junction temperatures for Cisco’s standard ambient conditions of 50°C at 6,000 feet and 40°C at 10,000 feet were 104°C and 96°C respectively. Adjustments to the test data for Cisco’s two standard ambient conditions with expected device characteristics suggested the hybrid liquid-air cooling design could meet the projected heat load.
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Diette, Christophe. "Measurement and analysis of forced convection phenomena in blade cooling channels." Valenciennes, 2003. http://ged.univ-valenciennes.fr/nuxeo/site/esupversions/c76547a4-820c-48f8-9717-ced740f0cb38.
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Dealing with gas turbine aircraft engines, the Turbine Entry Temperature (TET) is generally targeted as high as possible. Increasing this parameter leads to higher thermodynamic efficiency and power output and reduces the weight-to-thrust ratio and the Specific Fuel Consumption (SFC). Since the maximum permissible TET is determined by the temperature limitations of the turbine assembly, the choice of turbine material and the design of cooling systems applied to turbine blades are essential. This work reports both an experimental and numerical investigation on internal blade cooling cavities. Various cross sections are examined depending on the region of the blade to cool down. Numerous parameters regarding the promoters of turbulence and the flow conditions are varied to find an optimum solution in terms of both heat transfer and pressure losses. Numerical simulations are performed to support the analysis of the flow behaviour. A good agreement is found between the simulations and the aerodynamic measurements. Theoretical diagrams to interpret the flow field are finally proposed. This study provides a better understanding of flow features occuring in cooling channels together with a very detailed database. The later is useful for further numerical validations and the optimisation of cooling cavitiesEn matière de moteurs d'avion à turbine à gaz, une Température d'Entrée de Turbine (TET) aussi élevée que possible est souhaitée. Augmenter sa valeur permet en effet d'obtenir un rendement thermodynamique plus élevé tout en réduisant le rapport poids-poussée et la consommation spécifique (SFC). Parce que la TET maximum permise est liée aux limites de température supportées par les composants de la turbine, le choix des matériaux et la conception des circuits de refroidissement d'aubes sont cruciaux. Cette recherche rend compte d'une étude expérimentale et numérique sur les cavités internes de refroidissement d'aubes. Des sections de passage différentes sont examinées, en fonction de la région de l'aube à refroidir. Plusieurs paramètres en ce qui concerne les promoteurs de turbulence et les conditions de l'écoulement, sont variés pour définir une solution optimale en termes de transfert de chaleur et pertes de charges. Des simulations numériques sont réalisées pour appuyer l'analyse de l'écoulement. La comparaison de ces résultats avec les mesures aérodynamiques se révèle très satisfaisante. Enfin, des diagrammes sont proposés, pour décrire l'écoulement dans chaque cavité étudiée. De cette étude, il ressort une meilleure compréhension des phénomènes mis en jeu dans les cavités de refroidissement, ainsi qu'une base de données détaillée. Cette dernière est utile pour la validation de codes de calcul et l'optimisation des systèmes de refroidissement
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Kim, Myeongsub. "Microscale optical thermometry techniques for measuring liquid phase and wall surface temperatures." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/43754.
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Thermal management challenges for microelectronics are a major issue for future integrated circuits, thanks to the continued exponential growth in component density described by Moore¡¯s Law. Current projections from the International Technology Roadmap for Semiconductors predict that local heat fluxes will exceed 1 kW/cm2 within a decade. There is thus an urgent need to develop new compact, high heat flux forced-liquid and evaporative cooling technologies.
Thermometry techniques that can measure temperature fields with micron-scale resolution without disturbing the flow of coolant would be valuable in developing and evaluating new thermal management technologies. Specifically, the ability to estimate local convective heat transfer coefficients, which are proportional to the difference between the bulk coolant and wall surface temperatures, would be useful in developing computationally efficient reduced-order models of thermal transport in microscale heat exchangers.
The objective of this doctoral thesis is therefore to develop and evaluate non-intrusive optical thermometry techniques to measure wall surface and bulk liquid temperatures with O(1-10 micronmeter) spatial resolution. Intensity-based fluorescence thermometry (FT), where the temperature distribution of an aqueous fluorescent dye solution is estimated from variations in the fluorescent emission intensity, was used to measure temperatures in steady Poiseuille flow at Reynolds numbers less than 10. The flow was driven through 1 mm square channels heated on one side to create temperature gradients exceeding 8 ¡ÆC/mm along both dimensions of the channel cross-section. In the evanescent-wave fluorescence thermometry (EFT) experiments, a solution of fluorescein was illuminated by evanescent waves to estimate the solution temperature within about 300 nm of the wall. In the dual-tracer FT (DFT) studies, a solution of two fluorophores with opposite temperature sensitivities was volumetrically illuminated over most of the `cross-section of the channel to determine solution temperatures in the bulk flow. The accuracy of both types of FT is determined by comparing the temperature data with numerical predictions obtained with commercial computational fluid dynamics software. The results indicate that EFT can measure wall surface temperatures with an average accuracy of about 0.3 ¡ÆC at a spatial resolution of 10 micronmeter, and that DFT can measure bulk water temperature fields with an average accuracy of about 0.3 ¡ÆC at a spatial resolution of 50 micronmeter in the image plane. The results also suggest that the spatial resolution of the DFT data along the optical axis (i.e., normal to the image plane) is at least an order of magnitude greater than the depth of focus of the imaging system.
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Koveal, Catherine Helene. "An experimental study of evaporative cooling from liquid droplets impinging on a hot surface." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/32951.
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Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.Includes bibliographical references (p. 41-42).
We have performed a series of experiments to characterize the different regimes observed in drop impacts during evaporative cooling of heated surfaces. We found four regimes which were named splashing, fizzing, flat film, and marbling based on the dynamic properties of the drop impact. We found that the emergence of these regimes is primarily controlled by the Jacob number, a dimensionless group describing the ratio of sensible to latent energy absorbed during liquid-vapor phase change. Using our classification scheme, we can predict a range of useful Jacob numbers to use in the cooling of electronic components. From these Jacob numbers, we can extract the material properties of a fluid required to cool a given system.
by Catherine Helene Koveal.
S.B.
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Hashem, Gamal. "Numerical and experimental study of dynamic solar cooling system with a liquid piston converter." Thesis, Northumbria University, 2016. http://nrl.northumbria.ac.uk/30324/.
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Solar energy has been actively used to drive cooling cycles for domestic and industrial applications, especially in remote areas with a lack of electricity supply for running conventional refrigeration or air-conditioning systems. A number of solar cooling technologies exists but their market penetration level is relatively low due to the high capital costs involved and a long pay-back period. Extensive R & D activities are underway at Universities and industrial companies across many countries to improve performance and reduce capital and running costs of solar cooling systems. Systems based on application of a liquid piston converter for solar water pumping and dynamic water desalination have been developed at Northumbria University. Some preliminary work has been completed on the development of a new solar cooling system built around the above fluid piston converter. In this work, the task is to experimentally and numerically investigate performance of the solar cooling system with the fluid piston converter. The developed theoretical model then can be used for determination of its rational design parameters. Experimental tests were conducted in the Energy Laboratory of the Faculty. The test rig consisted of a solar simulator and evacuated tube solar collector, coupled to the liquid piston converters, equipped with a heat exchanger. Three different configurations of the solar cooling unit were tested and a data acquisition system with pressure, temperature and liquid piston displacement sensors was used to evaluate the experimental performance on the cooling capacity. In the theoretical part of the study, the thermodynamic model of the solar cooling system was developed. In the calculation scheme, the system was split into a number of control volumes and ordinary differential equations of energy and mass conservation were used to describe mass and heat transfer in each such volume. The system of ordinary equations then was solved numerically in MATLAB/Simulink environment and information on the variations of pressure and temperatures in the control volumes of the system over the cycle were obtained. Calibration of the mathematical model with the use of experimental data demonstrated that the model predicts the performance of the system with accuracy acceptable for engineering purposes. Experimental investigations showed that laboratory prototypes of the system demonstrate a stable operation during the tests with an amplitude and frequency of liquid piston oscillations being about 4- 6 cm and 3 Hz, respectively. The reduction in the air temperature in the cooling space was about 1 and 2 K, compared to the ambient temperature. The cooling effect increases with the raise in the heat input into the solar collector and in the flow rate of cooling water. The developed mathematical model of the system describes the pressure variation in the cycle, amplitude and frequency of oscillation of pistons with a level accuracy sufficient for performing engineering design calculations. Overall, both experimental and theoretical investigations confirm that the system demonstrates a capacity to produce a cooling effect with utilisation of solar energy. However, further R & D is required to enhance its performance.
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Li, Li. "COORDINATING LIQUID AND FREE AIR COOLING WITH WORKLOAD ALLOCATION FOR DATA CENTER POWER MINIMIZATION." The Ohio State University, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=osu1395743682.
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Medina, Theresa J. "Physiological responses of men during the continuous use of a portable liquid cooling vest." [Tampa, Fla.] : University of South Florida, 2004. http://purl.fcla.edu/fcla/etd/SFE0000444.
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Boswell, Brian. "Use of air cooling and its effectiveness in dry machining processes." Thesis, Curtin University, 2008. http://hdl.handle.net/20.500.11937/157.
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Traditional liquid coolants used in metal machining are known to contain chemical carcinogens that could present serious health risks for machine operators and have inherent waste disposal concerns on the environment. In lessening these adverse effects, the manufacturing industry continually seeks to develop machining techniques incorporating liquid-less (dry) methods or environmentally benign coolants. Air-jet cooling is widely regarded as a viable alternative for liquid coolants in machining processes. This thesis proposes a novel air jet cooling arrangement, and assesses its thermal effectiveness and operational compatibility for specific requirements in metal cutting operation. For tests, steel rods were machined on a standard lathe workbench at selected cutting depth, feed and speed. Type 1040 steel, which is commonly used in automobile industry, was chosen as work piece material. Instead of traditional liquid coolant, a specially designed compressed air jet is used to dissipate heat generation in the cutting zone at the tool tip. The tool tip is presented orthogonally to the work piece to maintain conformity with relevant established cutting tool theories. A special air jet configuration based on a Ranque-Hilsch vortex tube was designed and developed for cooling the cutting zone and tool tip. The tool tip temperatures were measured by installing thermocouples at strategic locations on the tool piece and recorded on a data-logger for a range of cutting depths, feeds and speeds. The cutting power was measured with a power meter attached to the electrical power supply to the lathe. For comparison purposes, tests were also conducted with conventional single-nozzle air jets in place of the vortex-tube jets, using traditional liquid coolant and without any cooling applied to the tool tip.A thermal vision camera was also deployed for selected tests to ascertain the temperature characteristics at the tool tip. The data was analysed to establish the thermal characteristics at the tool tip with vortex tube air jet, conventional air jet and no air jet cooling. The measured temperatures and cutting data were used to make assessments on cooling efficiency of jets used and surface finish quality of work piece. Estimates of tool life were made from the cutting theory to determine the effectiveness of the cooling systems used in the machining process. It is found that the proposed vortex tube based air jet cooling arrangement provides a highly efficient heat removal mechanism for metal cutting and delivers thermal cooling performance very much comparable to traditional liquid coolants without the inherent chemical exposure risks to machine operators and harmful impact on the environment. With the proposed air jet cooling, the tool life is very much unchanged and the surface finish quality of work piece shows no significant change while savings will realise though lesser dependency on liquid coolant requiring careful disposal and associated costs.
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Carson, Robert J. "Critical heat flux for a heated surface impacted by a stream of liquid droplets." Thesis, Georgia Institute of Technology, 1991. http://hdl.handle.net/1853/19579.
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Joshua, Nihal E. "Direct Immersion Cooling Via Nucleate Boiling of HFE-7100 Dielectric Liquid on Hydrophobic and Hydrophilic Surfaces." Thesis, University of North Texas, 2014. https://digital.library.unt.edu/ark:/67531/metadc699916/.
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This study experimentally investigated the effect of hydrophobic and hydrophilic surfaces characteristics on nucleate boiling heat transfer performance for the application of direct immersion cooling of electronics. A dielectric liquid, HFE – 7100 was used as the working fluid in the saturated boiling tests. Twelve types of 1-cm2 copper heater samples, simulating high heat flux components, featured reference smooth copper surface, fully and patterned hydrophobic surface and fully and patterned hydrophilic surfaces. Hydrophobic samples were prepared by applying a thin Teflon coating following photolithography techniques, while the hydrophilic TiO2 thin films were made through a two step approach involving layer by layer self assembly and liquid phase deposition processes. Patterned surfaces had circular dots with sizes between 40 – 250 μm. Based on additional data, both hydrophobic and hydrophilic surfaces improved nucleate boiling performance that is evaluated in terms of boiling incipience, heat transfer coefficient and critical heat flux (CHF) level. The best results, considering the smooth copper surface as the reference, were achieved by the surfaces that have a mixture of hydrophobic/hydrophilic coatings, providing: (a) early transition to boiling regime and with eliminated temperature overshoot phenomena at boiling incipience, (b) up to 58.5% higher heat transfer coefficients, and (c) up to 47.4% higher CHF levels. The studied enhanced surfaces therefore demonstrated a practical surface modification method for heat transfer enhancement in immersion cooling applications.
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Marshall, Marionyt Tyrone. "Thermo-hygroscopic envelope to support alternative cooling systems: speculative feasibility study in a small office building." Thesis, Georgia Institute of Technology, 2014. http://hdl.handle.net/1853/53032.
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The thesis explores the technical feasibility of an alternative method of decoupling air-conditioning systems function within the context of ecological issues. The system is a variant of dedicated outdoor air systems to separate dehumidification and cooling in air conditioning equipment. The project specifically investigates locating these components within the building envelope. Placement in the envelope moves the systems closer to fresh air and offers architectural expression for components that are normally out of sight. Designers, engineers, building science, mechanical, structural, biologist, and architectural engineers ideally as agents offer beneficial improvement to the system. The reduction in size of components into the building envelope offers risk. The thesis design space uses historical works, biological analogues, and past work to ground the technical understanding of the topic. Specific use of biological inspired design realizes translation from other systems to improve the alternative decoupled air conditioning system. The thesis develops prototype models for lighting analysis and for sensible and latent heat calculations. Psychrometric charts serve as tools to understand the thermodynamic air-conditioning process in conventional direct expansion vapor compression and solar liquid desiccant air conditioning systems. Data, models, and sketches provide tools for improvements to the 'thick' building envelope. Finally, the diagrams translate into functional decompositions for modifications to improve the system. The thesis probes the constraints in the areas of cost, fabrication, and technology that may not yet exist for selective improvement rather than a barrier to development of the thesis.
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Hoffs, Alexander. "Experimental investigations of heat transfer and film cooling effectiveness using the transient liquid crystal technique /." Lausanne : EPFL, 1996. http://library.epfl.ch/theses/?nr=1510.
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Rada, Mihai Catalin. "Electrohydrodynamics (EHD) pumping of liquid nitrogen - application to spot cryogenic cooling of sensors and detectors." College Park, Md. : University of Maryland, 2004. http://hdl.handle.net/1903/212.
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Thesis (Ph. D.) -- University of Maryland, College Park, 2004.Thesis research directed by: Mechanical Engineering. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
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Paje, Rufino A. "Experiments on liquid immersion natural convection cooling of leadless chip carriers mounted on ceramic substrate." Thesis, Monterey, California. Naval Postgraduate School, 1989. http://hdl.handle.net/10945/25932.
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Cooke, Geoffrey Herbert. "Study of fluorocarbon liquid as a dielectric and cooling medium in fire resistant power transformers." Thesis, University of Salford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.240032.
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Boswell, Brian. "Use of air cooling and its effectiveness in dry machining processes." Curtin University of Technology, Dept. of Mechanical Engineering, 2008. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=18869.
Full textAbstract:
Traditional liquid coolants used in metal machining are known to contain chemical carcinogens that could present serious health risks for machine operators and have inherent waste disposal concerns on the environment. In lessening these adverse effects, the manufacturing industry continually seeks to develop machining techniques incorporating liquid-less (dry) methods or environmentally benign coolants. Air-jet cooling is widely regarded as a viable alternative for liquid coolants in machining processes. This thesis proposes a novel air jet cooling arrangement, and assesses its thermal effectiveness and operational compatibility for specific requirements in metal cutting operation. For tests, steel rods were machined on a standard lathe workbench at selected cutting depth, feed and speed. Type 1040 steel, which is commonly used in automobile industry, was chosen as work piece material. Instead of traditional liquid coolant, a specially designed compressed air jet is used to dissipate heat generation in the cutting zone at the tool tip. The tool tip is presented orthogonally to the work piece to maintain conformity with relevant established cutting tool theories. A special air jet configuration based on a Ranque-Hilsch vortex tube was designed and developed for cooling the cutting zone and tool tip. The tool tip temperatures were measured by installing thermocouples at strategic locations on the tool piece and recorded on a data-logger for a range of cutting depths, feeds and speeds. The cutting power was measured with a power meter attached to the electrical power supply to the lathe. For comparison purposes, tests were also conducted with conventional single-nozzle air jets in place of the vortex-tube jets, using traditional liquid coolant and without any cooling applied to the tool tip.A thermal vision camera was also deployed for selected tests to ascertain the temperature characteristics at the tool tip. The data was analysed to establish the thermal characteristics at the tool tip with vortex tube air jet, conventional air jet and no air jet cooling. The measured temperatures and cutting data were used to make assessments on cooling efficiency of jets used and surface finish quality of work piece. Estimates of tool life were made from the cutting theory to determine the effectiveness of the cooling systems used in the machining process. It is found that the proposed vortex tube based air jet cooling arrangement provides a highly efficient heat removal mechanism for metal cutting and delivers thermal cooling performance very much comparable to traditional liquid coolants without the inherent chemical exposure risks to machine operators and harmful impact on the environment. With the proposed air jet cooling, the tool life is very much unchanged and the surface finish quality of work piece shows no significant change while savings will realise though lesser dependency on liquid coolant requiring careful disposal and associated costs.