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1
Alexseev, Alexandre Viktorovich. "Micro loop heat pipe evaporator coherent pore structures." Texas A&M University, 2003. http://hdl.handle.net/1969.1/1303.
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Loop heat pipes seem a promising approach for application in modern technologies where such thermal devices as cooling fans and radiators cannot satisfy overall requirements. Even though a loop heat pipe has a big potential to remove the thermal energy from a high heat flux source, the heat removal performance of heat pipes cannot be predicted well since a first principles of evaporation has not been established. An evaporation model based on statistical rate theory has been recently suggested by Ward and developed for a single pore by Oinuma. A loop heat pipe with coherent pore wick structure has been proposed as a design model.
To limit product development risk and to enhance performance assurance, design model features and performance parameters have been carefully reviewed during the concept development phase and have been deliberately selected so as to be well-founded on the limited existing loop heat pipe knowledge base. A first principles evaporation model has been applied for evaporator geometry optimization. A number of iteration calculations have been performed to satisfy design and operating limitations. A set of recommendations for design optimization has been formulated. An optimal model has been found and proposed for manufacture and experimental investigation.
2
Zhang, Xingxing. "Investigation of a novel solar photovoltaic/loop-heat-pipe heat pump system." Thesis, University of Hull, 2014. http://hydra.hull.ac.uk/resources/hull:8422.
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With the widespread deployment of solar photovoltaic (PV) and thermal devices imminent, this research aims to resolve some engineering barriers to the existing solar photovoltaic/thermal (PV/T) technologies by incorporating an innovative loop heat pipe (LHP) and a typical heat pump. In addition, a coated aluminium-alloy (Al-alloy) sheet replaces the conventional baseboard for the PV cells to improve heat exportation. As a result, this research has developed a novel solar PV/LHP heat pump system to maximise the electrical output of a PV module and generate an additional amount of heat simultaneously. The overall investigation followed the basic methodology of combined theoretical and experimental analysis, including procedures for a critical literature review, optimal concept design, mathematical derivation, the development of simulation models, prototype fabrication, laboratory-controlled and field testing, simulation model validation and socio-economic analysis. A full range of specialised simulation models was developed to predict the system performance with reasonable accuracy. The proposed LHP device has a maximum heat transfer limit of about 900W. The Al-alloy baseboard improved PV efficiency by nearly 0.26% when compared with a traditional PV baseboard. During the real-time measurement conditions, the mean electrical, thermal and overall energetic/exergetic efficiencies of the PV/LHP module were 9.13%, 39.25% and 48.37%/15.02%, respectively. The basic thermal and advanced system coefficients of performance (COPth/COPPV/T) were almost 5.51 and 8.71, respectively. The test results indicated that this system performed better than conventional solar/air energy systems. The feasibility analysis illustrated that this system could generate a substantial amount of energy in subtropical climatic regions, such as Hong Kong. It is cost effective to operate this system in areas with high energy charging tariffs, such as London and Hong Kong. The research results are expected to configure feasible solutions for future PV/T technologies and develop a new solar-driven heating system. The core technologies may enable a significant reduction in or even elimination of the carbon footprint in the built environment.
3
Hanks, Daniel Frank. "Design, fabrication, and characterization of a multi-condenser loop heat pipe." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/74985.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 67-68).
A condenser design was characterized for a multi-condenser loop heat pipe (LHP) capable of dissipating 1000 W. The LHP was designed for integration into a high performance aircooled heat sink to address thermal management challenges in advanced electronic systems. The multi-layer stack of condensers utilizes a sintered wick design to stabilize the liquidvapor interface and prevent liquid flooding of the lower condenser layers in the presence of a gravitational head. In addition a liquid subcooler was incorporated to suppress vapor flashing in the liquid return line. The condensers were fabricated using photo-chemically etched Monel frames with Monel sintered wicks with particle sizes up to 44 pm. The performance of the condensers was characterized in a custom experimental flow rig that monitored the pressure and temperatures of the vapor and liquid. Two condensers arranged in parallel were demonstrated to dissipate the required heat load while maintaining a stable liquidvapor interface with differences in liquid and vapor side pressures in excess of 6.2 kPa. The experimental results defined the stable operating limits of multiple condensers within a LHP given a range of convective heat transfer coefficients and differences in liquid and vapor side pressures. The inclusion of a wicking element in the condenser of the LHP increases the flexibility in design by allowing a modular construction with multiple condensers which can be integrated into air-cooled heat exchangers to cool devices with high power density.
by Daniel Frank Hanks.
S.M.
4
Fleming, Andrew J. "Aircraft Thermal Management Using Loop Heat Pipes." Wright State University / OhioLINK, 2009. http://rave.ohiolink.edu/etdc/view?acc_num=wright1238086423.
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Suh, Junwoo. "Proof of Operation in a Planar Loop Heat Pipe (LHP) Based on CPS Wick." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1131033062.
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Kariya, H. Arthur (Harumichi Arthur). "Development of an air-cooled, loop-type heat pipe with multiple condensers." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/78237.
Full textAbstract:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 169-172).
Thermal management challenges are prevalent in various applications ranging from consumer electronics to high performance computing systems. Heat pipes are capillary-pumped devices that take advantage of the latent heat of vaporization of a working fluid to achieve low thermal resistance (~0.1 °C/W), and have been of particular interest to address these thermal management needs for cooling solutions such as air-cooled heat sinks. This thesis reports the design, fabrication, and characterization of a novel loop-type heat pipe with multiple condensers for a high performance air-cooled heat sink. While multiple-condenser heat pipes have been developed in the past, this heat pipe layout is the first to ensure equal operation of the individual condensers. The layout incorporates wicks in both evaporator and condenser; the wick in the evaporator supplies the capillary pressure to drive the circulation and the wick in the condenser uses capillary pressure to separate the vapor and liquid phases for controlled condensation. Additionally, methods of liquid and vapor pressure control are developed to modulate the capillary pressure in the condenser. The heat pipe was first evaluated using an analytical model to determine the required thermophysical properties and geometries of the capillary wicks in the evaporator and condenser. The model results were subsequently used to obtain a detailed evaporator design that is compatible with the multiple-condenser layout. The evaporator was fabricated with a multi-step metal sintering process, characterized, and integrated into both single-condenser and six-condenser prototypes. The prototypes successfully operated in a wide range of angles, with automatic heat pipe startup and with a heat pipe thermal resistance as low as 0.0065 °C/W with equal condenser performance. The air-cooled, six-condenser prototype demonstrated removal of 500 W from a heat source at 75 °C. The heat pipe cycle developed in this study enables the use of multiple condensers in a loop-type heat pipe to achieve a large surface area with little thermal resistance for heat sink applications.
by Harumichi Arthur Kariya.
Ph.D.
7
Sircar, Jay D. "Manufacturing and characterization of welded, sintered condensers for a loop heat pipe." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/83744.
Full textAbstract:
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 55-56).
A manufacturing process plan was developed for a welded condenser utilizing a sintered wick. Electronic devices have progressed to the point where new designs are limited by the thermal management system used to ensure safe operating temperatures. Coupling the effects of high surface area of multiple condensers, the low thermal resistance of loop heat pipes, and the increased dissipation rates with an integrated fan system, a high efficiency heat exchanger has been previously designed. The multiplecondenser loop heat pipe required reliably manufactured condensers, with specified internal features composed of sinter wick material in order to prevent flooding and flash vaporization; key challenges faced by having multiple condensers in a loop heat pipe. The implementation of a functional sintered bond used to assemble the condenser and a welded flange design for the creation of a hermetic seal, resulted in a more reliable condenser, which functioned in a similar manner to previous designs. Additionally, the performance of the condenser under air restriction was addressed.
by Jay D. Sircar.
S.B.
8
HAMDAN, MOHAMMAD OMAR. "LOOP HEAT PIPE (LHP) MODELING AND DEVELOPMENT BY UTILIZING COHERENT POROUS SILICION (CPS) WICKS." University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1049987207.
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SHARMA, MONIKA. "THIN FILM EVAPORATION IN THE PORES OF MICRO LOOP HEAT PIPE WITH NON-UNIFORM HEAT FLUX." University of Cincinnati / OhioLINK, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1132344889.
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Gherlone, Joseph A. "Operating characteristics of a propylene charged loop heat pipe with potential spacecraft applications." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1995. http://handle.dtic.mil/100.2/ADA304826.
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Thesis (M.S. in Systems Technology (Space Systems Operations) and M.S. in Engineering Science (Astronautics)) Naval Postgraduate School, September 1995.Thesis advisor(s): Matthew Kelleher, P.J. Marto. "September 1995." Bibliography: p. 81. Also available online.
11
Wang, Zhangyuan. "Investigation of a novel façade-based solar loop heat pipe water heating system." Thesis, University of Nottingham, 2012. http://eprints.nottingham.ac.uk/12343/.
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Solar thermal is one of the most cost-effective renewable energy technologies, and solar water heating is one of the most popular solar thermal systems. Based on the considerations on the existing barriers of the solar water heating, this research will propose a novel façade-based solar water heating system employing a unique loop heat pipe (LHP) structure with top-level liquid feeder, which will lead to a façade-integrated, low cost, aesthetically appealing and highly efficient solar system and has considerable potential to provide energy savings and reduce carbon emissions to the environment. The research initially involved the conceptual design of the proposed system. The prefabricated external module could convert the solar energy to heat in the form of low-temperature vapour. The vapour will be transported to indoors through the transport line and condensed within the heat exchanger by releasing the heat to the service water. The heated water will then be stored in the tank for use. An analytical model was developed to investigate six limits to the loop heat pipe’s operation, i.e., capillary, entrainment, viscous, boiling, sonic and filled liquid mass. It was found that mesh-screen wick was able to obtain a higher capillary (governing) limit than sintered-powder. Higher fluid temperature, larger pipe diameter and larger exchanger-to-pipes height difference would lead to a higher capillary limit. Adequate system configuration and operating conditions were suggested as: pipe inner diameter of 16 mm, mesh-screen wick, heat transfer fluid temperature of 60oC and height difference of 1.5 m. This research further developed a computer model to investigate the dynamic performance of the system, taking into account heat balances occurring in different parts of the system, e.g., solar absorber, heat pipes loop, heat exchanger, and tank. Data extracted from two previously published papers were used to compare with the established model of the same setups, and an agreement could be achieved under a reasonable error limit. This research further constructed a prototype system and its associated testing rig at the SRB (Sustainable Research Building) Laboratory, University of Nottingham and conducted testing through measurement of various operational parameters, i.e., heat transfer fluid temperature, tank water temperature, solar efficiency and system COP (Coefficient of Performance). Two types of glass covers, i.e., evacuated tubes and single glazing, were applied to the prototype, and each type was tested on two different days of 8 hours from 09:00:00 to 17:00:00. By comparison of the measurement data with the modelling results, reasonable model accuracy could be achieved in predicting the LHP system performance. The water temperature remained a steady growth trend throughout the day with an increase of 13.5oC for the evacuated tube system and 10.0oC for the single glazing system. The average testing efficiencies of the evacuated tube system were 48.8% and 46.7% for the two cases with the testing COPs of 14.0 and 13.4, respectively. For the single glazing system, the average testing efficiencies were 36.0% and 30.9% for the two cases with the COPs of 10.5 and 8.9, respectively. Experimental results also indicated that the evacuated tube based system was the preferred system compared to the single glazing system. This research finally analysed the annual operational performance, economic and environmental impacts of the optimised evacuated tube system under real weather conditions in Beijing, China by running an approved computer model. It was concluded that the novel system had the potential to be highly-efficient, cost-effective and environmentally-friendly through comparison with a conventional flat-plate solar water heating system.
12
Koveal, Catherine Helene. "Design of parallel plate condensers with sintered wicks for a loop heat pipe." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/61880.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 129-131).
New innovations and integrations of existing cooling methods are needed to enable high performance operation of high power electronic equipment. Air-cooled solutions are attractive due to their simplicity; however these solutions are normally limited to low power dissipation rates. Through a novel design and integration of a blower and a compact heat exchanger, low thermal resistance and high efficiency heat transfer can be achieved. This device combines the increased surface area of a finned geometry with the isothermal heat transfer of a heat pipe and the low speed operation of integrated fan blades to dissipate 1000 W using 30 W of input electrical power in a 10x1Ox10 cm3 volume. This thesis focuses on the design and experimental validation of the 2.5 mm thick, 200 cm2 surface area flat plate condenser repeated in parallel in the loop heat pipe structure. The condenser was designed to ensure even mass flow distribution and phase-separation within each layer. To better understand the physics and governing parameters within the thin geometry of the condenser, an experimental setup was designed and fabricated that allowed for visualization and measurement of the condensing flow. Experimental studies were conducted to explore condensation within open and sinter channel geometries while varying flow rate, backside cooling, and gravitational orientation. Open channel flow exhibited sensitivity to cooling heat transfer and orientation resulting in a variable condensing length connected to a sharp drop in surface temperature and gravity-dominated flow patterns. In contrast, testing with sinter wick in the channel demonstrated an isothermal surface over the length of the condenser and gravitationally independent flow stability due to separation of the liquid and vapor phases. The addition of a sub-cooling length within the sinter channel was shown to retain high isothermal temperatures upstream while reducing condensate temperature below saturation before the condenser outlet. However, to prevent large pressure drops incurred by flow through the sinter, balance is required between desired sub-cooling and sinter permeability. This work demonstrates the potential for a condenser design with a sintered wick and a sub-cooling section to mitigate the failure modes of parallel condensers. These results serve as guidelines for the continued development of the parallel plate condensers for the loop heat pipe integrated into the compact heat exchanger.
by Catherine Helene Koveal.
S.M.
13
Santos, Nadjara dos. "Desenvolvimento de tubo de calor circuitado (Loop Heat Pipe-LHP) para aplicações espaciais." Instituto Nacional de Pesquisas Espaciais, 2009. http://urlib.net/sid.inpe.br/mtc-m18@80/2009/04.07.18.33.
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Satélites artificiais são constituídos de vários equipamentos eletrônicos e mecânicos que, na maioria dos casos, dissipam calor e requerem condições térmicas de operação bastante diferenciadas. Sistemas compostos por tubos de calor circuitados-LHP são de grande confiabilidade no controle térmico de equipamentos eletrônicos, estruturas e satélites, por manterem suas temperaturas em faixas de operação bem restritas e não utilizarem partes móveis. Esses sistemas operam passivamente por efeitos de forças capilares geradas no evaporador capilar, o qual adquire calor de uma fonte quente sendo transferido a um fluido de trabalho que opera em seu estado puro. Tubos de calor circuitados são dispositivos bifásicos de transferência de calor, os quais foram estudados em ambos os casos, experimentalmente e analiticamente. Testes foram realizados em condições de laboratório para o sistema na posição horizontal e testes em condições simuladas de espaço foram realizados (em câmara de termo-vácuo e em vibração), visando avaliar a potencialidade do uso do LHP proposto em futuras missões espaciais. A qualificação do dispositivo bifásico de controle térmico foi um processo necessário e importante para o desenvolvimento dessa tecnologia. Testes de vida com o LHP foram realizados, buscando-se identificar a potencialidade de geração de gases não condensáveis no interior do LHP em virtude da interação química entre os materiais e o fluido de trabalho utilizado. Um programa computacional foi desenvolvido em que o objetivo foi obter uma ferramenta de projeto para LHPs. O programa utilizou um modelo térmico e de perda de carga hidráulica, onde ambos trabalharam de forma interativa buscando as condições ótimas de operação de uma dada geometria de LHP, aliada às condições de operação e ao fluido de trabalho. Os resultados obtidos proporcionaram a qualificação da tecnologia envolvida para fabricação de LHPs para uso espacial, baseados em testes extensivos em condições de laboratório, bem como avaliação da vida útil desses dispositivos. Os resultados ainda serviram para validar o modelo matemático concebido, o qual apresentou boa correlação com os dados experimentais, servindo assim como uma ferramenta de projeto para novos LHPs.Artificial satellites are constituted of several electronic and mechanical equipment, which usually dissipate heat and thermal conditions of operation require quite different approach. Systems consisting of loop heat pipe-LHP are of great reliability in thermal control of electronic equipment, structures and satellites, by keeping their temperatures within very restricted operation range and uses no moving parts. Those systems operate passively by effects of capillary forces generated in the capillary evaporator, which acquires heat of a power source being transferred to a working fluid that operates in its pure state. Loop heat pipe is a two-phase heat transfer device, which they were studied in both cases, experimentally and analytically. Tests were accomplished in laboratory conditions for the system in a horizontal position and test in simulated conditions of space have also been done (in the thermal-vacuum chamber and vibration), which demand to evaluate the potentiality of use the proposed LHP in future space missions. The qualification of the two-phase thermal control device was necessary and very important process for the development of this technology. Life testing with LHP has been done, being a demand to identify the potentiality of non-condensable gases generation in LHP by virtue of the chemical interaction between the working fluid and materials used. A computer program was developed in which the objective was to obtain a design tool for LHPs. The program has used a thermal and a hydraulic pressure drop models, where both worked in interactive way seeking the optimum conditions of operation for a given geometry of LHP, allied to the conditions of operation and working fluid. The results provided a description of the technology involved in making LHPs for space, based on an extensive testing in laboratory conditions, as well as assessment of the useful life of the devices. The results also served to validate the developed mathematical model, which showed good correlation with the experiments, serving as a tool to design new LHPs.
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MANTRAVADI, NARESH VENKATA. "MEMS-BASED DEVELOPMENT OF A SILICON CPS WICK FOR LOOP HEAT PIPE APPLICATIONS." University of Cincinnati / OhioLINK, 2001. http://rave.ohiolink.edu/etdc/view?acc_num=ucin978637264.
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Roche, Nicholas Albert. "Development of a compensation chamber for use in a multiple condenser loop heat pipe." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/81623.
Full textAbstract:
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.Cataloged from PDF version of thesis.
Includes bibliographical references (p. 89-90).
The performance of many electronic devices is presently limited by heat dissipation rates. One potential solution lies in high-performance air-cooled heat exchangers like PHUMP, the multiple condenser loop heat pipe presented here. This device features a number of design improvements that lead to significant increases in performance relative to state of the art heat exchangers. In this work, a compensation chamber is developed and implemented to ensure the operational stability of the device across a wide range of operating conditions. A computational model of the device was developed using COMSOL Multiphysics v3.5a to allow for design optimization and performance evaluation. The accuracy of this computational model was established by comparing simulation results to experimental data. Analytical models were used to identify operating points of interest, which were simulated to compare the performance of various designs. The final design featured reduced thermal resistance between the vapor in the evaporator and the compensation chamber, and increased thermal resistance between the compensation chamber and the ambient air relative to past designs. This design reduced the risk of condenser flooding and evaporator dry out, improving the operational stability of the device. This design was implemented into a ten-condenser prototype, where experiments validated its performance. The compensation chamber did not require any electrical heaters, reducing the power consumption of the device and increasing its COP. Finally, general recommendations and guidelines are presented for use during the design process of future compensation chambers.
by Nicholas Albert Roche.
S.M.
16
Hamdan, Mohammad Omar Mohammad. "Loop heat pipe (LHP) modeling and development by utilizing coherent porous silicon (CPS) wicks." Cincinnati, Ohio : University of Cincinnati, 2003. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=ucin1049987207.
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Shuja, Ahmed A. "Material and Processing Development Contributions Toward the Development of a MEMS Based Micro Loop Heat Pipe." University of Cincinnati / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1179501051.
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PONUGOTI, PRIYANKA. "STUDY OF TRANSIENT BEHAVIOR OF THE EVAPORATOR OF THE MICRO LOOP HEAT PIPE AND MODIFICATIONS TO THE EXISTING GLOBAL MODEL." University of Cincinnati / OhioLINK, 2006. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1152120818.
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SHUJA, AHMED. "DEVELOPMENT OF A MICRO LOOP HEAT PIPE, A NOVEL MEMS SYSTEM BASED ON THE CPS TECHNOLOGY." University of Cincinnati / OhioLINK, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1054220863.
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Anand, A. R. "Investigations on Miniature Loop Heat Pipe with Flat Evaporator." Thesis, 2017. http://etd.iisc.ac.in/handle/2005/4308.
Full textAbstract:
The present investigation on a miniature loop heat pipe (LHP) with flat evaporator is motivated by two factors. Firstly, miniature loop heat pipes are required for thermal management of small electronics in spacecraft with heat dissipation ranging from 50 W to 100 W (heat flux up to ~ 10 W/cm2). An LHP with flat evaporator is easier to mount on an electronic package (heat source) without a saddle. Though axially grooved aluminium – ammonia heat pipes are being used for thermal management in spacecraft, when the electronic package is located far away from the radiator, conventional heat pipes are no longer useful as the number of bends in axially grooved heat pipes is restricted. LHPs can overcome this issue since they have smooth walled tubes for vapour and liquid transport lines that can easily be bent and routed inside the spacecraft. Furthermore, high pressure fluids such as ammonia require thick-walled container to withstand the high operating pressure and are more hazardous to humans in human space programs. For thermal management of small electronics with heat dissipation in the above range, there is scope for alternate working fluids that are less hazardous. Thus, issues related to design, miniaturization of the heat transport devices and use of working fluids that are less hazardous are still open for research. Secondly, the operating characteristics of an LHP are strongly influenced by the flow and heat transfer characteristics in the wick which need to be explored in detail. Thus, the present research focuses on the investigation of an LHP with a flat evaporator with various working fluids – acetone, methanol, n-pentane and ethanol.
An LHP with a flat evaporator has been built and tested with acetone, methanol, n-pentane and ethanol for heat inputs starting from 25 W till deprime for two coolant set points (-20 °C and 0 C). The LHP is also provided with a visualization arrangement to observe the phenomena occurring inside the compensation chamber (CC). Experimental results reveal that methanol has the highest deprime limit, followed by acetone, ethanol and n-pentane in decreasing order. It was also found that n-pentane has the lowest operating temperature followed by acetone, methanol and ethanol in increasing order. It was observed that increase in the sink temperature causes an increase in the operating temperature, a decrease in the deprime limit and a decrease in the total thermal resistance offered by the LHP to the heat transport from the evaporator to the sink. Visualization studies reveal that the LHP operates without any nucleation in the CC for all the heat inputs till deprime. However, the deprime of the LHP is characterised by intense nucleation inside the CC, an increase in the operating temperature and a decrease in the condenser exit temperature indicating ceasing of the fluid flow inside the LHP. Since the LHP evaporator will be directly in contact with the electronic package for its temperature control, the evaporator wall temperature will influence the electronic package temperature and its life. Hence, a model for prediction of the evaporator wall temperature under the assumption that the wick is always saturated with liquid is developed which can serve as a design platform for miniature LHPs for thermal management of electronic packages. The maximum underprediction of the evaporator wall temperature with respect to the measured evaporator wall temperature in the model is found to be 16.4 °C. Based on the results of this model, it is inferred that there exists a vapour blanket in the wick causing an additional resistance for the heat flow from the evaporator to the working fluid for its vapourization and another model is developed to estimate the vapour blanket thickness.
By balancing the loop pressure drop with the capillary pressure, an equivalent apparent contact angle which is a measure of wettability of a working fluid is estimated on a relative scale for each working fluid. It was found that ethanol has the highest wetting, followed by methanol, acetone, and n-pentane in decreasing order, or the lowest contact angle, followed by methanol, acetone, and n-pentane in increasing order. It was also found that fluid with less wetting recedes faster into the wick.
The impact of the location of liquid-vapour interface on the evaporative heat transfer coefficient is studied for all the fluids. It was found that decrease in the evaporative heat transfer coefficient is mainly due to increase in the vapour blanket thickness in the wick.
In order to compare different working fluids with respect to their operating characteristics, an improved LHP figure of merit with a correction factor is presented. This figure of merit clearly distinguishes the operating temperatures of a given LHP with different working fluids and is superior to other figures of merit available in literature. The proposed figure of merit can serve as a predictive tool for making qualitative assessment of the operating characteristics of an LHP.
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Chang, Wen-Hua, and 張文華. "A Parametric Study on Loop Heat Pipe." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/16314135586510414488.
Full textAbstract:
碩士國立臺灣大學
機械工程學研究所
89
This study presents the effects of parameters on loop heat pipe theoretically and experimentally. The theoretical model, based on steady-state energy balance, is ultilized to determine the operating temperature. The parameters of wick, condenser and transport length are discussed theoretically and the results are: (1) After start-up, the influences of wick parameters are negligible. (2) When sink temperature is lower than ambient, the performance curve can be attributed to fixed and variable resistance regime. (3) In accordance with increasing cooling intensity, varible resistance regime extends and the operating temperature in fixed resistance regime decrease. (4) When operating temperature is lower than ambient, the increase of transport length results in an elevated temperature. Besides, the influence is obvious at low heat load. Experimental studies focus on effects of working fluid invertory and porosity. The results are arranged as follow: (1) When invertory equals theoretical value, the LHP exhibits the best performance. (2) The effect of porosity is not significant at high heat load. The comparision between theoretical and experimental results shows good agreement and the deviation is within 10%.
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Adoni, Abhijt Avinash. "Theoretical And Experimental Studies Of Capillary Pumped Loop And Loop Heat Pipe." Thesis, 2008. https://etd.iisc.ac.in/handle/2005/747.
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Capillary pumped loop (CPL) and loop heat pipe (LHP), are two-phase heat transport devices which rely on surface tension induced by a fine pore wick to drive a working fluid in a loop. These are based on a working principle similar to that of heat pipes -closed evaporation and condensation cycle being maintained by capillary pumping. CPLs and LHPs are gaining importance as a part of the thermal control system of modern high power spacecraft, electronic thermal management, cryogenics, etc.
A mathematical model to simulate the thermo-hydraulic performance of CPLs and LHPs is developed to aid in the design of such a spacecraft thermal control system. In this study a unified mathematical model to estimate thermal and hydraulic performance of a CPL and an LHP -with a two-phase or a hard-filled reservoir is presented. The steady state model is based on conservation of energy and mass in the system. Heat exchanges between the loop and the surroundings and pressure drops in the loop are calculated. The constant conductance regime in a CPL or an LHP occurs when the reservoir is hard-filled. It also occurs in an LHP if the condenser is fully utilised. The heat leak across the wick becomes significant in a hard-filled LHP since the core is no longer saturated and hence the mass flow rate must be calculated using an energy balance on the outer surface of the wick. Theoretical studies indicate that the core of a hard-filled CPL and LHP is always sub-cooled. Hard-filled LHPs (with a bayonet) cannot be operated under all conditions. If the heat exchange between the compensation chamber (of an LHP with bayonet) and the ambient is small then such an LHP will not deprime if the hard-filling occurs before the condenser opens. Deprime due to hard-filling is not expected if it occurs after the condenser opens.
A laboratory model is built to demonstrate the operation of these two devices and to correlate the theoretical predictions with the experimental observations. The CPL/LHP laboratory model is fabricated and designed so that different evaporator and reservoir designs can be integrated into the test-rig and tested with different working fluids.
Experiments are conducted on a three-port CPL with a tubular axially grooved (TAG) evaporator. This CPL is operated with three different fluids -namely -Ammonia, Acetone and R134a. The CPL is operated for heat loads in the range of 75W to 400W with sink temperatures of -10◦C and 0◦C. The influence of reservoir temperature (35◦C and 43◦C) is also studied. The TAG evaporator is modified to operate in an LHP mode with R134a as the working fluid with heat loads in the range of 75W to 150W. This LHP does not exhibit typical “√” shaped operating characteristic due to large liquid inventory in the compensation chamber (CC). The R134a based LHP results suggest that large liquid inventory (in the CC) and absence of secondary wick significantly influence the thermal coupling between the core and the compensation chamber. Experiments are also conducted with a flat plate (FP) evaporator, in LHP operating mode, with Ammonia as the working fluid. This LHP can transport heat loads from 25W to 300W with a sink temperature at -15◦C. The experimental results indicate that ammonia is the best working fluid (moderate temperature regime) among all the working fluids tested, and that evaporation heat transfer coefficients in sintered Ni-wick are better. The correlation of the predicted temperatures on the transport lines and the saturation temperature (in LHPs) with the observations is good. Some of the salient conclusions from these experiments are that mass of charge can significantly influence the operating characteristics of a TAG LHP, even though the fluid in the CC is in two-phase condition. Theoretical predictions can be significantly affected when thermal and hydraulic development lengths in the condenser are comparable with the length of the sub-cooling section.
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Adoni, Abhijt Avinash. "Theoretical And Experimental Studies Of Capillary Pumped Loop And Loop Heat Pipe." Thesis, 2008. http://hdl.handle.net/2005/747.
Full textAbstract:
Capillary pumped loop (CPL) and loop heat pipe (LHP), are two-phase heat transport devices which rely on surface tension induced by a fine pore wick to drive a working fluid in a loop. These are based on a working principle similar to that of heat pipes -closed evaporation and condensation cycle being maintained by capillary pumping. CPLs and LHPs are gaining importance as a part of the thermal control system of modern high power spacecraft, electronic thermal management, cryogenics, etc.
A mathematical model to simulate the thermo-hydraulic performance of CPLs and LHPs is developed to aid in the design of such a spacecraft thermal control system. In this study a unified mathematical model to estimate thermal and hydraulic performance of a CPL and an LHP -with a two-phase or a hard-filled reservoir is presented. The steady state model is based on conservation of energy and mass in the system. Heat exchanges between the loop and the surroundings and pressure drops in the loop are calculated. The constant conductance regime in a CPL or an LHP occurs when the reservoir is hard-filled. It also occurs in an LHP if the condenser is fully utilised. The heat leak across the wick becomes significant in a hard-filled LHP since the core is no longer saturated and hence the mass flow rate must be calculated using an energy balance on the outer surface of the wick. Theoretical studies indicate that the core of a hard-filled CPL and LHP is always sub-cooled. Hard-filled LHPs (with a bayonet) cannot be operated under all conditions. If the heat exchange between the compensation chamber (of an LHP with bayonet) and the ambient is small then such an LHP will not deprime if the hard-filling occurs before the condenser opens. Deprime due to hard-filling is not expected if it occurs after the condenser opens.
A laboratory model is built to demonstrate the operation of these two devices and to correlate the theoretical predictions with the experimental observations. The CPL/LHP laboratory model is fabricated and designed so that different evaporator and reservoir designs can be integrated into the test-rig and tested with different working fluids.
Experiments are conducted on a three-port CPL with a tubular axially grooved (TAG) evaporator. This CPL is operated with three different fluids -namely -Ammonia, Acetone and R134a. The CPL is operated for heat loads in the range of 75W to 400W with sink temperatures of -10◦C and 0◦C. The influence of reservoir temperature (35◦C and 43◦C) is also studied. The TAG evaporator is modified to operate in an LHP mode with R134a as the working fluid with heat loads in the range of 75W to 150W. This LHP does not exhibit typical “√” shaped operating characteristic due to large liquid inventory in the compensation chamber (CC). The R134a based LHP results suggest that large liquid inventory (in the CC) and absence of secondary wick significantly influence the thermal coupling between the core and the compensation chamber. Experiments are also conducted with a flat plate (FP) evaporator, in LHP operating mode, with Ammonia as the working fluid. This LHP can transport heat loads from 25W to 300W with a sink temperature at -15◦C. The experimental results indicate that ammonia is the best working fluid (moderate temperature regime) among all the working fluids tested, and that evaporation heat transfer coefficients in sintered Ni-wick are better. The correlation of the predicted temperatures on the transport lines and the saturation temperature (in LHPs) with the observations is good. Some of the salient conclusions from these experiments are that mass of charge can significantly influence the operating characteristics of a TAG LHP, even though the fluid in the CC is in two-phase condition. Theoretical predictions can be significantly affected when thermal and hydraulic development lengths in the condenser are comparable with the length of the sub-cooling section.
24
Ramesh, Uppala. "Thermal Analysis of Closed Loop Pulsating Heat Pipe." 2004. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-2507200514185500.
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Yu, Cheng-Jung, and 余政融. "Investigation of Loop Heat Pipe Energy Storage System." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/89259290174143322073.
Full textAbstract:
碩士國立臺灣大學
機械工程學研究所
95
The energy storage system has been widely researched and used in recent years due to the energy crisis and environment protection. The development of energy storage system can help to collect the natural energy such as solar energy, or recycle the excess heat generated from the industrial processes. The loop heat pipe employs the phase-change mechanism, and hence has better efficiency. Loop heat pipes are not only cheap and easy to get, its passive design also makes it more reliable. Thus a loop heat pipe is used in our energy storage system. The liquid inside the evaporation tube will absorb the energy transferred from the heat source and becomes vapor, then moves toward the condenser and releases the latent heat into the water inside the energy storage tank. In our experiments, smooth, sintered and meshed copper tubes were used as different evaporation tubes. Other parameters were the fill-ratio of the system, power input, and different working fluids, inclusive of pure water and Al2O3 nanofluid (0.5wt%). Boiling characteristics and efficiencies are discussed. For the experiments with pure water as working fluids at low fill-ratio, results showed that the sintered tube had the best average energy storage efficiency, about 3%~7% better than meshed tube; and the meshed tube was 3%~10% better than smooth tube. At higher fill-ratio, the performances of sintered and meshed tubes were similar, but both were better than smooth tube about 3%~10%. When the nucleate boiling occurred in the smooth tube, its average efficiency became comparable to the meshed tube. The best average efficiencies of sintered, meshed and smooth tubes were 37.80%, 35.38%, and 33.30%, respectively. For the smooth and meshed tubes experiments with nanofluid as working fluids, results showed that the nanofluid did not aggressively enhance the average efficiency due to its higher superheat and late occasion of nucleate boiling characteristics. But it is able to enhance the efficiency for sintered tubes at low input power (5W) experiments about 5.86%~8.47%.
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Uppala, Ramesh, and 迦文西. "Thermal Analysis of Closed Loop Pulsating Heat Pipe." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/91437765245664491044.
Full textAbstract:
碩士國立臺灣大學
機械工程學研究所
93
This study aims to flow visualization and thermal analysis of a closed loop pulsating heat pipe based on inclination angle, charging ratio, type of fluid and heat flux for thermal control of micro electronic equipments. Although a variety of designs are in use, understanding of the fundamental processes and parameters affecting the PHP operation are still vague. A vertical, closed loop, glass PHP with water, methanol and 2-propanol as working fluids is first experimentally investigated for a range of heat inputs, inclination angles and charging ratios. Experimental studies are performed on a PHP, consisting of a heating section, an adiabatic section and a condensation section incorporating heat sink. The capillary tube used in this study has an inside diameter of 2mm and a wall thickness of 3mm.Total length of the pulsating heat pipe is 350cm. The experiments are conducted under forced convection cooling at the condenser section, with heating powers from 10 to 110W, with different heating modes (locations) and charging ratios from 30% to 80%. The experimental results show that the system presented better performance when operating at vertical orientation. Optimal charging ratio is 50% for DI water, 40% for methanol and 40% for 2-propanol. Regarding working fluid the PHP shows better performance when Methanol is used in vertical orientation with the lowest evaporator section temperatures.
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Chu, Mao-Long, and 朱茂榕. "Heat Transfer Enhancement of Loop Heat Pipe with Self-Rewetting fluid." Thesis, 2014. http://ndltd.ncl.edu.tw/handle/62422980327924299494.
Full textAbstract:
碩士國立臺灣大學
機械工程學研究所
102
The objective of this study is the application of self-rewetting fluid as the working fluid on loop heat pipe (LHP), with sintered copper as the chosen capillary structure material; this study also investigates the effect of using different contents and concentrations of self-rewetting fluid on heat transfer performances of LHP as well as compares the results with those from using water as working fluid. Previous studies have shown that using self-rewetting fluid as working fluid can enhance the heat transfer mechanisms of pool boiling, traditional heat pipes, and wickless heat pipes. Compared to using pure substance as working fluid, where the surface tension decreases linearly with increasing temperature, self-rewetting fluid’s surface tension has a non-linear relationship with temperature changes; therefore, at a certain temperature, the self-rewetting fluid’s surface tension increases with increasing temperature, resulting in the Marangoni effect, and the condensed liquid can be transported to the heating surface, delaying the occurrence of dry out and thus increasing the critical heat load. Concerning the effect of varying the concentration of butanol and petanol aqueous solutions on heat transfer performance of LHP, butanol concentrations ranging from 2% to 8% is investigated, and pentanol concentrations ranging from 1% to 3% is investigated. Experimental results show that 6% butanol aqueous solution results in the best heat transfer performance of LHP; compared with that of water, the critical heat load is increased by 100% and the total thermal resistance is decreased on average by 30%. Concerning the effect of changing the components of self-rewetting working fluid, the fluids considered are butanol, pentanol, hexanol, with the concentration of each being the maximum solubility concentration in water under standard conditions. Experimental results show that, compared with those from using water as working fluid, using self-rewetting fluid can allow the total thermal resistance of LHP system to decrease, increasing the critical heat load. Concerning the heat transfer performance of different self-rewetting fluids, under operating temperature of 90°C or lower, hexanol aqueous solution achieves the largest heat load of 200W and lowest total thermal resistance of 0.33°C/W; at operating temperatures higher than 90°C, hexanol aqueous solution has already reach the critical heat load, causing the system to be unstable, but butanol aqueous solution achieves the best results, with maximum critical heat load of 500W and minimum total thermal resistance of 0.26°C/W. Therefore, after analysis of the heat transfer performance of various self-rewetting fluids, butanol water solution has the largest operating temperature range, highest critical heat load, and lowest total thermal resistance, indicating that butanol aqueous solution is the most effective in enhancing the heat transfer performance of LHP.
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Chen, Chun-Nan, and 陳俊男. "Heat Transfer Analysis of a Loop Heat Pipe with Biporous Wicks." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/40969420730557999181.
Full textAbstract:
碩士國立臺灣大學
機械工程學研究所
96
In recent years, the high-power electronic devices cause the increasing demand of heat dissipation. Thus, how to improve the heat transfer capacity of a loop heat pipe (LHP) by the wick structure will be an important topic. The purpose of this article is to discuss the heat transfer performance and behavior of biporous wick which made by the mixture of nickel powders and pore former. The study was conducted following a statistical method using a two-level factorial plan involving three variables: the particle of pore former (32~88μm), the pore former content(20~25vol%),and sintering temperature (650~750℃). Moreover, the empirical model was built to determine the optimized parameter combination of the biporous wick. Finally, the heat transport capability of the LHP between monoporous wicks and biporous wicks has been investigated. The results showed that the pore former content is a primary effect (percent contribution is 76.8%) for performance of LHP. Particle size of pore formers is minor effect (percent contribution is 15.6%), and sintering temperature is a little effect. The better parameters of biporous wick is tend to have smaller particle size of pore former, more pore former contents. The best parameters of the biporous wick is obtained with the empirical model: The range of particle size of pore former is 20~32μm, pore former content is 25vol%, and sintering temperature is 750℃. Experimental results showed that, at the sink temperature of 10℃ and the allowable evaporator temperature of 85℃, the maximum heat transfer capacity of the best biporous wick achieved 570W and the minimum total thermal resistance was 0.08℃/W. Comparing to a monoporous wick for 350W and 0.22℃/W. In addition, the heat transfer coefficient in the evaporator of the best biporous wick reached to a maximum value of 68KW/m2•℃, which was approximately 6.8 times higher than that of the monoporous wick. With the increase of the imposed heat flux, the heat transfer coefficient of the best biporous wick increases to a maximum value and then decreases afterwards. The special heat transfer curve can be divided into three different regions. In lower heat flux(below 130KW/m2), the heat transfer performance of biporous wick is almost like that of a monoporous wick. The biporous wick had an increased surface area available for thin film evaporation at higher heat flux(130~210KW/m2). Therefore, the heat transfer coefficient reaches rapidly a maximum value. In high heat flux (above 210KW/m2), the performance of biporous wick decay gradually because the dryout starts to occur in the wick.
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Chen, Chun-Nan. "Heat Transfer Analysis of a Loop Heat Pipe with Biporous Wicks." 2008. http://www.cetd.com.tw/ec/thesisdetail.aspx?etdun=U0001-1107200813350600.
Full text
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Juan, Chun-Chia, and 阮俊嘉. "Heat Transfer Enhancement of a Loop Heat Pipe with Bidispersed Wicks." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/89053937052331807590.
Full textAbstract:
碩士臺灣大學
機械工程學研究所
98
The purpose of this article is to develop high-performance bidispersed wicks utilized in a LHP’s evaporator and to improve heat transfer crisis in formerly monoporous wicks. The influence of heat transfer performance about difference pore-size parameters will be discussed. The study was conducted by sintering the nickel powder clusters, which mixed with binder into a bidispersed wick. A two-level factorial plan of statistical design was introduced involving two variables: the average cluster size (53、82μm), and the cluster size distribution range (14、42μm). Moreover, the statistical model was built to determine the optimized parameter combination of the bidispersed wick. Finally, the heat transport capability of the LHP between monoporous wicks and bidispersed wicks has been investigated. The experimental results indicated that average cluster size is the major effect (92.8%) on LHP’s performance about pore-size parameters, and the effect of cluster size distribution range was not significant (2.9%) within the parametric range. The better pore-size parameter tended to smaller average cluster size and wider cluster size distribution range. The best pore size parameter of the bidispersed wick was 20μm~62μm, which obtained by follow-up experiments. Experimental results also showed that at the sink temperature of 10℃ and the allowable evaporator wall temperature of 85℃ the maximum heat transfer capacity of monoporous wick achieved 400W and the minimum total thermal resistance was 0.16℃/W. Comparing to the monoporous wick, the corresponding values of the best bidispersed wick was 575W for heat transfer capacity and 0.13℃/W for total thermal resistance. In addition to the heat transfer ability of porous wicks, the best Bidispersed wick showed higher heat transfer coefficient of 23.3 kW/m2℃ at 400W than monoporous wick of 10.3 kW/m2℃ by 2.3 times. In conclusion, bidispersed wicks are very attractive for high heat flux applications.
31
Huang, Hsin-Fu, and 黃信輔. "The Study of Double Closed-Loop Pulsating Heat Pipe Heat Exchangers." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/bs3434.
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Kao, Cheng-Chun, and 高政群. "Design and Fabrication of the Micro Loop Heat Pipe." Thesis, 2002. http://ndltd.ncl.edu.tw/handle/04273706136085447176.
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Tu, Tang-Hung, and 涂堂烘. "Fabrication and Test of Closed-loop Pulsating Heat Pipe." Thesis, 2005. http://ndltd.ncl.edu.tw/handle/25477134870862668660.
Full textAbstract:
碩士國立清華大學
動力機械工程學系
93
Pulsating heat pipe (PHP) is a newly developed two-phase-flow heat transfer device, which can transfer heat very efficiently in both sensible and latent forms. Due to the simple structure and the bent characteristics, PHP becomes a prosperous heat transfer machine. The purpose of this study is to build several closed-loop PHPs made by copper tube (outer diameter 1/8”, inner diameter 2mm) or glass tube (outer diameter 3mm, inner diameter 2mm), which is partially filled with a working fluid such as water. Based on the above developed PHP, the experiments were conducted as follows: (1) to observe visualization of flow pattern inside the PHP tube, (2) to measure the thermal transport performance of PHPs, and (3) to compare the performance of PHP and traditional heat pipe (THP). The experimental results show that (1) the type of flow pattern inside the PHP tube depends on the input heat loading. It was found that the flow pattern changes from the oscillating to transiting and then to stable period with increasing input heat loading; (2) the thermal resistance of PHP decreases with increasing heat loading. In addition, when the filling ratio is equal to 30%, it reaches the best heat transfer efficiency. When the angle of inclination changes, main parameter that effects efficiency of PHP, will be different; and (3) in case that both heat loading and area of heat transfer surface are equal, PHP may have the better heat transfer efficiency than THP at the vertical operating condition.
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Yen, Yu-Yuan, and 葉裕源. "Study of Temperature Control Technology by Loop Heat Pipe." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/17898209543487450655.
Full textAbstract:
碩士國立臺灣大學
機械工程學研究所
91
The main purpose of the present research is to develop a temperature control box by loop heat pipe. By modifying the rotational speed of the fan, we can attain a constant temperature in the box. In order to accurately control temperature in the box, a temperature controller is designed by means of dynamic system identification and simulation. A prototype of temperature control box by loop heat pipe using PIC 16F877 micro-processor was built and tested. The experiment results show that temperature control error is less than 0.5℃. The performance of the designed temperature control box by loop heat pipe is shown satisfactory.
35
Cheng, Kuo-Chang, and 鄭國章. "Loop heat pipe with the fine-pore wick structure." Thesis, 2003. http://ndltd.ncl.edu.tw/handle/15798444874056762824.
Full textAbstract:
碩士國立臺灣大學
機械工程學研究所
91
In this paper, the effects of the capillary structure parameters on heat transfer capacity were analyzed theoretically. Then, a wick structure with high capillary capacity was manufactured with fixed porosity by pressed sintering process. Furthermore, the various capillary parameters (porosity, pore radius and permeability) were measured and the relationships among them were also developed. Finally, the present fine-pore wick structure was installed in a loop heat pipe, and the system performance such as heat transfer capacity, thermal resistance and anti-gravity ability were tested. Summing up the measured results of capillary parameters, an experimental formula was established by which the wick structure could be designed. The performance test results showed that the present loop heat pipe achieved the heat transfer capacity of 800 , and its thermal resistance was 0.12℃/W. Such a performance was better than that manufactured by loose powder sintering process.
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Chen, Tai-Yu, and 陳泰宇. "The Fabrication and Performance Test of Loop Heat Pipe." Thesis, 2001. http://ndltd.ncl.edu.tw/handle/49766522754308179578.
Full textAbstract:
碩士國立臺灣大學
機械工程學研究所
89
The subject of this study is to develop a loop heat pipe with a heat transport capacity of 200W. First, the effects of wick structure''s parameters, like powder radius, porosity, thermal conductivity, and thickness were discussed. Then, design was made according to the following condition; hydrodynamic condition, start-up condition and fluid supercooling condition. Secondly, the facility and procedure of fabrication were set up. These include the die of wick structure, test facility, clean and working fluid charging system. The fabricated loop heat pipes were tested, The maximum heat transport capacity was 300W and the thermal resistance was 0.09 K/W. During the experiment, some typical and interesting phenomenon of loop heat pipe, for instance, turn-key start, hot and cold start-up, auto-regulation, varied and constant thermal resistance, were observed.
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Yang-Hsin, Wang, and 王彥勛. "A Study of Biporous Wicks for Loop Heat Pipe." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/46881563777138096765.
Full textAbstract:
碩士臺灣大學
機械工程學研究所
95
The purpose of this study was to investigate the effects of various pore size distributions of biporous wicks for a Loop heat pipe (LHP). The study was conducted following a statistical method using a two-level factorial plan involving three variables (particle size of pore former：48~62μm and 74~88μm Na2CO3, pore former content： 20vol% and 25vol%). Finally, a comparison was made between monoporous wicks and biporous wicks for the heat transport capability of the LHP. Experimental results showed that the better parameters of the biporous wick seem to tend to more pore former contents (25vol%), and smaller particle size of pore former (48~62μm), in particular pore former content (percent contribution B＝80%). At the sink 10 ℃ and the allowable evaporator temperature 85℃, the heat transfer capacity of the better biporous wick achieved 350W and the thermal resistance was 0.19 /W ℃ . In comparison to a monoporous wick for 300W and 0.23 /W, the performance is ℃ enhanced. LHPs with biporous wicks are very attractive for high heat flux applications in the future.
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Chen, Zheng-Hong, and 陳政宏. "Loop Heat Pipe Performance Enhancement With Bilayer Wick Structure." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/27544863794839885759.
Full textAbstract:
碩士國立臺灣大學
機械工程學研究所
99
Loop heat pipe (LHP) is a passive two phase heat transfer device, which have ability to transport long-distance, low thermal resistance, and high heat transfer capacity advantages as compared with traditional heat pipe. In recent years, the high heat flux thermal solution requirement follows the electronic device become more powerful and smaller size.LHP developed smaller evaporator size. Therefore, the purpose of this article is to overcome the LHP heat transfer performance decrease sharply when using mono-porous wick in evaporator. In this study, nickel powder were used to produce bi-layer wick structure by sintered twice. The primary wick is arranged for vapor escape and the secondary wick is for the purpose of managing the fluid flow between the compensation chamber and evaporator. The configuration of wick’s place is in order to separate the vapor and liquid flow that could reduce the heat leakage from evaporator to compensation chamber. According to the present research, it is lake of parametric studies on wick thickness in loop heat pipe. So that, the aim of this study is to understand the thickness effect and find the optimized case. Experiment result show that the evaporator temperature had significant decrease at the situation of primary wick thickness 1.75mm and the secondary wick thickness increase from 0.75mm to 1.5mm.But when the secondary wick thickness increase from 1.5mm to 2.25mm, there is a sharp decrease in heat transfer performance. So as the result show that there exist an appropriate thickness which have the best heat transfer performance. And in this study, the best secondary wick thickness is 1.5mm. On the other hand, when the sink temperature set at 10℃and the evaporator temperature not to exceed 100℃, the mono-porous wick have the maximum heat load 600W and total thermal resistance is 0.15℃/W; Bilayer wick structure have the maximum heat load up to 1000W and total thermal resistance is below 0.09℃/W. The bilayer wick structure not only increases at least 400W heat load but also decreases the total thermal resistance about 70%.
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Hsu, Chao-Hsiang, and 許超翔. "The Radiation and Stagger Loop Heat Pipe Evaporator Design." Thesis, 2006. http://ndltd.ncl.edu.tw/handle/cnd893.
Full textAbstract:
碩士國立臺北科技大學
製造科技研究所
94
This article is using R-134a as the working fluid to design and produce a loop heat pipe (LHP) with a flat evaporator. It not only sinter the wick structure in single process forming at the bottom of the evaporator, but also strengthen the bottom of the evaporator then improve the disadvantage of hard start-up in the system by vapor backflow into compensation chamber in traditional LHP. Moreover, using radiation type vapor groove can lower flux resistance to increase quantity of vapor cycle, and then lower the thermal resistance. Such cogitation is the point of this design. Discussing the design and producing method of LHP, and start-up in the system, follow the standard process in this laboratory as “Active and Passive Test of Thermal Resistance”, measuring the heat flux in different fill rate, and the test shows the result of this design corresponds with the computer soft "SINDA" simulation, gaining the best fill rate, 80 percent. The radiation type vapor groove in this design under horizontal heat transfer configurations, the thermal resistance is better than traditional type by 18%. It''s enough to see that radiation type is efficient in hasten evaporation rate and lower system thermal resistance. Under different wick structure (copper powder and nickel powder), different cooling wind mass (50、70、90CFM), different transmission pipe length (1050mm、1550mm), discuss the influence to the system thermal resistance and convection thermal resistance, it shows that when LHP under the “Junction Temperature” of lower than 95℃, maximum heat transfer can be 300W under vertical heat transfer configurations, and the system (thermal resistance) is 0.15℃/W; Maximum heat transfer is 200W under horizontal heat transfer configurations; system (thermal resistance) is 0.38℃/W.
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Hsu, Chang-Jung, and 許展榕. "Nondimensional Parameters’ Simulation of Open-Loop Pulsating Heat Pipe." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/r6a8at.
Full textAbstract:
碩士國立臺北科技大學
製造科技研究所
96
This research is to make a description of open-loop pulsating heat pipe’s parameter by using four nondimentional parameterα（energy ratio）,β（density empty ratio）,γ（empty filling ratio）,Rm（mass ratio）.After simulating,we can find no oscillation zone and oscillation zone.In our simulation,α is meaning of internal energy divided by kinetic energy’s ,βis meaning of empty volume ratio divided by density ratio,γis meaning of empty filling ratio divided by filling ratio,Rm is meaning of mass evaporating rate divided by flow rate. In this research,we develop two software by EES（Engineering Equation Solver）,one is PHP.ees ,this software is using slug’s continuity and momemtum equation , plug’s continuity and energy equation and state equation,these five equation will solve by EES in order to understand open-loop pulsating heat pipe’s thermal property’s variety;another is Txt.ees,this software is using slug’s energy equation to slove a slug’s temprature distribution,then calcuting the slug’s heat transfer rate.EES is a software with bulid-in thermal property’s database and can create GUI ,it is why we use this software in this research .After creating GUI ,it will be easier to operate for people who doesn’t understand EES very much ,and it will let open-loop pulsating heat pipe’s design more easier. When we let geometry fixed ,β becomes function of filling ratio .Then we could find out an oscillation area changed with filling ratio ,when α is 4126 .As Fig 4.11 ,Fig 4.12,Fig 4.13 and Fig 4.14 ,filling ratio changes from 0.6 to 0.68 in oscillation area. After simulating Table 4.1 , we could find there is a maximum heat transfer rate 16.15(W) in one slug , and there are two equal slugs in this system , the maximum heat transfer rate in this system is 32.3(W).
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Huang, Chun-Ying, and 黃俊穎. "Simulation and Manufacturing of The Miniature Loop Heat Pipe." Thesis, 2008. http://ndltd.ncl.edu.tw/handle/xtbyz6.
Full textAbstract:
碩士國立臺北科技大學
製造科技研究所
96
This article is to describe that the EES software is developed by myself to simulate the heat-conduction situation of steady-state of a miniature loop heat pipe and to consider its heat-leakage condition. I use software simulation to get the design parameter and the heat load to develop a miniature loop heat pipe, and testify it by our laboratory standard process of thermal resistance measure . According to the result of experiment, we know that this loop heat pipe designed by design parameter from software simulation fits the physical phenomenon under stable-circumstance operation. When working fluid is ammonia and we measure the influence of system function by different fill rate，we get the optimal fill rate 80%. Under the circumstance of low heat laod (＜25W), when we change the working fluid to R-134a whose optimal fill rate is also 80%, we know thermal resistance of the LHP is 0.22℃/W which is lower than the thermal resistance of the LHP 0.32℃/W when using ammonia as the working fluid. However, when heat load increases （＞25W), the system of ammonia has the thermal resistance 0.27℃/W which is lower than the thermal resistance 0.41℃/W from the system of R-134a. Without exceeding the Max Temperature of evaporator temperture 110℃, heat load of ammonia system is 50W higher than R-134a system''s 40W. From this experiment of loop heat pipe examination, the minimum start-up power is 5W which is as the same as the minimum start-up power mentioned by Maydanik[41]. From the phenomenon that pool boiling and results in lowering the temperature dramatically, we know when heat load is more than 10W, temperature lowers slowly; when heat load is less than 10W, temperature doesn''t lower dramatically due to insufficient vaporization. Therefore, we regard 10W as the optimal start-up power in this system. Finally, compared with the maximum heat load of software simulation, 44W with the 50W one from the experiment, there is an approximately 13.6% error.
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Fu-Rung, Yu, and 余富榮. "Study on Multi-heat Source Management using Three-Dimensional Loop Heat Pipe." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/02218987489554446688.
Full textAbstract:
碩士國防大學理工學院
機械工程碩士班
101
This research is to pre-develop a new highly adaptable loop heat pipe, which is featured with simplicity in making, high thermal efficiency, and configuration adaptability to the heat source position and heat flux volume, and used to treat three-dimensional multiple heat sources in a limited space. This research uses pressurized gas generated by capillary structure to resist gravity, and in the same conditions uses the bending curvature design to explore the gravity impact on the entire device. In the end, heat sources of different quantities, positions and powers are discussed to find out the variations of the parameters for an effective heat dissipation result. In this research, electronic instruments of military specifications are studied, and the loop heat pipe's unique features of stand-alone operation, anti-vibration, low thermal resistance, and long thermal transmission distance are applied for the design and production of the three-dimensional loop heat pipe in a multiple heat sources environment. The low-cost, highly heat-transfer efficient loop cooling mechanism is used to make the electronic devices in a sealed environment highly reliable, and able to tackle other extended dissipation issues as well. This three-dimensional, multiple-heat-sources loop heat pipe developed in this research has descending powers by the targets in phases, in order to measure the thermal resistance variation along with the decreasing of the input powers. Vacuuming is used to reduce the working substance saturation and capillary structure in order to increase the contact area between the working substance and the heat sources for expediting the change of the working substance phase. After the working substance phase is changed, the generated pressure will make the working substance within the system transmit heat in the designed directions. This research has found out that when the input power of the main heat sources of the three-dimensional, triple-heat-sources loop heat pipe is at its peak (60W) and the input power of the secondary heat sources is at its bottom (15W), the lowest thermal resistance of this research can be obtained; while the input power of the main heat sources is at its bottom (40W) and the input power of the secondary heat sources is at its peak (30W), the highest thermal resistance of this research can be obtained, and result remains unchanged even if the bottom input power of the heat sources vary.
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Chan, Chun-Yao, and 詹竣堯. "The Impact of Wick Wettability on Heat Transfer Performance of Loop Heat Pipe." Thesis, 2012. http://ndltd.ncl.edu.tw/handle/93986796337792331094.
Full textAbstract:
碩士國立臺灣大學
機械工程學研究所
100
Loop heat pipe (LHP) is a passive two phase heat transfer device, which has ability to transport heat in long-distance, low thermal resistance, and high heat transfer capacity compared with a traditional heat pipe. During thermal transfer process, the wettability of the wick in the evaporator of LHP has impacts on capillary force, disjoining pressure and evaporative thin film. Then, it could affect the heat transfer performance of LHP significantly. However, the related research about the effect of wettability on LHP’s evaporation still lacks. Therefore, the purpose of this article is to discuss the impact of wick wettability on heat transfer performance of loop heat pipe. In this study, the material of wick was copper, and the working fluid was water. The methods to change wick’s wettability were the oxidation and the layer-by-layer thin film coating. In the experiment results of monoporous wick, as the wick’s wettability increased, the critical heat load reduced. While the wick’s contact angle was more than 90°the working fluid did not penetrate into the wick. That caused that loop heat pipe could not start. The impact of wick wettability on film evaporation also varies with pore size. Therefore, in this study, the biporous wick was manufactured by using Na2CO3 powder as pore former which has 105~125μm in diameter. The impact of wettability in biporous wick on the heat transfer performance in LHP was discussed. The biporous experiment result indicated that the wick had a good wettability which leaded a lower evaporator wall temperature as well as a lower total thermal resistance.
44
Hsuan, Chuang Yu, and 莊宇軒. "The Effectiveness Analysis of Double Closed-Loop Pulsating Heat Pipe." Thesis, 2016. http://ndltd.ncl.edu.tw/handle/h5atfs.
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WEI, LIN CHIN, and 林金緯. "Radial-type Closed Loop Pulsating Heat Pipe Design and Fabrication." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/96486077280910849802.
Full textAbstract:
碩士聖約翰科技大學
自動化及機電整合研究所
97
In this paper, in order to create a number of different length and bend the new type of Radial-type closed loop pulsating heat pipe and to analyze its effectiveness; "RCLPHP" is the abbreviation of Radial-type closed loop pulsating heat pipe. The production process of RCLPHP, in addition to do flow visualization to observe the situation, but also joined the different design parameters such as copper pipe and brass pipe (external diameter = 3 mm, internal diameter = 2.5 mm), the number of radiation (8, 10, 12) and radiation length (50mm, 100mm, 150mm) as a change in mix and match parameters, the working fluid is pure water, filling rate are 40%, 50%, 60%, and use the different heating power (10W, 20W, 30W, 40W, 50W, 60W) compared with solid and filling the heat transfer performance of RCLPHP. The evaporation side of RCLPHP are heated by the square copper of the central bottom 40 mm , and the condensation side use the forced air cooling for heat dissipation. Experimental results show, that the radiation length 150 mm and radiation number of 12, filling rate of 60%, due to liquid and vapor bubble pulsating cycle frequency, and significantly lower temperature, it is better heat dissipation.
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Chan, Chien-Hsuan, and 詹前軒. "Study on Circulation Flow in Closed Loop Pulsating Heat Pipe." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/61314848247762995792.
Full textAbstract:
碩士淡江大學
機械與機電工程學系碩士班
98
This research utilized 6 mm outer diameter and 3 mm inner diameter glass tubes to manufacture 9 turns closed loop Pulsating Heat Pipe(PHP) with a total length of 1980mm. For achieving the loop circulation easily, a water cooling system kept at 35 ° C was used as the condenser. The experiment was conducted to evaluate the thermal resistance under different fluid filling ratios (20%, 30%, 40%, 50%, 60%, 70% and 80%), and at a series change of heat inputs (40W, 80W, 120W, 160W, 200W). Through a digital video camera, the visualization experiment was carried out to observe the circulation flow period in the PHP. A styrofoam ball was designed to put into the tube for a better observation and a correct estimation of fluid flow direction. Circulation times and circulation period were observed and calculated from different filling ratio tests. We also analyze the effect of inclination angles to the performance and circulation period in the PHP. The results showed that PHP reached fully circulation under the filling ratio of 60%, 70%, and 80%, at an input power of 200W. The circulation can be categorized into clockwise circulation, counter-clockwise circulation and transition circulation status. The shorter circulation period happened as filling ratio was 80%. We also found that there were more counter-clockwise circulation occurred in each experiment. Due to gravity effects, better performance and shorter period took place when the inclination angle was 45 °. Key words: pulsating heat pipes, PHP, circulation flow, circulation period
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Hsu, Chin-Chun, and 許欽淳. "Application of Nanofluids in Fabrication of Micro Loop Heat Pipe." Thesis, 2004. http://ndltd.ncl.edu.tw/handle/47592649691974683658.
Full textAbstract:
碩士淡江大學
機械與機電工程學系
92
A 60 mm×33 mm×0.8 mm micro loop heat pipe (MLHP), consisting of an evaporator, vapor line, condenser, and two liquid lines, was fabricated and characterized. The wicking structure consists of parallel V-grooves with a hydraulic diameter of 76 m formed using bulk silicon etching. MLHP were realized by bonding a glass wafer onto a silicon substrate, resulting in a transparent cover for two-phase flow observation. Methanol and silver nanofluid were used as the working fluid. The test results showed that silver nanofluid demonstrates a higher heat load performance range (12.96 W~15.13 W) than methanol (4.35 W~6.34 W) with an evaporator area of 1 cm0.8 cm and condenser temperature of 12C. The thermal resistances of methanol and silver nanofluid were 0.84 ℃/W (4.98 W) and 0.89 ℃/W (15.13 W) separately.
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Chou, Wei-Cheng, and 周煒程. "Parametric Analysis of a Polymer Wick for Loop Heat Pipe." Thesis, 2007. http://ndltd.ncl.edu.tw/handle/05924778363169757224.
Full textAbstract:
碩士臺灣大學
機械工程學研究所
95
This research focuses on the parametric analysis of a polymer wick for the heat transfer performance of loop heat pipe. The parameters on the wick structure, including pore radius, porosity, and permeability. It is difficult to predict and control well in the manufacturing method of sintered metal powder. Then, small form factor LHP causes the problem of the heat transpiration easily. Therefore, polystyrene which is low thermal conductivity coefficient is chosen as the material and is fabricated by salt leaching. Adjusting the size of sodium chloride powder and its percentage in the polystyrene material, it could not only control the pore radius and porosity efficiently, but also be discussed the relationship of the parameters deeply among them. The results of the test show that the pore size parameter lies in the desired range, and the porosity is able to be controlled within 1.65% MAE. With repeatedly tests, a formula between permeability and porosity expresses as Kw=6.24×10-23ε6.87. Furthermore, this would promote both the LHP design and the prediction of heat transfer. What the results of the test reveal when the smaller the thinness and pore radius are, and the bigger the porosity is , the heat transfer would be much better. Hence, a wick structure with the thinness of 1.5mm, the pore radius of 0~20 micron, the porosity of 80%, and the permeability of 9.2×10-12m2 is installed into a LHP system to carry out the performance. The capacity of heat transfer in LHP with polymer wick structure approaches 300W, the thermal resistant is 0.25℃/W under the evaporator temperature of 85℃. The same result could be discovered within sintered metal powder method. In short, polymer wick structure, comparing with metal wick structure, has some advantages in the characteristics in its production, such as low cost, easily controllable, perfect processing, and so forth. Moreover, these merits would promote the potential of LHP as much as possible.
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Lin, Wei-Jhih, and 林威志. "The Application of Self-Rewetting Fluids on Loop Heat Pipe." Thesis, 2013. http://ndltd.ncl.edu.tw/handle/95945667975312908438.
Full textAbstract:
碩士國立臺灣大學
機械工程學研究所
101
The objective of this study is the application of self-rewetting fluid as the working fluid on loop heat pipe (LHP), with sintered copper as the chosen capillary structure material; this study also investigates the effect of using different components and concentrations of self-rewetting fluid as well as compares their heat transfer performances with that of water. Previous studies have show that using self-rewetting fluid as working fluid can enhance the heat transfer mechanisms of pool boiling,traditional heat pipe, and wickless heat pipe. Compared with using pure substance as working fluid, where the surface tension decreases linearly with increasing temperature, self-rewetting fluid’s surface tension has a non-linear relationship with temperature changes; therefore, at a certain temperature, the self-rewetting fluid’s surface tension increases with increasing temperature, resulting in the Marangoni effect, and the condensed liquid can be transported to the heating surface, delaying the occurrence of dryout and thus increasing the critical heat load. Concerning the effect of varying the concentration of butanol aqueous solution on heat transfer performance of LHP, concentrations ranging from 2% to 8% is investigated. Experimental results show that 6% butanol aqueous solution results in the the best heat transfer performance of LHP; compared with that of water, the critical heat load is increased by 130% and the total thermal resistance is decreased on average by 50%. Concerning the effect of changing the components of self-rewetting working fluid, the fluids considered are butanol, pentanol, hexanol, and heptanol, with the concentration of each as the maximum solubility concentration in water under standard conditions. Experimental results show that, compared with using water as working fluid, using self-rewetting fluid can allow the total thermal resistance of LHP system to decrease, increasing the critical heat load. Concerning the heat transfer performance of different self-rewetting fluids, under operating temperature of 90°C or lower, hexanol aqueous solution achieves the largest heat load of 250W and lowest total thermal resistance of 0.33°C/W; at operating temperatures higher than 90°C, hexanol aqueous solution has already reach the critical heat load, causing the system to be unstable, but butanol aqueous solution achieves the best results, with maximum critical heat load of 350W and minimum total thermal resistance of 0.32°C/W. Therefore, after analysis of the heat transfer performance of various self-rewetting fluids, butanol water solution has the largest operating temperature range, highest critical heat load, and lowest total thermal resistance, indicating that butanol water solution is most effective on heat transfer performance of LHP.
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Yu, Guan-Shun, and 余冠勳. "The development of a double loop heat pipe solar heater." Thesis, 2009. http://ndltd.ncl.edu.tw/handle/9rjst4.
Full textAbstract:
碩士國立臺北科技大學
能源與冷凍空調工程系碩士班
97
The purpose of this study is development a double loop heat pipe solar heater which can be set up in the balcony. For experimental to test the thermal storage performance. Experimental variables are changing the volume filling in heat pipe, adding a partition in the storage tank and inclining the solar heater to explore energy efficiency. In order to use the variables to test and improvement the solar water heater, the working fluid is pure water. Heating for 2 hours, the heat pipe filling with 40% will have the highest thermal efficiency. Adding a partition in the storage tank will to improve natural convection. Inclines the solar heater will change the working fluid surface in the heat pipe. It makes the solar heater reduce saving energy.