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1
Hall, D. A., G. C. Vliet, and T. L. Bergman. "Natural Convection Cooling of Vertical Rectangular Channels in Air Considering Radiation and Wall Conduction." Journal of Electronic Packaging 121, no. 2 (1999): 75–84. http://dx.doi.org/10.1115/1.2792671.
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Temperature distributions on the surfaces of vertical channels formed by parallel plates heated uniformly and symmetrically and cooled by conduction, radiation, and natural convection in air are determined numerically and experimentally. Effects of wall separation, thickness, thermal conductivity, and emissivity on the wall temperature distribution are determined. Both cases of controlled and uncontrolled channel edge leading and exit edge temperatures are examined. Optimum channel widths and correlations for the maximum wall temperature rise are offered for both the controlled and uncontrolled edge temperature conditions.
2
Alharbi, Ali Y., Deborah V. Pence, and Rebecca N. Cullion. "Thermal Characteristics of Microscale Fractal-Like Branching Channels." Journal of Heat Transfer 126, no. 5 (2004): 744–52. http://dx.doi.org/10.1115/1.1795236.
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Heat transfer through a fractal-like branching flow network is investigated using a three-dimensional computational fluid dynamics approach. Results are used for the purpose of assessing the validity of, and providing insight for improving, assumptions imposed in a previously developed one-dimensional model for predicting wall temperature distributions through fractal-like flow networks. As currently modeled, the one-dimensional code fairly well predicts the general wall temperature trend simulated by the three-dimensional model; hence, demonstrating its suitability as a tool for design of fractal-like flow networks. Due to the asymmetry in the branching flow network, wall temperature distributions for the proposed branching flow network are found to vary with flow path and between the various walls forming the channel network. Three-dimensional temperature distributions along the various walls in the branching channel network are compared to those along a straight channel. Surface temperature distributions on a heat sink with a branching flow network and a heat sink with a series of straight, parallel channels are also analyzed and compared. For the same observed maximum surface temperature on these two heat sinks, a lower temperature variation is noted for the fractal-like heat sink.
3
Kim, S. H., N. K. Anand, and L. S. Fletcher. "Free Convection Between Series of Vertical Parallel Plates With Embedded Line Heat Sources." Journal of Heat Transfer 113, no. 1 (1991): 108–15. http://dx.doi.org/10.1115/1.2910512.
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Laminar free convective heat transfer in channels formed between series of vertical parallel plates with an embedded line heat source was studied numerically. These channels resemble cooling passages in electronic equipment. The effect of a repeated boundary condition and wall conduction on mass flow rate (M), maximum surface temperature (θh,max and θc,max), and average surface Nusselt number (Nuh and Nuc) is discussed. Calculations were made for Gr*=10 to 106, K=0.1, 1, 10, and 100, and t/B=0.1 and 0.3. The effect of a repeated boundary condition decreases the maximum hot surface temperature and increases the maximum cold surface temperature. The effect of a repeated boundary condition with wall conduction increases the mass flow rate. The maximum increase in mass flow rate due to wall conduction is found to be 155 percent. The maximum decrease in average hot surface Nusselt number due to wall conduction (t/B and K) occurs at Gr*=106 and is 18 percent. Channels subjected to a repeated boundary condition approach that of a symmetrically heated channel subjected to uniform wall temperature conditions at K≥100.
4
Vasnev, I. R., and N. N. Fedorova. "Numerical modeling of heating a heat flux gauge in a supersonic flow." Journal of Physics: Conference Series 2389, no. 1 (2022): 012010. http://dx.doi.org/10.1088/1742-6596/2389/1/012010.
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Abstract This paper has developed a mathematical model for calculating the conjugate heat transfer between a supersonic airflow at the freestream Mach numbers M ∞ = 3, 4, 5, and a copper plate simulating the sensitive thermocouple element. The calculation results are compared with the experiment. The calculations show the effect of turbulence intensity, temperature boundary condition, and flow rate on sensor heating. The results of the sensor's initial heat fluxes, maximum temperatures, and heating times in different flow regimes are presented. Also, the flow regimes with an adiabatic wall are considered. As a result of calculations, it is shown that for the given freestream Mach numbers under "cold" wall temperature conditions, the sensor warms up to the maximum temperature in 1.5-3 seconds and reaches temperatures from 789 to 1076 K. If the adiabatic conditions are assumed at the channel walls, depending on the Mach number at the channel entrance, the sensor is heated from 1600 to 2250 K.
5
Webb, B. W., and D. P. Hill. "High Rayleigh Number Laminar Natural Convection in an Asymmetrically Heated Vertical Channel." Journal of Heat Transfer 111, no. 3 (1989): 649–56. http://dx.doi.org/10.1115/1.3250732.
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Experiments have been performed to determine local heat transfer data for the natural convective flow of air between vertical parallel plates heated asymmetrically. A uniform heat flux was imposed along one heated wall, with the opposing wall of the channel being thermally insulated. Local temperature data along both walls were collected for a wide range of heating rates and channel wall spacings corresponding to the high modified Rayleigh number natural convection regime. Laminar flow prevailed in all experiments. Correlations are presented for the local Nusselt number as a function of local Grashof number along the channel. The dependence of both average Nusselt number and the maximum heated wall temperature on the modified Rayleigh number is also explored. Results are compared to previous analytical and experimental work with good agreement.
6
Manca, Oronzio, Marilena Musto, and Vincenzo Naso. "Experimental Investigation of Natural Convection in an Asymmetrically Heated Vertical Channel with an Asymmetric Chimney." Journal of Heat Transfer 127, no. 8 (2005): 888–96. http://dx.doi.org/10.1115/1.1928909.
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An experimental investigation on air natural convection, in a vertical channel asymmetrically heated at uniform heat flux, with downstream unheated parallel extensions, is carried out. One extension is coplanar to the unheated channel wall and the distance between the extensions is equal to or greater than the channel gap (geometrically asymmetric chimney). Experiments are performed with different values of the wall heat flux, aspect ratio (Lh∕b), extension ratio (L∕Lh) and expansion ratio (B∕b). For the largest value of the aspect ratio (Lh∕b=10), the adiabatic extensions improve the thermal performance in terms of lower maximum wall temperature of the channel. Optimal configurations of the system with asymmetrical chimney are detected. Flow visualization shows a cold inflow in the channel-chimney system that penetrates down below the channel exit section. Maximum wall temperatures and channel Nusselt numbers are correlated to the channel Rayleigh number, Ra*, and to the geometrical parameters, in the ranges 3.0×102⩽Ra*B∕b⩽1.0105, 1.0⩽B∕b⩽3.0 and 1.0⩽L∕Lh⩽4.0 with Lh∕b=5.0 and 10.0.
7
Lv, Junjie, Guanquan Du, Ping Jin, and Ruizhi Li. "Heat Transfer Analysis and Structural Optimization for Spiral Channel Regenerative Cooling Thrust Chamber." International Journal of Aerospace Engineering 2023 (June 14, 2023): 1–17. http://dx.doi.org/10.1155/2023/8628107.
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There is currently a lack of efficient heat transfer analysis methodologies for spiral channel regenerative cooling that has been increasingly applied in liquid rocket engines. To figure out the heat transfer characteristics of the spiral channel regenerative cooling thrust chamber, a simple 1D method based on the traditional semi-empirical formula after correcting the flow velocity is proposed. The accuracy of this approach is verified by the 3D numerical simulation. The verified method is further used to analyze the distribution of inner wall temperature in the test case and optimize the channel’s parameters. The research shows that the maximum inner wall temperature cooled by the spiral channel is 8.5% lower than that of the straight channel under the same channel size and boundary condition, indicating that the application of the spiral channel significantly improves the cooling effect. In addition, the 1D model combined with the second-order response surface model is employed to optimize the channel width, channel height, pitch, and inner wall thickness aiming for the best cooling effect. The calculated maximum temperature of the inner wall after the structure optimization is 586.6 K, which is 29.8% lower than the initial structure before optimization.
8
Liu, Chun-Ho. "Turbulent Plane Couette Flow and Scalar Transport at Low Reynolds Number." Journal of Heat Transfer 125, no. 6 (2003): 988–98. http://dx.doi.org/10.1115/1.1571084.
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The turbulence structure and passive scalar (heat) transport in plane Couette flow at Reynolds number equal to 3000 (based on the relative speed and distance between the walls) are studied using direct numerical simulation (DNS). The numerical model is a three-dimensional trilinear Galerkin finite element code. It is found that the structures of the mean velocity and temperature in plane Couette flow are similar to those in forced channel flow, but the empirical coefficients are different. The total (turbulent and viscous) shear stress and total (turbulent and conductive) heat flux are constant throughout the channel. The locations of maximum root-mean-square streamwise velocity and temperature fluctuations are close to the walls, while the location of maximum root-mean-square spanwise and vertical velocity fluctuations are at the channel center. The correlation coefficients between velocities and temperature are fairly constant in the center core of the channel. In particular, the streamwise velocity is highly correlated with temperature (correlation coefficient ≈−0.9). At the channel center, the turbulence production is unable to counterbalance the dissipation, in which the diffusion terms (both turbulent and viscous) bring turbulent kinetic energy from the near-wall regions toward the channel center. The snapshots of the DNS database help explain the nature of the correlation coefficients. The elongated wall streaks for both streamwise velocity and temperature in the viscous sublayer are well simulated. Moreover, the current DNS shows organized large-scale eddies (secondary rotations) perpendicular to the direction of mean flow at the channel center.
9
Trenc, F., and R. Pavleticˇ. "Combined Air-Oil Cooling on a Supercharged TC & IC TAM Diesel Engine." Journal of Engineering for Gas Turbines and Power 115, no. 4 (1993): 742–46. http://dx.doi.org/10.1115/1.2906768.
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In order to reduce the maximum cylinder wall temperatures of an air-cooled TC&IC diesel engine with large longitudinal and circumferential temperature gradients, a curved, squared cross-sectional channel supplied with engine lubrication oil was introduced into the upper part of the cylinder wall. Numerical analyses of the heat transfer within the baseline air-cooled cylinder and intensive experimental work helped to understand the temperature situation in the cylinder at diverse engine running conditions. The results of the combined cooling were greatly affected by the design, dimensions, position of the channel, and the distribution of the cooling oil flow, and are presented in the paper.
10
Lotfian, Ali, and Ehsan Roohi. "Radiometric flow in periodically patterned channels: fluid physics and improved configurations." Journal of Fluid Mechanics 860 (December 7, 2018): 544–76. http://dx.doi.org/10.1017/jfm.2018.880.
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With the aid of direct simulation Monte Carlo (DSMC), we conduct a detailed investigation pertaining to the fluid and thermal characteristics of rarefied gas flow with regard to various arrangements for radiometric pumps featuring vane and ratchet structures. For the same, we consider three categories of radiometric pumps consisting of channels with their bottom or top surfaces periodically patterned with different structures. The structures in the design of the first category are assumed to be on the bottom wall and consist of either a simple vane, a right-angled triangular fin or an isosceles triangular fin. The arrangements on the second category of radiometric pumps consist of an alternating diffuse–specular right-angled fin and an alternating diffuse–specular isosceles fin on the bottom wall. The third category contains either a channel with double isosceles triangular fins on its lowermost surface or a zigzag channel with double isosceles triangular fins on both walls. In the first and the third categories, the surfaces of the channel and its structures are considered as diffuse reflectors. The temperature is kept steady on the horizontal walls of the channel; thus, radiometric flow is created by subjecting the adjacent sides of the vane/ratchet to constant but unequal temperatures. On the other hand, for the second category, radiometric flow is introduced by specifying different top/bottom channel wall temperatures. The DSMC simulations are performed at a Knudsen number based on the vane/ratchet height of approximately one. The dominant mechanism in the radiometric force production is clarified for the examined configurations. Our results demonstrate that, at the investigated Knudsen number, the zigzag channel experiences maximum induced velocity with a parabolic velocity profile, whereas its net radiometric force vanishes. In the case of all other configurations, the flow pattern resembles a Couette flow in the open section of the channel situated above the vane/ratchet. To further enhance the simulations, the predictions of the finite volume discretization of the Boltzmann Bhatnagar–Gross–Krook (BGK)–Shakhov equation for the mass flux dependence on temperature difference and Knudsen number are also reported for typical test cases.
11
Zhang, Shurui, Yong Li, Xudong Wang, Songcai Lu, Yusong Yu, and Jun Yang. "Effects of the Wall Temperature on Rarefied Gas Flows and Heat Transfer in a Micro-Nozzle." Micromachines 15, no. 1 (2023): 22. http://dx.doi.org/10.3390/mi15010022.
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When the satellite is in orbit, the thruster will experience drastic temperature changes (100–1000 K) under solar radiation, which will affect the rarefied gas flow state in the micro-nozzle structure of the cold gas micro-thruster. In this study, the effect of different wall temperatures on the rarefied flow and heat transfer in the micro-nozzle is investigated based on the DSMC method. The micro-nozzle structure in this paper has a micro-channel with a large length-to-diameter ratio of 10 and a micro-scale needle valve displacement (maximum needle valve displacement up to 4 μm). This leads to more pronounced multiscale flow characteristics in the micro-nozzle, which is more influenced by the change in wall temperature. At wall temperatures ranging from 100 K to 1000 K, the spatial distribution of local Kn distribution, slip velocity distribution, temperature, and wall heat flux distribution in the micro-nozzle were calculated. The slip flow region is located in the flow channel and transforms into transition flow as the slip velocity reaches approximately 50 m/s. The spatial distribution of the flow pattern is dominated by the wall temperature at small needle valve opening ratios. The higher the wall temperature, the smaller the temperature drop ratio in the low-temperature region inside the micro-nozzle. The results of the study provide a reference for the design of temperature control of micro-nozzles in cold gas micro-thrusters.
12
Kuzevanov, Vyacheslav S., and Sergey K. Podgorny. "Gas-cooled nuclear reactor core shaping using heat exchange intensifiers." Nuclear Energy and Technology 5, no. (1) (2019): 75–80. https://doi.org/10.3897/nucet.5.34294.
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The need to shape reactor cores in terms of coolant flow distributions arises due to the requirements for temperature fields in the core elements (Safety guide No. NS-G-1.12. 2005, IAEA nuclear energy series No. NP-T-2.9. 2014, Specific safety requirements No. SSR-2/1 (Rev.1) 2014). However, any reactor core shaping inevitably leads to an increase in the core pressure drop and power consumption to ensure the primary coolant circulation. This naturally makes it necessary to select a shaping principle (condition) and install heat exchange intensifiers to meet the safety requirements at the lowest power consumption for the coolant pumping. The result of shaping a nuclear reactor core with identical cooling channels can be predicted at a quality level without detailed calculations. Therefore, it is not normally difficult to select a shaping principle in this case, and detailed calculations are required only where local heat exchange intensifiers are installed. The situation is different if a core has cooling channels of different geometries. In this case, it will be unavoidable to make a detailed calculation of the effects of shaping and heat transfer intensifiers on changes in temperature fields. The aim of this paper is to determine changes in the maximum wall temperatures in cooling channels of high-temperature gas-cooled reactors using the combined effects of shaped coolant mass flows and heat exchange intensifiers installed into the channels. Various shaping conditions have been considered. The authors present the calculated dependences and the procedure for determining the thermal coolant parameters and maximum temperatures of heat exchange surface walls in a system of parallel cooling channels. Variant calculations of the GT-MHR core (NRC project No. 716 2002, Vasyaev et al. 2001, Neylan et al. 1994) with cooling channels of different diameters were carried out. Distributions of coolant flows and temperatures in cooling channels under various shaping conditions were determined using local resistances and heat exchange intensifiers. Preferred options were identified that provide the lowest maximum wall temperature of the most heat-stressed channel at the lowest core pressure drop. The calculation procedure was verified by direct comparison of the results calculated by the proposed algorithm with the CFD simulation results (ANSYS Fluent User's Guide 2016, ANSYS Fluent. Customization Manual 2016, ANSYS Fluent. Theory Guide 2016, Shaw1992, Anderson et al. 2009, Petrila and Trif 2005, Mohammadi and Pironneau 1994).
13
Dresia, Kai, Eldin Kurudzija, Jan Deeken, and Günther Waxenegger-Wilfing. "Improved Wall Temperature Prediction for the LUMEN Rocket Combustion Chamber with Neural Networks." Aerospace 10, no. 5 (2023): 450. http://dx.doi.org/10.3390/aerospace10050450.
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Accurate calculations of the heat transfer and the resulting maximum wall temperature are essential for the optimal design of reliable and efficient regenerative cooling systems. However, predicting the heat transfer of supercritical methane flowing in cooling channels of a regeneratively cooled rocket combustor presents a significant challenge. High-fidelity CFD calculations provide sufficient accuracy but are computationally too expensive to be used within elaborate design optimization routines. In a previous work it has been shown that a surrogate model based on neural networks is able to predict the maximum wall temperature along straight cooling channels with convincing precision when trained with data from CFD simulations for simple cooling channel segments. In this paper, the methodology is extended to cooling channels with curvature. The predictions of the extended model are tested against CFD simulations with different boundary conditions for the representative LUMEN combustor contour with varying geometries and heat flux densities. The high accuracy of the extended model’s predictions, suggests that it will be a valuable tool for designing and analyzing regenerative cooling systems with greater efficiency and effectiveness.
14
Gao, Feng, Qian Zhang, Hongyu Xiao, Chengtao Zhang, and Xuefeng Xia. "Modeling and analysis of regenerative cooling channels for scramjet engine." MATEC Web of Conferences 316 (2020): 03002. http://dx.doi.org/10.1051/matecconf/202031603002.
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This paper presents a CFD simulation analysis method for the regenerative cooling channel of a supercombustion ramjet engine, and performs three-dimensional modeling and analysis. The influences of inlet mass flow, inlet pressure, and inlet temperature on the flow and heat transfer characteristics of kerosene in the cooling channel were analyzed, and the conclusions are as follows: The larger the inlet mass flow, the lower the maximum wall temperature and oil temperature. The change trend of wall temperature is basically the same under different inlet pressure conditions, all of which increase violently first, then stabilize and then suddenly increase suddenly, then decrease almost to the outlet, and the temperature is almost the same under different conditions.As the inlet temperature decreases, the temperature difference between the wall surface and kerosene becomes larger, and the convective heat transfer coefficient gradually increases.
15
Liu, Yang, Xintao Hu, Feng Gao, and Yanan Gao. "Heat Transfer and Flow Characteristics of Coal Slurries under the Temperature Difference between Inside and Outside of the Channel." Applied Sciences 12, no. 23 (2022): 12028. http://dx.doi.org/10.3390/app122312028.
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The pipeline transportation of coal slurries is always subject to a temperature difference between the outdoors environment and the fluid body. As slurries’ viscosity is typically temperature dependent, the flow is accompanied by the heat transfer. In this study, we used the CFD method to investigate temperature distributions and flow structures in straight and curved channels, which has not previously been investigated, according to our knowledge. First, the results demonstrate that the cooling process influences the flow structures along the stream. The fluid turns more sharply in the cooler fluid in the curved channel, the streamlines overlap at an earlier position within the bend, and the velocity maximum zone is wider. Cooling also has a significant impact on transverse flow. Because of the higher viscosity of the more cooled fluid and thus the difficulty of shearing the fluid in the stream-wise direction, the vorticity and strength of the vortex flow are greater. The fluid velocity at the central part of the channel points toward the inner wall at the beginning of the bend, resulting in an inner-wall biased temperature distribution, as the heat transfer is partially carried out by the fluid velocity. The central velocity points toward the outer wall at the end of the bend, resulting in the outer-wall biased temperature profile.
16
Lozynskyi, V. "Numerical analysis of wall temperature in underground channel during pulverized coal combustion modeling." Collection of Research Papers of the National Mining University 79 (December 30, 2024): 49–62. https://doi.org/10.33271/crpnmu/79.049.
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Purpose. To determine the optimal approach for evaluating the temperature characteristics of the channel wall and analyze them in numerical modeling of pulverized coal combustion. Methods. The study was conducted using numerical modeling of the pulverized coal combustion process in a cylindrical channel 30 m long and 1 m in diameter, which is formed after auger coal mining. The Ansys Fluent software was used for modeling, applying the non-premixed combustion model and the k-ε turbulence model. Calculations were performed for time intervals of 1, 12, 24, 36, and 48 hours. Findings. Analysis of the obtained temperature fields showed that the maximum temperature in the combustion zone increases from 1220ºC (1 hour) to 1540°C (24 hours). The process stabilizes by the 12th hour at a temperature of 1490ºC. It was found that the temperature in the channel rapidly decreases after 7–10 m from the inlet, stabilizing at 490–520 ºC. The primary cause of heat loss is the high thermal conductivity of the surrounding rocks. It was determined that the Twall parameter most accurately represents the actual temperature regime of the wall and allows for an assessment of the system’s thermal state. The originality. For the first time, a comprehensive analysis of the temperature field dynamics of the channel wall during prolonged pulverized coal combustion in a coal seam channel was conducted. Critical zones of heat loss and temperature stabilization were identified, allowing for the justified selection of the optimal wall temperature parameter for numerical modeling. Indicators of the percentage distribution of static temperature in the channel and the temperature of the wall around the channel over time were obtained. Practical implementation. The obtained results can be used to improve numerical modeling methodologies for underground coal combustion and co-gasification processes. The identified temperature distribution patterns enable the optimization of fuel and air supply parameters to enhance the efficiency of thermochemical conversion. The proposed approach can be applied in the design of coal seam co-gasification technologies.
17
Kosugi, Ryouji, Kenji Suzuki, Kazuto Takao, et al. "Fabrication of 4H-SiC DIMOSFETs by High-Temperature (>1400°C) Rapid Thermal Oxidation and Nitridation Using Cold-Wall Oxidation Furnace." Materials Science Forum 527-529 (October 2006): 1309–12. http://dx.doi.org/10.4028/www.scientific.net/msf.527-529.1309.
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A passivation annealing in nitric oxide (NO) ambient significantly reduces the interfacial defects of the SiO2/4H-SiC interface and improves the inversion MOS channel mobility. Effects of the nitridation in NO ambient become more pronounced at high temperatures in general. However, the maximum process temperature in a standard hot-wall oxidation furnace is restricted around 1200oC due to the softening point of quartz. Meanwhile, by use of a cold-wall oxidation furnace, high temperature and short time thermal processes become possible. In this study, we have developed an extremely high temperature (>1400oC) rapid thermal processing for the gate oxidation in the 4H-SiC DIMOSFET fabrication process. The peak MOS channel mobility of lateral MOSFETs on the DIMOSFET chip shows as high as 19cm2/Vs. The specific on-resistance of the device was 12.5mcm2 and the blocking voltage was 950V with gate shorted to the source.
18
Zditovets, A. G., N. A. Kiselev, S. S. Popovich, and Yu A. Vinogradov. "The effect of the initial swirl of the supersonic flow of humid air on the adiabatic wall temperature." Journal of Physics: Conference Series 2088, no. 1 (2021): 012056. http://dx.doi.org/10.1088/1742-6596/2088/1/012056.
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Abstract The paper presents the results of measuring the adiabatic wall temperature of an axisymmetric channel during acceleration of the moist air flow in it to supersonic speed. The initial swirl was imparted to the flow (swirling parameter S = 0.5, 1.0, 2.5). The relative initial humidity (RH) of the flow varied in the range of 10 ÷ 90%. When the flow was accelerated to supersonic speeds, part of the moisture condensed, which influenced the wall temperature. It is shown experimentally that with an increase in the initial moisture content of the flow to certain values, the distribution of the wall temperature for a flow without initial swirl (S = 0) and with swirl with S = 0.5, 1.0 practically coincide. However, from a certain value of RH, the wall temperature in the case of a swirling flow decreases in comparison with a flow without swirling. The maximum decrease in the wall temperature was achieved at RH = 90%. An increase in the initial swirl to S = 2.5 led to a greater decrease in the wall temperature, while the mass air flow through the channel decreased by 26% at an identical pressure drop.
19
Tiwari, Ambrish K., and Ashok K. Singh. "Natural Convection in a Porous Medium Bounded by a Long Vertical WavyWall and a Parallel Flat Wall." Zeitschrift für Naturforschung A 65, no. 10 (2010): 800–810. http://dx.doi.org/10.1515/zna-2010-1006.
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This paper presents natural convection in a porous medium bounded by a long vertical wavy wall and a parallel wall. The shape of the wavy wall is assumed to follow a profile of cosine curve. The wall is kept at a constant heat flux while the parallel wall is kept at a constant temperature. The governing systems of nonlinear partial differential equations in their non-dimensional form are linearised by using the perturbation method in terms of amplitude and the analytical solutions for velocity and temperature fields have been obtained in terms of various parameters occurring in the model. A numerical study of the analytical solution is performed with respect to the realistic fluid air in order to illustrate the interactive influences of governing parameters on the temperature and velocity fields as well as skin friction and Nusselt number. It is found that in the case of maximum waviness (positive and negative), the velocity component along the wall has a reverse trend near the flat wall. It is observed that the parallel flow through the channel at zero waviness is greater than at maximum waviness (positive and negative) while the same trend occurs for perpendicular flow in the opposite direction. Examination of the Nusselt number shows that in the presence and absence of a heat source, the heat flows from the porous region towards the walls but in the presence of a sink, the heat flows from the walls into the porous region.
20
Liu, Zhong Bao, and Ya Xin Su. "An Unsteady Model for Natural Ventilation with Solar Chimney." Advanced Materials Research 354-355 (October 2011): 286–89. http://dx.doi.org/10.4028/www.scientific.net/amr.354-355.286.
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A one dimensional unsteady mathematical model for predicting the air mass flow rate in a solar chimney has been proposed. The thermal resistance and thermal inertia of both the glass cover and heat absorbing wall were considered in the present model. Crank-Nicolson finite difference numerical method was used to solve the differential equations. The variation of the air temperature in the solar chimney was solved by integrating the controlling equation for the air along the chimney height. Results show the absorber wall reaches its peak temperature 2 hours later with respect to the maximum ambient temperature. The air temperature in the channel varies with the solar radiation in a day and researches its peak value at about 2:00pm. The air mass flow rate increases remarkably with the increase of the channel depth when the solar radiation is higher from 11:00 am to 3:00 pm. The maximum of air mass flow rate occurs at around 2:00pm
21
Kuzevanov, Vyacheslav S., and Sergey K. Podgorny. "Gas-cooled nuclear reactor core shaping using heat exchange intensifiers." Nuclear Energy and Technology 5, no. 1 (2019): 75–80. http://dx.doi.org/10.3897/nucet.5.34294.
Full textAbstract:
The need to shape reactor cores in terms of coolant flow distributions arises due to the requirements for temperature fields in the core elements (Safety guide No. NS-G-1.12. 2005, IAEA nuclear energy series No. NP-T-2.9. 2014, Specific safety requirements No. SSR-2/1 (Rev.1) 2014). However, any reactor core shaping inevitably leads to an increase in the core pressure drop and power consumption to ensure the primary coolant circulation. This naturally makes it necessary to select a shaping principle (condition) and install heat exchange intensifiers to meet the safety requirements at the lowest power consumption for the coolant pumping. The result of shaping a nuclear reactor core with identical cooling channels can be predicted at a quality level without detailed calculations. Therefore, it is not normally difficult to select a shaping principle in this case, and detailed calculations are required only where local heat exchange intensifiers are installed. The situation is different if a core has cooling channels of different geometries. In this case, it will be unavoidable to make a detailed calculation of the effects of shaping and heat transfer intensifiers on changes in temperature fields. The aim of this paper is to determine changes in the maximum wall temperatures in cooling channels of high-temperature gas-cooled reactors using the combined effects of shaped coolant mass flows and heat exchange intensifiers installed into the channels. Various shaping conditions have been considered. The authors present the calculated dependences and the procedure for determining the thermal coolant parameters and maximum temperatures of heat exchange surface walls in a system of parallel cooling channels. Variant calculations of the GT-MHR core (NRC project No. 716 2002, Vasyaev et al. 2001, Neylan et al. 1994) with cooling channels of different diameters were carried out. Distributions of coolant flows and temperatures in cooling channels under various shaping conditions were determined using local resistances and heat exchange intensifiers. Preferred options were identified that provide the lowest maximum wall temperature of the most heat-stressed channel at the lowest core pressure drop. The calculation procedure was verified by direct comparison of the results calculated by the proposed algorithm with the CFD simulation results (ANSYS Fluent User’s Guide 2016, ANSYS Fluent. Customization Manual 2016, ANSYS Fluent. Theory Guide 2016, Shaw1992, Anderson et al. 2009, Petrila and Trif 2005, Mohammadi and Pironneau 1994).
22
Wang, Jiale, Shaohuan Qi, and Yu Xu. "Numerical Investigations of the Thermal-Hydraulic Characteristics of Microchannel Heat Sinks Inspired by Leaf Veins." Energies 17, no. 2 (2024): 311. http://dx.doi.org/10.3390/en17020311.
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A microchannel heat sink (MCHS) is a potential solution for chip and battery thermal management. The new microchannel structure is beneficial for further improving the thermal-hydraulic performance of MCHSs. Inspired by leaf veins, six new channel structures were designed, and the effects of the channel structures (three parallel structures named PAR I, II, and III and three pinnate structures named PIN I, II, and III), channel depths (0.4, 0.8, and 1.6 mm), and heat fluxes (20, 50, and 80 kW/m2) were investigated via numerical simulation. The cooling medium was water, and the heating area was 40 × 40 mm2. Both PAR II and PIN III exhibit superior overall performance, characterized by the highest Nusselt number and the lowest heating wall temperature. Moreover, PIN III demonstrates the lowest standard deviation in heating wall temperature, while PAR II exhibits the lowest friction factor. The greater the channel depth is, the larger the solid–liquid contact area is, leading to a reduced wall temperature at the interface under identical conditions of inlet Reynolds number and heating wall heat flux. Consequently, an increase in the Nusselt number corresponds to an increase in the friction factor. The maximum value and standard deviation of the heating wall temperature increase with increasing heat flux, while the Nusselt number and friction factor remain unaffected. The overheating near the two right angles of the outlet should be carefully considered for an MCHS with a single inlet–outlet configuration.
23
Liu, Jian, Mengyao Xu, Pengchao Liu, and Wenxiong Xi. "Heat Transfer and Flow Structure Characteristics of Regenerative Cooling in a Rectangular Channel Using Supercritical CO2." Aerospace 10, no. 6 (2023): 564. http://dx.doi.org/10.3390/aerospace10060564.
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At an extremely high Mach number, the regenerative cooling of traditional kerosene cannot meet the requirement of the heat sink caused by aerodynamic heating and internal combustion in a scramjet propulsion system. As a supplement of traditional regenerative cooling, supercritical CO2 is regarded as an effective coolant in severe heating environments due to its excellent properties of heat and mass transportation. In this paper, the heat transfer and flow structure characteristics of regenerative cooling in a rectangular channel using supercritical CO2 are analyzed numerically using a validated model. The effect of heat flux magnitude, nonuniform heat flux, acceleration and buoyancy and flow pattern are considered to reveal the regenerative cooling mechanism of supercritical CO2 in the engine condition of a scramjet. The results indicate that the heat transfer deterioration phenomenon becomes obvious in the cooling channel loaded with relatively high heat flux. Compared with the cooling channels loaded with increased heat flux distribution, the maximum temperature increased for the channel loaded with decreased heat flux distributions. When larger acceleration is applied, a relatively lower wall temperature distribution and higher heat transfer coefficients are obtained. The wall temperature distribution becomes more uniform and the high-temperature region is weakened when the coolants in adjacent channels are arranged as a reversed flow pattern. Overall, the paper provides some references for the utilization of supercritical CO2 in regenerative cooling at an extremely high Mach number in a scramjet.
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Rahim Mashaei, Payam, Seyed Mostafa Hosseinalipour, and Mehdi Bahiraei. "Numerical Investigation of Nanofluid Forced Convection in Channels with Discrete Heat Sources." Journal of Applied Mathematics 2012 (2012): 1–18. http://dx.doi.org/10.1155/2012/259284.
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Numerical simulation is performed to investigate the laminar force convection of Al2O3/water nanofluid in a flow channel with discrete heat sources. The heat sources are placed on the bottom wall of channel which produce much thermal energy that must be evacuated from the system. The remaining surfaces of channel are kept adiabatic to exchange energy between nanofluid and heat sources. In the present study the effects of Reynolds number (, and 1000), particle volume fraction ( (distilled water), 1 and 4%) on the average heat transfer coefficient (h), pressure drop (), and wall temperature () are evaluated. The use of nanofluid can produce an asymmetric velocity along the height of the channel. The results show a maximum value 38% increase in average heat transfer coefficient and 68% increase in pressure drop for all the considered cases when compared to basefluid (i.e., water). It is also observed that the wall temperature decreases remarkably as Re andϕincrease. Finally, thermal-hydraulic performance (η) is evaluated and it is seen that best performance can be obtained for and %.
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Manca, Oronzio, Sergio Nardini, and Vincenzo Naso. "Effect on Natural Convection of the Distance Between an Inclined Discretely Heated Plate and a Parallel Shroud Below." Journal of Heat Transfer 124, no. 3 (2002): 441–51. http://dx.doi.org/10.1115/1.1470488.
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An experimental study on air natural convection on an inclined discretely heated plate with a parallel shroud below was carried out. Three heated strips were located in different positions on the upper wall. The distance between the walls, b, was changed in the range 7.0–40.0 mm and two values of the heat flux dissipated by the heaters were taken into account. Several inclination angles between the vertical and the horizontal were tested. The wall temperature distribution as a function of the channel spacing and the inclination angle, the source heat flux, the number and the arrangement of the heat sources are presented. The analysis shows that, for angles not greater than 85 deg, increasing the distance between walls does not reduce the wall temperatures, whereas at greater tilting angles (>85 deg) there is an opposite tendency. This is confirmed by flow visualization at angles equal to 85 deg and 90 deg and b=20.0 and 32.3 mm. Dimensionless maximum wall temperatures are correlated to the process parameters in the ranges 1.2s˙104⩽Ral cos θ⩽8.6s˙105; 0 deg⩽θ⩽88 deg; 0.48⩽l/b⩽1.6 and 10⩽L/b⩽32.6 with 1.0⩽d/l⩽3.0; the agreement with experimental data is good. The spacing which yields the best thermal performance of the channel is given. Local Nusselt numbers are evaluated and correlated to the local Rayleigh numbers and the tilting angles in the ranges 20⩽Rax′⩽8.0s˙105 and 0 deg⩽θ⩽88 deg. The exponent of monomial correlations between local Nusselt and Rayleigh numbers are in the 0.23–0.26 range. Comparisons with data from the literature, in terms of Nusselt number, exhibited minor discrepancies, mainly because of some difference in test conditions and of heat conduction in the channel walls.
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Jing, Hai Wei, and An Gui Li. "Experimental Study of a Vertical Channel Solar Chimney with Uniform Heat Flux for Natural Ventilation in Buildings." Advanced Materials Research 374-377 (October 2011): 585–89. http://dx.doi.org/10.4028/www.scientific.net/amr.374-377.585.
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A experimentally study has been carried out to predict airflow rate, temperature field and velocity field for different chimney gap and heat flux. Results showed that, for veritical solar chimney,there is an optimum ratio of chimney width-to height to achieve a maximum airflow rate. The optimum ratio is about 1：2. Meanwhile,temperature and velocity field of solar chimney channel were analyzed. The air temperature and the velocity approaching to the surface of the heated wall are higher than that away from the surface of the heated wall.
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Suzzi, Nicola, and Marco Lorenzini. "Performance assessment of electro-osmotic flow of rectangular microchannels with smoothed corners." Journal of Physics: Conference Series 2648, no. 1 (2023): 012069. http://dx.doi.org/10.1088/1742-6596/2648/1/012069.
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Abstract Microchannel heat sinks are a viable alternative to traditional thermal management systems when high fluxes over small surfaces are involved. To avoid high pressure drops especially when liquids are concerned, electro-osmotic flow, a phenomenon which is relevant at the microscales only, can be employed profitably. Joule heating, which occurs every time an electrical current is circulated through a conductor with finite electrical resistance, may hamper the application of electro-osmotic flows significantly; its effects must therefore be investigated, as should the influence of the entry length on the overall transport phenomena which occur in the microchannel, especially so since channels with uniform temperature at the walls tend to be somewhat short, to mitigate heat generation due to Joule heating. In this paper the transport phenomena occurring within a microchannel of rectangular cross-section with uniform wall temperature through which an electro-osmotic flow occurs is studied, while considering the flow fully developed hydrodynamically but thermally developing (Graetz problem). The corners are then smoothed progressively and the effect of this change in the shape of the cross-section over the non-dimensional dissipated power or temperature difference between wall and fluid is investigated using the performance evaluation criteria introduced by Webb. Correlations are suggested for the Poiseuille and Nusselt numbers for all configurations as are criteria to obtain the maximum allowable channel length, i.e. the length of the channel over which the walls start to cool the fluid, owing to Joule heating, in terms of the hydraulic diameter.
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Zevyakin, Aleksander S., Valery V. Kolesov, Artem V. Sobolev, and Oleg Yu Kochnov. "Possibility for using a low-enriched target to produce 99Mo in the MAK-2 research channel of the VVR-ts reactor." Nuclear Energy and Technology 8, no. 2 (2022): 133–37. http://dx.doi.org/10.3897/nucet.8.89351.
Full textAbstract:
Thermal-hydraulic calculations have been conducted with respect to the active part of the MAK-2 loop facility of the VVR-ts research reactor for the 99Mo production. The computational studies were undertaken both for the case of using a highly 235U enriched target and for a low-enriched target. The calculation was performed for the actual technical characteristics of the research channel. The power density for the two simulated cases was obtained in the course of a preliminary neutronic calculation and selected for the most heated channel. The problem is solved for the steady-state mode of the channel coolant flow and takes into account the dependence of the thermophysical parameters of materials on temperature. The volumetric temperature distribution in the channel was obtained in the process of the calculation. The calculation results present the maximum temperatures of the target materials for the 99Mo production. An analysis of the obtained results has shown that the maximum temperatures of the aluminum sleeve and the target filling materials do not exceed the critical values. For the analyzed calculation cases, the maximum coolant temperature is localized at a point near the sleeve wall surface and does not reach the boiling temperature for a given pressure. The study has therefore shown that it is possible to reduce the 235U enrichment of the target filling fissile material to 19.7%, provided the average density of the mixture and the amount of 235U in the target remain the same. At the same time, the amount of the medicinally important 99Mo generated will not practically change, which will lead to reduced capital costs for a highly enriched mixture of the target matrix.
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Kamali, Daryoush, Saeid Hejri, Narges Akbar, and Emad Hasani Malekshah. "Comprehensive hydrothermal analysis of an inclined mini-channel with fin array: by dual/multi-relaxation-time LBM and experimental process on SiO2-glycol rheological/thermal characteristics." International Journal of Numerical Methods for Heat & Fluid Flow 31, no. 7 (2021): 2405–29. http://dx.doi.org/10.1108/hff-08-2020-0527.
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Purpose The purpose of this study is to present a comprehensive hydrothermal analysis on an inclined mini-channel using numerical and experimental techniques. The fin array acts as heat source within the channel, and a wavy wall located at the top of the channel is heat sink. The side walls are insulated with curved profiles. Also, the channel is inclined with four known inclination angles. To solve the governing equations, the dual-multi-relaxation-time lattice Boltzmann method with D2Q9 and D2Q5 lattice models for flow and temperature fields is used, respectively. Also, the channel is filled with SiO2-glycol nanofluid. Design/methodology/approach Identifying the behavior of a thermal component during natural convective flow is a challenging topic due to its complexities. This paper focuses on analyzing the thermal and hydrodynamic aspects of a narrow channel equipping with fin array. Findings Two correlations are proposed considering temperature and volume fraction ranges for thermal conductivity and dynamic viscosity according to measured experimental data which are used in the numerical phase. Finally, the structure of flow, temperature distribution of fluid, local thermal and viscous dissipations, volume-averaged entropy production, Bejan number and heat transfer rate are extracted by numerical simulations. The results show that the average Nusselt number enhances about 57% (maximum enhancement percentage) when volume fraction increases from 1% to 3% at Ra = 106 and θ = 90°. In addition, the value of entropy generation is maximum at φ = 1%, Ra = 106 and φ = 90°. Also, the maximum enhancement of entropy generation in range of Ra = 103 to 106 is about 4 times at φ = 1% and θ = 90°. Originality/value The originality of the present study is combining a modern numerical method (i.e. dual/multi-relaxation-time LBM) with experimental observation on characteristics of SiO2-glycol nanofluid to study the thermal and hydrodynamic properties of the studied mini-channel.
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Andreozzi, Assunta. "Numerical study of mixed convection in a horizontal no parallel-plates channel with an unheated moving plate." International Journal of Numerical Methods for Heat & Fluid Flow 28, no. 3 (2018): 547–70. http://dx.doi.org/10.1108/hff-09-2016-0340.
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Purpose The purpose of this paper is to analyze the thermal and fluid dynamic behaviors of mixed convection in air because of the interaction between a buoyancy flow and a moving plate induced flow in a horizontal no parallel-plates channel to investigate the effects of the minimum channel spacing, wall heat flux, moving plate velocity and converging angle. Design/methodology/approach The horizontal channel is made up of an upper inclined plate heated at uniform wall heat flux and a lower adiabatic moving surface (belt). The belt moves from the minimum channel spacing section to the maximum channel spacing section at a constant velocity so that its effect interferes with the buoyancy effect. The numerical analysis is accomplished by means of the finite volume method, using the commercial code Fluent. Findings Results in terms of heated upper plate and moving lower plate temperatures and stream function fields are presented. The paper underlines the thermal and fluid dynamic differences when natural convection or mixed convection takes place, varying minimum channel spacing, wall heat flux, moving plate velocity and converging angle. Research limitations/implications The hypotheses on which the present analysis is based are two-dimensional, laminar and steady state flow and constant thermo physical properties with the Boussinesq approximation. The minimum distance between the upper heated plate of the channel and its lower adiabatic moving plate is 10 and 20 mm. The moving plate velocity varies in the range 0-1 m/s; the belt moves from the right reservoir to the left one. Three values of the uniform wall heat flux are considered, 30, 60 and 120 W/m2, whereas the inclination angle of the upper plate θ is 2° and 10°. Practical implications Mixed convection because of moving surfaces in channels is present in many industrial applications; examples of processes include continuous casting, extrusion of plastics and other polymeric materials, bonding, annealing and tempering, cooling and/or drying of paper and textiles, chemical catalytic reactors, nuclear waste repositories, petroleum reservoirs, composite materials manufacturing and many others. The investigated configuration is used in applications such as re-heating of billets in furnaces for hot rolling process, continuous extrusion of materials and chemical vapor deposition, and it could also be used in thermal control of electronic systems. Originality/value This paper evaluates the thermal and velocity fields to detect the maximum temperature location and the presence of fluid recirculation. The paper is useful to thermal designers.
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Lee, Hamin, Seokjun Park, and Chang-Wan Kim. "Electrochemical–Thermal Fluid Coupled Analysis and Statistical Analysis of Cooling System for Large Pouch Cells." Mathematics 12, no. 20 (2024): 3261. http://dx.doi.org/10.3390/math12203261.
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In large-format pouch cells for electric vehicles, the issues of elevated and non-uniform temperatures resulting from heat generation are intensified, necessitating the use of liquid cooling systems. The design factors of the liquid cooling system influence the maximum temperature and temperature differences in the module as well as the pumping power of the cooling system. Although it is known that these design factors interact, research on these interactions and their effects is currently lacking. In this study, the individual as well as interaction effects of design factors on the performance of the liquid cooling system for a large-format pouch cell module were investigated using design of experiment and analyzed through statistical methods. Electrochemical–thermal fluid coupled analysis was used to calculate the performance according to the design factors of the liquid cooling system. The wall and channel widths are factors that directly determine the coolant flow velocity and cooling plate heat capacity, and they exhibited major effects on all three responses. Moreover, the influence of each design factor tended to change in response to variations in the other design factors. Thus, the effects of each factor individually and of interactions between factors were quantitatively compared and evaluated for significance. The width of the walls was found to contribute the most to the maximum temperature (36.00%) and pumping power (57.56%), while the width of the channels contributed the most to the temperature difference (38.24%), indicating that they are the main influencing factors.
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Zevyakin, Aleksander S., Valery V. Kolesov, Artem V. Sobolev, and Oleg Yu. Kochnov. "Possibility for using a low-enriched target to produce 99Mo in the MAK-2 research channel of the VVR-ts reactor." Nuclear Energy and Technology 8, no. (2) (2022): 133–37. https://doi.org/10.3897/nucet.8.89351.
Full textAbstract:
Thermal-hydraulic calculations have been conducted with respect to the active part of the MAK-2 loop facility of the VVR-ts research reactor for the <sup>99</sup>Mo production. The computational studies were undertaken both for the case of using a highly <sup>235</sup>U enriched target and for a low-enriched target. The calculation was performed for the actual technical characteristics of the research channel. The power density for the two simulated cases was obtained in the course of a preliminary neutronic calculation and selected for the most heated channel. The problem is solved for the steady-state mode of the channel coolant flow and takes into account the dependence of the thermophysical parameters of materials on temperature. The volumetric temperature distribution in the channel was obtained in the process of the calculation. The calculation results present the maximum temperatures of the target materials for the <sup>99</sup>Mo production. An analysis of the obtained results has shown that the maximum temperatures of the aluminum sleeve and the target filling materials do not exceed the critical values. For the analyzed calculation cases, the maximum coolant temperature is localized at a point near the sleeve wall surface and does not reach the boiling temperature for a given pressure. The study has therefore shown that it is possible to reduce the <sup>235</sup>U enrichment of the target filling fissile material to 19.7%, provided the average density of the mixture and the amount of <sup>235</sup>U in the target remain the same. At the same time, the amount of the medicinally important <sup>99</sup>Mo generated will not practically change, which will lead to reduced capital costs for a highly enriched mixture of the target matrix.
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Hernández-Pérez, Iván, Álan Rodriguez-Ake, Daniel Sauceda-Carvajal, Irving Hernández-López, Balaji Kumar, and Ivett Zavala-Guillén. "Experimental Thermal Assessment of a Trombe Wall Under a Semi-Arid Mediterranean Climate of Mexico." Energies 18, no. 1 (2025): 185. https://doi.org/10.3390/en18010185.
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The conventional Trombe wall (TW) with concrete construction has been shown to enhance the indoor environment of buildings in cold and Mediterranean climates. Thus, a TW is an option for reducing energy consumption related to thermal comfort for buildings in the northwestern region of Mexico, characterized by arid and semi-arid conditions with low winter temperatures. The thermal behavior of the TW and a conventional facade (CF) of concrete were compared when installed in the southern wall of reduced-scale test boxes in Ensenada, B.C. Unlike other research works available in the literature, which typically monitored a data point measure of the wall and room temperatures, the present study measured the temperature of key components: the absorber wall, the air at the bottom and top vents, the glass cover, and the air at the cross-section plane of the TW test box. The results showed that the TW increases the air temperature through its channel up to 14 ∘C and yields a maximum thermal efficiency of 84% during a sunny winter week. Further, the indoor air temperature at the midpoint of the TW test module is up to 6 ∘C greater than the obtained on the CF-test module; therefore, the TW improved the thermal comfort conditions during winter.
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Lei, Zhiliang, and Zewei Bao. "Supercritical Heat Transfer and Pyrolysis Characteristics of n-Decane in Circular and Rectangular Channels." Energies 16, no. 9 (2023): 3672. http://dx.doi.org/10.3390/en16093672.
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In this research, the effects of different channel cross-section shapes on the flow, heat transfer and pyrolysis characteristics of n-decane were analyzed and compared based on CFD simulations. The interactions between cracking, heat transfer and flow field in a circular tube and a rectangular tube were studied. The results showed that the mean pressure drop in the rectangular channel is 1.18 times as high as that in the circular channel with pyrolysis due to its smaller equivalent diameter. The maximum value of the chemical heat sink in the rectangular channel is 1.6 times as high as that in the circular channel. The high temperature zone of any cross section in the rectangular channel is much larger than that in the circular channel due to the superposition of the boundary layer and lower turbulent kinetic energy in the corners of the rectangular channel. The maximum value of the Nu in the circular channel is 1.3 times as high as that in the rectangular channel with pyrolysis due to larger heat capacity, lower viscosity and higher wall shear stress.
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Abbasi, F. M., T. Hayat, and F. Alsaadi. "Hydromagnetic peristaltic transport of water-based nanofluids with slip effects through an asymmetric channel." International Journal of Modern Physics B 29, no. 21 (2015): 1550151. http://dx.doi.org/10.1142/s0217979215501519.
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This paper addresses the effects of applied magnetic field and partial slip effects in peristalsis of water-based nanofluids in an asymmetric flow configuration. Analysis is carried out using silver and copper nanoparticles. Viscous dissipation, mixed convection, Ohmic heating and heat generation/absorption are considered. Mathematical modeling is done employing lubrication approximations. Resulting coupled system is solved numerically. Physical quantities like axial velocity, pressure gradient, temperature and heat transfer rate are graphically analyzed. Comparison between the silver–water and copper–water nanofluids is presented and analyzed. Results show that the maximum velocity, temperature and heat transfer rate at the wall in silver–water nanofluid are comparatively greater than that of copper–water nanofluid. It is also observed that addition of nanoparticles results in a decrease in the velocity and temperature of fluid. However, the heat transfer rate at the wall is enhanced through addition of nanoparticles.
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Hou, Qiong Wei, En Hui Yuan, Jin Gang Jiang, and Kun Zhang. "Synthesis and Characterizations of MCM-41 Silica with Thick Pore Wall." Advanced Materials Research 233-235 (May 2011): 2034–37. http://dx.doi.org/10.4028/www.scientific.net/amr.233-235.2034.
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Nano-structured mesoporous silica with highly ordered 2D hexagonal topology has been synthesized using novel surfactant cetyltrimethylammonium tosylate (CTATos) as template via directly hydrothermal treatment at high temperature of 175 °C and varied crystallization time. The maximum pore wall thickness is up to 2.2 nm calculated by BdB method from desorption branch. The enlargement of pore wall thickness and unit-lattice of currently synthesized MCM-41 silica is attributed to the migration and subsequent deposition of the silicate species in the inner pore channel.
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Yin, Liang, Jiaqiang E, and Jie Ding. "Effect of Cooling Header on the Hydrocarbon Fuel Flow Distribution in a Regenerative Cooling Channel." International Journal of Aerospace Engineering 2022 (September 8, 2022): 1–10. http://dx.doi.org/10.1155/2022/3471421.
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Regenerative cooling technology is the most widely used cooling technology in liquid rocket engines, and flow distribution is very important for regenerative cooling heat transfer. In this work, the flow distribution characteristics of Z -type parallel channels were studied through numerical simulation, and the effects of flow area ratio, inlet header shape, and inlet aspect ratio were analyzed. Results showed that changing the inlet cooling header can improve the uniform distribution of flow rate effectively. The nonuniformity coefficient and fuel temperature varied with change in the flow area ratio, inlet header shape, and inlet aspect ratio. The maximum temperature of the wall decreased from 1334.52 K to 1220.61 K when the flow area ratio was changed from 1 to 0.25. An appropriate decrement in the inlet header shape was beneficial to the uniform flow distribution. The inlet aspect ratio should be reduced properly to ensure that each channel experiences similar pressure drop. This research has a certain reference value for the structural design of regenerative cooling channels.
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Campo, Antonio, Oronzio Manca, and Biagio Morrone. "Numerical Investigation of the Natural Convection Flows for Low-Prandtl Fluids in Vertical Parallel-Plates Channels." Journal of Applied Mechanics 73, no. 1 (2005): 96–107. http://dx.doi.org/10.1115/1.1991867.
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Laminar natural convection of metallic fluids (Pr⪡1) between vertical parallel plate channels with isoflux heating is investigated numerically in this work. The full elliptic Navier-Stokes and energy equations have been solved with the combination of the stream function and vorticity method and the finite-volume technique. An enlarged computational domain is employed to take into account the flow and thermal diffusion effects. Results are presented in terms of velocity and temperature profiles. The investigation also focuses on the flow and thermal development inside the channel; the outcomes show that fully developed flow is attained up to Ra=103, whereas the thermal fully developed condition is attained up to Ra=104. Further, correlation equations for the dimensionless induced flow rate, maximum dimensionless wall temperatures, and average Nusselt numbers as functions of the descriptive geometrical and thermal parameters covering the collection of channel Grashof numbers 1.32×103⩽Gr∕A⩽5.0×106 and aspect ratios 5⩽A⩽15. Comparison with experimental measurements has been presented to assess the validity of the numerical computational procedure.
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Moscato, Giorgio, and Giovanni Paolo Romano. "An Experimental Investigation Of Local Thermo-Fluidic Heat Transfer In A U-Shaped Mini-Channel Sink." Proceedings of the International Symposium on the Application of Laser and Imaging Techniques to Fluid Mechanics 21 (July 8, 2024): 1–21. http://dx.doi.org/10.55037/lxlaser.21st.182.
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This study investigates experimentally a heated U-shaped mini-channel heat sink using Infrared Thermography and Particle Image Velocimetry for a water coolant flow of Reynolds numbers of 280, 650, and 1350 (based on the hydraulic channel diameter). The choice of this cell geometry is based on its role as a simplified unit of a serpentine heat exchanger, which is proved to be one of the most promising for cooling processes. The use of the infrared camera allows the detection of temperature fields on top of the external surface of the cell. Therefore, aiming to derive the temperature distribution on the channel roof, a dedicated transfer function is implemented. Moreover, we employed the lumped capacitance model for thermal analysis on both infrared measurements and thermocouple data. The latter are recorded to capture the cooling process of the aluminium base and water temperature at the end of the outlet tube. As a result, thermal transient rate, cooling magnitude and equilibrium temperature are obtained. These parameters indicate that higher Reynolds numbers correspond to increased thermal transient rates, enhanced cooling effects, and lower equilibrium temperatures. A non-uniform distribution of heat transfer along the channel is reported, with the most efficient cooling area localized close to the first 90-degree corner. These findings are consistent with numerical simulations and previous experimental observations. PIV results reveal the presence of two fluid acceleration zones following both 90-degree corners, which contribute to improve the water cooling ability in their respective regions. Additionally, the formation of two recirculating bubbles is reported at the inner wall from corners vertices, whose intensity is dependent on Reynolds number, pushing the main flow towards the outer channel wall and reducing the local heat transfer. Turbulent kinetic energy distributions are also investigated, pointing out the presence of intense areas that better match with regions of minimum equilibrium temperature than maximum velocity zones. This suggests the presence of local turbulent unsteadiness and three-dimensional phenomena, which contributes significantly to cooling enhancement.
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Lukashin V. M, Pashkovskii A. B., and Pashkovskaya I. V. "GaN field-effect transistor with efficient heat dissipation on Si substrate." Technical Physics Letters 49, no. 1 (2023): 51. http://dx.doi.org/10.21883/tpl.2023.01.55349.19327.
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A simple design of a GaN field-effect transistor on a Si substrate with efficient heat removal through polydiamond layers formed on the walls of grounding holes is proposed. According to calculations, as a result of the introduction of such a heat sink with the same average distance between the gate sections, the maximum temperature in the channel of the GaN transistor on the Si substrate decreases significantly and becomes comparable to the maximum temperature in the channel of the GaN transistor on the SiC substrate.. Keywords: GaN FET, ground hole, channel temperature, polydiamond.
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Ranjbar, Pouria, Rasul Mohebbi, and Hanif Heidari. "Numerical investigation of nanofluids heat transfer in a channel consisting of rectangular cavities by lattice Boltzmann method." International Journal of Modern Physics C 29, no. 11 (2018): 1850108. http://dx.doi.org/10.1142/s0129183118501085.
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In this study, lattice Boltzmann method (LBM) simulation is performed to investigate laminar forced convection of nanofluids in a horizontal parallel-plate channel with three rectangular cavities. Two cavities are considered as located on the top wall of the channel and one on the bottom wall. The effects of the Reynolds number (100–400), the cavity aspect ratio (AR = 0.25, 0.5), the various distances of the cavities from each other ([Formula: see text]) at different solid volume fractions of nanofluids ([Formula: see text]) on the velocity and the temperature profiles of the nanofluids are studied. In addition, the flow patterns, i.e. the deflection and re-circulation zone inside the cavities, and the local and averaged Nusselt numbers on the channel walls are calculated. The results obtained are used to ascertain the validity of the written numerical code, which points to the excellent agreement across the results. The results show that, as the solid volume fraction of nanofluids is enhanced, the transfer of heat to working fluids increases significantly. Further, the results show that the maximum value of the averaged Nusselt number in the channel is obtained at [Formula: see text] for AR = 0.5 and [Formula: see text] for AR = 0.25. The interval [0.1224, 0.1304] is the best position for the second cavity. It is concluded that the results of this paper are very useful for designing optimized heat exchangers.
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ZIMPAROV, VENTSISLAV D., MILCHO S. ANGELOV, and VALENTIN M. PETKOV. "MAXIMUM BENEFITS FROM THE USE OF T-SHAPED TREE FLOW GEOMETRY WITH RECTANGULAR SHAPE OF THE CHANNELS: PERFORMANCE EVALUATION." 14th CONSTRUCTAL LAW CONFERENCE | 10-11 October 2024, Bucharest, Romania 2024, no. 1 (2024): 85–88. https://doi.org/10.59277/clc.2024.22.
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The study defines the conditions and constraints that must be obeyed to obtain the maximum benefit from using a heat exchanger with a T-shaped tree flow configuration and rectangular shape of the channels. The flow is laminar and fully developed with constant physical properties. The boundary condition is the fixed temperature of the channel wall. The variation of the heat flow ratio and augmentation entropy generation number Nsa with the dimensionless mass flow rate, shape factor ratio, and complexity have been investigated. Comparisons of the thermal performance with other heat exchanger configurations like serpentine for two cases have been made. The requirement for Nsa <=1 has been implemented as a constraint instead of one of fixed pumping power. The performance evaluation criterion has been introduced as a general criterion to define the most beneficial complexity and working parameters.
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Li, Weichen, Jieliang Zhao, Xiangbing Wu, Lulu Liang, Wenzhong Wang, and Shaoze Yan. "Structure Design and Heat Transfer Performance Analysis of a Novel Composite Phase Change Active Cooling Channel Wall for Hypersonic Aircraft." Micromachines 15, no. 5 (2024): 623. http://dx.doi.org/10.3390/mi15050623.
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Efficient and stable heat dissipation structure is crucial for improving the convective heat transfer performance of thermal protection systems (TPSs) for hypersonic aircraft. However, the heat dissipation wall of the current TPS is limited by a single material and structure, inefficiently dissipating the large amount of accumulated heat generated during the high-speed maneuvering flight of hypersonic aircraft. Here, a convection cooling channel structure of TPS is proposed, which is an innovative multi-level structure inspired by the natural honeycomb. An active cooling channel (PCM-HC) is designed by using a variable-density topology optimization method and filled with phase change material (PCM). Numerical simulations are used to investigate the thermal performance of the PCM-HC wall, focusing on the influence of PCM properties, structural geometric parameters, and PCM types on heat transfer characteristics. The results demonstrate that the honeycomb-like convection cooling channel wall, combined with PCM latent heat of phase change, exhibits superior heat dissipation capability. With a heat flux input of 50 kW/m2, the maximum temperature on the inner wall of PCM-HC is reduced by 12 K to 20 K. Different PCMs have opposing effects on heat transfer performance due to their distinct thermophysical properties. This work can provide a theoretical basis for the design of high-efficiency cooling channel, improving the heat dissipation performance in the TPS of hypersonic aircraft.
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Lemanov, Vadim, Vladimir Lukashov, and Konstantin Sharov. "Hydrogen Vortex Flow Impact on the Catalytic Wall." Energies 16, no. 1 (2022): 104. http://dx.doi.org/10.3390/en16010104.
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An experimental study of a hydrogen-containing jet’s impact on a palladium-based catalyst in an air atmosphere was carried out. High-intensity temperature fluctuations on the catalyst surface are obtained in the case when large-scale vortex structures are contained in the jet. These superstructures have a longitudinal size of 20–30 initial jet diameters and a transverse size of about 3–4 diameters. To form such structures, it is necessary to use long, round tubes in the Reynolds number range of 2000–3000 as a source of the impinging jet when a laminar-turbulent transition occurs in the channel according to the intermittency scenario. This effect was obtained at a low hydrogen content in the mixture (XH2 = 3…15%) and a low initial temperature of the catalyst (180 °C). It is shown that the smallest temperature fluctuations are obtained for the laminar flow in the tube (<1.5%), and they are more significant (<4%) for the turbulent regime at low Reynolds numbers (Re < 6000). The greatest temperature fluctuations were obtained during the laminar-turbulent transition in the tube (up to 11%). Two important modes have been established: the first with maximum temperature fluctuations in the local region of the stagnation point, and the second with the greatest integral increase in temperature fluctuations over the entire area of the catalyst.
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Jalil, Saad Mohammed. "Effect of Oscillatory Motion in Enhancing the Natural Convection Heat Transfer from a Vertical Channel." Journal of Engineering 18, no. 12 (2012): 1390–402. http://dx.doi.org/10.31026/j.eng.2012.12.07.
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This paper reports an experimental study regarding the influence of vertical oscillations on the natural convection heat transfer from a vertical channel. An experimental set-up was constructed and calibrated; the vertical channel was tested in atmosphere at 25oC. The channel-to-ambient temperature difference was varied with the power supply to the electrical heater ranging between 15W to 70W divided into five levels. Data sets were measured under different operating condition from a test rig under six vibrating velocities (VVs) levels ranging from (5-30 m/s) in addition to the stationary state. The results show that the maximum heat transfer enhancement factor (E) occurs at Rayleigh number (Ra=2.328×103 ) and vibrational Reynolds number ( Rev=6.365×103 ); this enhancement reached to (7.685%).The results also illustrated that the temperature gradient along the channel wall length was enhanced by inducing the oscillatory motion to the channel. Rayleigh and vibrational Reynolds numbers were ranging between (2.306×103 - 5.564×103) and (0.0 - 19.86×103) respectively. Finally, A correlation which summarized the effects of both Ra and Rev was determined for the Nusselt numbers.
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Abchouyeh, Monireh Asadi, Rasul Mohebbi, and Omid Solaymani Fard. "Lattice Boltzmann simulation of nanofluid natural convection heat transfer in a channel with a sinusoidal obstacle." International Journal of Modern Physics C 29, no. 09 (2018): 1850079. http://dx.doi.org/10.1142/s0129183118500791.
Full textAbstract:
The aim of this work is to conduct numerical study of fluid flow and natural convection heat transfer by utilizing the nanofluid in a two-dimensional horizontal channel consisting of a sinusoidal obstacle by lattice Boltzmann method (LBM). The fluid in the channel is a water-based nanofluid containing Cuo nanoparticles. Thermal conductivity and nanofluid’s viscosity are calculated by Patel and Brinkman models, respectively. A wide range of parameters such as the Reynolds number ([Formula: see text]–400) and the solid volume fraction ranging ([Formula: see text]–0.05) at different non-dimensional amplitude of the wavy wall of the sinusoidal obstacle ([Formula: see text]–20) on the streamlines and temperature contours are investigated in the present study. In addition, the local and average Nusselt numbers are illustrated on lower wall of the channel. The sensitivity to the resolution and representation of the sinusoidal obstacle’s shape on flow field and heat transfer by LBM simulations are the main interest and innovation of this study. The results showed that increasing the solid volume fraction [Formula: see text] and Reynolds number Re leads to increase the average Nusselt numbers. The maximum average Nusselt number occurs when the Reynolds number and solid volume fraction are maximum and amplitude of the wavy wall is minimum. Also, by decreasing the [Formula: see text], the vortex shedding forms up at higher Reynolds number in the wake region downstream of the obstacle.
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Nizamova, A. D., V. N. Kireev, and S. F. Urmancheev. "Research of eigenfuctions perturbation of the transverse component velocity thermoviscous liquids flow." Multiphase Systems 14, no. 2 (2019): 132–37. http://dx.doi.org/10.21662/mfs2019.2.018.
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The viscous model fluid flow in a plane channel with a linear temperature profile is considered. The problem of the thermoviscous fluid flow stability is solved on the basis of the previously obtained generalized Orr–Sommerfeld equation by the spectral method of decomposition into Chebyshev polynomials. We study the effect of taking into account the linear and exponential dependences of the viscosity of a liquid on temperature on the eigenfunctions of the hydrodynamic stability equation and on perturbations of the transverse velocity of an incompressible fluid in a plane channel when various wall temperatures are specified. Eigenfunctions are found numerically for two eigenvalues of the linear and exponential dependence of viscosity on temperature. Presented pictures of their own functions. The eigenfunctions demonstrate the behavior of the transverse velocity perturbations, their possible growth or attenuation over time. For the given eigenfunctions, perturbations of the transverse flow velocity of a thermoviscous fluid are obtained. It is shown that taking the temperature dependence of viscosity into account affects the eigenfunctions of the equations of hydrodynamic stability and perturbations of the transverse flow velocity. Perturbations of the transverse velocity significantly affect the hydrodynamic instability of the fluid flow. The results show that when considering the unstable eigenvalue over time, the velocity perturbations begin to grow, which leads to turbulence of the flow. The maximum values of the eigenfunctions and perturbations of the transverse velocities are shifted to the hot wall. It is seen that for an unstable eigenvalue, the perturbations of the transverse flow velocity increase over time, and for a stable one, they decay.
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Xu, Qijun, and Jing Xie. "Effect of different inlet pressures of vortex tube on internal flow field." Journal of Physics: Conference Series 2029, no. 1 (2021): 012147. http://dx.doi.org/10.1088/1742-6596/2029/1/012147.
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Abstract Numerical simulations were used to investigate the distribution of the internal pressure, velocity, and temperature fields in the vortex tube (VOTU) at inlet pressures of 1-4 MPa to reveal the causes of temperature separation. A three-dimensional model with a nozzle flow channel number of 5 was drawn, and the simulation was performed in Fluent 19.0 with CO2 as the working fluid. The simulation results show that when the inlet pressure of the VOTU is greater than 2 MPa, the temperature separation between the hot and cold air streams of the VOTU gradually increases with the increase of the inlet pressure. The maximum temperature is 285 K and the minimum temperature is 257 K at an inlet pressure of 1.0 MPa, and the maximum temperature is 319 K and the minimum temperature is 243 K at an inlet pressure of 4.0 MPa. As the inlet pressure increases, the temperature difference inside the VOTU will also increase. In the high-pressure condition, the wall thickness and sealing degree of the VOTU design should be increased accordingly, while the inner wall side of the VOTU needs to use wear-resistant materials to delay the long-term scouring of the VOTU caused by high-speed airflow. The results of the study have certain guiding significance for the design and manufacture of VOTUs.
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Medwell, J. O., W. D. Morris, J. Y. Xia, and C. Taylor. "An Investigation of Convective Heat Transfer in a Rotating Coolant Channel." Journal of Turbomachinery 113, no. 3 (1991): 354–59. http://dx.doi.org/10.1115/1.2927883.
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A numerical method is presented for the determination of heat transfer rates in a cylindrical cooling duct within turbine blades that rotate about an axis orthogonal to its own axis of symmetry. The equations of motion and energy are solved in conjunction with the k–ε model of turbulence using the finite element method. The predicted results are compared with experimental data and it is clearly demonstrated that conduction in the solid boundary must be taken into account if satisfactory agreement is to be achieved. Excluding these effects can lead to an overestimation of the maximum wall temperature by approximately 50 percent.
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Li, Yuqing, Huimin Zhang, Zi Ye, et al. "A Novel Flexible Liquid Metal Microheater with a Textured Structure." Micromachines 15, no. 1 (2023): 75. http://dx.doi.org/10.3390/mi15010075.
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In this paper, we propose a novel liquid metal microheater utilizing a textured structure. This microheater effectively solves the problem of the liquid metal in the PDMS flow channel fracturing at a certain temperature and significantly increases the maximum operating temperature that can be achieved by the current liquid metal microheater. Experimental results demonstrate that this new structured microheater can achieve a maximum operating temperature exceeding 300 °C. To explain the performance improvement and the reasons behind liquid metal fracture, corresponding experiments were conducted, and explanations were provided based on the experimental results. Subsequently, we verified the mechanical flexibility of the microheater and found that it exhibits excellent tensile and bending resistance. Finally, utilizing its good mechanical flexibility, the microheater was successfully attached to the side wall of a cup, resulting in the boiling of water.