Performance Investigation on Porous Micro Heat Sink for Cooling of High Power LEDs

2011 ◽  
Vol 204-210 ◽  
pp. 1481-1484
Author(s):  
Zhong Min Wan ◽  
Zheng Kai Tu ◽  
Jing Liu
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
High Power ◽  
Heat Sink ◽  
Heated Surface ◽  
High Heat ◽  
Heat Fluxes ◽  
Local Thermal Equilibrium ◽  
Micro Pump

A novel porous micro heat sink system is presented for thermal management of high power LEDs, which has high heat transport capability. Numerical model for the micro heat sink is developed to describe liquid flow and heat transfer based on the local thermal equilibrium of porous media, and it is solved with SIMPLE algorithm. The numerical results show that the heated surface temperature of porous micro heat sink is low at high heat fluxes and is much less than the bearable temperature level of LED chips. The heat transfer coefficient of heat sink is very high, and increasing the liquid velocity can enhance the average heat transfer coefficient. The overall pressure loss of heat sink system increases with the increasing the inlet velocity, but the overall pressure drop is much less than the pumping pressure provided by micro pump.

Flow Boiling Heat Transfer in a Silicon Microchannel Heat Sink Using Liquid Crystal Thermography

2008 ◽  
Author(s):  
Ayman Megahed ◽  
Ibrahim Hassan ◽  
Tariq Ahmad
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Microchannel Heat Sink

The present study focuses on the experimental investigation of boiling heat transfer characteristics and pressure drop in a silicon microchannel heat sink. The microchannel heat sink consists of a rectangular silicon chip in which 45 rectangular microchannels were chemically etched with a depth of 295 μm, width of 254 μm, and a length of 16 mm. Un-encapsulated Thermochromic liquid Crystals (TLC) are used in the present work to enable nonintrusive and high spatial resolution temperature measurements. This measuring technique is used to provide accurate full and local surface-temperature and heat transfer coefficient measurements. Experiments are carried out for mass velocities ranging between 290 to 457 kg/m2.s and heat fluxes from 6.04 to 13.06 W/cm2 using FC-72 as the working fluid. Experimental results show that the pressure drop increases as the exit quality and the flow rate increase. High values of heat transfer coefficient can be obtained at low exit quality (xe < 0.2). However, the heat transfer coefficient decreases sharply and remains almost constant as the quality increases for an exit quality higher than 0.2.

scholarly journals Deterioration in Heat Transfer to Fluids at Supercritical Pressure and High Heat Fluxes

1969 ◽  
Vol 91 (1) ◽  
pp. 27-36 ◽  
Author(s):  
B. S. Shiralkar ◽  
Peter Griffith
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
High Heat ◽  
Supercritical Pressure ◽  
Heat Fluxes ◽  
Bulk Temperature ◽  
Operating Pressure ◽  
The Heat Transfer Coefficient

At slightly supercritical pressure and in the neighborhood of the pseudocritical temperature (which corresponds to the peak in the specific heat at the operating pressure), the heat transfer coefficient between fluid and tube wall is strongly dependent on the heat flux. For large heat fluxes, a marked deterioration takes place in the heat transfer coefficient in the region where the bulk temperature is below the pseudocritical temperature and the wall temperature above the pseudocritical temperature. Equations have been developed to predict the deterioration in heat transfer at high heat fluxes and the results compared with previously available results for steam. Experiments have been performed with carbon dioxide for additional comparison. Limits of safe operation for a supercritical pressure heat exchanger in terms of the allowable heat flux for a particular flow rate have been determined theoretically and experimentally.

Thermal Management of Time-Varying High Heat Flux Electronic Devices

2014 ◽  
Vol 136 (2) ◽  
Author(s):  
T. David ◽  
D. Mendler ◽  
A. Mosyak ◽  
A. Bar-Cohen ◽  
G. Hetsroni
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Steady State ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Heat Fluxes ◽  
Vapor Quality ◽  
Flow Loop ◽  
Pin Fin ◽  
The Heat Transfer Coefficient

The thermal characteristics of a laboratory pin-fin microchannel heat sink were empirically obtained for heat flux, q″, in the range of 30–170 W/cm2, mass flux, m, in the range of 230–380 kg/m2 s, and an exit vapor quality, xout, from 0.2 to 0.75. Refrigerant R 134a (HFC-134a) was chosen as the working fluid. The heat sink was a pin-fin microchannel module installed in open flow loop. Deviation from the measured average temperatures was 1.5 °C at q = 30 W/cm2, and 2.0 °C at q = 170 W/cm2. These results indicate that use of pin-fin microchannel heat sink enables keeping an electronic device near uniform temperature under steady state and transient conditions. The heat transfer coefficient varied significantly with refrigerant quality and showed a peak at an exit vapor quality of 0.55 in all the experiments. At relatively low heat fluxes and vapor qualities, the heat transfer coefficient increased with vapor quality. At high heat fluxes and vapor qualities, the heat transfer coefficient decreased with vapor quality. A noteworthy feature of the present data is the larger magnitude of the transient heat transfer coefficients compared to values obtained under steady state conditions. The results of transient boiling were compared with those for steady state conditions. In contrast to the more common techniques, the low cost technique, based on open flow loop was developed to promote cooling using micropin fin sinks. Results of this experimental study may be used for designing the cooling high power laser and rocket-born electronic devices.

Nucleate Pool Boiling of a TURBO-B Bundle in R-113

1994 ◽  
Vol 116 (3) ◽  
pp. 670-678 ◽  
Author(s):  
S. B. Memory ◽  
S. V. Chilman ◽  
P. J. Marto
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Tube Bundle ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Fluxes ◽  
Smooth Tube ◽  
Vertical Array ◽  
Wall Superheat

Heat transfer measurements were made during nucleate boiling of R-113 from a bundle of 15 electrically heated, copper TURBO-B tubes arranged in an equilateral triangular pitch, designed to simulate a portion of a flooded evaporator. Five of the tubes that were oriented in a vertical array on the centerline of the bundle were each instrumented with six wall thermocouples. For increasing heat flux, the incipient boiling wall superheat of upper tubes decreased as lower tubes were activated. In the boiling region at low heat fluxes (≈ 1 kW/m2), the average bundle heat transfer coefficient was 4.6 times that obtained for a smooth tube bundle (under identical conditions) and 1.6 times greater than that obtained for a single TURBO-B tube; a similar bundle factor has been reported for a smooth tube bundle. At high heat fluxes (100 kW/m2), the average bundle heat transfer coefficient was 3.6 times that of a smooth tube bundle. Furthermore, there was still a significant bundle factor (1.22), contrary to a smooth tube bundle, where all effect of lower tubes was eliminated at high heat fluxes.

scholarly journals Numerical prediction of nucleate pool boiling heat transfer coefficient under high heat fluxes

2016 ◽  
Vol 20 (suppl. 1) ◽  
pp. 113-123 ◽  
Author(s):  
Milada Pezo ◽  
Vladimir Stevanovic
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Pool Boiling ◽  
Heating Surface ◽  
High Heat ◽  
Bubble Nucleation ◽  
Heat Fluxes ◽  
Two Phase ◽  
Boiling Heat Transfer Coefficient

This paper presents CFD (Computational Fluid Dynamics) approach to prediction of the heat transfer coefficient for nucleate pool boiling under high heat fluxes. Three-dimensional numerical simulations of the atmospheric saturated pool boiling are performed. Mathematical modelling of pool boiling requires a treatment of vapor-liquid two-phase mixture on the macro level, as well as on the micro level, such as bubble growth and departure from the heating surface. Two-phase flow is modelled by the two-fluid model, which consists of the mass, momentum and energy conservation equations for each phase. Interface transfer processes are calculated by the closure laws. Micro level phenomena on the heating surface are modelled with the bubble nucleation site density, the bubble resistance time on the heating wall and with the certain level of randomness in the location of bubble nucleation sites. The developed model was used to determine the heat transfer coefficient and results of numerical simulations are compared with available experimental results and several empirical correlations. A considerable scattering of the predictions of the pool boiling heat transfer coefficient by experimental correlations is observed, while the numerically predicted values are within the range of results calculated by well-known Kutateladze, Mostinski, Kruzhilin and Rohsenow correlations. The presented numerical modeling approach is original regarding both the application of the two-fluid two-phase model for the determination of heat transfer coefficient in pool boiling and the defined boundary conditions at the heated wall surface.

Numerical Simulation of Supercritical Water Heat Transfer in the Vertically Heated Tube

2013 ◽  
Author(s):  
Feng Wang ◽  
Bo Cui ◽  
Shijun Zhang ◽  
Xue Qin
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Turbulence Model ◽  
Mesh Size ◽  
High Heat ◽  
Heat Fluxes ◽  
Symmetric Model ◽  
Heated Tube ◽  
The Heat Transfer Coefficient

The heat transfer of water in a vertically heated tube at 24.52 MPa is numerically simulated by computational fluid dynamics software of FLUENT. The IAPWS-IF97 formulation is applied to obtain the water properties, which vary substantially at supercritical condition. The two-dimensional axi-symmetric model using RNG k-ε turbulence model with enhanced wall treatment gives fine prediction of wall temperature and heat transfer coefficient. The mesh size near the wall adapted smaller when at high heat fluxes for the accuracy of computed results. The wall heat fluxes were set to be 233, 698, 930 and 1100 kW/m2 to match the simulation with experiment performed by Yamagata. It is found that k-ε turbulence model with enhanced wall treatment can give outstanding prediction of heat transfer enhancement and heat transfer deterioration. The heat transfer coefficient value reaches a maximum near the pseudocritical point and it decreases with increase of heat flux.

scholarly journals Influence of Changing Porosity and Height of Fins on Thermal Performance of The Metal Foam Heat Sink: Numerical Investigation

2020 ◽  
Vol 7 (3) ◽  
pp. 50-65
Author(s):  
Abbas J. Jubear ◽  
Aqeel Mtasher Uglah
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Metal Foam ◽  
Heat Fluxes ◽  
Working Fluid ◽  
Base Temperature ◽  
Maximum Enhancement ◽  
The Impact

Abstract— With the major advances in technology, the extreme need for more powerful and efficient electronic devices and equipment has increased, that is requiring more heat generation as a result. So, it is necessary to find a cooling method commensurate with heat generated. This leads to the use of the foam heat sink which is considered as one of more powerful cooling methods for this purpose. The target of this work is to numerically investigate the impact of changing the porosity and the ratio between height of the fin respect to its length on base temperature and heat transfer coefficient in the case of natural convection conditions. The dimensions of the foam fins were 100 * 10 in mm (length * width) and the spacing between fins was 8 mm, while the height of fins was variable with ratio ranging from 0.2 to 2.4. The porosity of model was changing from 0.95 to 0.71 with fixed pore density of 10 PPI. The investigations have been performed by using ANSYS Fluent software (R16.1) and the model of a local thermal non-equilibrium (LINE) has been used in the analysis where, the temperature of the solid part in foam matrix and the fluid are solved individually in energy equation. The heat fluxes were various from 4 to 30 W, and air has been used as a working fluid. The results showed that the average improvement in base temperature of the heat sink is 16.7 %, and the maximum enhancement of heat transfer coefficient reaches about 21.3%, when the porosity reduced from 0.95 to 0.79. The highest enhancement in base temperature and heat transfer coefficient obtains when the height to length ratio is (2.2) and estimated by 30 % and 83.8% respectively, compared with the ratio of (0.2).

Forced Convective Boiling in a Vertical Annular Test Section with Seawater Coolant

2020 ◽  
Author(s):  
Zayed Ahmed ◽  
Steve Eckels ◽  
Seth Eckels ◽  
Hitesh Bindra
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
High Speed ◽  
Bubble Dynamics ◽  
Heated Surface ◽  
Reactor Core ◽  
Heat Fluxes ◽  
Subcooled Boiling ◽  
Convective Boiling

Abstract In case of some nuclear reactors, seawater is used as an emergency resource to remove the decay heat from the reactor core. This study aims to improve the understanding of boiling heat transfer with seawater coolants. Under the boiling conditions with seawater, the mass transfer of the dissolved impurities to the heated surface is expected to significantly impact the heat transfer characteristics. The focus of this experimental work is to measure the differences of the heat transfer performance between seawater and tapwater with electrically heated cylindrical section in a vertical annulus. High speed visualization is performed to quantify and characterize the bubble dynamics parameters. The experimental results indicate an enhanced heat transfer coefficient with seawater in the initial transient under saturated boiling followed by an asymptotic reduction to values similar to tapwater. Under subcooled boiling, a consistent reduced heat transfer coefficient was observed in seawater for a range of heat fluxes. The high speed visualization of subcooled boiling showed fewer and smaller bubbles nucleating off the heat transfer surface in seawater indicating a lower evaporative flux as compared to tapwater.

Using Infrared Thermography to Study Thermal Development in the Entrance Region of a Rectangular Microchannel

2013 ◽  
Author(s):  
W.-H. Chen ◽  
M.- X. Ho ◽  
Chin Pan
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Temperature Distribution ◽  
Transfer Coefficient ◽  
Infrared Thermography ◽  
High Heat ◽  
Heat Fluxes ◽  
Entrance Region ◽  
Rectangular Microchannel ◽  
High Heat Transfer

Microchannel heat sink with its high heat transfer area density and potentially high heat transfer coefficient has been proposed for applications with high heat fluxes. The objective of this study is to investigate single-phase convection in the thermally developing region of a rectangular microchannel. An infrared thermography provides an effective approach for non-intrusive and spatio-temporal measurement of temperature. The entrance region, where the heat transfer coefficient is higher than that of the fully developed region, is of particular interest for microchannel cooling applications. The present study establishes an innovative benchmark experimental measurement uaing an infrared thermography. The experiments are conducted on a rectangular cross-section microchannel made of aluminum alloy 6061 with dimensions 22mm×1.5mm×0.3mm and covered on the top with a 5mm thick infrared transmitting germanium glass window. Consequently, the temperature distribution in the channel can be observed via the window directly. In order to measure the temperature correctly, all of the aluminum channel surface substrate was anodized such that emissivity can be increased to 0.95. The results show that the temperature distribution can be measured correctly using infrared thermography. And local heat transfer coefficient can be acquired successfully.

scholarly journals COMPARATIVE ANALYSES OF THE THERMAL PERFORMANCE OF REFRIGERANTS R134A, R245fa, R407C AND R600a DURING FLOW BOILING IN A MICROCHANNELS HEAT SINK

2018 ◽  
Vol 17 (2) ◽  
pp. 57
Author(s):  
H. L. S. L. Leão ◽  
D. B. Marchetto ◽  
G. Ribatski
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Flow Boiling ◽  
Saturation Temperature ◽  
Nucleate Boiling ◽  
Heat Fluxes ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

A comparative study of the performance of of refrigerants R134a, R407C, R245fa and R600a during flow boiling was performed for a 123x494 µm2 heat sink composed of 50 parallel rectangular microchannels. Heat transfer experimental results for heat fluxes up to 310 kW/m2, mass velocities from 300 to 800 kg/(m2 s), liquid subcoolings of 5 and 10 °C and saturation temperature close to 30 ºC were obtained. Global heat transfer coefficients (footprint) up to 10 kW/(m2 °C) were found. The liquid superheating necessary for the onset of nucleate boiling (ONB) was also characterized, and the fluids R245fa and R407C presented the highest and lowest, respectively, superheating to trigger the boiling process. Moreover, for a fixed averaged vapor quality, the average effective heat transfer coefficient increases with increasing mass velocity and liquid subcooling. The refrigerants R600a and R407C presented the highest and the lowest heat transfer coefficients, respectively. Five heat transfer predictive methods from literature provided accurate predictions of the data for R134a, R245fa and R600a, capturing most of the data trends. No one method provided accurate predictions of the heat transfer coefficient data of R407C.

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