Flow Boiling in a Heat Sink Embedded With Hexagonally Linked Minichannels

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
Shubhankar Chakraborty ◽  
Omprakash Sahu ◽  
Prasanta Kr. Das
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Flow Boiling ◽  
Heat Sinks ◽  
Vapor Quality ◽  
Maximum Heat ◽  
Maximum Heat Transfer ◽  
The Heat Transfer Coefficient

The thermal hydraulic performance of a miniature heat sink during flow boiling of distilled water is presented in this article. The unique design of the heat sink contains a number of microchannels of 1 mm × 1 mm cross section arranged in a regular hexagonal array. The design facilitates repeated division and joining of individual streams from different microchannels and thereby can enhance heat transfer. Individual slug bubble experiences a typical route of break up, coalescence, and growth. The randomness of these processes enhances the transport of heat. With the increase of vapor quality the heat transfer coefficient increases, reaches the maximum value, and then drops. The maximum heat transfer coefficient occurs at an exit vapor quality much higher than that observed in conventional parallel microchannel heat sinks. Repeated redistribution of the coolant in the interlinked channels and the restricted growth of the slug bubbles may be responsible for this trend.

Cooling Performances of Perforated-Finned Heat Sinks

2016 ◽  
Author(s):  
Mohammad Reza Shaeri ◽  
Bradley Richard ◽  
Richard Bonner
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Cooling System ◽  
Thermal Characteristics ◽  
Heat Sinks ◽  
Pumping Power ◽  
Maximum Heat ◽  
Maximum Heat Transfer

Cooling performances of perforated-finned heat sinks (PFHS) are investigated in the laminar forced convection heat transfer mode, through detailed experiments. Perforations like windows with square cross sections are placed on the lateral surfaces of the fins. Cooling performances are evaluated due to changes in both porosities and perforation sizes. Thermal characteristics are reported based on pumping power, in order to provide more practical insight about performances of PFHSs in real applications. It is found that at a constant perforation size, there is an optimum porosity that results in the largest heat transfer coefficient. For a fixed porosity, increasing the number of perforations (reducing the perforation size) results in an enhancement of heat transfer rate due to repeated interruption of the thermal boundary layer. The opposite trend is observed for PFHSs with larger perforation sizes. This indicates that there is an optimum perforation size and distance between perforations in order to achieve the maximum heat transfer coefficients at a constant porosity. Also, a PFHS results in a smaller temperature non-uniformity across the heat sink base, as well as a more rapid reduction in temperature non-uniformity on the heat sink base by increasing pumping power. In addition, the advantage of a PFHS to reduce the overall weight of the cooling system is incorporated into thermal characteristics of the heat sinks, and demonstrated by the mass specific heat transfer coefficient.

scholarly journals Comparison of heat transfer performance of ZnO-PG, α-Al2O3-PG, and γ-Al2O3-PG nanofluids in car radiator

2019 ◽  
Vol 9 ◽  
pp. 184798041987646 ◽  
Author(s):  
XiaoRong Zhou ◽  
Yi Wang ◽  
Kai Zheng ◽  
Haozhong Huang
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Propylene Glycol ◽  
Flow Rate ◽  
Volume Concentration ◽  
Maximum Heat ◽  
Cooling Performance ◽  
Maximum Heat Transfer ◽  
The Heat Transfer Coefficient

In this study, the cooling performance of nanofluids in car radiators was investigated. A car radiator, temperature measuring instrument, and other components were used to set up the experimental device, and the temperature of nanofluids passing through the radiator was measured by this device. Three kinds of nanoparticles, γ-Al2O3, α-Al2O3, and ZnO, were added to propylene glycol to prepared nanofluids, and the effects of nanoparticle size and type, volume concentration, initial temperature, and flow rate were tested. The results indicated that the heat transfer coefficients of all nanofluids first increased and then decreased with an increase in volume concentration. The ZnO-propylene glycol nanofluid reached a maximum heat transfer coefficient at 0.3 vol%, and the coefficient decreased by 25.6% with an increase in volume concentration from 0.3 vol% to 0.5 vol%. Smaller particles provided a better cooling performance, and the 0.1 vol% γ-Al2O3-propylene glycol nanofluid had a 19.9% increase in heat transfer coefficient compared with that of α-Al2O3-propylene glycol. An increase in flow rate resulted in a 10.5% increase in the heat transfer coefficient of the 0.5 vol% α-Al2O3-propylene glycol nanofluid. In addition, the experimental temperature range of 40–60°C improved the heat transfer coefficient of the 0.2 vol% ZnO-propylene glycol nanofluid by 46.4%.

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.

Microchannel Size Effects on Two-Phase Local Heat Transfer and Pressure Drop in Silicon Microchannel Heat Sinks With a Dielectric Fluid

2007 ◽  
Author(s):  
Tannaz Harirchian ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
Heat Sinks ◽  
Dielectric Fluid ◽  
Two Phase ◽  
Microchannel Heat Sinks ◽  
The Heat Transfer Coefficient

Two-phase heat transfer in microchannels can support very high heat fluxes for use in high-performance electronics-cooling applications. However, the effects of microchannel cross-sectional dimensions on the heat transfer coefficient and pressure drop have not been investigated extensively. In the present work, experiments are conducted to investigate the local flow boiling heat transfer in microchannel heat sinks. The effect of channel size on the heat transfer coefficient and pressure drop is studied for mass fluxes ranging from 250 to 1600 kg/m2s. The test sections consist of parallel microchannels with nominal widths of 100, 250, 400, 700, and 1000 μm, all with a depth of 400 μm, cut into 12.7 mm × 12.7 mm silicon substrates. Twenty-five microheaters embedded in the substrate allow local control of the imposed heat flux, while twenty-five temperature microsensors integrated into the back of the substrates enable local measurements of temperature. The dielectric fluid Fluorinert FC-77 is used as the working fluid. The results of this study serve to quantify the effectiveness of microchannel heat transport while simultaneously assessing the pressure drop trade-offs.

scholarly journals Heat Transfer Enhancement of Plate-Fin Heat Sinks with Different Types of Winglet Vortex Generators

Energies ◽  
2020 ◽  
Vol 13 (19) ◽  
pp. 5219
Author(s):  
Jin-Cherng Shyu ◽  
Jhao-Siang Jheng
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Heat Sinks ◽  
Vortex Generators ◽  
Airflow Velocity ◽  
Delta Winglet ◽  
The Heat Transfer Coefficient

Because the delta winglet in common-flow-down configuration has been recognized as an excellent type of vortex generators (VGs), this study aims to experimentally and numerically investigate the thermo-hydraulic performance of four different forms of winglet VGs featuring sweptback delta winglets in the channel flow in the range 200 < Re < 1000. Both Nusselt number and friction factor of plate-fin heat sinks having different forms of winglets, including delta winglet pair (DWP), rectangular winglet pair (RWP), swept delta winglet pair (SDWP), and swept trapezoid winglet pair (STWP), were measured in a standard wind tunnel without bypass in this study. Four rows of winglets with in-line arrangement were punched on each 10-mm-long, 0.2-mm-thick copper plate, and a total of 16 pieces of copper plates with spacing of 2 mm were fastened together to achieve the heat sink. The projected area, longitudinal and winglet tip spacing, height and angle of attack of those winglets were fixed. Besides that, three-dimensional numerical simulation was also performed in order to investigate the temperature and fluid flow over the plate-fin. The results showed that the longitudinal, common-flow-down vortices generated by the VGs augmented the heat transfer and pressure drop of the heat sink. At airflow velocity of 5 m/s, the heat transfer coefficient and pressure drop of plain plate-fin heat sink were 50.8 W/m2·K and 18 Pa, respectively, while the heat transfer coefficient and the pressure drop of heat sink having SDWP were 70.4 W/m2·K and 36 Pa, respectively. It was found that SDWP produced the highest thermal enhancement factor (TEF) of 1.28 at Re = 1000, followed by both RWP and STWP of similar TEF in the range 200 < Re < 1000. The TEF of DWP was the lowest and it was rapidly increased with the increase of airflow velocity.

Analytical Modeling of Annular Flow Boiling Heat Transfer in Mini- and Microchannel Heat Sinks

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
A. Megahed ◽  
I. Hassan
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Analytical Model ◽  
Boiling Heat Transfer ◽  
Annular Flow ◽  
Flow Boiling ◽  
Heat Sinks ◽  
Flow Boiling Heat Transfer ◽  
The Heat Transfer Coefficient

An analytical model is proposed to predict the flow boiling heat transfer coefficient in the annular flow regime in mini- and microchannel heat sinks based on the separated model. The modeling procedure includes a formulation for determining the heat transfer coefficient based on the wall shear stress and the local thermophysical characteristics of the fluid based on the Reynolds’ analogy. The frictional and acceleration pressure gradients within the channel are incorporated into the present model to provide a better representation of the flow conditions. The model is validated against collected data sets from the literature produced by different authors under different experimental conditions, different fluids, and with mini- and microchannels of hydraulic diameters falling within the range of 92–1440 μm. The accuracy between the experimental and predicted results is achieved with a mean absolute error of 10%. The present analytical model can correctly predict the different trends of the heat transfer coefficient reported in the literature as a function of the exit quality. The predicted two-phase heat transfer coefficient is found to be very sensitive to changes in mass flux and saturation temperature. However, it is found to be mildly sensitive to the change in heat flux.

A Study on the Fluid Flow and Heat Transfer for a Porous Architected Heat Sink Using the Idea of CFD Modelling

2019 ◽  
Author(s):  
Mohamed I. Hassan Ali ◽  
Oraib Al-Ketan ◽  
Nada Baobaid ◽  
Kamran Khan ◽  
Rashid K. Abu Al-Rub
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Fluid Flow ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Heat Dissipation ◽  
Heat Sinks ◽  
Cooling Power ◽  
Cfd Modelling ◽  
The Heat Transfer Coefficient

Abstract The drive for small and compact electronic components with higher processing capabilities is limited by their ability to dissipate the associated heat generated during operations. Therefore, these components are equipped with heat sinks to facilitate the dissipation of thermal energy. The emergence of additive manufacturing (AM) allowed for new degrees of freedom in terms of design and eliminated the need for excessive tooling that is associated with the conventional manufacturing processes. As such, AM facilitated the development of geometrically complex heat sinks that are capable of capitalizing on topological aspects to enhance their performance. The main objective of this study is to propose and develop architected heat sinks. We propose the use of heat sinks with topologies based on triply periodic minimal surfaces (TPMS). 3D CFD models are developed using Starccm+ platform for three architected heat sinks to study the heat transfer coefficient and surface temperature in free convection heat transfer domains. The heat dissipation versus the input heat sources as well as the heat transfer coefficient will be used for measuring the heat sink performance. The required fluid flow rate and pressure drop will be used to measure the required cooling power for the proposed heat sinks.

scholarly journals Time-Dependent Heat Transfer Calculations with Trefftz and Picard Methods for Flow Boiling in a Mini-Channel Heat Sink

Energies ◽  
2021 ◽  
Vol 14 (7) ◽  
pp. 1832
Author(s):  
Magdalena Piasecka ◽  
Sylwia Hożejowska ◽  
Beata Maciejewska ◽  
Anna Pawińska
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Flow Boiling ◽  
Time Dependent ◽  
Heated Wall ◽  
Trefftz Method ◽  
Mini Channels ◽  
The Heat Transfer Coefficient

The intensification of heat transfer using two-phase boiling flow in mini-channels is widely used to dissipate the high heat fluxes in miniaturized electronic devices. However, the process itself is not fully recognized and still requires experimental studies and developing computation methods appropriate for them. The main aim of this work was the mathematical modeling of time-dependent heat transfer process in FC-72 flow boiling in a mini-channel heat sink with five parallel mini-channels of 1 mm depth. Channels have an asymmetrically heated wall while its outer temperature was measured by infrared thermography. The opposite wall of the mini-channels was transparent, helping to record flow patterns due to a high-speed digital camera. The objective of the numerical calculations was to determine the heat transfer coefficient on the wall-fluid contact surface from the Robin boundary condition. The problem was solved using methods based on the Trefftz-type functions. Three mathematical methods were applied in calculations: the FEM with Trefftz type basis functions, the Classical Trefftz Method, and the Hybrid Picard-Trefftz Method. The results were compared with the values of the heat transfer coefficient obtained from theoretical correlations from the literature.

scholarly journals Optimization of Fin Spacing of Vertical Plate Fin Heat Sink in Natural Convection

2019 ◽  
Vol 9 (1) ◽  
pp. 1020-1024
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Surface Area ◽  
Heat Sink ◽  
Vertical Plate ◽  
Heat Sinks ◽  
Geometrical Parameters ◽  
Fin Spacing ◽  
The Heat Transfer Coefficient

Heat sinks are frequently used in the cooling of electrical and electronics devices If the heat sink have very close fin spacing, it increases the surface area but reduces the heat transfer coefficient. On the other hand, if heat sink has wide fin spacing, it reduces the surface area but increases the heat transfer coefficient. Therefore, there is need to optimize the fin spacing that enhanced the heat transfer from the heat sink. A properly selected heat sink may reduced the operating temperature and reduce the risk of failure of components. A steady state natural convective heat transfer from aluminum plate fin heat sink was examined experimentally. The length and thickness of fin was kept constant while height were varied from 5mm to 25mm and spacing varied between 5.5mm to 17mm.After experimentation, it was observed that fin spacing plays important role than any other geometrical parameters. Response surface methodology is used for optimization of fin spacing. It is observed that optimum fin spacing of heat sink is 8.28mm.The error analysis is done with the help of ANN and flow visualization were done using CFD

Dependence of Flow Boiling Heat Transfer Coefficient on Location and Vapor Quality in a Microchannel Heat Sink

2011 ◽  
Author(s):  
Ravi S. Patel ◽  
Tannaz Harirchian ◽  
Suresh V. Garimella
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Sink ◽  
Flow Boiling ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Local Heat Transfer Coefficient ◽  
Microchannel Heat Sink ◽  
Vapor Quality

Experiments were conducted to determine the influence of local vapor quality on local heat transfer coefficient in flow boiling in an array of microchannels. Additionally, the variation of local heat transfer coefficient along the length and width of the microchannel heat sink for given operating conditions was investigated over a range of flow parameters. Each test piece includes a silicon parallel microchannel heat sink with 25 integrated heaters and 25 temperature sensors arranged in a 5×5 grid, allowing for uniform heat dissipation and local temperature measurements. Channel dimensions ranged from 100 μm to 400 μm in depth and 100 μm to 5850 μm in width; the working fluid for all cases was the perfluorinated dielectric liquid, FC-77. The heat transfer coefficient is found to increase with increasing vapor quality, reach a peak, and then decrease rapidly due to partial dryout on the channel walls. The vapor quality at which the peak is observed shows a strong dependence on mass flux, occurring at lower vapor qualities with increasing mass flux for fixed channel dimensions. Variations in local heat transfer coefficient across the test piece were examined both along the flow direction and in a direction transverse to it; observed trends included variations due to entrance region effects, two-phase transition, non-uniform flow distribution, and channel wall dryout.

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