An Investigation of Scale Variation in Multi-Layer Mini- and Micro-Channel Heat Sinks in Single Phase Flow Using a Two Equation Porous Media Model

2009 ◽  
Author(s):  
Bryan Hassell ◽  
Alfonso Ortega
Keyword(s):  
Porous Media ◽  
Heat Sink ◽  
Heated Surface ◽  
Base Material ◽  
Heat Sinks ◽  
Small Scale ◽  
Micro Channel ◽  
Porous Media Model ◽  
Microchannel Heat Sinks ◽  
Scale Variation

Research in liquid cooled mini- and micro-channel heat sinks is growing due to the potentially high heat fluxes that can be dissipated with such devices. Ostensibly, mini- or microchannel heat sinks are derivatives of more generalized porous structures. They are porous, but the pores are continuous and deterministic in structure, with well defined geometries created by etching or cutting channels into solid base material. As such, deterministic small scale heat sinks of this type lend themselves to modeling using the well-developed theories for saturated porous media. Based on the principle that physical problems contain multiple scales with multiple objectives, it is of interest to examine the possibility that allowing scale change away from the heated surface in a multi-layered heat sink would yield greater global benefits. Modeled as a saturated porous medium, scale variation in stacked multi-layer microchannel heat sinks has been explored using an experimentally verified two equation porous model. This paper compares and rates scaling parameters based on the pressure drop across the heat sink along with the unit thermal resistance.

Two-Phase Electronic Cooling Using Mini-Channel and Micro-Channel Heat Sinks: Part 1—Design Criteria and Heat Diffusion Constraints

1994 ◽  
Vol 116 (4) ◽  
pp. 290-297 ◽  
Author(s):  
Morris B. Bowers ◽  
Issam Mudawar
Keyword(s):  
Heat Flux ◽  
Heat Sink ◽  
Structural Integrity ◽  
Flow Boiling ◽  
Heated Surface ◽  
Heat Sinks ◽  
Heat Diffusion ◽  
High Heat Flux ◽  
Micro Channel ◽  
Channel Diameter

Mini-channel (D = 2.54 mm) and micro-channel (D = 510 μm) heat sinks with a 1-cm2 heated surface were tested for their high heat flux performance with flow boiling of R-113. Experimental results yielded CHF values in excess of 200 W cm−2 for flow rates less than 95 ml min−1 (0.025 gpm) over a range of inlet subcooling from 10 to 32°C. Heat diffusion within the heat sink was analyzed to ascertain the optimum heat sink geometry in terms of channel spacing and overall thickness. A heat sink thickness to channel diameter ratio of 1.2 provided a good compromise between minimizing overall thermal resistance and structural integrity. A ratio of channel pitch to diameter of less than two produced negligible surface temperature gradients even with a surface heat flux of 200 W cm−2. To further aid in determining channel diameter for a specific cooling application, a pressure drop model was developed, which is presented in the second part of the study.

Effect of Flow Arrangements on Thermohydraulic Performance of a Microchannel Heat Sink

2009 ◽  
Author(s):  
Satbir S. Sehgal ◽  
Krishnan Murugesan ◽  
S. K. Mohapatra
Keyword(s):  
Heat Transfer ◽  
Heat Sink ◽  
Experimental Studies ◽  
Heat Sinks ◽  
Heat Transfer Analysis ◽  
Maximum Temperature ◽  
Micro Channel ◽  
Flow Conditions ◽  
Micro Channels ◽  
Microchannel Heat Sinks

The advancements in fabricating and utilizing microchannel heat sinks (MCHS) for cooling of electronic devices during the last decade has not been matched by corresponding advances in our fundamental understanding of the unconventional micro fluidics. Many theoretical and experimental studies have been reported for the heat transfer analysis along the direction of flow within the microchannels, but to the best knowledge of the authors, the effect of the size of the inlet and outlet plenum and direction of the flow to the plenums was not studied exhaustively till date. The liquid is supplied to the microchannels via the inlet and outlet plenums and this can be achieved by many flow arrangements. Due to the small size of the channel dimensions, the entrance and exit conditions will significantly affect the heat transfer characteristics of the flow field in the channel. Instability effects at the entrance and exit regions of the micro-channel also need to be fully understood for efficient design of microchannel heat sinks. This paper presents an experimental study that has been conducted to explore the effect of entrance & exit conditions of the liquid flow within a copper micro-channel heat sink (MCHS). Three test pieces having inlet & outlet plenum dimensions of 8mm × 30mm, 10mm × 30 mm and 12 mm × 30 mm each with constant depth of 2.5 mm have been selected. Three different flow arrangements (U-Type, S-type and P-type) are studied for each test piece resulting in total nine flow arrangements. Each micro-channel heat sink contains an array of micro-channels in parallel having individual width of 330μm and channel depth of 2.5 mm. A comparison is made based on thermohydraulic performance of MCHS for different flow conditions at inlet and outlet plenums maintaining constant heat flux. Deionised water has been used in the experiments for the Reynolds number ranging from approximately 220 to 1100. The results are interpreted based on pressure drops and maximum temperature variations for these nine flow arrangements. Tests has been conducted to look for optimized dimensions and flow conditions at inlet and outlet plenums for the given fixed length of microchannels under same conjugate heat transfer conditions. Evaluations of experimental uncertainties have been meticulously made while selecting the instruments used in the experimental facility.

Parametric Studies of Single-Phase Multi-Layer Heat Sinks Using a Porous Media Approach: Effects of Spatially-Varying Porosity and Total Porosity

2014 ◽  
Author(s):  
John J. Podhiny ◽  
Alfonso Ortega
Keyword(s):  
Porous Media ◽  
Heat Sink ◽  
Heated Surface ◽  
Continuous Variation ◽  
Heat Sinks ◽  
Optimum Level ◽  
Fluid Temperature ◽  
Porosity Variation ◽  
Aspect Ratios ◽  
Spatially Varying

Prior analyses and experiments have demonstrated that varying or scaling the number of fluid channels in each layer of a stacked multi-layer heat sink yields distinct advantages over traditional single-layer designs which use channels with high aspect ratios. Specifically, a design which implements scaling in order to vary the porosity (or equivalently, the number of channels) from one layer to the next allows a given thermal performance to be realized at a lower pressure drop than the corresponding non-scaled design. In previous work, the authors have used volume-averaged non-equilibrium porous media heat transfer theory to analyze a range of heat sinks of this type, including those with discrete or step-wise porosity variation (in earlier efforts) and continuous porosity variation (in more recent efforts). The authors have used discrete variation to model stacked mini-channel multi-later heat exchangers, and continuous variation as a more general investigative tool for this class of heat sinks. The continuous variation approach can also be used as a design tool for heat sink envelopes that use scaled micro- or nano-channels or engineered porous media with spatially varying porosity or pore diameter. This paper reports on the results of a parametric study of water-cooled copper heat sinks which employ 0.50 mm × 0.50 mm square channels in a range of porosity scaling profiles that yield and total integrated porosities of 0.10 to 0.95. The investigation identifies the highest and lowest performing designs based upon temperatures on the heated surface, and analyzes their performance characteristics in terms of the spatial distributions of solid and fluid temperature distributions, thermal resistance components and ratios, and conductive and convective heat flows. In general, the results imply the existence of an optimum level and distribution of porosity and confirm the potential benefits of spatial variation of porosity.

Fluid Flow and Heat Transfer of Liquid Sodium in Small-Scale Heat Sinks With Different Geometries

2021 ◽  
Author(s):  
Mahyar Pourghasemi ◽  
Nima Fathi
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Cross Sections ◽  
Heat Sink ◽  
Volume Ratio ◽  
Heat Sinks ◽  
Liquid Sodium ◽  
Small Scale ◽  
Nusselt Numbers ◽  
The Difference

Abstract 3-D numerical simulations are performed to investigate liquid sodium (Na) flow and the heat transfer within miniature heat sinks with different geometries and hydraulic diameters of less than 5 mm. Two different straight small-scale heat sinks with rectangular and triangular cross-sections are studied in the laminar flow with the Reynolds number up to 1900. The local and average Nusselt numbers are obtained and compared against eachother. At the same surface area to volume ratio, rectangular minichannel heat sink leads to almost 280% higher convective heat transfer rate in comparison with triangular heat sink. It is observed that the difference between thermal efficiencies of rectangular and triangular minichannel heat sinks was independent of flow Reynolds number.

On the Cooling of Electronics With Nanofluids

2011 ◽  
Vol 133 (5) ◽  
Author(s):  
W. Escher ◽  
T. Brunschwiler ◽  
N. Shalkevich ◽  
A. Shalkevich ◽  
T. Burgi ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Thermophysical Properties ◽  
Heat Sink ◽  
Relative Viscosity ◽  
Volumetric Flow Rate ◽  
Silica Nanoparticle ◽  
Particle Morphology ◽  
Heat Sinks ◽  
Conductivity Enhancement ◽  
Microchannel Heat Sinks

Nanofluids have been proposed to improve the performance of microchannel heat sinks. In this paper, we present a systematic characterization of aqueous silica nanoparticle suspensions with concentrations up to 31 vol %. We determined the particle morphology by transmission electron microscope imaging and its dispersion status by dynamic light scattering measurements. The thermophysical properties of the fluids, namely, their specific heat, density, thermal conductivity, and dynamic viscosity were experimentally measured. We fabricated microchannel heat sinks with three different channel widths and characterized their thermal performance as a function of volumetric flow rate for silica nanofluids at concentrations by volume of 0%, 5%, 16%, and 31%. The Nusselt number was extracted from the experimental results and compared with the theoretical predictions considering the change of fluids bulk properties. We demonstrated a deviation of less than 10% between the experiments and the predictions. Hence, standard correlations can be used to estimate the convective heat transfer of nanofluids. In addition, we applied a one-dimensional model of the heat sink, validated by the experiments. We predicted the potential of nanofluids to increase the performance of microchannel heat sinks. To this end, we varied the individual thermophysical properties of the coolant and studied their impact on the heat sink performance. We demonstrated that the relative thermal conductivity enhancement must be larger than the relative viscosity increase in order to gain a sizeable performance benefit. Furthermore, we showed that it would be preferable to increase the volumetric heat capacity of the fluid instead of increasing its thermal conductivity.

Natural Patterns Applied to the Design of Microchannel Heat Sinks

2009 ◽  
Author(s):  
Carlos Alberto Rubio-Jimenez ◽  
Abel Hernandez-Guerrero ◽  
Jose Cuauhtemoc Rubio-Arana ◽  
Satish Kandlikar
Keyword(s):  
Heat Flux ◽  
Reynolds Number ◽  
Heat Sink ◽  
Heat Sinks ◽  
Temperature Fields ◽  
Channel Inlet ◽  
Cooling Fluid ◽  
Microchannel Heat Sinks ◽  
Natural Forms ◽  
Hydrodynamic Behaviors

The present work shows a study developed of the thermal and hydrodynamic behaviors present in microchannel heat sinks formed by non-conventional arrangements. These arrangements are based on patterns that nature presents. There are two postulates that model natural forms in a mathematical way: the Allometric Law and the Biomimetic Tendency. Both theories have been applied in the last few years in different fields of science and technology. Using both theories, six models were analyzed (there are three cases proposed and both theories are applied to each case). Microchannel heat sinks with split channels are obtained as a result of applying these theories. Water is the cooling fluid of the system. The inlet hydraulic diameter is kept in each model in order to have a reference for comparison. The Reynolds number inside the heat sink remains below the transition Reynolds number value published by several researchers for this channel dimensions. The inlet Reynolds number of the fluid at the channel inlet is the same for each model. A heat flux is supplied to the bottom wall of the heat sink. The magnitude of this heat flux is 150 W/cm2. The temperature fields and velocity profiles are obtained for each case and compared.

Enhanced Thermal Transport in Microchannel Using Oblique Fins

2012 ◽  
Vol 134 (10) ◽  
Author(s):  
Y. J. Lee ◽  
P. S. Lee ◽  
S. K. Chou
Keyword(s):  
Heat Transfer ◽  
Boundary Layer ◽  
Heat Transfer Enhancement ◽  
Heat Sink ◽  
Heat Sinks ◽  
Maximum Temperature ◽  
Working Fluid ◽  
Microchannel Heat Sink ◽  
Transfer Enhancement ◽  
Microchannel Heat Sinks

Sectional oblique fins are employed, in contrast to continuous fins in order to modulate the flow in microchannel heat sinks. The breakage of a continuous fin into oblique sections leads to the reinitialization of the thermal boundary layer at the leading edge of each oblique fin, effectively reducing the boundary layer thickness. This regeneration of entrance effects causes the flow to always be in a developing state, thus resulting in better heat transfer. In addition, the presence of smaller oblique channels diverts a small fraction of the flow into adjacent main channels. The secondary flows created improve fluid mixing, which serves to further enhance heat transfer. Both numerical simulations and experimental investigations of copper-based oblique finned microchannel heat sinks demonstrated that a highly augmented and uniform heat transfer performance, relative to the conventional microchannel, is achievable with such a passive technique. The average Nusselt number, Nuave, for the copper microchannel heat sink which uses water as the working fluid can increase as much as 103%, from 11.3 to 22.9. Besides, the augmented convective heat transfer leads to a reduction in maximum temperature rise by 12.6 °C. The associated pressure drop penalty is much smaller than the achieved heat transfer enhancement, rendering it as an effective heat transfer enhancement scheme for a single-phase microchannel heat sink.

scholarly journals Optimal design of subcooled triangular microchannel heat sink exchangers with variable heat loads for high performance cooling

2021 ◽  
Vol 2116 (1) ◽  
pp. 012052
Author(s):  
David Olugbenga Ariyo ◽  
Tunde Bello-Ochende
Keyword(s):  
Heat Sink ◽  
High Performance ◽  
Flow Boiling ◽  
High Heat ◽  
Geometric Optimization ◽  
Heat Fluxes ◽  
Heat Sinks ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow ◽  
Microchannel Heat Sinks

Abstract Deionized water at a temperature of 25 °C was used as the cooling fluid and aluminium as the heat sink material in the geometric optimization and parameter modelling of subcooled flow boiling in horizontal equilateral triangular microchannel heat sinks. The thermal resistances of the microchannels were minimized subject to fixed volume constraints of the heat sinks and microchannels. A computational fluid dynamics (CFD) ANSYS code used for both the simulations and the optimizations was validated by the available experimental data in the literature and the agreement was good. Fixed heat fluxes between 100 and 500 W/cm2 and velocities between 0.1 and 7.0 m/s were used in the study. Despite the relatively high heat fluxes in this study, the base temperatures of the optimal microchannel heat sinks were within the acceptable operating range for modern electronics. The pumping power requirements for the optimal microchannels are low, indicating that they can be used in the cooling of electronic devices.

Numerical Study of the Pressure Drop in a Flame Arrestor Using a Porous Media Model

2020 ◽  
Author(s):  
Hoden A. Farah ◽  
Frank K. Lu ◽  
Jim L. Griffin
Keyword(s):  
Numerical Simulation ◽  
Porous Media ◽  
Numerical Study ◽  
Flow Characteristics ◽  
Small Scale ◽  
Forchheimer Equation ◽  
Flow Equations ◽  
Numerical Studies ◽  
Porous Media Model ◽  
Empirical Coefficients

Abstract A numerical study of the flow characteristics of a crimped flame arrestor element was conducted using a porous media model. The porous zone was modeled using the Forchheimer equation. The Forchheimer equation was incorporated into the governing conservation equations as a momentum sink. A small-scale crimped flame arrestor element was tested to determine the empirical coefficients in the Forchheimer equation. The numerical simulation result using this porous media model was verified using experimental data. The flow characteristics of a four-inch detonation flame arrestor with the same crimp design as the small-scale sample, was simulated using the porous media model. The numerical simulation flow data were compared against experimental values and agreed to within five percent. The method used to determine the Forchheimer coefficients and the experimental test setup are described in detail. The application of the Forchheimer equation into the governing flow equations is presented. The challenges and limitation of numerical studies in flame arrestors applications are discussed. The simplification gained by using the porous media model in flame arrestor numerical studies is presented.

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