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.

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.

The effect of viscous dissipation on laminar nanofluid flow in a microchannel heat sink

2009 ◽  
Vol 223 (11) ◽  
pp. 2697-2706 ◽  
Author(s):  
M Ghazvini ◽  
M A Akhavan-Behabadi ◽  
M Esmaeili
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Viscous Dissipation ◽  
Heat Sink ◽  
Volume Fraction ◽  
Numerical Study ◽  
Microchannel Heat Sink ◽  
Fluid Temperature ◽  
Nanofluid Flow ◽  
Aspect Ratios

The present article focuses on analytical and numerical study on the effect of viscous dissipation when nanofluid is used as the coolant in a microchannel heat sink (MCHS). The nanofluid is made from CuO nanoparticles and water. To analyse the MCHS, a modified Darcy equation for the fluid and two-equation model for heat transfer between fluid and solid sections are employed in porous media approach. In addition, to deal with nanofluid heat transfer, a model based on the Brownian motion of nanoparticles is used. The model evaluates the thermal conductivity of nanofluid considering the thermal boundary resistance, nanoparticle diameter, volume fraction, and the fluid temperature. At first, the effects of particle volume fraction on temperature distribution and overall heat transfer coefficient are investigated with and without considering viscous dissipation. After that, the influence of different channel aspect ratios and porosities is studied. The results show that for nanofluid flow in microchannels, the viscous dissipation can be neglected for low volume fractions and aspect ratios only. Finally, the effect of porosity and Brinkman number on the overall Nusselt number is studied, where asymptotic behaviour of the Nusselt number is observed and discussed from the energy balance point of view.

Optimizing a Functionally Graded Metal-Matrix Heat Sink Through Growth of a Constructal Tree of Convective Fins

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
Jacob Kephart ◽  
G. F. Jones
Keyword(s):  
Heat Sink ◽  
Metal Matrix ◽  
Heated Surface ◽  
Electronics Cooling ◽  
Functionally Graded ◽  
Aspect Ratios ◽  
Volume Porosity ◽  
Convective Fin ◽  
Matrix Heat ◽  
Fin Shape

Optimal material utilization in metal-matrix heat sink is investigated using constructal design (CD) in combination with fin theory to develop a constructal tree of optimally shaped convective fins. The structure is developed through systematic growth of constructs, consisting initially of a single convective fin enveloped in a convective medium. Increasingly complex convective fin structures are created and optimized at each level of complexity to determine optimal fin shapes, aspect ratios, and fin-base thickness ratios. One result of the optimized structures is a functional grading of porosity. The porosity increases as a function of distance from the heated surface in a manner ranging from linear to a power function of distance with exponent of about 2. The degree of nonlinearity in this distribution varies depending on the volume of the heat sink and average packing density and approaches a parabolic shape for large volume. For small volume, porosity approaches a linear function of distance. Thus, a parabolic (or least-material) fin shape at each construct level would not necessarily be optimal. Significant improvements in total heat transfer, up to 55% for the cases considered in this work, were observed when the fin shape is part of the optimization in a constructal tree of convective fins. The results of this work will lead to better understanding of the role played by the porosity distribution in a metal-matrix heat sink and may be applied to the analysis, optimization, and design of more effective heat sinks for electronics cooling and related areas.

Study of Flow and Heat Transfer Characteristics in Asymmetrically Heated Sintered Porous Heat Sinks With Periodical Baffles

2005 ◽  
Vol 128 (3) ◽  
pp. 226-235 ◽  
Author(s):  
Tzer-Ming Jeng ◽  
Sheng-Chung Tzeng
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Heat Sink ◽  
Average Nusselt Number ◽  
Heated Surface ◽  
Heat Sinks ◽  
Heat Transfer Characteristics ◽  
Fluid Medium ◽  
Nusselt Numbers ◽  
Flow And Heat Transfer

This work numerically examined the mechanism of heat transfer in a sintered porous heat sink with baffles. A channel filled with the sintered porous heat sink was asymmetrically heated and metallic baffles were periodically mounted on the heated surface. The fluid medium was air. The results indicate that no recirculation occurred between baffles. The metallic baffle obtained heat from the heated surface by conduction directly from the heated surface and indirectly through the porous media. It dissipated heat to the fluid that passed over the zone above the baffle. The Nusselt numbers in the cases with baffles exceeded those in cases without a baffle. The enhancement in the average Nusselt numbers of sintered porous heat sinks with baffles increased as the Reynolds number (Re) declined; the baffle height (h∕H) increased; the baffle length (w∕H) increased, or the baffle pitch (XL) decreased. However, at Re=500, the average Nusselt number in the case with h∕H=0.3 was higher than those with h∕H=0.7, 0.5, and 0.1. Additionally, the minimum enhancement appeared at around Re=3000 for various h∕H, w∕H, and XL. For the cases with h∕H⩽0.3 and various w∕H as well as XL, at Re>3000, sintered porous heat sinks with baffles insignificantly improved heat transfer.

Analysis of Single-Phase Multi-Layer Heat Sinks Using a Porous Media Approach: Influence of Spatially Varying Porosity

2013 ◽  
Author(s):  
John J. Podhiny ◽  
Alfonso Ortega
Keyword(s):  
Porous Media ◽  
Heat Exchangers ◽  
Scaling Laws ◽  
Design Method ◽  
Single Layer ◽  
Heat Sinks ◽  
Design Parameters ◽  
Discrete Variation ◽  
Performance Improvements ◽  
Aspect Ratios

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. While previous studies use porous media theory for their analytical foundation just as the current studies do, they also focused on heat exchangers with machined channels, and have consequently been limited to discrete variation of the porosity (or number of channels) in each layer. Extending this approach by allowing for continuous porosity variation provides a generalized and powerful design method for scaled multi-layer heat exchangers by mathematically modeling them using two-equation volume averaged quantities. This approach also yields insight into the fundamental design parameters which control the performance of this class of heat exchangers, and suggests that their performance-governing parameters are similar to those which govern fin performance. This paper focuses primarily on the thermal behavior of these liquid cooled heat sinks which employ various scaling functions to define the spatial variation of porosity. Comparisons are made with available closed-form solutions as well as results available from prior studies of discretely-scaled designs. The results indicate that scaling laws which have not been investigated previously can likely yield further performance improvements relative to prior designs.

VAT Based Modeling of Plate-Pin Fin Heat Sink and Obtaining Closure From CFD Solution

2011 ◽  
Author(s):  
Feng Zhou ◽  
Nicholas Hansen ◽  
Ivan Catton
Keyword(s):  
Heat Transfer ◽  
Porous Media ◽  
Heat Sink ◽  
Volume Averaging ◽  
Heat Sinks ◽  
Averaging Theory ◽  
Conservation Of Energy ◽  
Pin Fin ◽  
Fast Running ◽  
Volume Averaging Theory

A plate-pin fin heat sink (PPFHS) is composed of a plate fin heat sink (PFHS) and some pin fins planted between the flow channels. Just as the other kinds of heat sinks, it is a hierarchical multilevel device with many parameters required for its description. Volume Averaging Theory (VAT) is used to rigorously cast the point-wise conservation of energy, momentum and mass equations into a form that represents the thermal and hydraulic properties of the plate-pin fin (porous media) morphology and to describe the hierarchical nature of the heat sink. Closure for the upper level is obtained using VAT to describe the lower level. At the lower level, the media is described by a representative elementary volume (REV). Closure terms in the VAT equations are related to a local friction factor and a heat transfer coefficient of the REV. The terms in the closure expressions are complex and relating experimental data to the closure terms resulting from VAT is difficult. In this work, we model the plate-pin fin heat sink based on Volume Averaging Theory and use CFD to obtain detailed solutions of flow through an element of PPFHS and use these results to evaluate the closure terms needed for a fast running VAT based code. The VAT based code can then be used to solve the heat transfer characteristics of the higher level heat sink. The objective is to show how plate-pin fin heat sinks can be modeled as porous media based on Volume Averaging Theory and how CFD can be used in place of a detailed, often formidable, experimental effort.

Heat Sink With Stacked Multi-Layer Porous Media

2014 ◽  
Author(s):  
Arun K. Karunanithi ◽  
Fatemeh Hassanipour
Keyword(s):  
Porous Media ◽  
Pressure Drop ◽  
Thermal Resistance ◽  
Thermal Performance ◽  
Heat Sink ◽  
Lower Pressure ◽  
Heat Sinks ◽  
Rectangular Channels ◽  
Mini Channels

Previous studies have shown that stacked multi-layer mini-channels heat sinks with square or circular channels have advantages over traditional single layered channels in terms of both pressure drop and thermal resistance. In this work, porous media is used in the multi-layered stacked mini-channels instead of square or rectangular channels and the effect of the same on pressure drop and thermal performance is studied. Porosity scaling is done between the layers of porous media and is compared with unscaled stacked multilayer channel. Porosity scaling allows the porosity to vary from one layer to the next layer and could result in a lower pressure drop and better thermal performance.

On heated surface transport of heat bearing thermal radiation and MHD Cross flow with effects of nonuniform heat sink/source and buoyancy opposing/assisting flow

Heat Transfer ◽  
2021 ◽  
Author(s):  
Assad Ayub ◽  
Hafiz A. Wahab ◽  
Syed Zahir Hussain Shah ◽  
Syed Latif Shah ◽  
Zulqurnain Sabir ◽  
...  
Keyword(s):  
Thermal Radiation ◽  
Heat Sink ◽  
Heated Surface ◽  
Cross Flow ◽  
Surface Transport
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