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Laminar flow
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Proceedings Papers
Lakshmi Balasubramaniam, Rerngchai Arayanarakool, Samuel D. Marshall, Bing Li, Poh Seng Lee, Peter C. Y. Chen
Proc. ASME. MNHMT2016, Volume 2: Micro/Nano-Thermal Manufacturing and Materials Processing; Boiling, Quenching and Condensation Heat Transfer on Engineered Surfaces; Computational Methods in Micro/Nanoscale Transport; Heat and Mass Transfer in Small Scale; Micro/Miniature Multi-Phase Devices; Biomedical Applications of Micro/Nanoscale Transport; Measurement Techniques and Thermophysical Properties in Micro/Nanoscale; Posters, V002T11A005, January 4–6, 2016
Paper No: MNHMT2016-6422
Abstract
Advancements in the field of microfluidics has led to an increasing interest to study laminar flow in microchannel and its potential applications. Understanding mixing at a microscale can be useful in various biological, heating and industrial applications due to the space and time reduction that micro mixing permits. This work aims to study mixing enhancement due to curved microchannel and the influence of varying microchannel cross sectional shape through numerical and experimental investigations. Unlike prior studies which use channel dimensions in the lower microscale range, this work has been conducted on channels with dimensions in the higher end of micrometer range. Using a cross sectional hydraulic diameter of 600 μm enables introduction of flow into the curved channel at a Reynolds Number ranging from 0.15 to 75, the findings of which show considerable improvement in the mixing performance as compared to that of equivalent straight channels, due to the development of secondary flows known as Dean Vortices.
Proceedings Papers
Proc. ASME. MNHMT2013, ASME 2013 4th International Conference on Micro/Nanoscale Heat and Mass Transfer, V001T04A007, December 11–14, 2013
Paper No: MNHMT2013-22156
Abstract
Detailed experimental investigations of condensation in microchannels where local heat flux and surface temperature were measured along the channel are compared with theoretical results for the special case of annular, laminar flow. The theoretical model includes surface tension driven transverse flow towards the corners of the channel as well as shear stress driven streamwise flow in an otherwise Nusselt treatment. The theory has no empirical input. When distributions along the channel of the local vapor and wall temperatures are given, local heat flux and heat-transfer coefficient, as well as local vapor quality, may be calculated. Such detailed experimental data have only recently become available. Strict implementation of the theory requires that the onset of condensation occurs within the channel, i.e. the vapor is saturated or superheated at the inlet. The comparisons show remarkably good agreement with the experimental data for two fluids and covering a wide range of experimental conditions.
Proceedings Papers
Proc. ASME. MNHMT2013, ASME 2013 4th International Conference on Micro/Nanoscale Heat and Mass Transfer, V001T06A002, December 11–14, 2013
Paper No: MNHMT2013-22204
Abstract
Micro-convection is a strategic area in transport phenomena, since it is the basis for a wide range of miniaturized high-performance heat transfer applications. Surface area is one of the important parameter for high flux heat transfer in microchannel performance. This experimental study deals with heat transfer using triangular microchannel having hydraulic diameters of 321μm and 289μm. Experimentation is carried out for triangular microchannel set for different heat input and flow rate condition. Triangular microchannel are manufactured with EDM technology. Testing of microchannel under laminar flow is considered with different tip angle, spacing, and length of microchannels. The different microchannels made up of copper material with 29 microchannel each having three different sets of length of 50 mm, 70 mm and 90 mm respectively. Tip angles for triangular microchannel is varied 50 ° and 60 ° with width of 30 mm each respectively are analyzed numerically. Spacing between triangular microchannels is also varied and 300μm and 400μm are considered for the analysis. Water flow rate is considered laminar flow. The flow rate of water is varied from 0.0167 kg/sec to 0.167 kg/sce to carry away heat. It is observed that as hydraulic diameters increase the heat transfer coefficient decreases. As the heat input to microchannel increases from 10 Watt to 100 Watt the temperature drop across varies from 2° C to 22°C as water flow rate increases. The numerical analysis is done using computer C programming. Experimental result differ from theoretical for temperature drop with variation of 2°C to 5°C. It is also observed that in all triangular microchannels its geometry i.e. tip angle and hydraulic diameter are dominant parameters which influences on rate of heat transfer. With increasing channel depth, increases flow passage area therefore enhances heat transfer sufficiently. From experimentation a Nu number correlation is proposed with considering tip angle, length, spacing of microchannel and other related parameters.
Proceedings Papers
Proc. ASME. MNHMT2013, ASME 2013 4th International Conference on Micro/Nanoscale Heat and Mass Transfer, V001T06A003, December 11–14, 2013
Paper No: MNHMT2013-22245
Abstract
This paper describes the CFD analysis of single rectangular microchannel for hydraulic diameter 319 μm. While CFD analysis the Nusselt number observed is 4 to 5 with different Reynolds Number variation for flow rate of 0.001 kg/sec to 0.012 kg/sec. The current work describes CFD analysis of single microchannels for length of 50 mm with water as a fluid medium with laminar flow. Computational Fluid dynamics analysis of Single rectangular microchannel Single rectangular microchannel of 319 μm hydraulic diameter is analyzed to study the flow characteristics in the inlet, microchannel test section and outlet test section with ANSYS CFX-11 for pressure drop, temperature drop, velocity counter of single micro-channel. For analyzing the weather the turbulence is created at inlet part of the microchannel a pressure drop analysis is carried for flow rate of 0.012 kg/sec with heat input 5.33 watt/cm 2 under laminar flow consideration. For analyzing the temperature profile across microchannel a for flow rate of 0.012 kg/sec with heat input 5.33 watt/cm 2 under laminar flow is considered.. For single microchannel the temperature rise of water is in range of 1 °K to 2 °K at center plane of microchannel. It is found that at leading edges or leaving edge the temperature rise in water is higher as compare to entering edge of microchannel. It is due to while entering to leaving of water particles in microchannel it collapse each other and try to increasing friction along each other so at outlet or leading edge the temperature rise is seen higher as compare to in let portion of single microchannel.
Proceedings Papers
Proc. ASME. MNHMT2012, ASME 2012 Third International Conference on Micro/Nanoscale Heat and Mass Transfer, 371-376, March 3–6, 2012
Paper No: MNHMT2012-75187
Abstract
The paper examines the special case of annular laminar flow pressure drop, or more precisely pressure gradient, during condensation in microchannels. This is the only flow regime permitting wholly theoretical solution without having recourse to experimental data. Solutions are obtained and comparisons made with empirical formulae for void fraction (needed to calculate the momentum pressure gradient) when obtaining the friction pressure gradient from experimentally measured or “total” pressure gradient. To date calculations and comparisons are restricted to one fluid (R134a), one channel section and one flow condition. For the case considered it is found that earlier approximate models for estimating void fraction agree quite well with the theoretical annular flow solutions. There is, however, significant difference between momentum pressure gradients obtained from approximate models used in the earlier investigations and that given by the theoretical annular flow solution which is (numerically) higher than all of them. The annular flow solution indicates that the momentum pressure gradient is not small in comparison with the friction pressure gradient. The friction pressure gradient in the annular flow case is appreciably smaller than given by the earlier correlations.
Proceedings Papers
Proc. ASME. MNHMT2012, ASME 2012 Third International Conference on Micro/Nanoscale Heat and Mass Transfer, 645-649, March 3–6, 2012
Paper No: MNHMT2012-75108
Abstract
Tailored materials with nano to micron dimensions are becoming increasingly important for niche applications in optics, personnel protection and biomedicine. Microfluidics is a robust platform for producing these tailored materials because of the spatial control that can be realized in microfluidic systems due to laminar flow profiles and small dimensions. For this work, a pre-polymer solution, consisting of water, polyethylene glycol diacrylate (PEGDA) and a photo-initiator, flows through a microfluidic channel. For the general scheme, the pre-polymer is exposed to UV light in the microfluidic channel to crosslink the polymer. Depending on the application, the model pre-polymer, PEGDA, may need to be substituted with a different photo-polymerizable pre-polymer to address issues such as chemical compatibility and moisture stability prior to commercialization. Nonetheless, proof-of-concept is demonstrated using PEGDA with results that are transferrable to other photo-polymerizable pre-polymers. For this work, two distinct applications will be presented. In one application, the pre-polymer has a graded profile of nanoparticles. The nanoparticles modify the refractive index of the heterogeneous material and allow light to be directed through the material according to Snell’s Law. When the pre-polymer solution is polymerized, a thin film with a controlled refractive index profile is produced with potential for waveguiding applications. In a second application, the light is masked during UV exposure to produce particles instead of thin films. The particles can be of any two-dimensional extruded shape. If the pre-polymer solution is loaded with ceramic nanoparticles and sintered, ceramic particles that retain the shape of the original composite particle are produced. To date, numerous particle cross sections of polymeric particles and limited ceramic particles have been demonstrated with applications in liquid body armor, abrasives and drug delivery.
Proceedings Papers
Proc. ASME. MNHMT2012, ASME 2012 Third International Conference on Micro/Nanoscale Heat and Mass Transfer, 125-133, March 3–6, 2012
Paper No: MNHMT2012-75274
Abstract
Characterizing the mainly incompressible and laminar flows of aqueous electrolyte solutions through channels with an overall dimension of O (1–100 μm) is of interest in a variety of microfluidics applications. Solid surfaces such as the channel wall become (usually negatively) charged due to direct ionization or dissociation of surface groups, where the charge is typically characterized by the wall zeta-potential ζ w . The surface in turn attracts mobile counterions from the fluid to form a (usually positively) charged screening, or electric double, layer (EDL). An external electric field can therefore be used to “pump” fluids through microfluidic Labs-on-a-Chip (LOC) by driving the charged fluid in the EDL. The resulting electroosmotic flow (EOF) is uniform outside the EDL, which has a thickness less than 50 nm in most cases. This uniform flow results in a more favorable scaling of the volume flowrate with channel diameter for microchannels, and also has less convective dispersion than shear flows. Electroosmotic flow is, however, very sensitive to changes in ζ w . Various studies have shown, for example, that adding multivalent counterions to a monovalent electrolyte solution can greatly change ζ w through both electrostatic and chemical interactions, even leading to “charge inversion” where the zeta-potential changes its sign. Evanescent-wave particle velocimetry, which tracks the motion of colloidal fluorescent tracer particles illuminated by evanescent waves within ∼400 nm of the wall, was therefore used to study the flow of various aqueous monovalent electrolyte solutions with small amounts of divalent cations such as Mg ++ driven by an electric field through channels with a minimum dimension of ∼30 μm. The technique measures both the velocity components parallel to the wall and the steady-state distribution of these near-wall tracers. In these experiments, the tracers are convected parallel to the wall by both the EOF and directly by the applied electric field via electrophoresis because the surfaces of the particles also become negatively charged when suspended in the electrolyte solution. The electrophoretic contribution to the measured particle velocity was determined by measuring the particle zeta-potential with light scattering, and subtracted from the particle velocity to determine the actual EOF velocity.
Proceedings Papers
Proc. ASME. MNHMT2012, ASME 2012 Third International Conference on Micro/Nanoscale Heat and Mass Transfer, 923-928, March 3–6, 2012
Paper No: MNHMT2012-75330
Abstract
Attention to inhalable particulate matter (PM10) has increased in recent years due to the growing threat of its pollution to public health. Behaviors of individual particles in various flow fields are of great interest, but few results from direct observation/measurement are available. The present work develops an integral image-based scheme consisting of a microscope, a high-speed CCD camera, a view chamber, a mass flow controller, and an image processing package. This system is used to investigate behaviors of inhalable particles in a laminar flow passing a triangular or circular cylinder. Moreover, numerical simulations are conducted and compared with experiments. The particles are found to follow the laminar fluid flow well, but still with small random fluctuations. When the flow is slow, the fluctuations are more obvious.
Proceedings Papers
Proc. ASME. MNHMT2012, ASME 2012 Third International Conference on Micro/Nanoscale Heat and Mass Transfer, 929-937, March 3–6, 2012
Paper No: MNHMT2012-75185
Abstract
The thermal ground plane (TGP) is an advanced planar heat pipe designed for cooling microelectronics in high gravitational fields. A thermal resistance model is developed to predict the thermal performance of the TGP, including the effects of the presence of non-condensable gases (NCGs). Viscous laminar flow pressure losses are predicted to determine the maximum heat load when the capillary limit is reached. This paper shows that the axial effective thermal conductivity of the TGP decreases when the substrate and/or wick are thicker and/or with the presence of NCGs. Moreover, it was demonstrated that the thermo-fluid model may be utilized to optimize the performance of the TGP by estimating the limits of wick thickness and vapor space thickness for a recognized internal volume of the TGP. The wick porosity plays an important effect on maximum heat transport capability. A large adverse gravitational field strongly decreases the maximum heat transport capability of the TGP. Axial effective thermal conductivity is mostly unaffected by the gravitational field. The maximum length of the TGP before reaching the capillary limit is inversely proportional to input power.
Proceedings Papers
Proc. ASME. MNHMT2009, ASME 2009 Second International Conference on Micro/Nanoscale Heat and Mass Transfer, Volume 2, 545-552, December 18–21, 2009
Paper No: MNHMT2009-18192
Abstract
The concept of head loss coefficients K for the determination of losses in conduit components is discussed in detail. While so far it has only been applied to fully turbulent flows it is extended here to also cover the laminar flow regime. Specific numbers of K can be determined by integration of the entropy production field (second law analysis). This general approach is discussed and illustrated with the specific example of a conical diffusor.
Proceedings Papers
Kyo Sik Hwang, Hyo Jun Ha, Seung Hyun Lee, Hyun Jin Kim, Seok Pil Jang, Hyung Mi Lim, Stephen U. S. Choi
Proc. ASME. MNHMT2009, ASME 2009 Second International Conference on Micro/Nanoscale Heat and Mass Transfer, Volume 1, 455-460, December 18–21, 2009
Paper No: MNHMT2009-18173
Abstract
This paper is to investigate flow and convective heat transfer characteristics of nanofluids with various shapes of Al 2 O 3 nanoparticles flowing through a uniformly heated circular tube under fully developed laminar flow regime. For the purpose, Al 2 O 3 nanofluids of 0.3 Vol.% with sphere, rod, platelet, blade and brick shapes are manufactured by a two-step method. Zeta potential as well as TEM image is experimentally obtained to examine suspension and dispersion characteristics of Al 2 O 3 nanofluids with various shapes. To investigate flow characteristics, the pressure drop of Al 2 O 3 nanofluids with various shapes are measured. In order to investigate convective heat transfer characteristics, the effective thermal conductivities of Al 2 O 3 nanofluids with various shapes, the temperature distribution at the tube surface and the mean temperature of nanofluids at the inlet are measured, respectively. Based on the experimental results, the convective heat transfer coefficient of Al 2 O 3 nanofluids with various shapes is compared with that of pure water and the thermal conductivity of Al 2 O 3 nanofluids with various shapes. Thus, the effect of nanoparticles shape on the flow and convective heat transfer characteristics flowing through a uniformly heated circular tube under fully developed laminar flow regime is experimentally investigated.
Proceedings Papers
Proc. ASME. MNHMT2009, ASME 2009 Second International Conference on Micro/Nanoscale Heat and Mass Transfer, Volume 2, 625-633, December 18–21, 2009
Paper No: MNHMT2009-18531
Abstract
In this study the effects of having multiple synthetic jet actuators and multiple orifices in a single jet actuator on creating better flow mixing and improving heat transfer in micro-channels have been investigated numerically. Unsteady computations of laminar flow have been performed for two dimensional configurations of micro-channel open at either end. A constant heat flux of 1 MWm −2 at the top of the silicon wafer represented the heat generated by the microchip. Synthetic jet actuators were attached to the bottom wall of the channel, with the 50 μm wide orifice. It is shown that by using double orifices single synthetic jet actuator, the heat transfer enhancement in micro-channels can be greatly improved. At the end of 30 cycles of actuation, the maximum temperature in the wafer has been reduced by approximately 27 K and the minimum temperature on the bottom of the wafer has been reduced by approximately 19 K in comparison with the steady flow values. In comparison with a single orifice synthetic jet actuator, double orifices synthetic jet actuator led to an additional 10 K reduction of the maximum temperature in wafer and 4 K reduction of minimum temperature on the interface of the wafer and water. It was demonstrated that the number of synthetic jet actuators is not the main factor influencing the thermal performance. The crucial factor is the number of impinging jets generated from the orifice which encourages better mixing in the flow. However, there is a distinct advantage associated with having multiple jet actuators in that out of phase flow could be generated which led to even lower temperatures than the in-phase jets.
Proceedings Papers
Proc. ASME. MNHMT2009, ASME 2009 Second International Conference on Micro/Nanoscale Heat and Mass Transfer, Volume 2, 247-252, December 18–21, 2009
Paper No: MNHMT2009-18007
Abstract
A continuously growing need for high energy density miniaturized power sources for portable electronic applications has spurred the development of a variety of microscale fuel cells. For portable applications, membrane-based fuel cells using small organic fuels (i.e., methanol, formic acid) are among the most promising configurations as they benefit from the high energy density and easy storage of the liquid fuels. Unfortunately, the performance of these fuel cells is often hindered by membrane-related issues such as water management (i.e., electrode dry-out / flooding) and fuel crossover. Furthermore, high costs of, for example, catalysts and membranes as well as durability concerns still hinder commercialization efforts. To address these challenges we have developed membraneless laminar flow-based fuel cells (LFFCs), which exploit microscale transport phenomena (laminar flow) to compartmentalize streams within a single microchannel. The properties of various fuel and media flexible LFFCs will be presented and novel strategies for improving fuel utilization and power density will be discussed. Furthermore, the performance of a scaled-out 14-channel LFFC prototype is presented. We have also developed a microfluidic fuel cell as a powerful analytical platform to investigate and optimize the complex processes that govern the performance of catalysts and electrodes in an operating fuel cell. This platform bridges the gap between a conventional 3-electrode electrochemical cell and a fuel cell, as it allows for standard electrochemical analysis (e.g., CV, CA, EIS) as well as fuel cell analysis (e.g., IV curves).
Proceedings Papers
Proc. ASME. MNHMT2009, ASME 2009 Second International Conference on Micro/Nanoscale Heat and Mass Transfer, Volume 2, 577-582, December 18–21, 2009
Paper No: MNHMT2009-18374
Abstract
The fractal characterization of the topography of rough surfaces by using Cantor set structures is introduced in this paper. Based on the fractal Cantor surface, a model of laminar flow in rough microchannels is developed and numerically analyzed to study the characterization of surface roughness effects on laminar flow. The effects of Reynolds number, relative roughness, and fractal dimension on laminar flow are all discussed. The results indicate that the presence of roughness leads to the form of the detachment, and eddy generation is observed at the shadow of the roughness elements. The pressure drop in the rough channel along the flow direction is no longer in a linear fashion and larger than that in the smooth channel. The fluctuation characteristic of pressure drop along the stream, which is due to the vortex formation at the wall, is found. Differing from the smooth channel, the Poiseuille number for laminar flow in rough microchannels is no longer only dependent on the cross-sectional shape of the channel, but also strongly influenced by the Reynolds number, relative roughness and fractal dimension of the surface.
Proceedings Papers
Proc. ASME. MNHMT2009, ASME 2009 Second International Conference on Micro/Nanoscale Heat and Mass Transfer, Volume 3, 315-321, December 18–21, 2009
Paper No: MNHMT2009-18490
Abstract
In this study, we explore the clear idea of drag change when the surface contains roughness. For that purpose, we performed a simple terminal velocity experiment using small solid spheres. The terminal velocity of Cu spheres is measured before and after they are surface treated to form superhydrophilic or superhydrophobic nanostructures and appreciable increase in the terminal velocity for both cases is observed. An analytic solution is derived to evaluate the corresponding slip length in an external flow and the result is comparable to values reported in previous studies of lithographically patterned superhydrophobic surfaces. To gain useful physical insight, incompressible Navier-Stokes equations are solved. From the solution, a simple explanation for the experimental observation is developed using the concept of friction drag and form drag. The total drag can be reduced when the reduction of the friction drag is larger than the increase of the form drag.
Proceedings Papers
Proc. ASME. MNHT2008, ASME 2008 First International Conference on Micro/Nanoscale Heat Transfer, Parts A and B, 1257-1264, June 6–9, 2008
Paper No: MNHT2008-52027
Abstract
A three-dimensional incompressible model of microchannel is proposed. Flow characteristics of nitrogen flow in different microchannels (hydraulic diameter ranging 100–500μm, the ratio of length-to-diameter ranging 60–150, the ratio of height-to-width ranging 0.2–1) have been investigated numerically. It is found that the velocity distribution in microchannels is obviously different from that in conventional channels, and the maximum velocity occurs not in the channel core as conventional theory expected but near the walls due to the surface effect. These phenomena result in the reduction of the thickness of hydrodynamic boundary layer. So the hydrodynamic entry length in microchannels is much larger than that in conventional channels. Theoretical analysis was given to explain these phenomena. The effects of Reynolds number, hydrodynamic diameter, length-to-diameter ratio and height-to-width ratio on hydrodynamic entry length were analyzed. The correlation between L/D and Re and height-to-width ratio, which is useful for designing and optimizing the microchannel heat sinks and other microfluidic devices, was suggested.
Proceedings Papers
Proc. ASME. MNHT2008, ASME 2008 First International Conference on Micro/Nanoscale Heat Transfer, Parts A and B, 1029-1040, June 6–9, 2008
Paper No: MNHT2008-52382
Abstract
Void fractions are determined in vertical downward annular two-phase flow of R134a inside a 7 mm i.d. smooth and microfin tube. The experiments are done at average qualities ranging between 0.67–0.99. The mass fluxes are around 29 kg/m 2 s. The pressures are between 0.77–0.9 MPa. The experimental setup is explained elaborately. Comparisons between the void fraction determined from 35 void fraction correlations are done. According to the use of various horizontal and vertical annular flow void fraction models together with the present experimental condensation heat transfer data, similar void fraction results were obtained mostly for the microfin and smooth tube. Effect of void fraction alteration on the momentum pressure drop is also presented.
Proceedings Papers
Proc. ASME. MNHT2008, ASME 2008 First International Conference on Micro/Nanoscale Heat Transfer, Parts A and B, 791-799, June 6–9, 2008
Paper No: MNHT2008-52313
Abstract
Microchannel are at the fore front of today’s cooling technologies. They are widely being considered for cooling of electronic devices and in micro heat exchanger systems due to their ease of manufacture. One issue which arises in the use of microchannels is related to the small length scale of the channel or channel cross-section. In this work, the maximum heat transfer and the optimum geometry for a given pressure loss have been calculated for forced convective heat transfer in microchannels of various cross-section having finite volume for laminar flow conditions. Solutions are presented for 10 different channel cross sections, namely parallel plate channel, circular duct, rectangular channel, elliptical duct, polygonal ducts, equilateral triangular duct, isosceles triangular duct, right triangular duct, rhombic duct and trapezoidal duct. The model is only a function of Prandtl number and geometrical parameters of the cross-section, i.e., area and perimeter. This solution is performed with two exact and approximate methods. Finally, in addition to comparison and discussion about these two methods, validation of the relationship is provided using results from the open literature.
Proceedings Papers
Proc. ASME. MNHT2008, ASME 2008 First International Conference on Micro/Nanoscale Heat Transfer, Parts A and B, 819-823, June 6–9, 2008
Paper No: MNHT2008-52374
Abstract
The ever-increasing density, speed, and power consumption of microelectronics has led to a rapid increase in the heat fluxes which need to be dissipated in order to ensure their stable and reliable operation. The shrinking dimensions of electronics devices, in parallel, have imposed severe space constraints on the volume available for the cooling solution, defining the need for innovative and highly effective compact cooling techniques. Microchannel heat sinks have the potential to satisfy these requirements. However, significant temperature variations across the chip persist for conventional single-pass parallel flow microchannel heat sinks since the heat transfer performance deteriorates in the flow direction in microchannels as the boundary layers thicken and the coolant heats up. To accommodate higher heat fluxes, enhanced microchannel designs are needed. The present work presents an idea to enhance the single-phase convective heat transfer in microchannels. The proposed technique is passive, and does not require additional energy to be expended to enhance the heat transfer. The idea incorporates the generation of a spanwise or secondary flow to enhance mixing and hence decrease fluid temperature gradients across the microchannel. Slanted grooves can be created on the microchannel wall to induce the flow to twist and rotate thus introducing an additional component to the otherwise laminar flow in the microchannel. Numerical results are presented to demonstrate the effectiveness of such an enhanced microchannel heat sink. The heat transfer was found to increase by up to 12% without incurring substantial additional pressure drops.
Proceedings Papers
Proc. ASME. MNHT2008, ASME 2008 First International Conference on Micro/Nanoscale Heat Transfer, Parts A and B, 285-292, June 6–9, 2008
Paper No: MNHT2008-52324
Abstract
The increased power dissipation and reduced dimensions of microelectronics devices have emphasized the need for highly efficient compact cooling technologies. Microchannel heat sinks are of particular interest due to the very high rates of heat transfer they enable in conjunction with greatly reduced heat sink length scales and coolant mass flow rate. Therefore, in the present work, optimization of laminar convective heat transfer in the microchannel heat sinks is investigated for uniform heat flux and different cross sectional areas of different aspect ratios. Three-dimensional numerical simulations of general form of energy equation were performed to predict Nusselt number in the laminar flow regime. Using these results, an optimum forced convective heat transfer coefficient was computed for several cross sectional areas and Reynolds numbers, utilizing the univariable search method. Different aspect ratios have different influences on Nusselt number in thermally developing and fully developed regions for different cross sectional areas and Reynolds numbers. There exists an optimum Nusselt number for each Reynolds number and cross sectional area by varying aspect ratio. Thus, optimized state is computed and related graphs are presented.