Heat Transfer Properties in Microchannel by Varying Aspect Ratio: Experimental and Simulation (original) (raw)
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Archives for Technical Sciences
Due to the shrinking of the industrial equipment, the heat transfer and cooling of these devices are ofparticular importance. Therefore, this paper studies fluid flow and heat transfer in a micro-channel. Inthis study three-dimensional laminar numerical simulations, based on the Navier–Stokes equations andenergy equation, are obtained for pressure drop and heat transfer in these micro-channel heat sinksunder the same conditions. In this article, the first step is to investigate the effect of channel shape andgeometry on the heat transfer and pressure drop in micro-channels. In, the second step, the effect ofundefined heat flux and distinct input condition is investigated, and third step, the effect of increasingthe number of channels is checked to do an ideal form of heat transfer in a micro-channel. According tothe results, heat transfer using a hexagonal micro-channel is improved 20% on the rectangular microchannel(with equal hydraulic diameter).
Study of Fluid Flow and Heat Transfer In Rectangular Micro Channel
The computational fluid dynamics (CFD) model equations are solved to predict the hydrodynamic and thermal behaviour of the exchanger. The geometry of the problem and meshing of it have been made in ANSYS 14.0. The models have been solved by ANSYS Fluent 14.0 solver. Water and its Nano fluids with alumina (A2O3) are used as the coolant fluid in the micro channel heat sink. The relation between heat transfer coefficient and thermal conductivity of the fluid i.e. h ∝ k is proved in the present study. Thus use of Nano fluids has been found beneficial both in laminar and turbulent zone. The result shows that Nano fluids help to increase the heat transfer coefficient by 15% and 12% respectively in laminar and turbulent zone. The entrance length for the fully developed velocities depends on Reynolds number. The temperature rise between outlet and inlet depends on the Reynolds number, Re and Peclet number, Pe Temperature distribution is found to be independent of radial position even for Pe<<1.0. The hydrodynamic and thermal behaviour of the system have been studied in terms of velocity, pressure and temperature contours. The velocity contours at the exit show that wall effect penetrates more towards the center and the thickness of the zone with maximum velocity shrinks with increase in Re. The pressure drop across the channel increases with increase in Re. The experimental work done by Lee and Mudawar (2007) has been predicted by the present CFD results. The hydrodynamics and thermal behaviour of a rectangular micro channel are studied here. The variation wall temperature, pressure drop in the channel and the friction factors calculated using ANSYS Fluent can well predict the experimental data. The effect of Re on the behaviour the channel are also studied. Its behaviour also has been analyzed with the help of temperature, pressure and velocity contours.
2015
In our research work its considered Due to the high performance of electronics components, Heat dissipation becomes a significant issue for stable operation of components. Micro channels provide very high heat transfer coefficients because of their small diameters. In this study, two dimensional fluid flow and heat transfer in a rectangular micro channel heat sink are analyzed using FLUENT as solver with water as cooling fluid. With strong literature study it is found that down to 50 μm of hydraulic diameter, macro scale model can be applicable. Three channels of height 50 μm, 100 μm and 150 μm are considered. The study is mainly focused on Nusselt Number and height effects on micro channel thermal performance. The highest temperature is encountered at the heated surface of the heat sink immediately above the channel outlet.
The design and fabricate of microchannel and fluidic devices required to understand the basic fundamental terms of heat transfer and fluid mechanic processes. Several authors have been work on microchannel heat sink by applying a traditional method which has been used in macroscale application mainly in laminar flow. In this paper a previous experimental results has been studied in depth and identify the descrepancies. The following data set to be for various researchers shows to describe the geometry used in the microchannel heat sink for laminar flow and turbulent flow. Also compare the different flow configuration used in different shapes of microchannel heat sink. This previous literature also predicts the better flow configuration in microchannel heat sink.
Numerical simulation of heat transfer in rectangular microchannel
Advances in Applied …, 2009
Numerical simulation of heat transfer in a high aspect ratio rectangular microchannel with heat sinks has been conducted, similar to an experimental study. Three channel heights measuring 0.3 mm, 0.6 mm and 1 mm are considered and the Reynolds number varies from 300 to 2360, based on the hydraulic diameter. Simulation starts with the validation study on the Nusselt number and the Poiseuille number variations along the channel streamwise direction. It is found that the predicted Nusselt number has shown very good agreement with the theoretical estimation, but some discrepancies are noted in the Poiseuille number comparison. This observation however is in consistent with conclusions made by other researchers for the same flow problem. Simulation continues on the evaluation of heat transfer characteristics, namely the friction factor and the thermal resistance. It is found that noticeable scaling effect happens at small channel height of 0.3 mm and the predicted friction factor agrees fairly well with an experimental based correlation. Present simulation further reveals that the thermal resistance is low at small channel height, indicating that the heat transfer performance can be enhanced with the decrease of the channel height.
ASME 2008 First International Conference on Micro/Nanoscale Heat Transfer, Parts A and B, 2008
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.
Study of Fluid Flow and Heat Transfer In Circular Micro Channel
The computational fluid dynamics (CFD) model equations are solved to predict the hydrodynamic and thermal behavior of the exchanger. The geometry of the problem and meshing of it have been made in ANSYS 14.0. The models have been solved by ANSYS Fluent 14.0 solver. Water and its nanofluids with alumina (A2O3) are used as the coolant fluid in the microchannel heat sink. The present CFD calculated heat transfer coefficient values have compared with the analytical values and very close agreement is observed. The relation between heat transfer coefficient and thermal conductivity of the fluid i.e. h ∠k is proved in the present study. Thus use of nanofluids has been found beneficial both in laminar and turbulent zone. The result shows that nanofluids help to increase the heat transfer coefficient by 15% and 12% respectively in laminar and turbulent zone. The entrance length for the fully developed velocities depends on Reynolds number. The experimental work done by Lee and Mudawar (2007) has been predicted by the present CFD results. The hydrodynamics and thermal behaviour of a rectangular microchannel are studied here. The variation wall temperature, pressure drop in the channel and the friction factors calculated using ANSYS Fluent can well predict the experimental data. The effect of Re on the behavior the channel are also studied. Its behavior also have been analysed with the help of temperature, pressure and velocity contours.
Numerical Modelling of Heat Transfer in Rectangular Microchannels
ASME 2nd International Conference on Microchannels and Minichannels, 2004
The paper presents both three and two-dimensional numerical analysis of convective heat transfer in microchannels. The three-dimensional geometry of the microchannel heat sink followed the details of the experimental facility used during a previous research step. The heat sink consisted of a very high aspect ratio rectangular microchannel. Two channel heights, namely 1mm and 0.3mm (0.1mm), were used for 3D (2D) numerical model respectively. Water was employed as the cooling liquid. The Reynolds number ranged from 200 to 3000. In the paper, the thermal entrance effect is analyzed in terms of heat transfer efficiency. Finally, the comparison between measured and computed heat flux and temperature fields is presented.
Applied Thermal Engineering, 2017
The effect of aspect ratio and hydraulic diameter on single phase flow and heat transfer in a single microchannel was investigated numerically and the results are presented in this paper. Previously, many studies in literature investigating the effect of geometrical parameters reached contradictory conclusions leaving some phenomena unexplained. Additionally, most researchers studied the effect of channel geometry by varying the channel height for a constant channel width or varying the width for a constant height. This means that the hydraulic diameter and aspect ratio vary simultaneously, which makes it difficult to identify the relative importance of the aspect ratio and the hydraulic diameter. In the present study, the effect of hydraulic diameter was studied by varying the channel width and depth while keeping the aspect ratio constant. The range of hydraulic diameters was 0.1-1 mm and the aspect ratio was fixed at 1. In the second set of simulations, the aspect ratio ranged from 0.39 to 10 while the hydraulic diameter was kept constant at 0.56 mm. The simulations were performed using the CFD software package ANSYS Fluent 14.5. The geometry investigated in this study includes symmetrical cylindrical inlet and outlet plenums and a microchannel. The fluid entered and left the channel vertically from the top in a direction normal to the channel axis. The dimensions of the inlet/outlet plenums (diameter and height measured from the channel bottom surface) were kept constant while the width and depth of the channel were varied. The simulations were conducted for a range of Reynolds numbers (Re = 100-2000) and water was used as the working fluid. A three dimensional thin wall model was used to avoid conjugate heat transfer effects. A constant heat-flux boundary condition was applied at the bottom and vertical side walls of the channel, while the upper wall was considered adiabatic. The friction factor was found to decrease slightly with aspect ratio up to AR % 2 after which it increased with increasing aspect ratio. The results demonstrated that the slope of the velocity profile at the channel wall changes significantly with aspect ratio for AR > 2. The effect of the aspect ratio and hydraulic diameter on the dimensionless hydrodynamic entry length is not significant. Also, the aspect ratio does not affect the heat transfer coefficient while the dimensionless Nusselt number increases with increasing hydraulic diameter. The friction factor was found to increase with increasing hydraulic diameter.
Flow Behavior and Temperature Distribution in Micro-Channels for Constant Wall Heat Flux
Procedia Engineering, 2013
An efficient micro-channel heat exchanger was designed which can be used for heat removal from components requiring micro level heat extraction. The heat exchanger is composed of 21 channels and each channel dimensions are 13 x 0.35 x 0.5 mm 3. The channel walls were at no slip and constant heat flux conditions. Different gaseous fluids were considered for the best performance. Hydrogen gave most uniform flow distributions among the channels. The heat exchanger was designed and simulated numerically using the non symmetric pattern multi frontal finite element method for predicting the flow behavior. Four different geometries were proposed and simulated in 2D to find the best geometry in terms of flow distribution. The best geometry was investigated in both 2D and 3D for temperature distributions among the channels. Simulations demonstrated that the effectiveness of the micro-heat exchanger varies with pressure difference, inlet geometry and wall heat flux.