Heat Transfer through Wire Cloth Micro Heat Exchanger

The main objective of this study is to calculate and determine design parameters for a novel wire cloth micro heat exchanger. Wire cloth micro heat exchangers offer a range of promising applications in the chemical industry, plastics technology, the recycling industry and energy technology. We derived correlations to calculate the heat transfer rate, pressure drop and temperature distributions through the woven structure in order to design wire cloth heat exchangers for different applications. Computational Fluid Dynamics (CFD) simulations have been carried out to determine correlations for the dimensionless Euler and Nusselt numbers. Based on these correlations, we have developed a simplified model in which the correlations can be used to calculate temperature distributions and heat exchanger performance. This allows a wire cloth micro heat exchanger to be virtually designed for different applications.

Temperature-Sensitive Paint Applications in the Heat Transfer Analysis of 90° Elbow Microchannel Flow with Sharp and Curved Turns

ABSTRACTThis study presents the heat transfer analysis of 90° elbow microchannel flow with sharp and curved turn designs. Experimental technique of temperature-sensitive paint was adapted in the experiment for measuring both fluid and surface temperature. The detailed information of fluid and surface temperature data were successfully acquired with a microscope system at Reynolds number varying from 50.5 to 101.1. Micro heaters were fabricated and positioned underneath the microchannel to provide the constant heat flux boundary condition. The utilization of micro heaters can prevent the axial heat conduction. The Nusselt number contours were obtained in this study with sharp and curved corners, which can provide detailed information of localized region with high and low heat transfer. The experimental approach performed in this study could be applied in the future for micro heat exchanger or heat sink design with complex microchannel systems.

A Hybrid Numerical Methodology Based on CFD and Porous Medium for Thermal Performance Evaluation of Gas to Gas Micro Heat Exchanger

In micro heat exchangers, due to the presence of distributing and collecting manifolds as well as hundreds of parallel microchannels, a complete conjugate heat transfer analysis requires a large amount of computational power. Therefore in this study, a novel methodology is developed to model the microchannels as a porous medium where a compressible gas is used as a working fluid. With the help of such a reduced model, a detailed flow analysis through individual microchannels can be avoided by studying the device as a whole at a considerably less computational cost. A micro heat exchanger with 133 parallel microchannels (average hydraulic diameter of 200 μ m) in both cocurrent and counterflow configurations is investigated in the current study. Hot and cold streams are separated by a stainless-steel partition foil having a thickness of 100 μ m. Microchannels have a rectangular cross section of 200 μ m × 200 μ m with a wall thickness of 100 μ m in between. As a first step, a numerical study for conjugate heat transfer analysis of microchannels only, without distributing and collecting manifolds is performed. Mass flow inside hot and cold fluid domains is increased such that inlet Reynolds number for both domains remains within the laminar regime. Inertial and viscous coefficients extracted from this study are then utilized to model pressure and temperature trends within the porous medium model. To cater for the density dependence of inertial and viscous coefficients due to the compressible nature of gas flow in microchannels, a modified formulation of Darcy–Forschheimer law is adopted. A complete model of a double layer micro heat exchanger with collecting and distributing manifolds where microchannels are modeled as the porous medium is finally developed and used to estimate the overall heat exchanger effectiveness of the investigated micro heat exchanger. A comparison of computational results using proposed hybrid methodology with previously published experimental results of the same micro heat exchanger showed that adopted methodology can predict the heat exchanger effectiveness within the experimental uncertainty for both cocurrent and counterflow configurations.