The Numerical Simulation Of Micro-channel Heat Exchanger

With the development of industry, the integration and miniaturization of electronic devices increase gradually, which may lead to a sharp increase in heat flux during operation and cause device damage. Microchannel heat exchangers are widely concerned and applied in the last few decades owing to their benefit of reduced dimension and high thermal performance for reasonable utilization of energy. So the structure design and optimization of microchannel heat exchanger, which can improve thermal and hydrodynamic performance, has an important practical significance.A numerical investigation has been carried out in this paper to examine the characteristics of heat transfer and flow resistance in counterflow rectangular microchannel heat exchanger. The comparison between experimental and numerical results show that numerical predictions are in good agreement with experimental observations. Effects of aspect ratio and Reynolds number (Re) on thermal and hydrodynamic performance has been presented in this paper. The results show that the Nusselt number and pressure drop increase and equivalent thermal resistance decrease with Reynolds number, as well as aspect ratio. The optimal thermal performance of microchannel heat exchanger has been found at aspect ratio 1.67. Correlations of thermal and hydrodynamic characteristics at Reynolds number from 40 to 830 are conducted applying nonlinear fitting method conduct, these correlations provide a basis for design and application of plain microchannel heat exchangers.In the final part of present numerical study, heat transfer enhancement in microchannel heat exchanger using extended surface has been carried out. The effects of shape, dimension, arrangement and number of blocks on thermal and hydrodynamic characteristics are studied in this paper. The numerical results show that, at the same heat transfer area, microchannels with rhombus blocks have the largest Nusselt number and the best heat transfer performance, and with ellipse blocks have the smallest flow resistance. Considering both thermal and hydrodynamic characteristics, the rhombus blocks have the best enhancement performance. The study on arrangement of blocks shows that, the symmetric and stagger arrangement has better heat transfer performance. The heat transfer performance is optimal when block number is 7. The heat transfer performance is optimal when the side length of rhombus is 0.35mm.