Experimental and numerical investigation of fluid flow and heat transfer in microchannels

Abstract

Microchannels are of current interest for use in heat exchangers where very high heat transfer performance is desired. Microchannels provide very high heat transfer coefficients because of their small hydraulic diameters. In this study, an investigation of fluid flow and heat transfer in microchannels is conducted. A review of the literature published regarding fluid flow and heat transfer in microchannels is provided in this study. A thorough background on the theory of internal convective heat transfer is provided as well. A critical analysis of some of the published heat transfer experiments on microchannels is also given. It was found that some of the experimental methods published recently employ experimental and data reduction techniques which may result in errors for reported Nusselt numbers. A brief computational fluid dynamics (CFD) investigation into the heat transfer and fluid flow performance of some channels with designed bumps is also presented. It was found that designed channels offer enhanced Nusselt numbers in the turbulent regime at the cost of a higher friction factor when compared to a plain channel. Fluid flow and heat transfer experiments were conducted on a copper microchannel heat exchanger (MHE). An experimental method of imposing a constant surface temperature to the MHE was used. A description of the experimental apparatus and procedure is provided. The friction factor results from the experiments agree fairly well with theoretical correlations. The experimental Nusselt number results agree with theory very well in the transition/turbulent regime, but the results show a higher Nusselt number in the laminar regime than predicted by theoretical correlations. A full description of the data reduction and analysis of the experimental data is given. A CFD model was created to simulate the fluid in the inlet plenum and the microchannels. The results from these simulations are presented, and they show good agreement with the experimental data in the transition/turbulent regime as well as with theoretical correlations for laminar and turbulent flow.