Heat transfer and fluid flow characteristics of microchannels with internal longitudinal fins

Abstract

Electronic components generate large amount of heat during their operation, which requires to be dissipated. Over the past decade, internal heat generation levels have exponentially increased due to the compact packaging of high-powered microelectronic circuitry in modern devices. The efficient removal of this internally generated heat from microelectronic components is a critical design consideration for enabling optimum performance, and improving the operational reliability of modern high-performance electronic devices. Traditional cooling techniques such as fan-cooled heat sinks are grossly inadequate, and impose severe limits on product design, and hence cannot be used for cooling modern electronic components. Microchannel based cooling systems are highly popular due to its high surface area to volume ratio, and are identified as a highly viable practical alternative for meeting the current and future cooling needs of advanced electronic components. There are several methods to enhance the heat transfer performance of a microchannel. One of the single-phase heat transfer enhancement methods is to provide internal fins in a microchannel. The internal fins provide an increase in the surface area for heat transfer, and under certain conditions, alter the internal flow to provide an enhancement in heat transfer as compared to a microchannel without internal fins.In this thesis, a numerical study is performed to investigate the heat transfer and fluid flow characteristics of microchannels with four longitudinal internal fins. The simulations are carried out in the presence of a hydrodynamically fully developed, thermally developing laminar flow. Constant heat flux boundary conditions are assumed on the external walls of the microchannel. A range of channel aspect ratios covering square and rectangular cross-sectioned microchannels, with four internal longitudinal fins of various heights and thicknesses are considered in the modeling. Results of the velocity and temperature distribution are analysed in detail, to examine the effects of fin height and thickness on the heat transfer and fluid flow characteristics of the microchannels. Based on the range of parameters analysed, an optimum fin geometry that provides the maximum heat transfer rate is obtained from the analysis. The result of the optimum fin geometry is also obtained using the thermal resistance method of analysis. A thermodynamic analysis based on the entropy generation minimization method is carried out by estimating the irreversibility due to both heat transfer and fluid friction, in order to obtain the an optimum fin geometry. The optimum fin geometry obtained from the above methods are further compared, and is found to be similar. The comprehensive study carried out in this thesis provide more physical insight, and useful results on the heat and fluid flow characteristics of this potential single-phase passive heat transfer enhancement technique.