Micro/nano fins for single phase heat transfer enhancement and development of heat flux boundary condition for DSMC-IP

摘要

High component densities and high power consumption has led a tremendous increase in the heat generated in electronics. The high thermal conductivity and large surface to volume ratios of nanostructures such as carbon nanotubes and metallic nanowires make them a potential solution for thermal management as micro/nano fins. Though experimental work has been attempted, not much theoretical/numerical work has been done to study the effect of the parameters involved, like fin-geometry, gas-rarefaction etc. Due to the small length scales involved, the gas flow through these structures cannot be considered as continuum and the phenomenon of velocity and temperature slips considerably affect the thermal performance. This thesis studies the single phase heat transfer from micro/nano fins and proposes a heat flux boundary condition for DSMC-IP, which would prove essential in further study of micro/nano fins.;Firstly, a simple analytical model is developed to study the effect of gas rarefaction, on the performance of micro/nano fins. It is shown that the rarefaction of gas significantly reduces the heat transfer achieved compared to that postulated by the continuum approach.;Second, a study of the fluid flow and heat transfer in a fin integrated microchannel has been conducted using DSMC-IP method. It is found that such integration significantly increases the heat transfer obtained per unit pumping power, proving that micro/nano fins lead to an increase in the efficiency of the heat transfer from the surface. During further study on the effect of fin separation on the thermal performance of microchannels, it was found that the use of constant temperature wall boundaries is ineffective in capturing the effect of fin separation. Therefore, a heat flux boundary condition for DSMC-IP has been developed and validated.;Finally, a study on the flow through constant heat flux microchannels is conducted to understand the effect of rarefaction on the fluid flow and heat transfer. It is seen that the fluid flow is accurately predicted by the new boundary condition but there is a considerable error in the Nusselt number calculated by the simulation. The possible reasons this error are iterated and future work is proposed.