Heat Transfer Cost-Effectiveness of Nanofluids

Abstract

When metal or oxide nano particles are dispersed in liquids to form nanofluids, the particles improve thermal conductivity of the liquids. Therefore, it is suggested to use nanofluids as coolants to improve heat-exchanger efficiency. However, the nano particles also cause the increase of fluid viscosity. The present paper has numerically studied the flow and heat transfer of the nanofluids in a 2-D microchannel by using Computational Fluid Dynamics method. It is found that although the nano particles enhance the heat transfer rate of the fluids about certain percentage, the nano particles also cause an increase of viscous shear stress, and further causes an increase of the power consumption to deliver the nanofluids through the microchannels. To explore their advantage, nanofluids are suggested to be used as coolants to improve the thermal efficiency and to reduce the size of heat exchangers. However, the nanofluids also enlarge fluid shear stresses on solid interfaces. This is because that the nano particles increase the viscosity of the fluids. The enlarged shear stresses will increase the fluid drags. This makes it difficult for the nanofluids to flow through the fluidic systems comparing with those base liquids (2, 3). Therefore, a big pressure difference is required to drive the nanofluids to flow through the fluidic systems. This in turn will cause more power consumption. So, one has to carefully analyze the gain and the loss or cost-effectiveness, before adopting the nanofluids as coolants. To investigate the cost-effectiveness of using nanofluids as coolants, Computational Fluid Dynamics method is employed to directly simulate the flow and heat transfer of the nanofluids in a 2-dimensional micro channel in the present paper. Basically there are two different numerical methods for doing these. One is based on molecular dynamics which directly focuses on the molecular behaviors of the nano particles. This method needs more CPU time and computer memory. The other is based on Navier-Stokes questions with introducing the thermal and dynamic parameters of the nanofluids obtained from the mixture fluid theory and experimental measurements. The latter provides useful information for researchers and engineers to understand the flow and heat transfer profiles of the fluidic devices with less CPU time and computer memory (2, 3). Therefore, it is employed in the present paper to study the cost-effectiveness of the nanofluids in a 2-dimensional micro channel.