ABSTRACT
In recent times nanofluids (NFs) have emerged as a promising medium which can be used to enhance heat transfer due to unique characteristics of these fluids. Present study provides a theoretical investigation of the entropy generation analysis of nanofluids. For this Alumina-water nanofluids are considered and entropy generation equation is presented. Since entropy is sensitive to tube diameter, three tube diameter in their regime has been considered. These are microchannel (0.1 mm), minichannel (1 mm) and conventional channel (10 mm). To consider the effect of conductivity and viscosity, two different models representing theoretical values and experimental values available in literature have been used.
It has been found that the reduced equation predicts entropy generation behaviour of microchannel and conventional channels very well. Nanofluids are better coolant to be used in minichannels and conventional channels with laminar flow and microchannels with turbulent flow. It is not advisable to use nanofluids in microchannels with laminar flow and minichannels and conventional channels with turbulent flow. The tube diameter effect has been shown and it indicates that at lower tube diameter, viscous effects on irreversibility are more significant and at higher tube diameter heat transfer irreversibility is more. Finally, for both laminar and turbulent flow, there is an optimum diameter at which the entropy generation rate is shown to be the minimum.
