Heat Transfer Enhancememt Using Nanofluids

Abstract

Nanofluids are the suspension of nanoparticles in base fluids (water, oil, ethylene glycol etc.), which leads to an increment in heat transfer efficiency of base fluids. In this study, the heat transfer and pressure drop characteristics of nanofluids have been studied. Also, the thermo-physical properties, synthesis and applications of nanofluids have been studied. The thermal conductivity and viscosity of nanofluids have been measured experimentally using KD2 pro thermal property analyzer and Brookfield viscometer respectively. The various heat transfer enhancement techniques (active & passive) have also been reviewed. It has been observed that the use of tube inserts like helical coils, twisted tapes and corrugated tubes enhances the heat transfer efficiency of fluid flowing through it. The effect of inclination angle on heat transfer coefficient of nanofluids flowing through a pipe has also been studied. For preparing nanofluids, nanoparticles of Aluminium oxide and distilled water is used as base fluid. Nanofluids of volume fraction 0.5 % are used in this work. The heat transfer coefficient and pressure drop is measured by using an experimental setup at various flow rates and inclination angels for distilled water and 0.5 volume % alumina/distilled water nanofluids. The experimental setup consists of a copper tube over which a nichrome wire of Power 500 W is wrapped. The outer surface of the tube is embedded with 6 RTD sensors for measuring temperature. Reynolds number, friction factor and Nusselt number have also been calculated for the same above. Results show that the prepared alumina/distilled water nanofluids have good stability and remain stable for 3 weeks without using any surfactant. It has been observed that the thermal conductivity of the both distilled water and nanofluids is increasing with increase in temperature. While, density and viscosity of both distilled water and nanofluids is decreasing with increase in temperature. The inlet and outlet temperatures of nanofluids, surface temperatures of pipe and pressure drop of nanofluids are measured at steady state for four different flow rates in horizontal and 3˚ inclined pipe (upward inclination). The heat transfer coefficients and friction factors are calculated for above experimental data. With increase in flow rate, heat transfer coefficient of 0.5 volume % nanofluids is much higher than that of distilled water. Heat transfer coefficient is also increasing as the inclination angle changes from 0˚ to 3˚. At 0˚ inclination i.e. in horizontal pipe, nanofluids show a maximum enhancement of 170 % in heat transfer coefficient. While at 3˚ inclination, a maximum enhancement of 268 % is observed, which is much higher as compared to horizontal pipe.