Study On Thermophysical Properties And Convective Heat Transfer Characteristics Of Medium-high Temperature Heat Transfer Fluid

Solar thermal collectors are the most popular and widespread techniques for solar energy utilization. And heat transfer fluid plays as a vital part in direct absortion solar collectors efficiency, which dicided the prospect of solar thermal collectors. However good heat transfer fluid has been lacked for a long time, particularly in the medium-high temperature solar energy use. Based on the lack of good heat transfer fluid,we studied the heat transfer and flow properties of carbon nanotube(MCNT)/ mineral oil nanofluids and ionic liquid [HMIM]BF4 in this dissertation,In this paper, thermal properties like viscosity, specific heat capacity, thermal conductivity of MCNT/mineral oil and ionic liquids [HMIM]BF4 were tested through professional methods. The results show that thermal properties of MCNT/mineral oil based nanofluids and ionic liquids [HMIM]BF4 affected significantly by the temperature. The add of MCNT can reduce viscosity, increase specific heat capacity and thermal conductivity of the base fluid at the same time.What’s more, the experimental platform that was used to test the convective heat transfer properties and flow properties of nanofluids and ionic liquid were designed and set up. Experiment results show that in laminar flow, convective heat transfer coefficient of MCNT/mineral oil based nanofluids in inner tube increases with temperature and Reynolds. while the friction factor has opposite trend with temperature and Reynolds. The flow characteristics of mineral oil fit well with the classical Poiseuille equation f=64/Re. Recirculation and swirl flow caused by the fins can increase the disturbance of nanofluid, and the convective heat transfer coefficients and friction factor have been strengthened; The convective heat transfer coefficient enhancement rate of MCNT/mineral oil based nano-fluids in finned heat exchanger are between 4%-16% and 4%-25% for the friction factor. The addition of MCNT can slightly improve the convective heat transfer coefficient of mineral oil. When the MCNT concentrations are 0.03%-0.12%, compared to the base fluid, the convective heat transfer coefficients were improved by 4%-15%, and friction factor enhanced by 3%-25%In laminar flow, the convective heat transfer coefficient of ionic liquid [HMIM]BF4 in inner tube increases with temperature and Reynolds. while the friction factor has opposite trend. The flow characteristics of ionic liquid [HMIM]BF4 fit well with the classical Poiseuille equation f = 64/Re. Recirculation and swirl flow caused by the fins can increase the disturbance of nanofluid, and the convective heat transfer coefficients and friction factor have been strengthened; The convective heat transfer coefficient enhancement rate of ionic liquid [HMIM]BF4 in finned heat exchanger are around 9.9%, and 7.65% for the friction factor.