Investigation Of Convective Heat Transfer Of Nanofluid In Separate Heat Pipe Parabolic Through Solar Collector System

The advantages of natural circulation solar heat pipe systems, such as high heat transfer ability at low temperature differences, simple construction, self-sufficient without pump etc, provide a new direction for solar collector system at medium-high temperature. On the other hand, low thermal conductivity of conventional heat transfer fluids such as water, oil and molten salts is a serious limitation in improving the performance of solar thermal electricity systems. Finding and developing advanced heat transfer fluids with substantially higher conductivity seems to be motivated. The conception of nanofluids provides an innovative way of improving the thermal conductivity of fluids. On consideration of combining both nanofluids and heat pipe applied to solar collector system, we provide a new natural circulation solar collector system using separate heat pipe at medium-high temperature range.On the base of achievements in hand, a theory calculation and system design of the modeled natural circulation solar collector system using separate solar heat pipe at medium-high temperature range was carried out in the present paper. Simultaneously, with some emphasis, flow resistance of the system was analyzed by single phase model and two phase model. And this analysis provided a theory base for the flow resistance of natural circulation steam generation system.Upon the upward work, the main work of the present paper focused on mixed heat transfer of Ai2O3nanofluids at a working pressure of0.5MPa in real sized solar receiver numerically. Characteristics of mixed heat transfer of nanofluids as incensement of the volume fraction at condition of velocity, Re and Pe were investigated, separately. Moreover, the mechanism of heat transfer enhancement of nanofluids and the effect of velocity were discussed. The results show that, nanofluids decreased mixed heat transfer as the incensement of the volume fraction for all conditions.The incensement of thermal conductivity and viscosity result in a decrease of natural convection. Homogonously, this result finally reduced mixed convection heat transfer at low velocity condition. However, as the incensement of velocity, the result of natural convection form a secondary flow near the heating wall, which resulted in a relative static area and increased the boundary layer of conduction, and at last, deteriorated convective heat transfer. Obviously, the additions of nanoparticles weaken this deterioration process, and then enhanced mixed convective heat transfer.At the same time, a comparative investigation of effects of heat flux was performed. The results indicated that the effect of heat flux could be negligible.