Thermal Conductivity And Application In Heat Pipe Of Nanofluid

Nanofluid contains suspended metallic or non-metallic nanoparticles in traditional fluid which is a new class of heat transfer fluid. It has been reported that nanofluid possesses higher thermal conductivity than their traditional base fluids. Adding nanofluid into heat pipe can enhance its heat transfer capabilities.In this paper, nanofluids were prepared by adding CuO, SiO₂, Al₂O₃ nanoparticles into traditional base fluids, analyse their thermal properties, and then applicate them in heat pipe. This study was designed to use nanofluid in heat transfer field, broad the application of nanotechnology and explore the base question in the thermal engineering. Nanofluid plays an important role in promoting the development of heat transfer equipment with high performance. This work mainly includes:1. The traditional base fluid and nanoparticles were mixed by adding dispersant, ultrasonication and controlling pH value directly. Nanofluids were prepared with different volume fraction using this two step method. Suspension stability of nanofluid was characterized and analyzed using zeta potential, average particle size and absorbancy method. The best disperant condition was gained. Not only properties of fluids and nanoparticles but also the interaction force between nanoparticles can influence the suspension stability of nanofluid.2. The transient hot wire appliance for measuring thermal conductivity of nanofluid was built. The thermal conductivities of CuO(30nm)-water, Al₂O₃(40nm)-water, Al₂O₃(65nm)-water, SiO₂(30nm)-water, SiO₂(30nm)-EG nanofluids were measured at different volume fraction(0.1-0.5%) and temperature(25-50℃) using this appliance. The properties, volume fraction, and size of nanoparticles, suspension stability and temperature effecting on thermal conductivity of nanofluid were studied. The results showed that adding nanoparticles into base fluid can enhance the thermal conductivity greatly. The thermal conductivity enhancement of nanofluid is about 2.86-33.70% at temperature 25℃. Comparing between experimental results and theoretical model, the heat transfer mechanism of nanofluid was studied.3. Model of thermal conductivity of nanofluid was proposed. It has a much better precision comparing with the traditional theoretical models whose precision can increase about 30%.4. A testing equipment of heat pipe was set up. An experimental study was performed to study the heat transfer characteristics of CuO-water, SiO₂-water, Al₂O₃-water nanofluids in heat pipe. The temperature distribution was analyzed. Comparing with the heat pipe filled with water, it can be found that heat transfer coefficient of heat pipe filled with nanofluid was higher than heat pipe filled with water while their thermal resistance was lower than heat pipe filled with water.