Compositive effect of nanoparticle parameter on thermal performance of cylindrical micro-grooved heat pipe using nanofluids

An experimental investigation was carried out to study the heat transfer performance of a cylindrically micro-grooved heat pipe using aqueous nanofluids as the working fluids. The base liquid was distilled water, while, the five kinds of nanoparticles: Cu with two mean diameters of 40 nm and 20 nm, CuO with two mean diameters of 50 nm and 20 nm and SiO with a mean diameter of 30 nm were added respectively into the base liquid to compose different kinds of nanofluids. Experiments were performed under three steady operating pressures of 7.45 kPa, 12.38 kPa and 19.97 kPa, respectively. Effects of nanoparticle kind, nanoparticle size, nanoparticle mass concentration and operating pressure on the evaporation and condensation heat transfer coefficients, the maximum heat flux and the total heat resistance of the heat pipe were investigated, compared and discussed. Experimental results show that adding Cu and CuO nanoparticles into the base fluid can apparently improve the thermal performance of the heat pipe and there is an optimal nanoparticle mass concentration to achieve the maximum heat transfer enhancement. However, adding SiO nanoparticles into the base fluid will contrarily deteriorate the heat transfer performance. The main reason that causes these differences in the heat transfer performance results from the surface structure of the coating layer formed by sediment of nanoparticles on the heated surface.