Experimental Study On Subcooled Pool Boiling Over Microwires With Self-Wetting Fluids

Working fluids play very important role in the study of heat transfer. The working fluids studied in this paper include the self-wetting fluids and nanofluids. Self-wetting liquid refers to the aqueous alcoholic solutions with the number of carbon atoms greater than four. The surface tension of self-wetting fluids increases with increasing temperature beyond a critical temperature. Nanofluid refers to a new kind of working fluid, in which metallic or non-metallic nanoparticles are added to the liquid medium in a certain way and proportion. Compared with the traditional heat transfer working fluids, these two new working fluids have different characteristics which can enhance the heat transfer. By measuring the boiling curve of the two working fluids as compared to the water, the characteristics of heat transfer enhancement by using the two working fluids is analyzed.In this paper, different working fluids are prepared, including self-wetting liquids made of different concentrations of alcoholic solutions, self-wetting fluids with different number of carbon atoms, and nanofluids added with alcohols as surfactants that have different numbers of carbon atoms. These liquids are heated by heating wires with diameters of 30 μm,60 μm and 100 μm, respectively. Parameters such as current, voltage, and temperature are recorded by data acquisition unit in order to obtain the boiling curves for these working fluids. Here the influence of the wire diameters, the mass fractions and the carbon numbers of alcohols on the boiling curves of these two kinds of working fluids are thoroughly analyzed. The analysis indicates that the influence of wire diameter, the mass fractions and the carbon numbers of alcohols on the boiling curves of these working fluids are similar. The slope of boiling curves decreases with increasing wire diameters for the first regime defined in this paper, and then the critical wall superheat, where the wall superheat starts reducing and the regime is defined as the second one, decreases with increasing wire diameters. The critical wall superheat exhibits an increasing trend in the second regime when increasing the mass fractions of alcohols. The slope of boiling curves in the first regime decreases with increasing carbon numbers of alcohols, and accordingly the critical wall superheat increases gradually. Thereby a better understanding of the heat transfer characteristics for these two kinds of working fluids can be achieved by analyzing these influencing factors.