Experimental Study Of Nucleate Pool Boiling On Micro Wires With Severai Working Fluids

The types of working fluids are important factors in convective heat transfer. One of the most recent progresses in working fluids is self-rewetting fluid and nanofluid. The surface tension gradient in self-rewetting fluid is different from that of pure fluid. The thermophysical properties of fluids may be changed by inclusion of nanoparticles, with deposition layer potentially formed on the heated surface. In the two typical working fluids, the bubble behaviors are quite different. Because of this, it is necessary that detailed observations of the interactions among bubble, heated surface, and working fluid would be performed. The experimental observation of the nucleate boiling process on a heated surface, and therefore the bubble movement and heat transfer coefficient, can provide important data for the impact analysis of bubble behavior on boiling heat transfer.In this paper, different working fluids are prepared or further observations. One is self-rewetting fluids made of aqueous n-butanol solutions, one is alumina nanofluids with different concentrations, and the other one is the nanofluids with inclusions of n-butanol as surfactant. The self-rewetting fluids exhibit enhanced heat transfer through emergence of fast detachment of very small bubbles on the heated wall for high heat flux conditions. While in the nanofluids, there are phenomena such as bubble sweeping existing from the lower part of heater to the upper part, small bubble circling at stationary bubble staying at the heated surface, and nanoparticle swirling in the vicinity of the bottom of a stationary bubble. Corresponding analysis indicates that these phenomena can be potential contributors for the enhanced heat transfer. The effect of surfactant, or n-butanol, on heat transfer of the nanofluid is also experimentally investigated. The result shows that n-butanol can further enhance heat transfer for nanofluid. The surfactant-induced liquid motion can severely eliminate the deposition of nanoparticles. Therefore the nanofluid with n-butanol can be a novel working fluid for enhanced heat transfer.