The effects of several factors on boiling heat transfer around horizontal circular copper tube in an acoustic cavitation field were investigated experimentally, and the inherent mechanism of the influences of acoustic cavitation parameters, fluid subcooling and nanometer particles were discussed in terms of local wall temperature. The experimental results show that the influence of cavitation bubbles reduced with the decreasing of cavitation distance, fluid subcooling and nanometer particle concentration, yet enhanced with the increasing of cavitation intensity. Boiling heat transfer could be remarkably intensified by acoustic cavitation due to not only sufficient provision of nucleated vapor embryos to the tube surface, but also increasing boiling area and consequently effective dissipation of heat. The addition of nanometer particles in liquid could result in roughness variation of heater surface and active reduction of cavitation bubbles.
Some algebraically explicit analytical solutions are derived for the anisotropic Brinkman model―an improved Darcy model―describing the natural convection in porous media. Besides their important theoretical meaning (for example, in analyzing the non-Darcy and anisotropic effects on the convection), such analytical solutions can be the benchmark solutions that can promote the development of computational heat and mass transfer. Some solutions considering the anisotropic effect of permeability have been given previously by the authors, and this paper gives solutions including the anisotropic effect of thermal conductivity and the effect of heat sources.
CAI Ruixian1, GOU Chenhua1, 2 & ZHANG Na1 1. Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100080, China
