Control of Minimum-Heat-Flux-Point Temperature by the Thermal Conductance of an Additional Surface-Layer

Abstract

In the present paper, the effects of thermal conductance of a boiling surface on the minimum-heat-flux-point temperature and film-boiling heat transfer of saturated pool boiling of liquid nitrogen on a horizontal flat-surface of copper are experimentally studied. The thermal conductance of the copper surface was changed by the following two additional-layers coated on it. The first is a thin layer of low thermal-conductivity material coated on the copper surface. The second is a additional double-layer that consists of a 0.3 mm PTFE layer and a thin metallic layer coated on it. The experimental results show that the effects of such additional layers on film boiling are negligible but are remarkable on the MHF-point temperature. For the single insulating layers, the MHF-point temperature increases with increased coating thicknesses. As for the additional double-layers, the MHF-point temperature decreses rapidly with increased thicknesses of the outer layer. In both cases, the MHF-point temperature reaches (or comes back to) a unique value when the coating material has a coating thickness of 0.1∼1 mm.