BOILING HEAT TRANSFER FROM AN EXTENDED TUBE SURFACES

Abstract

Since the boiling heat transfer is associated with high heat transfer rates, it is being used to cool devices requiring high heat transfer. Efforts are still going on to further enhance the boiling heat transfer coefficient. Two most important methods being tried to increase the boiling heat transfer are to provide the finned surface or the wrapping of mesh around the surface. The finned method to increase the heat transfer faces the problem of scaling after some duration of time, the process of wrapping the surface with wire is much simpler and easier to maintain. In the present work an experimental investigation has been carried out to study the boiling heat transfer on tubes wrapped with wire meshes of different sizes under pool and flow boiling conditions using distilled water at saturated temperature and atmospheric pressure. Heat transfer data were also collected for the bare tube so that performance of bare tube can be compared with that of wire mesh wrapped tubes. Stainless steel tubes (AISI 304) with outer diameter 19.5 mm, inner diameter 17 mm and wire meshes of sizes (h x p), (0.1x0.15) (0.05x0.075),(0.15x0.22) mm have been used in the present work. Tubes were resistively heated by passing high current through them. Data are collected for mass flux and heat flux values varying from 0 to. 838 kg/m2 and 12 to 55 kW/m2 respectively. From the experiment investigation it is found that this technique of wrapping tube surface with wire mesh enhances the boiling heat transfer coefficient in the narrow range of low heat flux region 20 to 30 kW/m2.Whereas, at high flux values its performance was poor than the plain surface.