CONTACT THERMAL RESISTANCE BETWEEN THE FIN AND PIPE-BASE FOR COMPOSITE HEAT TRANSFER SURFACES

Abstract

Experimental setup for investigation of contact thermal resistance (CTR) of composite heat-exchange tube, made of flat-oval steel tube – base and aluminum fins, which are connected to the base by means of contact welding, has been developed. By direct measurement, the СTR values for a composite heat exchanger tube are compared to the CTR values for three types of bimetallic tubes with rolled aluminium fins: carbon steel 20 base tube, stainless steel 1X18H10 base tube and brass base tube. It is established that for a composite heat-exchange tube the mean thermal resistance of contacting surfaces doesn't depend on the density of supplied heat flow and makes constant value Rk = 2,75×10–6 Km2/W, that is practically equal to zero for engineering calculations and it is possible to neglect it. For composite heat-exchange tube the application of contact welding technology makes it impossible to deteriorate thermal contact between monorail and tube due to temperature fluctuations in the process of operation of heat-exchange apparatuses. The results obtained show that the composite surface with welded aluminium monofin has two orders of magnitude lower CTR than the heat exchange surfaces made of widely used bimetallic tubes of all known types. This provides the highest heat transfer coefficient.