HEAT TRANSFER DURING BOILING. OF REFRIGERANTS UNDER SWIRL FLOW CONDITIONS

Abstract

Augmenting heat transfer rates in heat exchange equip-ment has always been the principal aim of design engineers. A review of literature with the basic purpose of finding a heat exchange equipment which would yield maximum heat trans-fer rates revealed that the insertion of objects, commonly known as turbulence promoters', in the fluid flow passages considerably increased heat transfer rates. Extensive research work has been done in the. last three to four decades on the possible application of this technique in both boiling and nonboiling systems, with water or air and other working fluids. Studies on two-phase flows are relatively fewer and the work on refrigerants are scantily reported. Considering the scarcity of data on swirl flow boiling of refrigerants and the possible advantages which is a turbu-lence promoter may offer in a refrigerant evaporator, the present investigation was taken up to carry out further re- ' search work in this direction. Twisted tape inserts were em-ployed as vortex generators and refrigerant 12 was chosen as the working fluid because of its extensive use in refrigera-tion systems. The experimental facility consisted of a refrigerant condensing unit, test-section, preheater, afterheater, expan, sion valves and necessary measuring instruments and controls, The test-section was a round stainless steel tube, 10 mm in internal diameter with 2.1 metres heated length. It was heated by passing regulated alternating current through the wall of the tube. Any desired vapour quality at the test-section in-let was obtained with the help of the preheater located ahead of the test-section. The afterheater prevented any liquid re-frigerant going to the compressor...