Intensification of heat transfer in falling films on a bundle of horizontal tubes with microstructured surface

Abstract

Experimental results on measuring heat transfer in falling films of R21 refrigerant on a bundle of horizontal tubes with structured surfaces are presented. The experiments were carried out in the range of Reynolds number of the saturated liquid film from 500 to 1500 at a pressure of 3 bar in the evaporator. To intensify heat transfer, copper tubes with an external surface treated by the method of deformational cutting (MDC) were used. Three types of structures were used: structure No. 1 with half-closed microcavities, structure No. 2 with a rhomboid shape, and structure No. 3 created on the basis of structure No. 2 with additional transverse ribbing. It was shown that the studied types of structures can significantly increase the heat transfer coefficient as compared to a smooth surface. The structure with half-closed microcavities was the most effective for heat transfer enhancement.