Falling film mode transition in an array of horizontal tubes : effect of two dimensional and three dimensional fins

Abstract

Problem of falling film heat transfer is widely associated with many processes, such as shell side condensation and falling film evaporation in shell and tube heat exchangers. Efficient design of such heat exchangers can’t be succeed without detailed knowledge of the falling film flow charts in a tube bundle, especially those consists of two or three dimensional finned tubes. A falling film bundle test facility was built for the above problem. Using water as a cyclic working medium, the effect of tube surface structures on falling film Reynolds number(Re) were investigated under the same flow mode. And falling film mode transitions were observed by image collection system. The results show: 1) Compared with the smooth tube, two dimensional enhanced tube has improved the mode transitions. 2) For two dimensional enhanced tube, surface structure caused the hysteresis occurred in the droplet and droplet-column, droplet-column and column modes. 3) For three dimensional enhanced tube, the hysteresis of it was lower than two dimensional tube occurred in the droplet and droplet-column, droplet and column. Under droplet and droplet-column, column and column-sheet, the transitions were lower than two dimensional tube. The results is the basic reference for the falling film heat transfer problem, and they can be used to guide the development of high efficient falling film evaporator with two and three dimensional finned tubes.