Falling film evaporation on enhanced tubes, part 1: Experimental results for pool boiling, onset-of-dryout and falling film evaporation

Abstract

Horizontal falling film evaporators have the potential of displacing flooded evaporators as the standard in the refrigeration industry due to compelling advantages, such as smaller refrigerant charge and lower pressure drop. However, there is a need to improve the understanding of falling film evaporation mechanisms to provide accurate thermal design methods. In this work, falling film evaporation measurements on a single tube, a vertical row of ten horizontal tubes and a small tube bundle with three rows of 10 tubes each are presented. Two enhanced boiling tubes, the Wolverine Turbo-B5 and the Wieland Gewa-B5, were tested using R-134a and R-236fa. The tests were carried out at a saturation temperature of Tsat = 5 °C, film Reynolds numbers ranging from 0 to 3000, and heat fluxes between 15 and 90 kW m−2 in pool boiling and falling film configurations. A visualization study was performed under diabatic conditions to study the flow.