Heat transfer enhancement characteristics for falling-film evaporation on horizontal enhanced tubes with aqueous LiBr solution

Abstract

Falling-film evaporation experiments with aqueous lithium bromide solution were performed to investigate the heat transfer characteristics of the enhanced copper tubes. Enhanced tubes (a knurled tube and a spirally grooved tube), a tube coaled with 20 mu m aluminum particles and a bare tube were selected as test specimens. Averaged evaporation fluxes of water and the heat transfer coefficients were obtained from the horizontal tube with various film Reynolds numbers, system pressures, solution concentrations, and degrees of wall superheat. The results of this work were compared with data reported previously, and the enhanced performance was compared between tubes with varying parameters. It was shown that the heat transfer performance of falling film evaporation was superior to pool boiling at a low wall superheat below 10K and the knurled tube geometry showed the most excellent performance among the tubes tested.