Optimal Design of Compact Horizontal Tube LiBr/Water Absorbers

Abstract

A three-flow-regime (falling film, droplet formation, and droplet fall) model is used to investigate the possibility of using small diameter tubes for falling-film lithium bromide-water absorbers. A systematic investigation of tube diameters and pass arrangements shows that for the same heat transfer area, tubes with a diameter of 6.35 mm deliver about 30% more cooling capacity than conventional tubes (OD = 15.88 mm). An even higher increase in capacity (about 55%) is obtained when 3.175 mm diameter tubes are used. This significant increase is primarily due to increased vapor absorption in the droplet formation regime, which plays a progressively larger role in vapor absorption as the tube diameter decreases. However, because it is expected that wetting of tubes becomes poorer as the tube diameter decreases, wetting characteristics should be considered in conjunction with these findings to select the optimal tube diameter.