Aspects of Sorption Processes in Thermosiphon and in Falling Film Arrangements

Abstract: A study concerning closure relations pertinent to the design of sorption equipment of absorption heat pumps has been undertaken. Specifically, thermosiphon and vertical falling film arrangements were studied. For the thermosiphon, experimental data on the void fraction, the friction and orifice pressure drops, and the heat transfer coefficient at sub-atmospheric pressures were obtained for vaporising water and vaporising water-sugar mixtures. Empirical correlations were produced for all quantities. Furthermore, a semi-theoretical model for the void fraction was derived; this model compared favourably to existing correlations. Sample thermosiphon calculations using a two-field two-phase flow model, including a heating condensate film, were performed. For the falling film, a penetration-type of turbulence model was developed. Experimental data found in the open literature were used in the derivation. Absorption calculations then indicated that the model is appropriate for wavy-laminar flows, but not for turbulent flows. Falling film calculation results compared favourably to existing film thickness and heat transfer correlations.