Experimental and numerical study of a falling film absorber in an ammonia-water absorption chiller

In this paper, experimental and numerical studies of heat and mass transfer in a falling film absorber are presented. The investigated absorber is a plate heat exchanger used in a falling film configuration. The ammonia-water solution flows in a falling film mode along the plates. The vapour flows co-current with the falling film and the coolant fluid is in a counter-current flow with the falling film. A prototype of ammonia-water absorption chiller is used to experimentally study the absorber behaviour in real operating conditions. A macro study of the absorber and a local analysis deduced from local temperatures measurements along the falling film are presented. A numerical model and a simulation tool are developed in order to complete the experimental investigations. The associated numerical parametric study aims to separate the coolant mass flow rate impact. The model is validated with experimental data and a maximal relative error of 15% is observed between experimental and numerical results. The results of this study suggest that during the absorption process, mass transfers are controlled by the falling film mass transfer resistance and that the liquid-side heat transfer resistance is negligible.