Study of the ammonia absorption process into ammonia/water solutions using polymeric membranes for absorption-resorption refrigeration systems

Identifier:  TDX:2809

Handle: https://hdl.handle.net/20.500.11797/TDX2809

Authors:  Berdasco Ruiz, Miguel Ángel

Abstract:
This thesis studies the ammonia absorption process into ammonia/water solutions using polymeric membranes as contactors in order to be used in the absorption-resorption refrigeration systems. The high surface/volume ratio provided by the membranes enable to reduce the size of the absorbers and, therefore, more compact and lighter designs can be made. The use of absorption-resorption refrigeration systems is proposed because they allow to reduce the typically high working pressure of the conventional absorption systems, making feasible the use of polymeric materials. Initially, the thesis presents a study of the ammonia/water absorption-resorption refrigeration cycle by means of thermodynamic models, as well as the analysis of the performance of a 25-kW absorption-resorption refrigeration plant. A test bench was designed and built for the experimental study of the adiabatic ammonia absorption process into ammonia/water solutions. Two different membrane modules were tested: a flat-sheet and a hollow fibre membrane module. In both cases, theoretical models were developed and validated with the experimental results. As a result of the study with the flat-sheet membrane, the characteristics required by a polymeric membrane to be used in the ammonia absorption process were determined. These characteristics were considered for the selection of the commercial hollow fibre membrane module. Finally, a theoretical model of a hollow fibre membrane absorber with heat exchanger integrated was developed. This model was used to design an absorber and a resorber for the 25-kW absorption-resorption refrigeration system. The results obtained confirm the potential in terms of size reduction provided by the membrane modules because heat duties/volume ratio up to 10000 kW/m3 were obtained, much higher than those provided by the plate absorbers (2000 kW/m3) or the shell and tube absorbers (300 kW/m3).