Performance characterization of a bubble pump for vapor absorption refrigeration systems

Abstract

A thermally driven bubble pump has been used for an ammonia (refrigerant)–water (absorbent) vapor absorption refrigeration (VAR) system, which is known as a diffusion absorption refrigeration (DAR) system since the 1920s. However, the use of a bubble pump in a water-based refrigerant VAR system has not been reported. In a bubble pump-operated VAR system, the cycle performance as well as the bubble pump performance completely depend on the refrigerant–absorbent solution properties and the bubble pump parameters. Although a few analytical models have been developed for the performance analysis of a bubble pump-operated refrigeration cycle, the analytical model of the bubble pump itself has not been reported. In this study, a dimensional analysis was performed, considering bubble pump geometry and the solution properties, and a mathematical model was developed to represent the bubble pump performance in terms of non-dimensional numbers, which can be used in all bubble pump driven absorption refrigeration systems. The analysis revealed that the bubble pump always operates in a turbulent condition with a Reynolds number higher than 104 and a Morton number between 10−11 and 10−12. The highest efficiency of the bubble pump (79%) is achieved at a high liquid Froude number at the beginning of the slug flow regime, when the non-dimensional pressure is low. The proposed analytical model was validated with the experimental results conducted with pure water and an LiCl-H2O solution and both results agreed within 12%.