Energetic analysis of a diffusion-absorption system: A bubble pump under geometrical and operational conditions effects

This paper presents an analytical model of the bubble pump in a commercial diffusion-absorption refrigerator. Moreover, the energetic analysis achieved is integrated with a heat transfer model and coupled to a thermodynamic model to evaluate the cooling capacity and the coefficient of performance of the refrigeration system, based on geometrical and operational parameters such as heat input, diameter ratio and bubble tube length as well as the ammonia fraction at the inlet of the bubble pump. The results show that the cooling capacity and COP are mainly influenced by geometrical parameters, such as diameter ratio and tube length of the bubble pump, and slightly influenced by the heat input supplied to the bubble pump. The strong concentration range, which is also considered in this work, is a parameter that does not affect the cooling capacity and COP. Moreover, the results reveal that the lowest cooling capacity and COP are obtained when the refrigerator operates at the manufacture design conditions. An increase in cooling capacity and COP of about 150% can be obtained when the diameter ratio is expanded up to 1.5 when comparing with the original configuration. It is expected that these results help researchers and manufacturers extend their analysis to increase the energy performance in diffusion-absorption refrigeration systems.