There were several approaches used to improve the performance of a single-effect absorption refrigeration system. Applying ejector to the conventional absorption system is one of the remarkable alternatives. The appropriate installation configuration introduces the magnificent improvement of COP to nearly to that of a typical double effect absorption cycle machine. Moreover, according to the simplicity of the hybrid ejector-absorption refrigeration machine, its capital investment cost is comparatively low when compared to other conventional high performance absorption cycle systems.
Many researchers have attempted to improve the performance of absorption systems by using an ejector to raise the absorber pressure to a level higher than that in the evaporator and, consequently, to reduce the solution concentration.Kuhlenschmidt proposed the development of an absorption system using working fluid based on salt-absorbent. This system utilized a two-stage generator similar to that used in a double-effect absorption system, Fig. 13. The low-pressure refrigerant from the second-effect generator is used as a motive fluid for the ejector and entrains vapour refrigerant from the evaporator. Therefore, the concentration of solution within the absorber can kept from crystallization when the system is required to operate with low evaporator temperature or with high absorber temperature. Neither theoretical nor experimental results of this system are available yet. However, it can be expected that the COP of the system will not be higher than that of a single-effect absorption system, as some of the vapour refrigerant generate discharged directly to the absorber (as the motive fluid) without producing any cooling effect. In contrast with Kuhlenschmidt, Chung et al. and Chen elevated the absorber pressure by using a high-pressure liquid solution returned from the generator as the ejector’s motive fluid (Fig. 14). Experimental investigation showed that,