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. 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,
by using DMETEG/R22 and DMETEG/R21 as working fluids, the pressure ratio between the absorber and the evaporator of 1.2 were found. The increasing in absorber pressure results in the circulation of the solution being reduced lower than that for a conventional system operate d at the same condition. Thus, an improvement of COP can be expected. The mathematical simulation of the similar system, for heat pump application, was conducted by Shi et al. Unfortunately, the inappropriate working fluids, LiBr/H2O were selected. A liquid-driven ejector is not suitable to operate with low-density vapor such water. Only high-pressure and high-density refrigerant can be used. Therefore, the calculated results showed that the cooling capacity at the evaporator and thus the COP of the system were almost unchanged.