Performance of a triple-pressure-level absorption cycle with R125-N,N′-dimethylethylurea

In the developed triple-pressure-level (TPL) single stage absorption cycle, a specially designed jet ejector was introduced at the absorber inlet. The device served two major functions: it facilitated pressure recovery and improved the mixing between the weak solution and the refrigerant vapour coming from the evaporator. These effects enhanced the absorption of the refrigerant vapour into the solution drops. To facilitate the design of the jet ejector for such absorption machines, a numerical model of simultaneous heat-and-mass transfers between the liquid and the gas phases in the ejector was developed. The refrigerant pentafluoroethane (R125) and the absorbent N,N′-dimethylethylurea (DMEU) were used as the working fluid. A computerized simulation program was used to perform a parametric study of the TPL absorption cycle. The influence of the jet ejector on the performance of the TPL absorption cycle was evaluated, and the performance of the TPL absorption cycle was compared with that of a double-pressure level (DPL) cycle. Four cases were studied that represent the improvements in the TPL absorption cycle performances as a result of the incorporation of the jet ejector. The four cases are: the ability to reduce the circulation ratio f, the ability to lower the evaporator temperature, the ability to lower the generator temperature and the ability to use higher-temperature cooling water.