Performance research of self regenerated absorption heat transformer cycle using TFE-NMP as working fluids

Abstract

A heat transformer is proposed in order to upgrade low-temperature-level energy to a higher level and to recover more energy in low-temperature-level waste heat. It is difficult to achieve both purposes at the same time using a conventional heat transformer cycle and classical working pairs, such as H 2O–LiBr and HN 3–H 2O. The new organic working pair, 2,2,2-trifluoroethanol (TFE)- N-methylpyrolidone (NMP), has some advantages compared with H 2O–LiBr and NH 3–H 2O. One of the most important features is the wide working range as a result of the absence of crystallization, the low working pressure, the low freezing temperature of the refrigerant and the good thermal stability of the mixtures at high temperatures. Meanwhile, it has some negative features like NH 3–H 2O. For example, there is a lower boiling temperature difference between TFE and NMP, so a rectifier is needed in refrigeration and heat pump systems. Because TFE–NMP has a wide working range and does not cause crystallization, it can be used as the working pair in the self regenerated absorption heat transformer (SRAHT) cycle. In fact, the SRAHT cycle is the generator–absorber heat exchanger (GAX) cycle applied in a heat transformer cycle. In this paper, the SRAHT cycle and its flow diagram are shown and the computing models of the SRAHT cycle are presented. Thermal calculations of the SRAHT cycle under summer and winter season conditions have been worked out. From the results of the thermal calculations, it can be found that there is a larger temperature drop when the waste hot water flows through the generator and the evaporator in the SRAHT cycle but the heating temperature can be kept the same. That means more energy in the waste heat source can be recovered by the SRAHT cycle.