Absorption heat pump with the TFE-TEGDME and TFE-H2O-TEGDME systems

The binary mixture trifluoroethanol (TFE)-tetraethylene glycol dimethyl ether (TEGDME) can be more advantageous for absorption cycles at high temperature levels than classical working systems such as H2O-LiBr and NH3-H2O. This system is non-corrosive, completely miscible over a wide temperature range, thermally stable up to 250 degrees C and has low working pressures. The low thermal conductivity and enthalpy of evaporation of TFE can be improved by using the TFE-H2O mixture as a refrigerant, instead of pure TFE, with TEGDME as an absorbent, The effect of adding water on the performance of a single-effect absorption heat pump has been analysed, The simulation of such a cycle with a partial evaporator has been carried out for binary and ternary systems, in order to recover thermal wastes at 80 degrees C and upgrade them to 120 degrees C. The maximum COP of about 1.6 obtained for the TFE-TEGDME system in these conditions is hardly affected by the addition of water, although the solution and reflux flow ratios increase with the water content. The results show that about 15 mass% of water gives optimum performance in terms of the COP and flow ratios. The thermodynamic properties of the pure compounds (TFE and TEGDME) and the binary and ternary mixtures needed to study the performance of the absorption cycles are also presented.