Screening Criteria for ILs used in NH3 Based Absorption Heat Pump Systems

This paper describes a properties-optimization work for the working fluids in NH3 / ionic liquid (ILs) based singleeffect absorption heat pumps. The optimum parameters of the IL can be used as criteria in screening task-specified ILs, which play the role of absorbents, in absorption heat pumps. First, a 8-parameter thermodynamic model to calculate performances of a single-effect absorption heat pump cycle was proposed, which is based on the non-random two-liquid (NRTL) activity coefficient model for the vapor pressure and a linear function for the heat capacity. Then, experimental data on the vapor-liquid equilibrium (VLE) of solutions and heat capacities of the pure ILs were reviewed and fitted to obtain ranges of those parameters. Within certain limits, the values of parameters were optimized in the following step using the above proposed mode. The objective is a maximum system performance. The optimized ILs have low molecular weights, low specific heats and have high absorption capabilities.