18 May 2017
Ionic liquids (ILs), as novel absorbents, draw considerable attention for their potential roles in replacing H2O or LiBr aqueous solutions in conventional NH3/H2O or H2O/LiBr absorption chiller or heat pump cycles. In this paper, NH3/IL working pairs are proposed for implementation in parallel double effect heat pump systems. To investigate their performance, a property-prediction method, based on experimental heat capacities and the non-random two-liquid (NRTL) activity coefficient model for the vapor pressure, was used to estimate the thermodynamic properties for the proposed NH3/IL mixtures. Then, parallel configuration double-effect absorption heat pump cycles driven by a high-temperature heat source were analyzed by means of evaluation of the thermodynamic operating limits and performance simulations with the aforementioned properties. The ILs investigated include [Mmim][DMP], [Emim][BF4], [Hmim][BF4], [Omim][BF4], [Bmim][BF4], [Bmim][PF6], [Emim][Tf2N], [Emim][EtSO4] and [Emim][SCN]. The performance, such as the coefficient of performance, COP, and circulation ratio f, along with the environmental temperature used as heat source were compared for these ILs based pairs and the conventional ones. This work on double-effect heat pumps with NH3/ILs pairs shows that there is an optimum distribution ratio between the parallel flows and that some of the investigated mixtures have the potential to show a better performance than that of the traditional NH3/H2O pair in cooling and heating applications.