Performance prediction of single-effect absorption heat pump cycles using ionic liquids

Ionic liquids (ILs), as novel absorbents, draw considerable attention for their potential roles in replacing water or LiBr aqueous solutions in conventional NH3/H2O or H2O/LiBr absorption refrigeration and heat pump cycles. In this paper, to investigate the absorption heat pump using ILs, a prediction method, based on non-random two-liquid (NRTL) activity coefficient model for the vapor pressure and Redlich–Kwong equation of state (RK EOS) for mixing heat, was used to estimate thermodynamic properties for the proposed NH3/IL solutions. Then, single effect absorption heat pump cycles with NH3 as refrigerant and IL as absorbent were analyzed by thermodynamic simulations based on the aforementioned properties. Some of the ILs used including [mmim][DMP], [emim][BF4], [hmim][BF4] and [omim][BF4], have not been previously reported in absorption cycles with NH3. The performance parameters such as coefficient of performance (COP) and circulation ratio (f) of them were then compared along with the reported ILs by Yokozeki and Shiflett (2007 a & b) including [bmim][PF6], [hmim]Cl, [emim][Tf2N], [bmim][BF4], [emim][Ac], [emim][EtSO4], [emim][SCN] and [DMEA][Ac].