ABSTRACT
Theoretical thermodynamic simulations (analyses) were carried out on the Extraction-System-Attached (ESA) Ammonia- Water Absorption Heat Pump cycles which were developed with the aim of improving the thermodynamic performance achievable with the conventional cycle. Theoretical simulation of the liquidliquid- equilibria (LLE) of amnion i a-water-3ol vent (ternary) systems using the tested semi-empirical model called UNIQUAC equation was the basis for determining whether or not the extracting solvents (of desirable physical properties) could form two-phase ternary systems with aqueous ammonia solution. The UNIQUAC binary parameters of ammonia-water mixtures and the binary mixtures of the selected solvents and water or ammonia, for use in the LLE simulation, were obtained from mutual solubility and infinite dilution coefficient data. Capacity and selectivity diagrams obtained from the data generated from LLE simulation were used for further confirmation of the suitability of the solvents for liquid-liquid-extraction process. Five cycles were derived from the conventional absorption system by using the extraction or stripping separation process as substitute for the non-isothermal separation process used in the conventional ammonia-water absorption heat pump. Thermodynamic analysis models used for obtaining the irreversibilities and COP of the cycles were derived from system's parameters and working fluid properties such as concentration of strong (XST) and weak (XWK) aqueous ammonia solution, reflux or recirculation ratio (R), solvent-to-feed ratio (SFR), enthalpy change. Simulation of these thermodynamic models for two ESA-ammonia-water absorption heat pump cycles (employing five different organic solvents in the extraction step of the system) and the conventional ammonia-water absorption heat pump cycle at two evaporator's temperatures indicated that better thermodynamic performance, in term of the COP (heating and cooling modes) and irreversibility, could be achieved by using liquid-liquid extraction process to recover ammonia from the strong aqua ammonia formed in the absorber during the pump's operation. The cycles employing nitrobenzene as the extract solvent, among the. KSA systems, gave the lowest irreversibilty and highest COP values.