[bmim][PF6] as absorbent, carbon-dioxide as refrigerant, exergy analysis, Redlich-Kwong equations of state, vapor absorption refrigeration
Vapor absorption refrigeration systems can be an alternative to vapor compression systems in many applications as they can operate on a low-grade heat source and are environment friendly. Widely used refrigerants such as CFCs and HFCs cause significant global warming. Natural refrigerants can be used instead of them, among which carbon dioxide is promising. Its inherent safety, ability to withstand high pressure and high heat transfer coefficient coupled with easy availability make it a likely choice for refrigerant. [Bmim][PF6] is a room temperature ionic liquid (RTIL) composed of a large organic cation and an inorganic anion. Its properties such as non-toxicity, stability over a wide temperature range and ability to dissolve gases like carbon dioxide, make it a suitable absorbent for a vapor absorption refrigeration system. In this paper, an absorption chiller utilising the CO2-[bmim][PF6] working pair and consisting of a generator, condenser, evaporator and absorber has been proposed. A thermodynamic model was set up using the Redlich-Kwong cubic equations of state to predict the behavior of the refrigerant and absorbent pair at different points in the system. A MATLAB code was used to obtain the values of enthalpy and entropy at selected points in the system. The exergy destruction in each component and exergetic coefficient of performance (ECOP) of the system were calculated by performing an exergy analysis based on the second law of thermodynamics. The effect of every component on the ECOP was examined by calculating the amount of exergy destruction in each of them. The exergetic coefficient of performance was calculated for five generator temperatures in the range of 60-100⁰C for an evaporator temperature of 10⁰C and was found to be in the range of 0.02-0.2. Such a chiller can be employed for refrigeration purposes, such as in the storage of food items.