Simulation of an absorption refrigerator working with ionic liquids and natural refrigerants.

Electrically-driven vapour compression or thermally-driven ammonia water absorption refrigeration systems are the commonly used technology for cooling below 0°C. Ionic liquids (IL) are versatile absorbents since they extend the use of natural refrigerants other than ammonia in thermally driven absorption technology. Moreover, room temperature ionic liquids (RTIL) do not crystallize at ambient temperature even up to high ionic liquid mass fractions just like water in ammonia water chillers. In addition, they exibit a nearly zero vapour pressure allowing for regeneration without rectification. The present study is concerned with the simulation of a single stage absorption refrigerator which has been designed specifically for the use of Ethanol as the refrigerant and an ionic liquid as the absorbent. The main feature of this study is the fact that no empirical heat and mass transfer coefficients have been used. Instead analytical functions for the combined heat and mass transfer using the molecular transport properties such as the mass diffusivity and heat conductivity for instance are used for the simulation. The vapor liquid phase equilibrium data as well as the transport and thermodynamic properties of Ethanol as refrigerant and [EMIM][DEP] as absorbent are presented in the paper at hand. The thermal efficiency and the refrigeration capacity of the absorption refrigeration system for varying driving temperatures are presented and discussed. As a special feature the behavior of this absorption refrigerator with two different heat rejection temperature levels is shown in order to determine its suitability for a double effect system.