A New Multidimensional Graph for the Einstein Refrigeration Cycle

Abstract

An analysis of the exergy use in an Einstein refrigeration cycle is presented. The analysis is performed through the use of a new graphical multidimensional representation of the cycle. The Einstein refrigeration cycle works with ammonia, butane and water. These compounds are present in the cycle as several ammonia-water and ammonia-butane mixtures that have different compositions. In essence, the cycle transfers ammonia from an ammonia-water mixture to an ammoniabutane mixture in a series of processes and then it transfers ammonia back again to an ammonia-water mixture in another series of processes. The ammonia transfers involve heat absorptions and heat rejections that have as an effect the transfer of heat from a low temperature reservoir to a high temperature reservoir. The aforementioned multidimensional graph was built with equilibrium data of the ammonia-water and ammonia-butane binary systems for a 4 bar pressure and a 240 K to 350 K temperature range. The graphical representation is multidimensional because it shows in one graph values of concentration, temperature, enthalpy, entropy and exergy for ammonia-water mixtures and ammonia-butane mixtures. The thermodynamic states of all the process currents present in the cycle are showed in the graph, as well as are the different thermodynamic processes of the cycle. The exergy destruction rate of each device is clearly represented. The usefulness of this graph is similar to that of the T-s graph for a Rankine cycle.