Useful Working Fluids for Feasible Super Efficient Trilateral Cycles

This work studies feasible trilateral thermal cycles which undergo controlled isothermal expansion path functions. The interest of the study focuses on choosing some working fluids that exhibit operating characteristics such that, first, fulfil the necessary conditions to yield high thermal efficiency in the supercritical region slightly above the critical point, and second, the critical point of each selected working fluid is located within the range of medium and low temperatures. The relevance of the studied working fluids resides in that the trilateral cycle performance can be increased by using the ability of the selected working fluids to exhibiting very high thermal efficiency when operating within the vicinity of its critical point. Thus, on the basis of thermo physical characteristics such the critical temperature, pressure and maximum allowable operating temperature, working fluids have been selected.

The analysis of the trilateral cycle undergoing the transformation of heat into mechanical work on the basis of an isothermal expansion for every selected working fluid has been carried out. The achieved results reveal that almost all candidate working fluids analysed provides high thermal efficiency when operating in the vicinity of the critical point, considering the two best fluids, water for medium top temperatures, and carbon dioxide for low temperatures.