Efficient Open Isobaric Expansion Based Thermal Cycles at Low Temperatures

Abstract

The work aims to provide feasible structures for the open processes based thermal cycle as well as the regenerative open processes based thermal cycle characterised by rendering high thermal efficiency at low temperatures. Both cycles differ from the conventional Carnot-based thermal cycles (Carnot, Otto, Diesel, Rankine, Brayton, Stirling, Ericsson, and variants of these cycles) in that the conversion of heat to mechanical work is performed undergoing load reaction based path functions which means an isobaric expansion process at constant load in which thermal energy absorption and conversion to mechanical work are performed simultaneously along a single transformation of the cycle, contrary to what happens in conventional Carnot-based engines, in which mechanical work is delivered by means of a quasi-entropic expansion along a single transformation. Because of the mentioned differences these cycles do not obey the Carnot statement. A performance analysis of the OPTC and the ROPTC operating with hydrogen, helium, and nitrogen was carried out and the results were compared with those for a Carnot cycle operating under the same range of temperatures. High theoretical thermal efficiency was achieved for the ROPTC, surpassing the Carnot factor under favourable conditions. These results, obtained with a structurally simple and compact engine, pave the way for a new generation of power convertors.