ANALYSIS OF THE DIRECT CYCLE WITHIN HEAT-USING COMPRESSION MACHINE WITH R 744

Compression refrigeration machine driven by turbine (working fluid is the same as for refrigeration machine) is classified as heat-using compression refrigeration machine. The scientific development of the heat-using compression refrigeration machines associates with introducing R744 (carbon dioxide) as the working fluid. It leads to an expand in the opportunities of these machines through (a) utilization of heat with different temperature levels, (b) development of new schematics and corresponding thermodynamic cycles, (c) contribution to the energy saving, and (d) contribution to the ecological problems associated with refrigeration. A heat-using compression refrigeration machine consists of two thermodynamic cycles: direct (for generation of work) and inverse (for generation of cold). Efficiency of each cycle depends on the schematic. In this paper, the two possibilities for the direct cycle have been evaluated: simple and with heat regeneration. The energetic and exergetic methods of thermodynamic analysis have been applied. It is shown that the thermodynamic effectiveness (exergetic efficiency) depends on the combination of schematic and operation parameters within the gas heater, and the magnitude is the function of the temperature level of utilized heat. Results obtained from the exergetic analysis showed the irreversibilities within each system component and identified the components that have highest priority to be improved in order to contribute to the energy saving problem.