ENERGETIC AND EXERGETIC INVESTIGATION OF A MODIFIED DUAL TEMPERATURE TRANSCRITICAL REFRIGERATION CYCLE WITH TWO CASCADE EJECTORS

摘要

The present paper proposes a modified dual temperature CO_2 transcritical refrigeration cycle. Two ejector and one expander is applied as expansion devices to enhance the performance of the proposed dual ejector, dual temperature refrigeration system. Thermodynamic analysis using energetic and exergetic methods are carried out. Applicability of expander in dual ejector CO_2 refrigeration cycle is analyzed on the basis of system performance parameters, namely COP, pressure ratios, entrainment ratios for various warm weather operating conditions like heat rejection pressure (8 MPa to 12 Mpa), heat rejection temperature (35°C to 50°C) and evaporator temperatures (-40°C to 0°C). Results show that modified dual ejector refrigeration cycle (MDERC) having expander, have better performance. In comparison with the dual ejector refrigeration cycle (DERC), the MDERC have 4.7% to 7.6% higher COP. The largest exergy destruction is found in the gas cooler, followed by ejectors. Exergy efficiency of MDERCis about 3.9% to 5.2% higher than DERC for the selected operating conditions.