EXPERIMENTAL INVESTIGATION ON THE EFFECTS OF INTERNAL HEAT TRANSFER IN A TWO-STAGE TRANSCRITICAL CARBON DIOXIDE CYCLE

The effect of internal heat transfer between suction line and gas-cooler outlet line is investigated experimentally in a transcritical carbon dioxide refrigerating circuit. The test rig is equipped with a semihermetic two-stage reciprocating compound compressor with a water cooled inter-stage heat exchanger and with a finned coil gas-cooler and evaporator. Fixed evaporation pressure was considered, while vapour superheating was varied from 0°C to 14 °C. Two-phase conditions at the evaporator outlet were also investigated. Gas-cooler outlet pressure was varied from 7.8 to 11 MPa. The experimental results are compared with available experimental data for the same system without internal heat exchange. The effect of the intercooler efficiency on the cycle performance is also investigated. The system Coefficient of Performance was found to increase up to 20%. Some hints about the effect of low-purity carbon dioxide on system efficiency are also proposed.