18 May 2017
In a CO2 water heater system, a water-CO2 double tube gas-cooler is an important component affecting the system performance. Due to the variation in the thermal properties of supercritical CO2 with the temperature, it is important to carefully design the gas-cooler used in the water heater. In this study, an analytical model of the water-CO2 double tube gas-cooler having several inner channels was developed using the finite-volume method. The gas-cooler model was validated by the experimental data for three gas-coolers having 2, 4, 8 inner tubes. To estimate the gas-cooler performance according to the number of inner tubes, the cross-sectional area ratio between the inner tubes and outer tube of the gas-cooler was defined, which was called as ‘GCAR’. The heat transfer rate and thermal effectiveness of the gas cooler were analyzed according to the GCAR. For the maximum heating capacity, the optimum design of the gas-cooler was suggested and the optimum operating conditions of the CO2 water heater system were recommended.