Abstract
This research aims to study a double-tube type CO2 gas cooler. A tube-in-tube heat exchanger model was developed to be suitable for supercritical fluid CO2 and water and validated with some existing measurements. Gas cooler, in which CO2 is cooled with persistent temperature drop, is different from those constant temperature condensation processes which heat exchangers called condenser. Normally the variation of the heat transfer rate for constant property working fluid shows a monotonical decrease from the inlet of Cmin. By contrast the CO2 may present a local minimum and a local maximum alongside the heat exchanger due to CO2 passes through the pseudo-critical temperature, and this phenomenon becomes more and more pronounced when the pressure is close to the critical pressure (73.8 bar). Investigation of the performance of the developed counter-flow water-cooled CO2 gas cooler operating above and near critical pressure was conducted using a heat pump water heater with CO2 flowing in the annulus side. The calculations show good agreement with the experimental results. The results demonstrate that the variation of CO2 temperature tends to show very slow decreasing near the pseudo-critical region when compared to the inlet region. In summary, the peculiar phenomenon in CO2 gas cooler that the local heat transfer rate of the heat exchanger peaks within the heat exchanger near the pseudo critical region is owing to the drastic rise of specific heat (CP value).