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Proceedings of the 27th National and 5th International ISHMT-ASTFE Heat and Mass Transfer Conference December 14-17, 2023, IIT Patna, Patna-801106, Bihar, India
December, 14-17, 2023, Bihar, India

Studies on CO2 based two-phase natural circulation loop

Get access (open in a dialog) DOI: 10.1615/IHMTC-2023.670
pages 409-415


A simple mathematical model based on homogeneous flow is developed to study the design and performance aspects of a two-phase, CO2 based, natural circulation loop. A constant heat flux and constant temperature boundary conditions are used for the heat source and heat sink, respectively. The operating conditions are so chosen that the loop can be used for low temperature refrigeration and air conditioning applications. As the operating temperature is lower than the ambient temperature, the loop pressure shoots up during the loop shutdown. As the standstill pressure during shutdown is a critical parameter, the effect of design and operating parameters on standstill pressure is studied. Results show that the loop size and mass flow rate have to be optimized based on minimum standstill pressure and minimum loop mass. Based on the results obtained, empirical equations are proposed for estimating important design parameters. It is expected that these correlations will be useful in quick sizing of the CO2 based, two-phase natural circulation loops.