Numerical Investigation of Thermohydraulic Characteristics in Supercritical CO 2 Natural Circulation Loop with Spatially Varying Temperature

Investigation of thermohydraulic characteristics is highly significant for any natural circulation loop (NCL) applications. The physical properties of supercritical fluids are highly sensitive to temperature when they cross pseudo-critical points. In the current study, steady state thermohydraulic characteristics of NCL with a spatially varying temperature distribution on the source along with different orientations of the source and sink are numerically investigated. A three-dimensional rectangular NCL with a uniform diameter and constant length of source and sink is modeled. The temperature of the sink is held constant, while the temperature of the source varies spatially with local maximum and minimum temperatures. The system performance is investigated for four different operating pressures ranging from 8 to 12 MPa. The mass flow rate is observed to increase with increasing operating pressure for all orientations and heat load distribution at the source. The results also indicate that heat transfer degrades when the fluid crosses the pseudo-critical point. It has been noticed that spatially varying temperature distribution has a maximum of 48% heat transfer variation compared to the constant temperature distribution. Furthermore, a source or sink located in the horizontal leg performs better than the vertical leg.