Experimental study on heat transfer and pressure drop of supercritical CO2 cooled in a large tube

Thermal performance analysis of a parabolic trough solar collector using supercritical CO2 as heat transfer fluid under non-uniform solar flux

“…It is well known that the heat transfer performance of the traditional HTFs, like steam and oil, in a circular tube under uniform heat flux or temperature can be predicted well by empirical correlations such as the Dittus-Boelter equation [24] and Gnielinski equation [25]. Nevertheless, because of the non-uniform solar flux on the absorber tube of the evacuated receiver and the strongly temperature-dependent properties of s-CO 2, these correlations are not suitable for calculating the heat transfer of s-CO 2 in the PTC receiver [26,27].…”

Heat transfer characteristics of supercritical CO2 flow in metal foam tubes

“…Expansion valve 1 is used to control the mass flow rate of SCO 2 entering the test section. In the end, two branches of sub-critical CO 2 are mixed at the inlet of the evaporator [19]. A type of special resistance wire coated by the insulation material is winded on the outer wall of the tube.…”

Computational investigations on heat transfer of turbulent supercritical CO2 in large tubes using RANS modelling

“…Dang and Hihara [22] experimentally studied the cooling heat transfer of sCO2 and pressure drop characteristics in horizontal micro/macro tubes within diameter range of = 1 − 6 mm , and explored the impact of operating conditions, including the heat flux. More recently, Liu et al [43] experimentally investigated turbulent heat transfer from sCO2 cooled in large horizontal tubes with diameters up to 10.7 mm to observe that the pipe diameter has a significant influence on heat transfer performance, which was also concluded in earlier studies for smaller tubes [22,31,33,44,193,194].…”

“…In direct cooling, the air-cooled finned tube heat exchangers (FTHEs) employed in the Natural Draft Dry Cooling Tower (NDDCT) need large pipes to reduce the pressure drop, to increase the heat rejection and to meet the higher sCO2 mass flow rate required for such applications (compared to those in residential air-conditioning and refrigeration systems). Past experimental research indicated lower pressure drop and higher Nusselt number with larger tube diameters [22,33,43,44]. Designing this kind of heat exchangers for future sCO2 power plants requires an understanding of the heat transfer and flow characteristics of turbulent sCO2 in large diameter tubes.…”

“…Most previous studies of buoyancy-affected turbulent sCO2 heat transfer focus on vertical flows, where the heat transfer performance could either be improved or impaired; some of these studies at early stages employed large vertical pipes ( ≈ 20 mm) [133,[167][168][169]. However, for horizontal orientations [44,108,110], the datasets are only available for small tubes, where the free convection [24,35,110,199,200] and pipe diameter [22,33,43,194], they usually did not offer the underlying physical explanations. In addition, the buoyancy effect within this diameter range tubes is also discussed.…”