A comprehensive numerical investigation of preventing supercritical heat transfer deterioration in the gas heaters of the CO2 Rankine cycles

• The heat transfer deterioration (HTD) in a tubular gas heater is numerically investigated. • The ( SSTk - ω ) turbulence model is recommended for similar geometries. • The heat transfer enhancement (HTE) is achieved when the gas-like layer has been reduced. • The thinnest gas-like layer is predicted for the inner-dimpled tube (IDT). The phenomenon of supercritical heat transfer deterioration (HTD) poses a significant challenge in optimizing energy systems, particularly in the gas heaters of Rankine cycles. This study offers a comprehensive investigation aimed at enhancing the heat transfer performance of a supercritical carbon dioxide (sCO 2 ) gas heater in Rankine cycles. To achieve the objectives, numerical simulations are conducted to analyze the flow fields under varying conditions, including inner diameter, uniform and non-uniform tube thickness, mass flux, heat flux, and operating pressures. These simulations are performed in a horizontal tubular gas heater by using the Eulerian method and validated against experimental data. The generated dataset of 35,000 data points revealed a direct relationship between the magnitude of the HTD phenomenon and the thickness of the gas-like layer on the tube wall. To mitigate the HTD, various tube configurations are applied. The tested configurations were including simple, eccentric, inner-grooved, and inner-dimpled tubes (IDT). The findings indicated that the thinnest gas-like layer was observed for the IDT configuration with a 30° angle between the dimples. Results showed that applying the IDT configuration with a 30° angle between the dimples, the gas-like layer thickness was reduced from 1 % to 67 % under operating conditions: including mass fluxes ranging from 200 kg/(m 2 s) to 800 kg/(m 2 s), heat fluxes varying from 25 kW/m 2 to 100 kW/m 2 , and operating pressures changing from 7.5 MPa to 30 MPa. It can be concluded that this research provides a valuable roadmap for designing modified tubular gas heater to enhance heat transfer performance and mitigate the HTD effects.