Numerical study of thermal and fluid characteristics of supercritical nitrogen flowing in an inclined semicircular flow channel

The thermal and hydraulic phenomena in an inclined semicircular channel through which nitrogen changes to supercritical state flows were studied through numerical analysis. The geometry of the flow channel was semicircular in cross-section with a diameter of 2 mm and a length of 350 mm. The heat fluxes applied to all sides of the semicircle were 20, 40, and 60 kW/m2; the angles of the inclined flow channel were 30 & DEG;, 45 & DEG;, 60 & DEG;, 90 & DEG;, and -90 & DEG;, and one more case was analyzed under zero gravity as a reference case. Under the given conditions, nitrogen changed to a supercritical state owing to the heat flux applied while flowing through the channel, and the pseudo-critical point differed depending on the size of the heat flux. However, with a change in the inclination angle, physical properties of the heated working fluid, such as the density, viscosity, and cp, changed rapidly, and the buoyancy effect and acceleration parameter values changed accordingly. As a result, a secondary flow appeared, and the change in the heat transfer performance was explained by the heat transfer coefficient. By calculating the change in the Nusselt number and the change in each variable according to the location of the channel, we developed correlations based on the change in the inclination angle and heat flux.

Automated summary

Numerical analysis was conducted to study the thermal and hydraulic phenomena in an inclined semicircular channel where nitrogen undergoes supercritical state flow. The channel had a semicircular cross-section with a diameter of 2 mm and a length of 350 mm. Different heat fluxes of 20, 40, and 60 kW/m2 were applied to the semicircle, and the inclination angles of the flow channel were varied. The study revealed that under given conditions, the heat flux induced nitrogen to transition into a supercritical state, and the critical point varied with the heat flux. The inclination angle caused significant changes in the physical properties of the heated working fluid, resulting in the appearance of secondary flow and alterations in heat transfer performance.