Numerical Investigation on Condensation Heat Transfer Characteristics and Flow Patterns of Hydrogen-Air-Steam Mixture Gas

In the containment of nuclear power plants, the effective assessment of the hydrogen accumulation and the corresponding combustion risks in severe accidents are of vital importance. The concentration of this combustible gas and its transport behavior can be greatly influenced by steam condensation occurring on compartment walls and some other cold surfaces. To have an insight on these phenomena, the applicability of the previous steam-air condensation model in evaluating steam-air-hydrogen mixture behavior should be further validated. Besides, the influence of thermal parameters including wall sub-cooling, pressure on mixture gas flow patterns have not been systematically analyzed. In the present work, the COAST and COPAIN tests are employed for the validation of a new modified condensation model. Mechanism simulations were performed at the helium concentration of 2~40 %, wall sub-cooling of 53~95 ℃, and gas pressures of 0.3~1.3 MPa. Results show that the relative deviation between the prediction results of the new modified model and the experimental value is maintained within ±15.5 %. Moreover, a validated flow pattern map was proposed to have a better understanding the hydrogen transport behavior. Analysis revealed that flow pattern mainly rely on the gas concentration, the effects of wall sub-cooling and pressure are negligible