Experimental study on flow patterns and pressure oscillation characteristics of vertical upward steam jets at low water temperatures

Experiments were conducted to examine flow-regime transitions and pressure responses of vertically upward steam jets at low water temperatures (0–50 °C) and steam mass fluxes of 40–550 kg/(m 2 ·s). By combining high-speed imaging with high-frequency dynamic-pressure measurements, a flow-regime map was constructed. Within the investigated parameter range, seven regimes were identified and their observed operating regions were mapped. The maximum positive pressure excursion, p max , was used as a descriptive peak metric over each displayed time interval. For the three displayed 5-s chugging records, p max increased from 4.94 to 20.53 kPa as pool-water temperature increased from 0 to 20 °C. Among the displayed 50-ms records, hemispherical condensation oscillation reached 88.53 kPa, ellipsoidal condensation oscillation reached 149.85 kPa, and the stable-jet cases ranged from 5.16 to 10.56 kPa. These values are single-run, non-duration-normalized maxima.