Critical heat flux in inclined and vertical smooth and ribbed tubes

An important design parameter for boiler tubes in high pressure natural circulation steam generators is the geometry of the flow circuit. The experimental results presented show that the critical heat flux (CHF) for a smooth tube decreases as the angle of inclination of the tube is decreased. However, a significant increase in heat flux or steam quality occurs for the ribbed tube when compared to the smooth tube at similar operating conditions. Also, the angle of inclination has little effect on the CHF at certain operating conditions. The improvement in the CHF for the ribbed tube is due to a swirling action promoted by the ribbing and was found to be dependent upon mass velocity. (U.S.)