Heat transfer correlations of rifled tubing for boilers under sliding pressure operating condition.

Abstract

A heat transfer experiment has been carried out under the same conditions as the furnace water wall tubes of an actual sliding pressure operation boiler, using a rifled tube of 28.6 mm in outer diameter with four spiral 0.83 mm-height ribs on its inner surface, and the data was systematically correlated in order to predict the heat transfer coefficients in each region of subcritical and supercritical pressures. In the subcritical pressure single phase region, Bishop's correlation, which is usually applied to smooth tubing in a supercritical pressure region, was applicable to the rifled tubing by use of hydraulic diameter. At the post-CHF region, the heat transfer coefficient could be correlated by the Groeneveld-type expression, but its value was enhanced more than that for the smooth tubing, with a decrease in steam quality. A new correlation was developed for the supercritical pressure region.