Effect of tube diameter on critical heat flux in vertical steam-water flow.

Abstract

The effect of tube diameter on critical heat flux (CHF) has been examined by (1) analyzing existing experimental data, (2) reviewing existing correlations and semi-analytical models, and (3) obtaining CHF measurements in two vertical tubes of different diameters. Based on constant local flow conditions, the parametric trend of available CHF data shows generally a decreasing CHF with increasing tube diameter. Due to the large data scatter (inherent uncertainty within different sets of data), a definite conclusion cannot be drawn. The observations indicated that the tube-diameter effect on CHF is a complex phenomenon and is affected by pressure, mass flux and thermodynamic quality as well as tube diameter itself. An improved correction factor has been derived to account for the effect of tube diameter on CHF. It is also presented in terms of the tube diameter to a power "n", consistent with existing recommendations. Rather than a constant value, the coefficient is expressed as a function of mass flux and thermodynamic quality to include other compounded effects. (Abstract shortened by UMI.)