Investigation of Pre- and Post-Dryout Heat Transfer in Upward Steam-Water Two-Phase Flow at Low Flow Rate

Abstract

A heat transfer experiment was performed on steam-water two-phase flow in an annular flow path with a uniformly heated rod under the conditions of the mass flow rates from 0.2xlO⁶ to l.Ox 10⁶ kg/m²-h, inlet qualities from 0.5 to 1.0, heat fluxes below 4.7x 10⁵ W/m² and pressure of 31 bar. Dryout of the heater rod surface was observed resulting in the sharp rise of the heater rod surface temperature. Measured heat transfer coefficients were compared with the several empirical and semi-empirical correlations with the emphasis on the applicability of the correlations to the present test conditions being important in the analysis of the thermal hydraulic behavior during a LOCA of a nuclear reactor. The measured heat transfer coefficient in the pre-dryout region is lower than the existing correlations. The cooling of the heat transfer surface by the liquid phase in the post-dryout region is significant, which is neglected in the existing correlations. The heat transfer coefficients calculated for the post-dryout region by the Groeneveld correlation show good agreement with the presently measured results within the accuracy of 0~27%.

KEYWORDS:

• two-phase flow
• heat transfer
• dryout
• pre-dryout
• post-dryout
• loss of coolant accident
• nuclear reactor
• heat transfer coefficient
• annulus
• flow rate
• accuracy