A Study on Premature Occurrence of Critical Heat Flux

Abstract

Two-phase natural circulation loops have extensive applications in nuclear and process industries. One of the major concerns with natural circulation is the occurrence of the various types of flow instabilities, which can cause premature boiling crisis due to flow and power oscillations. In this work, a transient computer code COPCOS (Code for Prediction of CHF under Oscillating flow and power condition) has been developed to predict the premature occurrence of critical heat flux (CHF) under oscillating flow conditions. The code incorporates conduction equation of the fuel and coolant energy equation. For CHF prediction, CHF lookup table developed by Groeneveld is used. Experimental investigation on CHF under oscillatory flow was also carried out in a facility named CHF and Instability Loop (CHIL). CHIL is a simple rectangular loop having a 10.5 mm ID and 1.1-m-long test section. The flow through the test section is controlled by a canned motor pump using a variable-frequency drive (VFD). The effect of frequency and amplitude of flow oscillation on premature occurrence of CHF has been investigated experimentally in CHIL loop. Further experimental data on degradation in CHF due to flow oscillations were compared with COPCOS’s simulated results. Full paper covers description of the facility, experimental procedure, experimental results and data analysis using COPCOS.