Parametric analysis on flooding limit and critical film thickness of a vertical two-phase closed thermosyphon

Abstract

Flooding limit is the most severe limitation in the operation of a two-phase closed thermosyphon (TPCT). However, the effect of condenser length to the critical heat flux (CHF) and the influences of structural and operational parameters to the critical liquid film thickness (CFT) were not universally concerned. In the present study, a comprehensive model for TPCT is developed to predict the CHF and CFT. In particular, the proposed model is validated through three criterions. Based on the validated model, parametric analysis of the structural and operational parameters is comprehensively carried out, and variations in CHF and CFT are illustrated and discussed in detail. Simplified correlations for CHF are finally proposed based on the numerical modeling results. The results indicate that the CHF decreases with increasing absolute length and evaporator length, while increases with increasing vapor temperature, condenser length, and inner diameter. However, the increment due to the condenser length is limited. The CFT has different fluctuation trends in comparison with the CHF. It increases first and then decreases with increasing vapor temperature and inner diameter, while reverses with increasing absolute length and condenser length, and remains unchanged with increasing evaporator length. Meanwhile, the effect of working fluids to the CHF and the effect of aspect ratios to the CFT both indicate that much efforts need to be made to further understanding the TPCT. However, correlations of CHF can be obtained in a good agreement with the numerical modeling results within 30% deviation for the whole limited scope.