Simplified Experimental and Computational Fuel Rod Models for Identifying Critical Heat Flux

The prediction of critical heat flux (CHF) phenomenon at atmospheric pressure was carried out using computational fluid dynamics (CFD) methods. Heat transfer experiments of flow boiling will be validated at the University of West Bohemia, where an experimental apparatus is built. The test section consists of one 3000 mm long resistance heated fuel rod imitator (HRI) with an outer diameter of 9.1 mm placed in an annular tube. Several spacer grids are used on the experimental device to hold the heated rod imitator in its position while improving the internal heat transfer. All simulations presented in this paper started with the same inlet conditions, while the heating input gradually increased until the two-phase flow reached a steady state. The successfully predicted CHF happened through a liquid sublayer dryout under very high vapor volume fractions (93+ %) which led to complete thermal isolation of the HRI. Thanks to the results of the CFD simulations, the temperature measuring system on the experimental loop could be optimized