A model for predicting diabatic pressure drops in multi-element fuel channels

One of the requirements for the thermalhydraulic analysis of a water-cooled nuclear reactor is the prediction of two-phase pressure drop in the fuel channels. Many existing methods, in combination with the thermodynamic equilibrium quality, employ correlations for the prediction of two-phase multipliers that are based on adiabatic gas-liquid flow. As indicated in the present paper, this practice results in unsatisfactory predictions of the pressure profile for a string of heated bundles.A model is recommended to predict the overall pressure drop for a diabatic flow in a string of 37-element CANDU®®CANDU - CANadian Deuterium Uranium, is a registered trademark of Atomic Energy of Canada Limited.-type bundles. It includes the D'Arcy-Weisbach equation (for estimating the single-phase pressure drop), an onset of nucleate boiling (ONB) correlation, and a two-phase pressure drop model.The ONB correlation is derived from the pressure drop results. It predicts the starting point where the pressure profile is affected by the presence of bubbles on the heat transfer interface.In horizontal two-phase flow, the overall pressure drop consists of frictional and accelerational components. For the former, several prediction models are evaluated, and the Friedel correlation, in general, gives the best results. The latter component is calculated based on the momentum balance.The proposed model has been applied to eleven sets of experimental results obtained with either water or refrigerant-12 as coolant. It predicts the pressure profiles accurately. The average and RMS errors of the overall pressure drop predictions for a total of 1217 data are 0.6% and 5.8%, respectively.