Prediction of subcooled flow boiling pressure drops in small circular tubes

Two-phase pressure drops in a mini-tube, in transition flow and subcooled boiling, are analyzed in the present paper, with the support of an experimental data set provided by ENEA with their BO.E.MI.A. test section. The methodology can be applied to different fluids according to similarity criteria. Single phase, subcooled and saturated conditions have been analyzed. The Reynolds number in the experiments was mainly in the transition zone between laminar and turbulent conditions, therefore a third order interpolation curve of the friction factor has been employed. The methodology is based on the model from Delhaye. The model considers the fluid properties, the energy, mass and momentum conservation equations to predict the ONB and OSV points and a hyperbolic function has been adopted to calculate the non-equilibrium vapor quality in the subcooled boiling region. The best agreement with the ENEA experimental data has been obtained using in the methodology the Chisholm correlation, with 83.59% of the predicted values with an error lower than 30%.