Differential Method for Predicting Heat Transfer Deterioration Regimes in Supercritical Channels and Rod Assemblies

Abstract The paper considers a method for determining the heat transfer and hydraulic resistance coefficients at supercritical parameters based on the “narrow channel” approximation. This approach takes into account the presence of transverse exchange of momentum and energy, the intensity of which depends on the radial profile of shear stresses and, to a first approximation, considers density pulsations in the gravity field. In contrast to the classical CFD approach of the same spatial dimension, the described method is simpler, although it remains unclosed with respect to the longitudinal pressure gradient. To overcome this issue, a one-dimensional approach based on the transfer matrix method is used. The technique incorporates an integral form to determine the local HTC (Lyon integral) and friction. The paper provides validation of the approach based on probe experimental studies for CO2, where not only axial temperature profiles during upward and downward flow were experimentally obtained, but also radial profiles were studied in the section with maximum temperature under heat transfer deterioration (HTD). Good agreement in the temperature profiles in the axial and radial directions was obtained in calculations. The considered method predicts the presence of “laminarization” under HTD. An attempt was made to adapt the method for calculations of assemblies in the channel approximation. The results were compared with the studies on the assemblies of fuel rod imitators with supercritical water. The proposed modification of the “narrow channel” method can be used as an alternative to correlations in system codes to perform improved estimations.