Special coupled 1D-2D procedure for predicting heat transfer regimes at supercritical parameters using differential approach

The paper represents a method for determining the heat transfer and hydraulic resistance coefficients at supercritical parameters based on the “narrow channel” approximation. The proposed approach considers 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, accounts for the 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 to adapt the method for calculations of rod bundles in channel approximation is described. The results are compared with the studies on fuel rod imitators’ assemblies at supercritical parameters. The proposed modification of the “narrow channel” model can be used as an alternative to heat transfer correlations in system codes to perform improved estimations. © 2025 Elsevier Ltd.