Experimental investigation on convective heat transfer from a horizontal miniature tube to methane at supercritical pressures

Heat transfer of supercritical cryogenic methane in miniature tube has been experimentally investigated. Experimental conditions included pressures of 5-15 MPa, mass velocities of 6000-150,000 kg m^-2 s^-1 and heat fluxes of 1-16 MW m^-2. The mass flux, heat flux and pressure effect were analyzed. A physically reasonable property averaging technique, Probability Density Function (PDF)-based time-averaged properties, were proposed for accounting for the effect of highly nonlinear dependency of properties on instantaneous turbulent temperature. A semi-empirical new correlation evaluated by PDF-based time-averaged properties for convection heat transfer of supercritical cryogenic methane was developed. The experimental Nusselt numbers were compared with those calculated with empirical correlations. The Dittus-Boelter and Gnielinski correlations overestimate the measurements in the pseudo-critical region since they could not accurately reflect the properties variations. The newly developed PDF correlation works so well that more than 85% experimental data are captured within an accuracy of 25%. Jackson acceleration criterion is found valid in evaluating the acceleration effect and works well in predicting heat transfer deterioration occurring in present experiments.