Flow regimes at water pressures above the critical pressure are characterized as supercritical flow. Supercritical flows have no phase change. The heat transfer from the wall to the fluid is single phase (there is no boiling or condensation). Experimental data indicate that for conditions that involve supercritical single-phase heat transfer, the Dittus-Boelter heat transfer correlation can be in significant error.
A pseudo-critical temperature can be defined as a function of pressure for pressures that exceed the supercritical pressure. The pseudo-critical temperature is defined for heat transfer purposes as the temperature at which the specific heat peaks as the pressure is held constant. There is significant variation in fluid properties across the heat transfer boundary layer at temperatures near the pseudo-critical temperature. The large variation in properties is the reason for the failure of the Dittus-Boelter heat transfer correlation.
Comparisons to experimental data indicate that the Mokry heat transfer correlation is a significant improvement over the Dittus-Boelter heat transfer correlation for single phase supercritical heat transfer. The Mokry correlation was chosen to be included into TRACE.