The development of SCWRs requires an intensive study of convective heat transfer at supercritical pressures. Heat transfer at a supercritical pressure is different from that of a subcritical pressure because the thermophysical properties of a light-water coolant undergo significant variations as the temperature of the coolant passes through the pseudocritical point. Therefore, the traditional Nusselt number and other related non-dimensional parameters developed at subcritical pressures based on the bulk-fluid temperature cannot be used (Bae and Kim, 2009).

At a supercritical pressure, the thermophysical properties of a coolant at the sheath-wall temperature differ significantly from those at the bulk-fluid temperature. Although, a fluid does not undergo a phase change at a supercritical pressure, a low-density fluid separates the sheath-wall from a high-density fluid at high heat fluxes and low mass fluxes. This results in a reduction in the convective Heat Transfer Coefficient (HTC). Consequently, the sheath-wall temperature increases. This phenomenon is known as the Deteriorated Heat Transfer (DHT) regime. Therefore, the sheath-wall temperature must be reflected in a correlation, which is used to study the heat transfer at supercritical conditions.

Many correlations have been developed for the calculation of HTC at supercritical conditions. The most widely used correlations include those developed by Bishop et al. (1964); Swenson et al. (1965); Krasnoscheckov et al. (1967); Jackson (2002); and Mokry et al. (2009). Zahlan et al. (2011) compared the prediction capabilities of sixteen correlations including the aforementioned correlations. The conclusion of the Zahlan et al. (2011) comparison study showed that the Mokry et al. (2009) correlation resulted in the lowest Root-Mean-Square (RMS) error within the supercritical region compared to all other examined correlations.