Measurements of convective heat transfer to vertical upward flows of CO2 in circular tubes at near-critical and supercritical pressures

A Critical Review of the Physics and Modeling of Deteriorated Heat Transfer in Supercritical Fluids

Modeling of deterioration of heat transfer (DHT) observed in fluid flows at supercritical pressure remains a challenge due to incomplete understanding of the underlying physics. Given the challenges involved in the experimental and computational study of this phenomenon, it is crucial that the growing collective experimental and computational data be periodically analyzed in a comparative manner through critical reviews. This paper aims to provide such a critical review. The experimental and computational evidence continues to support the postulate that streamwise acceleration of the lower density, near-wall fluid layer relative to the higher density bulk flow promotes reduced turbulent mixing and hence reduced convective heat transport. At lower mass flowrates, this may be driven by buoyancy force, whereas at higher thermal loading, the dominant driver may be the increased favorable streamwise pressure gradient prompted by the bulk flow acceleration. A discussion of these physical mechanisms and an assessment of related semi-empirical models constitute the scope of this review.

Assessment of Convective Heat Transfer Correlations Against an Expanded Database for Different Fluids at Supercritical Pressures

Canadian Nuclear Laboratories (CNL) has recently expanded the supercritical heat transfer (SCHT) databank with additional data provided by the Nuclear Power Institute of China (NPIC). These additional data cover flow conditions beyond the current databank, and are applicable for improving or validating existing correlations. The expanded databank comprises more than 41,000 points of heat-transfer measurements with different fluids flowing vertically upward in tubes, annuli, and bundles at supercritical (SC) pressures. It has been applied in assessing the prediction accuracy of 24 heat-transfer correlations, which were derived from experimental data obtained with water or nonaqueous fluids (such as carbon dioxide) flowing in tubes. For the correlation assessment, a sensitivity analysis has been performed by applying the measured wall temperature as an independent parameter. The assessment against the bundle data was based on cross-sectional-averaged flow conditions and the hydraulic diameter. The iterative approach (i.e., without prior knowledge of the wall temperature) overpredicted the wall temperature, which is conservative in safety analyses.