Convective heat transfer to CO2 flowing upward in electrically heated vertical tubes at supercritical pressures was studied for wall heat fluxes q within ranges that included values corresponding to the onset of heat transfer deterioration (HTD). The inlet pressure was P = 8.35 MPa, the mass flux was in the range 200 kg/m2s ≤ G ≤ 1500 kg/m2s, and the inlet temperature was in the range 0 ◦C ≤ Tin ≤ 35 ◦C. Wall temperature measurements were collected in three tubular test sections, having inner diameters of D = 4.6, 8, and 22 mm. The abilities of three different HTD identification methods to separate the entire data set into deteriorated and normal heat transfer modes were tested. Two types of buoyancy parameters were tested as HTD detection methods, and correction factors for changes in mass flux were devised. The minimum heat flux at HTD onset was found to follow a power law of mass flux with the same exponent for all three sections and the same proportionality coefficient for the two smaller sections but a smaller one for the larger test section. For heat flux values that were larger than this minimum, HTD was found to occur only within a limited range of Tin, whose width increased with increasing heat flux. The heat transfer coefficient for normal heat transfer was expressed as an exponential function of the diameter.

This thesis describes the development and validation of a look-up table capable of predicting heat transfer to water flowing vertically upward in a circular tube in the trans-critical pressure range from 19 to 30 MPa. The table was based on an extensive and screened experimental database and its trends were smoothened to remove unrealistic scatter and physically implausible discontinuities. When compared to other prediction methods, the present look-up table approximated the experimental data closer in values and trends. Moreover, unlike existing prediction methods, the table applies not only to normal heat transfer conditions but also to conditions with heat transfer deterioration and enhancement. A separate multi-fluid look-up table for trans-critical heat transfer was also developed, which besides the existing water database incorporated new measurements in carbon dioxide; the latter were collected at the University of Ottawa supercritical flow loop under conditions of interest for the current Super-Critical Water-Cooled Reactor designs, for which few water data were available in the literature. Existing fluid-to-fluid scaling laws were tested and two additional sets of scaling laws were proposed, which are applicable not only to the supercritical pressure region, but also to the high pressure subcritical region. The multi-fluid table is applicable to water at conditions of normal and abnormal heat transfer, but its applicability to model fluids is restricted to the normal heat transfer mode.