[en] The R-134a test loop is a forced-flow experimental facility for the study of heat transfer properties of R-134a under subcritical and supercritical thermodynamic conditions. The loop is designed to operate with pressures as high as 6 MPa and temperatures up to 140 °C. The intended mass flux is in the range of 500-6000 kg/m²s for the experiments with subcritical thermodynamic states and 500-4000 kg/m²s for supercritical conditions. The loop has been designed to accommodate a variety of test-section geometries, ranging from a straight circular tube to a 7-rod bundle, achieving heat fluxes up to 2.5 MW/m² depending on the test section geometry. The design of the loop allows for easy reconfiguration of the test-section orientation relative to the gravitational direction and adjustment to the length of the test section. (author)

[en] Modelling 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 flow rates, this may be driven by buoyancy force, whereas at higher thermal loading the dominant driver may be the increased favourable 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. (author)

[en] Highlights: • Numerically simulated forced-convection turbulent flow over convex-curved surface. • Analyzed effects of curvature and supercritical thermal state on heat transfer. • Near-wall streaks spaced farther apart due to curvature-induced radial equilibrium. • Curvature and supercritical effects on turbulence are of comparable magnitude. -- Abstract: Direct numerical simulation (DNS) results are used to establish the effect of convex streamwise curvature on the development of turbulent boundary layers, and the effect of such curvature on the forced-convection heat transfer variations observed at certain supercritical thermodynamic states. The results illustrate the stabilizing effects of this flow geometry through modification of the structure and distribution of hairpin-like vortical flow structures in the boundary layer. Furthermore, enhancement of convective heat transfer realized at a particular heat flux-to-mass flux ratio with the working fluid at a supercritical state is observed to be reduced by the stabilizing effect of convex surface curvature

[en] Experiments were conducted at supercritical pressures and temperatures on a vertically-oriented annular heating rod with a wire-wrap spacer using upward-flowing R134a to determine the effect of a wire-wrap spacer on heat transfer in proximity of the pseudocritical point. Measurements were taken at quasi-steady-state and pressure-transient conditions. During each instance of deteriorated heat transfer, the Nusselt number is greater than values predicted by the Dittus-Boelter correlation. Heat transfer during the pressure transients is observed to be insensitive to the time rate of change of the fluid pressure, which implies that the transience does not affect the instantaneous state of the heat-transfer process. (author)

[en] The Carleton University thermal-hydraulic water loop is a high-temperature high-pressure test loop developed for the study of forced-convection heat transfer in ducted water flow at supercritical conditions. The loop is designed to operate at pressures as high as 28 MPa and temperatures up to 600 "oC. The supercritical water loop is housed at Carleton University's high-temperature test facility. This paper describes this high-temperature test facility, the design features of the supercritical water loop, and the results of thermal and structural analyses performed as part of the design process. (author)