Heat Transfer to Sub-critical and Supercritical Water in an Inclined Upward Smooth Tube

摘要

From sub-critical pressure to supercritical pressure, the experimental research has been carried out on heat transfer to water in inclined upward smooth tubes with the diameter of Φ32 × 3mm and the inclined angle of α=20o. The experimental parameters were at p=13-30MPa, G = 600-1200kg/(m~2 s), and q=200-600kW/m~2. Based on experimental results, wall temperature distributed non-uniformly along the circumference of the inclined tube. Departure from Nucleate Boiling (DNB) can be postponed and even eliminated as mass velocity increased. Effects of pressures on heat transfer were complex at sub-critical pressure. Properties of supercritical fluid acutely vary with the temperature near the pseudocritical point. While the ratio of the mass velocity to the heat flux was comparatively high, heat transfer enhancement occurred near the pseudocritical point. On the contrary, heat transfer deterioration occurred while the ratio of the mass velocity to the heat flux was comparatively low. As the pressure increased far from the critical pressure, the amount of deterioration decreased. Correlations of minimum heat transfer coefficient at sub-critical pressure and heat transfer coefficient at supercritical pressure have been provided.