Zhendong Yang

Forced Convection Heat Transfer Using High Temperature and Pressure Water in an Upward-Inclined Tube

Within the range of pressure from 9 to 28 MPa, mass flux from 600 to 1500 kg/m2 s, heat flux at inside wall from 200 to 600 kW/m2 , and wall temperature up to 650 °C, experiments were conducted to research the forced convection heat transfer of water in an inclined upward tube with an inclination angle of 20 deg and an inner diameter of 26 mm. According to the experimental data, the effects of pressure and heat flux on heat transfer of water were analyzed in detail. In the subcritical pressure region, it was found that heat transfer characteristics of water are not uniform along the circumference of the inclined tube. Temperature of the top is always higher than that of the bottom, which can be attributed to the buoyancy effect in the inclined tube. In the supercritical pressure region, natural convection makes the low-density hot fluid gather at the top of the inclined tube; hence, heat transfer condition is deteriorated and wall temperature is increased. Furthermore, the criterions of Petukhov and Jackson were selected to judge the buoyancy effect in the inclined upward tube. The result seems acceptable but these criterions should be further improved to get a better applicability for an inclined tube.

Assessment of Heat-Transfer Correlations Against Experimental Data Obtained With Supercritical Water in Vertical Annuli

Eleven correlations proposed for supercritical heat-transfer coefficients were assessed against a set of experimental data obtained recently with supercritical water flow in a vertical annular test section at Xi’an Jiaotong University. The inner heated rod of the test section had an outer diameter of 8 mm, while the outer unheated tube had an inner diameter of 16 mm (resulting in a gap size of 4 mm). The experiment covered pressure range from 23 to 28 MPa, mass-flux range from 350 to 1000 kg/m2s, and heat-flux range from 200 to 1000 kW/m2. The assessment shows relatively good agreement between predicted and experimental heat-transfer coefficients for several correlations. Some discrepancies have been observed at the region where deteriorated heat transfer, and are attributed to the modified Dittus-Boelter formulation that captures mainly the normal heat-transfer region. Overall, the Dittus-Boelter correlation is shown applicable only for the normal heat-transfer region, and significantly overpredicts the heat-transfer coefficient at the deteriorated heat-transfer region. The correlation of Bishop et al. appears valid for the current experimental database, particularly for high mass fluxes.Copyright