Heat transfer of water flowing upward in vertical annuli with spacers at high pressure conditions

Experimental studies on heat transfer to water flowing upward in a concentric annular channel are carried out at the SWAMUP test facility at both subcritical and supercritical pressure conditions. The vertical annuli contain a heated inner tube of 8 mm outer diameter and an unheated outer tube of 15.3 mm inner diameter with spacers without mixing-vane. More than 500 test data were obtained with the following test conditions: pressure from 15.5 to 26.0 MPa, mass flux from 500 to 1600 kg/m2s, heat flux from 0.45 to 1.4 MW/m2 and bulk temperature from 310 to 390 °C. Test data are also compared with those obtained in tubes of similar hydraulic diameter. The results show that heat transfer coefficient in annuli without spacer effect is slightly lower than that in circular tubes, whereas a significant enhancement of heat transfer is obtained in annuli with spacer effect. The phenomenon of heat transfer enhancement and its decay behavior downstream of spacers were investigated and analyzed. A new correlation was developed to predict the local heat transfer enhancement due to spacers at supercritical pressure condition.