Heat transfer and pressure drop in horizontal tubes with supercritical water

Heat transfer and pressure drop for supercritical water flow in horizontal tubes are simultaneously measured. Large temperature differences between the top and the bottom of the corresponding cross sections are observed. Average heat transfer coefficient over the cross section is higher than that for the vertical upward flow in the region close to the critical point. This is due to the secondary flow induced by the buoyancy forces. Mean friction factor for heated flow is remarkably smaller than that for isothermal flow. The reduction of the friction factor can be accounted for by the physical property variation in the cross section. For the rough tube, however, the friction factor for heated flow is not less than that for isothermal flow, and the improvement of the heat transfer coefficient is considerable.