Experimental study on heat transfer to the supercritical water upward flow in a vertical tube with internal helical ribs

This paper presents some results of experimental research performed at the Hi-TaP-XJTU test loop on heat transfer to the supercritical water (SCW) upward flow in a vertical tube with internal helical ribs. The experiments include a large range of regime parameters: P = 22.5-28 MPa, G = 400-1000 kg/(m2 s), q = 300-700 kW/m2. These present data were compared with those known for smooth tubes and other types of ribbed tubes both under the heat transfer deterioration (HTD) and without it. The heat transfer coefficient (HTC) in the test ribbed tube is by 1.41-1.85 and 1.34 times higher as compared with smooth tubes and ribbed tubes of other types in the cases without HTD. The critical heat flux of HTD in the test ribbed tube is 1.8 times of that in the smooth tube, and the ratio of the critical heat flux to the mass flux is at least 1.13 times higher than ribbed tubes of other types. Moreover, the ratio of HTC in the test ribbed tube to that in the smooth tube in the large specific heat region (LSHR) is significantly larger than that beyond the LSHR region. The mechanism of heat transfer enhancement taking place in the tube with internal helical ribs was analyzed as well. Finally, the HTC piecewise correlation for the upward SCW flow in this tube was developed, which includes three equations for the following separated regions of the bulk fluid enthalpy: (1) H < 1700 kJ/kg, (2) 1700 ⩽ H ⩽ 2700 kJ/kg, (3) H > 2700 kJ/kg. It is of type Nu/Nus = CRemPrn, where Nus is the Nusselt number for a smooth tube determined by the Mokry-Pioro correlation and C is the numerical constant for the separate enthalpy region.