Experimental investigation on heat transfer characteristics of supercritical pressure water in a horizontal tube

In this study, heat transfer of water at supercritical pressures in a horizontal tube was investigated experimentally. The inner diameter of the tube was 26mm with a heated length of 2m. Experimental parameters included a mass flux ranging from 300 to 700kg/m²s, a heat flux from 200 to 400kW/m², a pressure from 23 to 25MPa, and a bulk fluid enthalpy from 1000 to 3000kJ/kg. The results indicated that heat transfer characteristics of supercritical water are not uniformly along the circumference of the horizontal tube. Decreasing in the heat flux could decrease the non-uniformity and eliminate deterioration on the top surface of the horizontal tube. With the pressure increasing, the amount of deterioration on the top surface is increased and enhancement on the bottom surface is decreased. By comparing with results of previous investigators, the effect of flow direction and diameter on heat transfer of water were analyzed in details. The criterions of Petukhov and Jackson were selected to judge buoyancy effects in a horizontal tube. It was found that the Petukhov criterion can accurately predict the onset of buoyancy effects. Furthermore, new heat transfer correlations have been proposed, which could be used to predict heat transfer coefficients of supercritical water flowing in horizontal tubes.