Heat Transfer Studies of Supercritical Water Flows in an Upward Vertical Tube

Abstract

In this paper, an investigation of heat transfer characteristics at supercritical pressure fluid flowing in a uniformly heated vertical tube has been carried out. In order to reduce thermal emissions and increase thermal efficiency, supercritical boilers were developed at various sizes. Above supercritical pressure, the distinction of liquid and gas phases disappears. This dispenses with the problem of critical heat flux and dry out phenomenon which occurs in subcritical pressure. However, the study of heat transfer behavior above supercritical pressure is indeed required due to the heat transfer deterioration operation at high heat flux to mass flux ratio. In the present work, numerical simulation has been employed in order to inquire about the effect of various parameters such as heat flux to mass flux ratio, diameter and pressure that causes heat transfer deterioration. Shear Stress Transport k-ω model has been applied in all the computations. It is observed that the metal temperature predicted by numerical simulation is more accurate than the empirical correlations available in the literature. A Visual Basic Program has also been developed to assess the empirical correlations in the context of predicting metal temperature under 5280 different operating conditions. Tube sizes of 10, 15 & 20 mm inner diameter with 4 m length, the pressure between 225 and 280 bar and heat flux to mass flux ratio between 0.27 and 0.67 have been chosen to explore the effect of diameter, pressure and heat flux respectively.

Keywords

• supercritical water
• heat transfer deterioration
• sst-kw model
• heat transfer enhancement
• vertical flow