Numerical investigation of diameter effect on heat transfer of supercritical water flows in horizontal round tubes

Abstract

The diameter effect on the heat transfer of supercritical water (SCW) flows in horizontal round tubes has been studied using computational fluid dynamics (CFD) technique. The numerical simulations are carried out by the STAR-CD solver combined with the user developed subroutines that control the numerical calculation procedures.Through the tests it is found that the discretization scheme using CD, LUD or MARS will not affect the accuracy of the numerical simulations. Through the diameter effect studies, it is found that the heat transfer of supercritical water flows in the horizontal round tube is strongly affected by the buoyancy especially for the large diameter tube.The large diameter (D=10mm) tube will have the high risk to have the strong heat transfer deterioration that can introduce 180 o C wall temperature difference between the top and bottom surfaces due to the buoyancy effects.The magnitudes of the effects can be quantificationally expressed by a ratio of Grashof number over Reynolds number square. Under the high mass flux regime, the heat transfer deterioration will disappear for all the diameters from 5mm to 10mm. The different secondary flow patterns at different tube diameters are also studied.

Effects of Heater Orientations on the Natural Circulation and Heat Transfer in a Supercritical CO2 Rectangular Loop

“…For numerical method, indeed there have developed several kinds for supercritical fluid modeling in literature, including computational fluid dynamics models based on finite volume, or finite difference models [34,35], or lattice Boltzmann method [36] and others [37]. Following those studies, finite-volume method and a second-order upwind scheme are used to solve the model goveming equations.…”

Effect of Buoyancy on the Mechanism of Heat Transfer Deterioration of Supercritical Water in Horizontal Tubes

“…Kao et al [22] concluded that buoyancy effect and Prandtl number play important roles in heat transfer deterioration of supercritical water inside vertical circular tubes. Shang and Chen [23] investigated the diameter effect on heat transfer. For supercritical fluid calculation, the turbulence model undoubtedly plays a key role in the simulations and the model selection is controversial.…”

Towards the Utilization of Wet Biomass Gasification in Supercritical Water

“…The influence of buoyancy is often minimal for a very small diameter tube due to the small Richardson number (i.e. below unity) [124]. A Richardson number of lower than 0.087 is observed for the investigated cases, and therefore, the gravitational force can be neglected.…”

“…The natural convection plays an important role in a supercritical flow with low mass flux, see [102,123,124] for further information. The Grashof number can be applied to quantify the influence of buoyancy to the flow field.…”

“…The Grashof number approximates the ratio of buoyancy force that might happen because of the temperature gradient to the viscous force, and is shown in Eq 3.12. This dimensionless parameter is commonly used in conjunction with the Reynolds number [124]. A ratio of the Grashof number to the square root of the Reynolds number that is higher than unity represents a significant influence of the flow field due to buoyancy.…”