Diameter effect on the heat transfer of supercritical hydrocarbon fuel in horizontal tubes under turbulent conditions

This article presented a numerical investigation of supercritical heat transfer of hydrocarbon fuel in a series of horizontal tubes with different diameters. It has been carried out by solving Reynolds averaging equations of mass, momentum and energy with the LS low-Reynolds number turbulence model using the pressure-based segregated solver based on the finite volume method. For the purpose of comparison, a four-species surrogate model and a ten-species surrogate model of aviation kerosene RP-3 (Rocket Propellant 3) were tested against the published experimental data. In the current study, tube diameter varied from 2 mm to 10 mm and pressure was 3 MPa with heat flux to mass flux ratios ranging from 0.25 to 0.71 kJ/kg. It has been found that the buoyancy has significant effect on wall temperature non-uniformity in the horizontal tube. With the increase of diameter, the buoyancy effect enhances and the thermal-induced acceleration effect reduces. The buoyancy effect makes wall temperature at the top and bottom generatrices of horizontal tube increase and decrease, respectively. Due to the coupled effect of buoyancy and thermal-induced acceleration caused by the significant change of the properties, as diameter increases, heat transfer deteriorates dramatically at the top generatrix but remains almost unchanged at the bottom generatrix at high heat flux to mass flux ratio. Heat transfer enhancement is observed at low heat flux to mass flux ratio when tube diameter is less than 6 mm. Moreover, the safety analysis has been performed in order to optimally design the supercritical cooling system.