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

Abstract

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.

Turbulent heat transfer characteristics of supercritical n ‐decane in a vertical tube under various operating pressures

“…Then the inner wall temperature decreases sharply, and it shows a normal pattern to grow finally. Such a phenomenon is called as a heat transfer deterioration . It is noted that the inner wall temperature decreases acutely because of the outlet effect.…”

“…Correspondingly, the shear stress between the flow layers is reduced, and the turbulent kinetic energy is also decreased. Consequently, the heat transfer is compromised, and further, the phenomenon of heat transfer deterioration appears . For the operating pressures of 4 and 5 MPa, there is no obvious M‐type velocity distribution and the velocity profile is the typical one for forced convective distribution.…”

“…However, the effect of hydrocarbon fuels at various conditions on heat transfer characteristics gets more attention with the development of scramjet engines . A scramjet engine always flies at a Mach number of 6‐10, and correspondingly, it may be ablated without thermal protection . Up to now, the regenerative cooling technique is considered as an effective way to overcome this problem .…”

“…Sun et al numerically studied the buoyancy effects at different conditions of the inlet flow direction, heat flux, and tube diameters, and the results showed that the buoyancy plays an important role at the conditions of a low inlet flow velocity, a high surface heat flux, and a large tube diameter. Cheng et al used various tube diameters to explore numerically the heat transfer of supercritical hydrocarbon fuel, and they stated that a larger tube diameter develops the buoyancy effect but diminishes the effect of thermal‐induced acceleration. From now onwards, horizontal tubes are no longer considered because the vertical tube is studied in the current paper.…”

“…6 A scramjet engine always flies at a Mach number of 6-10, and correspondingly, it may be ablated without thermal protection. [18][19][20] Up to now, the regenerative cooling technique is considered as an effective way to overcome this problem. 21 The hydrocarbon fuels are refrigerating media in regenerative cooling systems.…”