The Distortion of Turbulent Velocity and Temperature Profiles on Heating, for Mercury in a Vertical Pipe

Abstract

Measurements were made in mercury, for turbulent flow and constant flux heating in a vertical pipe, in order to determine the extent to which the velocity and temperature distributions are affected by buoyancy forces. With increasing heat flux, velocity profiles at Reynolds numbers of 20,000 to 60,000 were found to be markedly distorted in comparison with the isothermal velocity profile. Even very low heat input caused significant distortion, while at high heat input a limiting profile shape was approached, with the center velocity well below the mean and the maximum occurring in the vicinity of the wall. Eddy diffusivities of heat and momentum calculated from the measured profiles exhibit a considerable variation with heat input, indicating that buoyancy forces not only change the radial shear stress distribution but also alter the nature of the turbulence in the pipe.

Mixed-Convection Heat Transfer to Sodium in a Vertical Pipe

“…Buoyancy-opposed mixed-convection data for water [33]. 73 data have been presented [6][7][8]. The behavior observed is similar to that for moderate-Prandtl-number fluids, such as water or air: Heat transfer is impaired with modest buoyancy influences but recovers as buoyancy forces are increased.…”

“…That comparison also shows the inconsistency between the data of Kowalski [8) and that of Buhr et al [6) and Jacoby [7). Kowalski reported a large impairment of heat transfer due to buoyancy for Reynolds numbers of about 90,000 accompanied, rather surprisingly, by only minor distortion of velocity profiles.…”

“…Mixed convection can arise in fast reactors during fault or shutdown conditions, and it can also be the normal mode of heat transfer in components such as cold traps, where mean velocities are low. Previous experimental investigators have used NaK [2][3][4], mercury [4][5][6][7][8] (which has a similar Prandtl number to that of NaK), and sodium [3,[9][10][11], in pipes [2][3][4][5][6][7][8], a rectangular channel [9], and heat exchangers [10,11]. In assessing the data the considerable difficulties inherent in the measurement of liquid metal heat transfer should be noted.…”

“…All of the experiments with mercury [4][5][6][7][8] have involved the study of turbulent upward flow in passages that were heated electrically. In each case the primary objective appears to have been to obtain information on the distortion of velocity and temperature profiles by buoyancy forces, although some heat transfer .…”

Thermal behavior in a 180-deg turned channel with the perforation divider under rotational condition

“…In a rotating heated duct, the high rotational speed and the temperature gradient change in operating fluid result in different densities in fluid as well as buoyancy. As for the effect of buoyancy on the mixed convection, Metais and Eckert [1], Brundrett and Burroughs [2], Buhr et al [3], and Abdelmeguid and Spalding [4] found that in case of outward flow, the buoyancy effect would reduce the heat transfer of laminar flow, and increase the heat transfer of turbulent flow; however, in case of inward flow, the buoyancy effect could increase both the heat transfer rates of laminar and turbulent flows. Following studies [5][6][7][8][9][10][11] focused on the influences of the geometric configuration of flow channel and the rotation on the fluid flow and heat transfer characteristics.…”