ANALYTICAL AND EXPERIMENTAL STUDY OF COMBINED FREE AND FORCED CONVECTION IN TURBULENT LIQUID METAL PIPE FLOW
Abstract
This research consisted of an investigation of the effect of buoyancy on the profiles of mean and turbulent quantities for flow of mercury in a vertical heated pipe. To accomplish this goal, this work was divided into three parts: an Algebraic Stress Model of turbulence was extended to liquid metal flow, the model in a simplified form was applied to the geometry in question, and limited experimental work was performed to obtain a wall boundary condition specification for the equation for the one-half of the variance of temperature fluctuations, g(' )=(' )(theta)('2)/2. The modeled equation for the turbulent kinetic energy, k, the rate of turbulent energy dissipation, (epsilon), and the Reynolds stresses, u(,i)u(,j), were taken from the literature. The modeling of the thermal field was extended to account for Pr << 1 by making use of suggested forms for the dissipative correlation in the u(,j)(theta)-equation, and for the dissipative and turbulent diffusive terms in the g-equation. The model was written in its thin shear layer form and embodied in the STAN5 computer code. The required reprogramming consisted in a new treatment for the source terms for all turbulent quantities, implying a new set of coefficients for the finite difference equation. In order to provide a data base for wall boundary condition specification for the g-equation, data for the temperature fluctuations were obtained for the near wall region (y('+) < 100) for 30,000 < Re < 60,000 and 1.0 x 10('-6) < Ra < 1.0 x 10('-3). Temperature fluctuations were also measured in the pipe core region for the same experimental conditions, and the results were found to be in agreement with previous work in the same facility. The numerical results for isothermal mean and turbulent flow were found to be in agreement with experimental data for mercury and air. Non-isothermal results for the time-averaged flow were qualitatively in agreement with existing data. Results for the turbulent parameters for heated flows are more difficult to evaluate due to lack of measurements under these conditions. Nevertheless, the initial damping and posterior enhancement of turbulent transfer as the Ra/Re('2) increases is well predicted. The reversal of axial turbulent heat flux, as measured in several experiments in buoyancy affected flows, is calculated. The predicted dependence of the Nusselt number with increasing Ra/Re('2) is in agreement with the measurements in liquid metals. The friction factor, f, is also shown to be affected by buoyancy.
Degree
Ph.D.
Subject Area
Nuclear physics
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