Abstract-Temperature profiles measured in mercury and the NaK eutectic are reported for vertical flow in pipes under conditions of constant heat flux, and it is shown that the mercury profiles are distorted by a superimposed free convection effect up to Reynolds numbers of at least 5000% A correlation is presented whereby the amount of distortion under given conditions may be estimated, and the shape of the undistorted temperature profile may be predicted. These profiles are used to determine the ratio of eddy diffusivities and the Nusseh number for liquid metals in the Reynolds number range 3 x lo4 to 3 x 105.
Vapor-liquid flow of a potassium-8% sodium mixture was studied with the use of o boiling heat transfer test loop. Pressure drop data were obtained from a 36-in. long, 0.495-in. I.D. unheated test section. Void fractions were measured at the midpoint of the test section with gamma ray attenuation.Flows were essentially frictional. Quality, total flow rate, and absolute pressure were the principal variables affecting the pressure drop results, which were correlated in terms of a two-phase friction factor. A metallic void fraction correlation was developed from previously reported data for other metollic fluids together with the potassium data of this study. The potassium two phase friction factors fall substantially lower than volues predicted by wellknown frictional pressure drop correlations. Metallic void friction values are appreciably lower than data for other fluid systems. Velocity slip ratios appear to be much higher than for other fluid systems due to high liquid-to-vapor density ratios and low void fractions.In recent years metallic fluids have received consideration as possible heat transfer media in space electrical power generation cycles which involve boiling and condensing of the carrier fluid. The rigorous designs required in such applications necessitate the ability to make highly accurate predictions of two-phase flow phenomena. Although a voluminous literature exists on the subject of two-phase fluid flow, little has been reported on flow of metallic systems. The two-phase pressure drop along a tube in general is the summation of losses due to friction, acceleration effects, and hydrostatic head. Two-phase values usually are greater than those experienced in singlephase flows with comparable fluid throughputs. Frictional losses are always present and occur for any orientation of the flow channel and for adiabatic or heated conditions. Acceleration losses occur in forced-circulation boiling flows, where the continuous phase chan e causes the mixin adiabatic flow at low pressure levels. Hydrostatic head terms are present only for vertical or inclined flow systems.Knowledge of the mean two-phase mixture density is necessary in prediction of acceleration losses and hydrostatic head. In vapor-liquid flow, the mean velocities of the two phases, based on the cross-sectional area of each, generally are not equal. Because of this "slip," the true fraction of the pipe cross section occupied by either phase differs from that calculated on the basis of the volumes of gas and liquid entering the tube. As a result, the mean mixture density cannot be calculated on the basis of quality (vapor mass fraction) alone, but requires a knowledge of the void fraction (fraction of the channel cross section occupied by vapor). Void fraction, then, is an important parameter in predicting the hydraulics of many two-phase flow systems, since without it the accelerative and hydrostatic contributions to the pressure drop cannot be evaluated.In this study, potassium two-phase pressure drop and void fraction data were obtained f...
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