Ryoji Ishiguro

Sodium Evaporation into a Forced Argon Flow, (I) Measurements of Evaporation under Condition of Fog Formation

Abstract Measurements were made on the rate of evaporation from a rectangular-shaped free surface of liquid sodium into argon flow. Tests were carried out at various levels of sodium temperature, of argon velocity and of argon temperature, under conditions where fog formation could be expected. To gain information on the enhancement of evaporation occasioned by fog formation, a supplementary experiment was performed on convection heat transfer into flowing air from a heated plate of the same geometry as the free surface of the sodium in the preceding measurements. The values obtained for the rate of evaporation and Sherwood number were compared with those predicted by the heat transfer experiment and by the theory by Hill & Szekely. The overall results revealed that the rate of sodium evaporation can amount to as much as three times that predicted by the heat transfer experiment, and that it varies roughly linearly with the heat transfer rate and with the sodium vapor pressure prevailing at the free surface.

Application of Galerkin finite element method to subchannel analysis. II: Unsteady-state two-phase flow

Up to now, the finite difference method has been used in the two-phase flow thermal-hydraulic analysis of the reactor core and also in analyses of other thermal apparatuses. AS a replacement for this method, the Galerkin finite element method was used in the present study for the purpose of understanding the characteristics of the method and its application to the subchannel analysis. This method is expected to give more accurate solutions and better calculation efficiency. Moreover, it can be applied to various problems including multi-dimensional thermal-hydraulic analysis. The present paper treats, as an example, unsteady-state two-phase flow analysis, and compares the accuracy of calculation between the Galerkin finite element method and the usual finite difference method.

Simulation of Potassium Condensation by DSMC Method.

The evaporation and condensation phenomena of alkali metals are not correctly described by the analysis using the continuum equations, because discontinuity of physical quantities such as temperature at the vapor-liquid interface occurs in the phase change process. The authors apply the direct simulation Monte Carlo (DSMC) method, which is based on the molecular gas dynamics, to the problem of potassium condensation. The simulation results are found to be in excellent agreement with the experimental results previously reported by two of the authors, when the condensation and evaporation coefficients are set to unity. It is also confirmed that a slight shift of evaporation and condensation coefficients from unity considerably changes the simulation result so that it disagrees with the experimental data. The authors conclude from these results that the direct simulation Monte Cairo method is very useful to predict the phase change problems of alkali metals.

Combined convective heat transfer of liquid sodium flowing across tube banks Examination with single row of tube normal to flow in direction of gravity.

In order to clarify the heat transfer characteristics of combined convection of liquid sodium, a numerical analysis is performed for liquid sodium which flows through a single horizontal row of tubes in the direction of gravity. The correlation of heat transfer char- acteristics between liquid sodium and ordinary fluids is also discussed.The heat transfer characteristics at large Reynolds numbers are improved when the Richardson number is increased, and the improvement rate is enlarged with increase in p/d value, since convection effect is relatively large. However heat transfer coefficients do not differ from those of forced convection at small Reynolds numbers even when the Richardson number reaches a high value bacause of conduction effect. A good consistence of heat transfer characteristics of combined convection between liquid sodium and air is obtained at the same Peclet number and Richardson number, This means that the fundamental heat transfer characteristic of combined convection of liquid sodium can be investigated with ordinary fluids.

Flow patterns and heat transfer mechanism of circular closed thermosyphons.

Measurements of the heat transfer and the visualization of the flow are carried out on vertical closed and open thermosyphons using water and ethylene glycol as a working fluid. The sizes of the closed thermosyphons are 10 and 20 mm in radius and 300 mm in length, and that of the open thermosyphon is 20 mm in radius and 150 mm in length. The present Nusselt number and flow pattern of the closed thermosyphons are compared with those of the open thermosyphon and the experimental and theoretical Nusselt numbers of the closed thermosyphon by Bayley et al.. The Nusselt number of the closed thermosyphons significantly decreases for the predominant flow of the conduction mode and the weak flow of the convection mode in the coupling region. The fraction of the flow of the convection mode is usually small and sensitively varied with the change of the tube diameter and the Rayleigh number for the range of diameter from 20 to 50 mm. This is the reason that the present Nusselt number of the closed thermosyphons is quite small, as compared with that of an open thermosyphon, and smaller than the other sources of data.

Natural Convection Heat Transfer from a Horizontal Cylinder to Liquid Sodium

The objective of the present study is to clarify the heat transfer characteristics of laminar natural convection around a horizontal circular cylinder immersed in liquid sodium. We show at first that the Boussinesq approximation is more applicable to sodium than to air with a good accuracy. The Boussinesq-approximated Navier-Stokes and energy equations are solved by using a finite-difference method. The following correlation equation is obtained from the present numerical results:ln Nu=0.172+0.164 ln GrPr2+0.003 (ln GrPr2)2, (104≤Gr≤109). It is found from the comparison with the present results that previous correlation equations predict lower value than the present one.

Heat transfer performance of liquid sodium open thermosyphons.

Experimental studies are carried out on the heat transfer of open circular thermosyphons (the radius of length to radius are 6 and 10) using liquid sodium. The Nusselt numbers (Nur) measured for liquid sodium are plotted against the Rayleigh number (Rar) and the product of the Rar and Prandtl number (Pr). These results cover a range of Rar from 4×102 to 1.7×105 or Rar·Pr from 10 to 9.5×103 and are compared to the previous results of mercury. It is shown that the arrangement of Nur against Rar·Pr is more appropriate than that against Rar. The heat transfer of open thermosyphons for liquid sodium and mercury shows similar characteristics. The effect of convection flow on Nur becomes significant over about 60 Rar·Pr.

Sodium Evaporation into a Forced Argon Flow, (II): Comparison between Experimental Results and Theoretical Predictions by Critical Supersaturation Model

The critical supersaturation model (CSM) was examined by comparing its predictions with the experimental data of the forced evaporation of sodium reported in Part (I) of this series of papers. The results revealed that the CSM predicted a fairly lower Sherwood number than that predicted in the experiment. This discrepancy may be due mainly to the oversimplified assumptions in the CSM. A calculation of the fog movement in a boundary layer was also attempted by taking into account the force on fog particles by thermophoresis. The calculation showed that the particles were submerged deeply in the boundary layer and that they absorbed sodium vapor in accordance with their size. It was concluded that the fog movement in the boundary layer was essentially important for the exact estimation of the evaporation rate.