[en] Under severe reactor accident scenarios, pools of molten core material may form in the reactor core or in the hemispherically shaped lower plenum of the reactor vessel. Such molten pools are internally heated due to the radioactive decay heat that gives rise to buoyant flows in the molten pool. The flow in such pools is strongly influenced by the turbulent mixing because the expected Rayleigh numbers under accidents scenarios are very high. The variation of the local heat flux over the boundaries of the molten pools are important in determining the subsequent melt progression behavior. This study reports results of an ongoing effort towards providing a well validated mathematical model for the prediction of buoyant flow and heat transfer in internally heated pool under conditions expected in severe accident scenarios

No abstract available

[en] An analysis of multidimensional melting is performed which takes account of natural convection induced by temperature differences in the liquid melt. Consideration is given to the melt region created by a heated vertical tube embedded in a solid which is at its fusion temperature. Solutions were obtained by an implicit finite-difference scheme tailored to take account of the movement of the liquid-solid interface as melting progresses. The results differed decisively from those corresponding to a conventional pure-conduction model of the melting problem. The calculated heat transfer rate at the tube wall decreased at early times and attained a minimum, then increased and achieved a maximum, and subsequently decreased. This is in contrast to the pure conduction solution whereby the heat transfer rate decreases monotonically with time. The thickness of the melt region was found to vary along the length of the tube, with the greatest thickness near the top. This contrasts with the uniform thickness predicted by the conduction solution. These findings indicate that natural convection effects, although unaccounted for in most phase change analyses, are of importance and have to be considered

[en] A control-volume based finite element method has been used in conjunction with equal order interpolation for pressure and velocity for the calculation of fluid flow in ducts with irregular geometries. The partially parabolic approximation to the equations of motion used in the study incorporated downstream pressure effects; hence flows with strong variations of pressure in the cross-section are predicted accurately. Test problems are presented to demonstrate the viability of the proposed method

[en] This report describes a general numerical procedure for the calculation of steady/unsteady, single-phase/two-phase, three-dimensional fluid flow. The procedure is based on the control-volume approach, which enables the derivation of physically meaningful finite-difference equations. The conservation equations employed are based on a two-fluid model. This permits the analyses of nonhomogeneous and nonequilibrium flow conditions. In addition, surface permeabilities and volume porosities are included in the finite-difference formulations to account for dispersed solid objects in a flow domain. The derivation of the equations and the required iteration scheme are presented, and flow charts are provided for the planning and design of a computer program

[en] Combined free and forced convection in vertical annular passages is important in the design of coolant channels for power transformers, nuclear reactors, double-pipe heat exchangers, certain types of catalytic converters, and modern electronic equipment. Although most such equipment is designed to operate in a turbulent flow regime, laminar flow and heat transfer become important when the equipment operates under reduced power or during accidental pump failure. This paper presents a numerical study of laminar, fully developed mixed convection in vertical eccentric annular ducts. The equations governing the velocity and temperature are solved on a body-conforming grid by using a finite-volume technique. The effects of radius ratio, eccentricity, and Rayleigh number on the friction factor and the Nusselt number are discussed. The buoyancy forces significantly increase both friction and heat transfer. The effect of buoyancy is stronger for configuration with larger eccentricities

[en] A review is presented which survey results published in various fields of heat transfer during 1975, and which includes over 650 references. (U.K.)

No abstract available

[en] Several new methods of computing radiation heat transfer have emerged in recent Years, and thorough testing is often required to validate these. Monte Carlo methods can provide exact solutions within statistical limits, hence are attractive for validation purposes. Unfortunately, many Monte Carlo solutions currently available in the literature are not useful for testing new solution techniques for complex geometries, because they either treat simple cases or application-specific irregular geometries. The intent of this paper is to provide solutions of general interest for two-dimensional irregular geometries using the Monte Carlo method. The paper presents radiative heat flux solutions for three enclosures with absorbing, emitting, and anisotropically scattering medium. 8 refs., 6 figs

[en] A calculation procedure is described for the class of flows in which the flow domain contains numerous dispersed solid objects such as tubes or rods. The central idea is to treat the solid objects as distributed resistances to flow and heat transfer. The calculation procedure is illustrated by an application to a steam generator of a nuclear power plant. The three-dimensional flow field and the enthalpy distribution are calcualted. Since details of the thermal-hydraulic behaviour of the steam generator can thus be inexpensively predicted, the procedure can be useful to designers. (orig.)