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Abstract: In this paper we rely on the constructal law of maximization of flow access in order to construct a theory of geometry generation (selection, evolution) during molten droplet impact. We show that immediately after impact the liquid spreads inviscidly as a ring with a radial velocity that scales with the initial impact velocity. If the initial droplet is small and slow enough, the ‘splat’ comes to rest (dies) viscously, as a disc. If the droplet is large and fast enough, the ring splashes and is continued outward by needles that grow radially until they are arrested by viscous effects. We optimized the number of needles such that the total splash time is minimum. The theoretical dimensionless group that governs the selection of geometry (G) is the ratio of two lengths, the final radius of the disc that dies viscously, divided by the radius of the still inviscid ring that just wrinkles. Splats form when G ⩽O(1) and splashes are favored when G ⩾O(1). Experimental measurements reported in the literature confirm several of the features of the constructal development of splat vs. splash flow architecture. [Copyright &y& Elsevier]

Abstract: This paper deals with natural convection driven by combined thermal and solutal buoyancy forces in a binary fluid. The configuration under study is a confined enclosure partially filled with a vertical porous layer. The mathematical description of the problem is based on a one-domain formulation of the conservation equations. The set of numerical results presented here quantitatively shows the influence of the porous layer on the flow structure and on heat and species transfer in the enclosure. The paper is focused on the analysis of the influence of the characteristic parameters governing double diffusive convection, namely the ratios of solutal and thermal parameters: the diffusivities and the buoyancy forces. Heat and mass transfer is analyzed as a function of the permeability of the porous layer. It is shown that the coupling of the flow penetration in the porous layer with the combined buoyancy forces induces a specific behavior of the flow structure and average heat transfer in the enclosure. [Copyright &y& Elsevier]

Abstract: This paper presents the results of experimental tests carried out to investigate the performance of a household refrigerator using a phase change material (PCM). The PCM is located on the back side of the evaporator in order to improve its efficiency and to provide a storage capacity allowing several hours of refrigeration without power supply. The system has been tested with water and with a eutectic mixture (freezing point −3°C) and for a range of operating conditions (PCM thickness, ambient temperature, thermal load). The analysis of the results shows a significant improvement of the performance compared to a conventional system. [Copyright &y& Elsevier]

Abstract: Stability analyses of thermal and/or solutal natural convection in a configuration composed by a fluid layer overlying a homogeneous porous medium have been performed using different modeling approaches, especially for the treatment of the interfacial region. Comparisons between the one-domain approach and the two-domain formulation have shown important discrepancies of the marginal stability curves. This note shows that, according to Kataoka [I. Kataoka, Local instant formulation of two-phase flow, Int. J. Multiphase Flow 12(5) (1986) 745–758.], the differentiation of the macroscopic properties of the porous layer at the interface (porosity, permeability, thermal effective diffusivity) must be considered in the meaning of distributions. In that case, the one- and the two-domain approaches are shown to be equivalent and very good agreement is indeed found when comparing the results obtained with both approaches. [Copyright &y& Elsevier]

Abstract: This paper studies the effect of adding a phase change material (PCM) slab on the outside face of a refrigerator evaporator. A dynamic model of the vapour compression cycle including the presence of the phase change material and its experimental validation is presented. The simulation results of the system with PCM show that the addition of thermal inertia globally enhances heat transfer from the evaporator and allows a higher evaporating temperature, which increases the energy efficiency of the system. The energy stored in the PCM is yielded to the refrigerator cell during the off cycle and allows for several hours of continuous operation without power supply. [Copyright &y& Elsevier]

Abstract: This study deals with the onset of thermal natural convection in a system consisting of a fluid layer overlying a homogeneous porous medium. A linear stability analysis is carried out, using the so-called two-domain approach and including the Brinkman term in the porous region (2Ω DB). Results are systematically compared to those obtained using the one-domain approach (1Ω) and the classical Darcy formulation of the two-domain approach (2Ω D). A better agreement is found between the and 2Ω D neutral curves, than with the 1Ω curves, indicating that the inclusion of the Brinkman term plays a secondary role on the stability results. The different treatment of the interfacial region is discussed on the basis of these results. [Copyright &y& Elsevier]

Abstract: This paper deals with the macroscopic modeling and numerical simulation of columnar dendritic solidification of binary alloys. The macroscopic governing equations and associated effective transport properties were previously derived using a volume averaging technique with local closure. The macroscopic model takes into account the spatial variation of the pore-scale geometry within the mushy zone, which leads to additional terms involving porosity gradients. The second important feature concerns solute mass conservation, which is described by considering a macro-scale non-equilibrium accounting for chemical exchanges at the solid–liquid interface. A simplified version of the model is validated through a comparison of the numerical solution to three experiments available in the literature. Porosity extra terms are systematically estimated on the basis of these numerical simulations, and the influence on solidification of effective transport properties such as permeability and interfacial solute exchange coefficients is investigated. [Copyright &y& Elsevier]

This study deals with the experimental analysis of double diffusive effects on the solidification process of a binary mixture. Solidification experiments from a horizontal plate heat exchanger are performed in a cavity filled with a hypoeutectic NH4Cl–H2O solution. Solute redistribution at the interface creates concentration gradients in the fluid phase and a dendritic front growth is expected. We analyze the influence of solute rejection on the equilibrium conditions at the solid–liquid interface, on the solidification front kinetics and on the solid structure. Local front temperature measurements and estimation of the solid fraction of the growing solid allow us to quantitatively analyze the coupled influence of solute rejection and solid fraction on the front growth. A simplified numerical analysis shows that the role played by these two phenomena is very weak in the range of parameters under study. [Copyright &y& Elsevier]

This paper presents experimental results concerning the solidification of a binary aqueous solution flowing along a cold surface. Forced convection in the liquid phase is assumed to dominate over possible natural convection effects at the interface and the influence of the initial solute concentration is analyzed. Solute rejection at the interface is shown to influence the equilibrium temperature at the solidification front and the time evolution of the solid phase. Comparison with the numerical solution of a simple thermal phase change model shows that the solidification dynamics is compatible with a porous structure of the solid phase (solid fraction about 0.90), accounting for dendritic structure at the microscale. [Copyright &y& Elsevier]

The momentum balance at the interface between a liquid and a porous substrate is investigated for a configuration with forced flow parallel to the interface. An heterogeneous continuously varying transition layer between the two outer bulk regions is introduced. The stress jump coefficient earlier introduced in the jump interface condition is here derived as an explicit function of the variations of the velocity and effective properties of the transition layer. Agreement is found between our numerical results based on the single-domain approach and the existing ad hoc estimates in the literature. Further advantages of this non-homogeneous analysis are also provided. [Copyright &y& Elsevier]

A macroscopic model for solidification of pure metal in porous media is derived using the volume averaging method. Solidification starts when the infiltration of the porous mould is completed and therefore the phase change problem involving three phases (liquid and solid metal, mould) is governed by diffusion. The upscaled model is first characterized by the local thermal equilibrium assumption (LTE) between the liquid and the solid metallic phases leading to one energy conservation equation for the equivalent metallic phase. On the other hand, local thermal non-equilibrium (LTNE) between the equivalent continuous metallic phase and the mould is considered, giving rise to two coupled energy conservation equations. The associated closure problems are derived and numerically solved allowing for the determination of the effective transport properties. Numerical solutions of the macroscopic model are qualitatively compared with available experiments. [ABSTRACT FROM AUTHOR]

Abstract: A one-dimensional model has been developed to address the non-equilibrium heat transfer between an alumina lamella deposited by plasma spraying, and a steel or alumina substrate. The model includes under-cooling phenomenon, heterogeneous nucleation and crystal growth kinetics, allowing for the prediction of the temperature evolution in the lamella and substrate and of the nucleation temperature, grain density and size distribution. The effect on the nucleation process of the contact angle between the nucleus and substrate surface and of the quality of the contact at the splat–substrate interface is emphasized. The influence of the splat thickness, substrate material and substrate oxidation on the grain size distribution is also discussed. [Copyright &y& Elsevier]

Abstract: This call describes a numerical comparison exercise for the simulation of ingot solidification of binary metallic alloys. Two main steps are proposed, which may be treated independently: 1. The simulation of the full solidification process. First a specified ‘minimal’ solidification model is used and the contributors are provided with the corresponding sets of equations. The objective is to verify the agreement of the numerical solutions obtained by different contributors. Then different physical solidification models may be compared to check the features that allow for the best possible prediction of the physical phenomena. 2. A separate preliminary exercise is also proposed to the contributors, only concerned with the convective problem in the absence of solidification, in conditions close to those met in solidification processes. Two problems are considered for the case of laminar natural convection: transient thermal convection for a pure liquid metal with a Prandtl number on the order of 10−2, and double-diffusive convection in an enclosure for a liquid binary metallic mixture with a Prandtl number on the order of 10−2 and a Lewis number on the order of 104. [Copyright &y& Elsevier]

This paper deals with the derivation of the macroscopic momentum transport equation in a non-homogeneous solidifying columnar dendritic mushy zone using the method of volume averaging. One of the originalities of this study lies in the derivation of an associated closure problem for the determination of the spatial evolution of the effective transport properties in such a complex situation. In this analysis—where the phase change has been included at the different stages of the derivation—all the terms arising from the averaging procedure (geometrical moments, phase interactions, interfacial momentum transport due to phase change, porosity gradients, etc.) are systematically estimated and compared on the basis of the characteristic length-scale constraints associated with the porous structures presenting evolving heterogeneities. For dendritic structures with “moderate” (but not small) evolving heterogeneities, we show that phase change and non local effects could hardly affect the determination of the permeability and inertia tensors. Finally, a closed form of the macroscopic momentum equation is proposed and a discussion is presented about the need to consider inertia terms and the second Brinkman correction (explicitly involving gradients of the liquid volume fraction) in such non-homogeneous systems. [Copyright &y& Elsevier]