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Using extensive molecular dynamics simulation of a coarse-grained model, we demonstrate the possibility of sustained unidirectional motion (durotaxis) of droplets without external energy supply when placed on a polymer brush substrate with stiffness gradient in a certain direction. The governing key parameters for the specific substrate design studied, which determine the durotaxis efficiency, are found to be the grafting density of the brush and the droplet adhesion to the brush surface, whereas the strength of the stiffness gradient, the viscosity of the droplet, or the length of the polymer chains of the brush have only a minor effect on the process. It is shown that this durotaxial motion is driven by the steady increase of the interfacial energy between droplet and brush as the droplet moves from softer to stiffer parts of the substrate whereby the mean driving force gradually declines with decreasing roughness of the brush surface. We anticipate that our findings indicate further possibilities in the area of nanoscale motion without external energy supply.

•In-house experiments on a PCM-integrated roof artificially subjected to hot climatic conditions have been carried out.•A RC model to capture heat transfer in PCM-integrated structures was developed.•RC model validated with the in-house experiments and numerical simulations.•Illustrative applications of the RC model to study the performance of a PCM encapsulated roof are shown.

In this study the delicate invasion nature of pure supercritical carbon dioxide sCO2, alongside the determination of the main boundaries for sCO2flow-pattern transitions inside the nanopores of treated 3D-porous matrix are investigated numerically. Sensitivity parameters under various sCO2injection rates and flow regimes are discussed. The numerical outcomes are relied on MRT-Lattice Boltzmann method utilized in this study, while unyielded zones and inactive pores are identified by 3D voxels. The structural complexity of near-spherical porous matrices is addressed to study the flow behaviors of sCO2. This micrometer media followed a spherical approach with a studied random arrangement. The lengths of the computational domain in transverse directions were set to be five times as long as the highest diameter dpof the solid matrix, (highest dp=50 nm), while the longitudinal direction was set to be 40 times dp. The simulations are carried out for a wide range of initial sCO2velocities, which adimensionally denoted by Reynolds values. As well, unsteady-state flow regimes are adopted for precise interpretations of complex flow patterns and interactions in the nanopores. This numerical methodology allowed the study of the injection boundaries toward each flow regime of sCO2inside the complex porous structure. Based on the above analysis, a primary flow-pattern chart is established for the invasion of sCO2.

This work presents a numerical study on the performance of a stand-alone adsorption cooling system based on the silica gel/water couple driven by hybrid photovoltaic/thermal (PVT) collectors. This system is intended for the conservation of perishable agricultural products which require air-conditioned premises to preserve them. The weather conditions are those of North Africa (Algiers). Considering the above, this paper aims at analyzing the PVT-Adsorption system with energy storage to guarantee a stabilized production and increase the solar coverage. trnsys was used to simulate the system taking into account hourly series of irradiation and ambient temperature covering one year. The performance study reveals that the DualSun PVT hybrid collectors used provide optimal annual production and that the adsorption cooling system offers more reliable production during summer. The temperature difference between the inside and outside of the cooled enclosure balances supply and demand. The loss analysis of the storage device indicates that losses depend, on the one hand, on the interior/exterior temperature difference of the storage tank with more significant values during the summer season. On the other hand, the losses also depend on the volume of the storage tank which was optimized in order to limit the heat exchange with the surroundings.

AbstractThe present work deals the heat and mass transfer generated in horizontal partially porous enclosure. The vertical walls are subjected to of uniform conditions of temperature and concentration whereas the horizontal walls are assumed to be adiabatic and impermeable. The set of equations describing the double diffusive convection are solved numerically using the numerical control volume approach. The numerical results are presented and analyzed in terms of streamlines, isotherms, isoconcentrations lines and for the average Nusselt and Sherwood numbers.

The present work deals the heat and mass transfer generated in horizontal partially porous enclosure. The vertical walls are subjected to of uniform conditions of temperature and concentration whereas the horizontal walls are assumed to be adiabatic and impermeable. The set of equations describing the double diffusive convection are solved numerically using the numerical control volume approach. The numerical results are presented and analyzed in terms of streamlines, isotherms, isoconcentrations lines and for the average Nusselt and Sherwood numbers.

The present work aims to study convection and heat transfer and mass in a porous cubic cavity. The configuration considered is a cavity cube with vertical walls left and right are subjected to temperatures required while others are impermeable and adiabatic. We realized that the results depend on several characteristic parameters, and general correlations are established for the calculation of heat and mass transfer, according to various studied parameters. The study focuses on the influence of the control parameters on the structure of the flow, heat and mass transfer.

Concrete pumpability is determined by the friction at the interface between the concrete and the wall of the pumping pipes (which are generally made of steel); called the concrete–steel interface. This friction is related directly to the thickness and composition of the boundary layer (BL) that occurs during the movement of fresh concrete in a pipe. These BL characteristics are rigorously linked with concrete composition parameters. To highlight this complicated relationship, an apparatus called a ‘tribometer’ was used in two experimental programs. This apparatus allows measurement of the steel–concrete interface friction and deduction of interface parameters (also called the pumping parameters), namely viscous constant and interface yield stress. The first program focuses on the effect of the concrete composition on pumping parameters, and the second program focuses on the relationships between the concrete composition and the BL composition. The results of the first program show that increases in cement paste volume, water/cement ratio and super-plasticiser dosage enhance concrete pumpability. Increased content of fine sand in concrete induces negative effects on the interface frictions and on the pumpability. The results of the second program show that the BL is formed by water, cement and fine sand particles with a diameter lower than 0.25 mm. It also shows that the proportions of water and cement volume in BL and micro-concrete (concrete with the largest grain diameter lower than 0.25 mm) are almost the same. The relative enrichment produced by fine sand in the BL decreases with increasing proportion of fine sand volume in the concrete.La pompabilité d’un béton est déterminé par le frottement à l’interface entre le béton et la paroi des tuyaux de pompage généralement en acier (appelé l’interface béton-acier). Ce frottement est relié directement à l’épaisseur et la composition de la couche limite (note BL) formée au cours d’écoulement du béton frais dans un tuyau de pompage. Ces caractéristiques de la BL sont rigoureusement liées avec les paramètres de composition du béton. Afin de mettre en évidence cette relation complexe, les auteurs ont utilisé dans ses deux programmes expérimentaux son appareil, qui a été récemment développé, appelé ‘tribomètre’. Cet appareil permet de mesurer les frottements à l’interface béton - acier et d’en déduire les paramètres d’interface (appelé aussi les paramètres de pompage), à savoir la constante visqueuse et le seuil d’interface. Le premier programme se focalise sur l’influence des paramètres de composition du béton sur les paramètres de pompage et le deuxième programme se focalise sur la relation entre la composition du béton et la composition de la couche limite. Les résultats du premier programme montrent que l’augmentation du volume de pâte, du rapport eau/ciment et du dosage en super-platifiant favorise la pompabilité du béton. L’augmentation du dosage en sablon substitué au sable de béton induit des effets négatifs sur les frottements et sur la pompabilité. Les résultats du deuxième programme prouvent que cette couche est constituée de l’eau, du ciment et des particules fines de sable du béton dont le diamètre est inférieur à 0,25 mm. Ils montrent également que la proportion volumique de l’eau et du ciment de la couche limite et du micro – béton (béton avec le plus grand diamètre des grains inférieur à 0,25 mm) sont presque identiques. L’enrichissement relatif en sable fin dans la couche limite diminue avec l’augmentation de la proportion volumique des fines de diamètre inférieur à 0,25 mm dans le sable béton.

The performance of the hybrid wall powered by solar energy was numerically simulated. The factor of H/W was discussed The performance parameters include the induced air mass of the outlet, the induced air velocity of the outlet and the temperature difference between the inlet and the outlet. The results show that ratio of H/W has an important effect on the performance of the hybrid wall powered by solar energy. The induced air mass of the outlet is decreased linearly with the ratio of H/W in a logarithmic coordinate. The temperature difference between the inlet and the outlet increases with the increasing of the ratio of H/W. But for the induced air velocity, it increases with the increasing of the ratio of H/W, and when the ratio is higher than 10, it decreases with the increasing of the ratio of H/W.

The present study deals with a compression-absorption machine. The proposed hybrid cooling system uses water-ammonia as a working fluid and operates at three pressure levels. The absorber is at an intermediate pressure (Pint) taken between the evaporator pressure (PEV) and the condenser pressure (PCD), unlike the single stage machine which works between two pressure levels. The proposed new system is studied and compared to the conventional machine. In order to evaluate the performance of the invoked machine, a procedure based on the MAPLE software is set up to compute accurately the thermodynamic properties of the working fluid. The analyses of the numerical results highlight that the performance of the novel proposed configuration is better than that relative to the conventional system. The study reveals the great impact of the intermediate pressure on the performance improvement and on reducing the generator temperature allowing the system to work at low enthalpy. In fact, for an evaporator temperature and a condenser temperature fixed respectively at -10°C and 40°C, the proposed hybrid refrigeration cycle operates at a generator temperature TGE = 75°C and the installation’s COP is about 0.56. While for the same conditions, the single stage machine COP cannot exceed 0.51 with a generator temperature of about 135°C. Consequently, our enhanced novel configuration presents the opportunity to operate at low enthalpy sources.

A numerical study of the behavior for a finite porous journal bearing lubricated with Newtonian fluid is undertaken considering both thermal and piezo-viscous effects. The modified Reynolds equation is obtained by using the thermo-hydrodynamic aspect to account for the viscous variation versus pressure and temperature where Barus law has been used for the visous formulation. To determine the flow in the porous media, the Darcy’s law has considered. The governing equations were solved numerically using a finite difference approach. Obtained results compared with the case of a thermo-viscous aspect, the piezo-viscous parameter increases the load carrying capacity significantly and improves the characteristics of the journal bearings.

The primary aim of this study is to simulate numerically the heat and mass transfer characteristics in the annular adsorber that is the most important component of the solar cooling machine, and to evaluate the solar and thermal coefficients of performance as an optimisation criterion of the system, for different adsorbent/adsorbate pairs. The porous medium constituted of the adsorbent/adsorbate is contained in the annular space and it is heated by solar energy. A general model equation is used for modeling the transient heat and mass transfer. The adsorption phenomenon is described by using different models of solid-adsorbate equilibrium. Effects of the key parameters on the adsorbed quantity, the generating temperature, the performance coefficients and thus on the system performances are investigated.

We present the results of an experimental investigation of the evaporation of a liquid meniscus in a high aspect ratio micro-channel. The study investigates evaporation rates of a stationary liquid meniscus in a high aspect ratio microchannel, the wall of which is electrically heated using transparent resistive coating. Four different liquids are used as working fluids. We report on the dependence of the measured overall evaporation rate on the applied power. The results indicate, and consistently, that the evaporation rate increases with the applied power then peaks before declining. In order to gain insight into these results, we used thermographic infra red imaging to map the temperature field on the external wall of the microchannel. The measurements show that there is a good correlation between the maximum in the evaporative rate and the onset of instabilities of the interface. These instabilities, to our mind, are induced by an increasing temperature gradient along the microchannel wall around the three phase contact line region. These instabilities are revealed by a high speed camera used to record the behaviour of the interface during evaporation.

AbstractThe friction at the steel-concrete interface on the boundary layer that occurs during the flow of a fluid concrete in a drain plays an important part in its pumpability. These frictions are directly related to the composition of the formed boundary layer which depends on the concrete composition parameters. In order to highlight the relationship between concrete composition and friction interface, the authors initially developed and validated an apparatus called tribometer allowing them to make steel-concrete interface friction measurements and deduce interface parameters. Its' simple use at building sites enabled the authors to study the influence of the concrete composition on the resulting interface friction and its parameters, namely, viscous constant and interface yield stress. The results show that the increase in the cement paste volume, the water per cement ratio and the proportioning in superplasticizer support the concrete pumpability. The increase of the fine sand quantity in concrete induces negative effects on the interface frictions and on pumpability.

The present study deals with a solid adsorption refrigerator analysis using activated carbon/methanol pair. It is a contribution to technology development of solar cooling systems. The main objective consists to analyse the heat and mass transfer in an annular porous adsorber that is the most important component of the system. The porous medium is contained in the annular space and the adsorber is heated by solar energy. A general model equation is used for modelling the transient heat and mass transfer. Effects of the key parameters on the adsorbed quantity, the coefficient of performance, and thus on the system performance are analysed and discussed.

A 3D numerical analysis is carried out to investigate heat and mass transfer in a partly porous cavity of high aspect ratio. The goal is to determine the best physical and geometrical parameters that allow optimal heat and mass transfer rate in such domain used in a solar adsorption cooling system. The computational domain consists of a tall cavity heated on the left vertical wall and cooled on the opposing wall. The SIMPLE algorithm is used to handle the velocity pressure coupling. Simulation results allow determining the optimal configuration of the used porous substrate and plain fluid position in the cavity in order to optimize the performance of such solar adsorption cooling installation.

In this work the influence of thermal effects on the performance of a finite porous journal bearing has been investigated using a thermo-hydrodynamic analysis. The Reynolds equation of thin viscous films is modified taking into account the oil leakage into the porous matrix, by applying Darcy’s law to determine the fluid flow in the porous media. The governing equations were solved numerically using the finite difference approach. Obtained result show a reduction in the performance of journal bearings when the thermal effects are accounted for and, this reduction is greater when the load capacity is significant.

This paper presents a numerical study of mixed convection heat and mass transfer in horizontal rectangular channels partially filled with porous medium. The main contribution of this research is to characterize how the porous block will create a heterogeneity that will induce a change on the Poiseuille-Rayleigh-Benard (PRB) fluid circulation dynamics. For a broad range of dimensionless parameters, which control the mixed convection, we show that the effect of the insertion of the porous block changes the thermal and solutal boundary layers; we find that the exchanges are intensified near the sidewalls in the porous region compared to upstream and downstream of the porous medium; and inversely in the core region. We describe, also, the onset of the longitudinal rolls at both upstream and downstream of the porous region. And finally, we compared the heat transfer, for different positioning of the porous medium with the purely fluid mixed convection.

Salinity currently has the highest priority of all environmental issues nowadays. The only means of preventing the development of soil salinity was combining leaching and artificial drainage. Recently a new method of capturing and removing salt from the soil surface called a dry drainage method [1-4] has been studied (fig.1) to help arid soils prevention against such threat. This work is a numerical simulation of the simultaneous water, solute and heat transfer in an unsaturated porous media during the simultaneous evaporation and drainage of saline dry land soils. A detailed mathematical model was formulated to describe the non-isothermal transport of water in the unsaturated porous media [5]. The model consists of the coupled conservative equations of mass for liquid phase, gas phase, water vapour, species and the energy. The boundary conditions at the soil–atmosphere interface include dynamical mass flux and energy flux. Comparison of numerical simulations with analytical results demonstrated that the present model is able to describe water and energy transport dynamics.

Nucleate boiling is an efficient mechanism of heat transfer. The rate of bubble growth and the subsequent bubble motion has a tremendous influence on heat transfer. The study of bubble dynamics is a coupled problem. The rate of evaporation controls the interface speed. One approach to study bubble dynamics is to decouple the problem from energy conservation equation and use an input value of rate of evaporation. The objective is to observe how irregular evaporation rate controls bubble dynamics and the shape of bubble and to study the local over-pressure. The level set method is used to track the liquid-vapor interface. The model consists of the Navier-Stokes equations which govern the momentum and mass balances and the level set equation which governs the interface motion due to phase change. The dynamics of a single bubble under different rates of evaporation and varying levels of gravity have been studied. The results of the numerical simulation show that this model adequately describes bubble dynamics in nucleate boiling, including conditions of microgravity.

The shape and surface texture of a liquid droplet were studied in two-dimension when a droplet impinges on a solid substrate under isothermal condition. The lattice Boltzmann moment model was applied to simulate the fluid dynamics considering the adhesive interaction between fluid particles and surfaces. The results show the influence of wetting on the process and the drop shape. For the hydrophobic surface, the process after impinging may be divided into two stages: the spreading process driven by inertial forces and the subsequent oscillation (recoiling process) driven by surface tension forces. While for the hydrophilic surface, the droplet will only deposits on the surface and there is no the recoiling stage. In addition, the effects of the impinging speed on the shape and texture of the droplet were studied. The spreading speed and the maximum diameter of the spreading droplet increase with the rise of the impinging speed.

The contribution of this work is to characterize the travelling wave’s appearance and to generalize the behavior of Poiseuille-Rayleigh-Benard (PRB) systems for a broad range of dimensionless parameters, which control the double diffusive mixed convection. The numerical results consist to analyzing the flow regimes of the steady longitudinal thermoconvectives rolls for the case of purely thermal mixed convection and for both thermal and mass diffusion. The passage from an opposed volume forces to cooperating one at fixed Rayleigh (Ra), Reynolds (Re) and Lewis (Le) numbers, affects considerably the birth and the development of the longitudinal rolls R//. The distribution of the heat and mass transfer, presented by the average Nusselt and Sherwood numbers, is also examined.

The ice-temperature storage is one of the most important methods in the preservation of fresh fruits and vegetables, while the theory about ice-temperature storage is still not mature at present. In order to study the effect of the pre-thermal processes and the post-thermal processes on the ice-temperature storage, some experiments were carried out. The experimental conditions included two different cooling rates (5°C/day and 3.5°C /day) and two different heating rates (3.2°C /day and 5.1°C/day). After the cooling, the cooled Kiwi and Pear had been stored in the ice-temperature storage for one month. During the storing time, the total sugar, the acidity and the soluble solid were measured by the national standards each two weeks. The present obtained results show that a lower cooling rate would be beneficial for sustaining hydrocarbons and increasing the acidity in fruits after ice-temperature storage; while a quicker cooling rate would increase the soluble solid in fruits after ice-temperature storage.

The problem of unsteady natural convection heat transfer in a vertical opened porous cylinder submitted to a sinusoidal time variation temperature on the lateral wall has been investigated numerically. The widely used Darcy flow model without flow establishment at the cylinder exit has been used. In the case of constant wall temperature, two types of flows were obtained, with and without fluid recirculation, depending on the filtration Rayleigh number (Ra), the aspect ratio (A) and the Biot number (Bi) have been obtained. The obtained heat transfer, in case of low dimensionless oscillations amplitude (XA<0.5), shows a non significant enhancement (less than 5%) in comparison to the constant wall temperature case.

Many industrial and biological phenomena involve the evaporation of liquids in porous media. In drying processes the evaporation of a liquid meniscus from the solid is the key mechanism in the process and its efficiency. After a first steady stage of evaporation the meniscus becomes unsteady and recedes inside the pore. Diffusion of vapour becomes the controlling mechanism for evaporation in a later stage. In this work an experimental investigation is undertaken to study the various stages of evaporation of different liquids in capillary tubes (pores) of various sizes. The analysis of the data obtained from this investigation reveals some interesting behaviours and emphasizes the role played by vapour diffusion in the case of unsteady interface. The preliminary transient regime allowing the thermal field establishment, is followed by the first stage of evaporation is found to be dominated by thermocapillary effects associated with non-uniform evaporation and temperature gradients. The laste stage is a molecular diffusion-limited mode. The liquid volatility and the effect of the size of the tube (ranging from 200 to 900 μm) are also analysed to show the interaction between the various effects at different scales.

The control of a process dealing with heat pipe exploitation needs the thermal analysis of the evaporation-condensation cycle and noticeably the imposed external conditions (in instance modeling the heating). In this work a numerical model has been developed to describe the local coupling near the liquid/vapour interface. Simulations exhibits and quantify the response of the capillary motion to the thermal conditions.

Les transferts par convection naturelle sont fréquemment utilisés dans les différents procédés et sont également rencontrés dans diverses situations dans la nature. Afin d'améliorer ces transferts sans modifier la géométrie, il est possible de perturber l'écoulement d'origine par un obstacle poreux le long du trajet de l'écoulement principal. Cet obstacle modifie la structure de l'écoulement et affecte les transferts locaux. Cette modification est plus prononcée dans une configuration cylindrique au vu de la dissymétrie des écoulements résultants. La variation temporelle du transfert de chaleur est analysée pour différentes courbures et différentes valeurs du nombre de Darcy dans le milieu poreux. Cela nous permettra d'étudier les trois configurations : l'absence de l'obstacle (cas fluide), sa présence (bloc solide) et le cas intermédiaire du bloc poreux. Les conditions nécessaires pour améliorer le transfert dans chaque configuration sont illustrées.

The heat transfer by natural convection are frequently used in the various processes and is also met in various situations in nature. In order to improve these transfers without modifying the geometry, it is possible to disturb the flow of origin by a porous obstacle along the way of the principal flow. This obstacle modifies the structure of the flow and affects the local transfers. This modification is more marked in a cylindrical configuration within sight of the dissymmetry of the resulting flows. The temporal variation of the heat transfer is analyzed for different curvatures and different values of Darcy number in the porous environment. That will enable us to study the three configurations: the absence of the obstacle (fluid case), its presence (solid block) and the intermediate case of the porous block. We illustrate the conditions necessary in order to improve the transfer in such a configuration. Les transferts par convection naturelle sont fr?quemment utilis?s dans les diff?rents proc?d?s et sont ?galement rencontr?s dans diverses situations dans la nature. Afin d'am?liorer ces transferts sans modifier la g?om?trie, il est possible de perturber l'?coulement d'origine par un obstacle poreux le long du trajet de l'?coulement principal. Cet obstacle modifie la structure de l'?coulement et affecte les transferts locaux. Cette modification est plus prononc?e dans une configuration cylindrique au vu de la dissym?trie des ?coulements r?sultants. La variation temporelle du transfert de chaleur est analys?e pour diff?rentes courbures et diff?rentes valeurs du nombre de Darcy dans le milieu poreux. Cela nous permettra d'?tudier les trois configurations?: l'absence de l'obstacle (cas fluide), sa pr?sence (bloc solide) et le cas interm?diaire du bloc poreux. Les conditions n?cessaires pour am?liorer le transfert dans chaque configuration sont illustr?es.

The aim of the study is to characterise the thermal properties of new materials, used in thermal protections: the degradable materials. To this end, specifically measurement techniques answering to the intrinsic characteristic, of these materials were developed by ONERA. L'objectif de l'?tude est de caract?riser thermiquement des nouveaux mat?riaux, utilis?s dans les protections thermiques?: les mat?riaux thermo-d?gradables. ? cet effet, des moyens de mesure r?pondant aux sp?cificit?s, intrins?ques et d'utilisations, des mat?riaux thermo-d?gradables ont ?t? d?velopp?s par l'onera.

L'objectif de l'étude est de caractériser thermiquement des nouveaux matériaux, utilisés dans les protections thermiques : les matériaux thermo-dégradables. À cet effet, des moyens de mesure répondant aux spécificités, intrinsèques et d'utilisations, des matériaux thermo-dégradables ont été développés par l'onera.

Ce travail concerne l'étude des instabilités convectives et l'interaction solide/liquide pour une configuration de croissance dirigée horizontale d'un matériau à faible nombre de Prandtl (Pr=0,015). Les configurations de ce type ont fait l'objet de plusieurs études restreintes à la phase fluide. Il s'agit ici d'étudier les transitions au sein du bain fondu en présence de la convection thermocapillaire et l'interaction avec le front. L'interaction se focalisant dans cette étude sur les aspects convectifs sans prise en compte des effets de la chaleur latente. L'approche de résolution est basée sur la méthode de localisation du front couplée à une approximation de type volumes finis. La convection thermocapillaire agissant dans le même sens que la convection thermogravitationnelle amorti les oscillations introduites par la convection thermogravitationnelle. D'autre part, l'effet de la vitesse de translation de l'ampoule pour le contrôle du processus est également analysé.

With the increasing demand for improved electronics cooling, thermal management and cooling techniques have evolved in design and efficiency over the last three decades. The paper focuses on heat pipes as practical as possible inexpensive alternatives to cool electronic components. An analysis of the necessary conditions allowing the appearance of convective motion and its interaction with energy exchange at the liquid/vapour interface is performed. The numerical simulation allows the access to the evaporation profile and its dependence with the operating conditions. The role of the inversion of the thermal distribution on the development and the orientation of the Marangoni cells and the local convection near the contact line is presented.

With the increasing demand for improved electronics cooling, thermal management and cooling techniques have evolved in design and efficiency over the last three decades. The paper focuses on heat pipes as practical as possible inexpensive alternatives to cool electronic components. An analysis of the necessary conditions allowing the appearance of convective motion and its interaction with energy exchange at the liquid/vapour interface is performed. The numerical simulation allows the access to the evaporation profile and its dependence with the operating conditions. The role of the inversion of the thermal distribution on the development and the orientation of the Marangoni cells and the local convection near the contact line is presented.