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The phase precipitation curves of carbidic ductile iron with Nb element were simulated by the thermodynamic module in JMatPro software. The lattice mismatch between NbC and M3C was analyzed using Bramfitt two-dimensional mismatch theory, and the bonding strength (adhesive work) and interface stability (interfacial energy) of M3C(100)/NbC(110) interface were calculated by using the first principles method. The microstructure of carbidic austempered ductile iron (CADI) was observed by scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that NbC particles precipitate previously at 1420 °C, and the lattice mismatch of M3C(100)/NbC(110) is 3.75 %. Six interface models have been constructed according to different case and termination conditions, in which interface adhesive work of Case I/C interface is the largest (1.35 J/m2), interfacial energy of Case I/Fe interface is the smallest. The covalent bond has been formed on the interface, which proves that M3C(100) and NbC(110) can form a stable interface. The experimental results confirm the precipitation of NbC particles. In addition, M3C grows beside NbC particles and they are combined tightly, indicating that NbC can act as an effective heterogeneous nucleation site of M3C.

Grinding balls in wet ball mill are important consumables in mine grinding equipment, which have poor wear resistance and large consumption. It is imperative to find excellent wear-resistant materials for the grinding balls. Carbidic Austempered Ductile Iron (referred to as CADI) was used as small and medium-sized wet ball mills. This grinding ball has the advantages of less wear, low crushing rate, power saving and low noise. However, the CADI grain boundaries are distributed with net-like eutectic carbides, which seriously damage the continuity of the matrix. In addition, the mechanism of corrosion wear and impact fatigue is lack of research due to complex phase composition and unclear mechanism of phase properties on improving performance. So CADI can’t be applied to the grinding balls in large wet ball mill. Based on the above problems, this paper first analyzed the heteronucleation mechanism and adsorption mechanism of M3C type carbides by using the first principle of microalloying elements, and then verified it by combining with experimental results. Then the thermodynamics and kinetics of austenite homogenization and isothermal transformation of ductile iron containing carbides were analyzed by means of modeling calculation and experiment. On this basis, a new type heat treatment process comprising super-high temperature pretreatment and austempering treatment (S&A treatment) was used to process CADI, which provides a new idea for further improving toughness of CADI. Finally, the CADI corrosion wear and impact fatigue failure mechanism were revealed by analyzing the change rule of the sample surface and cross section after corrosion wear and impact fatigue.

Present study reports a computational investigation on heat transfer and pressure drop characteristics for flow through a heat exchanger tube fitted with novel hybrid ribs by using magnetic nanofluid (Fe3O4). Effects of different rib geometry on heat transfer and pressure drop characteristics have been investigated for Reynolds number ranging from 3 000 to 22 000. Until now, there is little information available in the literature on the method of quantifying the effect of forced convection on the heat transfer and pressure drop of hybrid rib (HR) inserts by using magnetic nanofluid (MNF). The transition SST models along with governing equations (continuity, momentum, and energy equations) are numerically solved with ANSYS Fluent 19.2. The simulation results are validated with established correlations and excellent agreement was found. Heat transfer coefficient is more in combined arrangement (HR and MNF) compared to acting alone arrangement (only MNF).

The performance of the air-cooler in the refrigeration system plays a key role in improving the energy efficiency. Here, the plenum chamber coefficient was defined to study a possible way of enhancing the refrigeration system performance. In order to investigate the influence of the plenum chamber coefficient on the frosting and the cooling system of the chillers, three plenum chamber coefficients (0.74,0.97,1.2) were studied under high humidity. The temperature decreasing curve of the environmental chamber, the velocity distribution of the air cooler, and the frost accumulation under and on the air-cooler were analysed. The results show that the frost accumulation on the tube will increase with the increase of the plenum chamber coefficient and the frost accumulation on the fin will increase at first and then decrease with the increase of the plenum chamber coefficient. On the whole, in this study, frosting is the most obvious when the plenum chamber coefficient was 0.97

The change of evaporation liquid on another immiscible liquid has important guiding significance for many applications. In this experiment, the geometric temperature distribution and evaporation rate of n-hexane droplets were observed and recorded by changing the temperature of deionized water. The results show that with the increase of temperature of deionized water-based solution, the maximum diameter of n-hexane droplet spreading after titration increases gradually, while the minimum diameter of n-hexane droplet disappearing decreases gradually. Meanwhile, the evaporation rate of n-hexane droplet is constant during the whole evaporation process. It should also be mentioned that if the base solution is changed from deionized water to a certain concentration of salt solution, the maximum diameter of n-hexane droplet spreading will be reduced, and the evaporation intensity will be relatively reduced. These experimental results will give us a better understanding of the mechanism and characteristics of droplet evaporation.

Flow and heat transfer analysis in ventilated cavities is one of the most widely studied problems in thermo-fluids area. Two-dimensional mixed convection in a ventilated rectangular cavity with baffles is studied numerically and the fluid considered in this study is hot air (Pr = 0.71). The horizontal walls are maintained at a constant temperature, higher than that imposed on the vertical ones. Two very thin heat-conducting baffles are inserted inside the enclosure, on its horizontal walls, to control the flow of convective fluid. The governing equations are discretized using the finite volume method and the SIMPLER algorithm to treat the coupling velocity–pressure. Line by line method is used to solve iteratively the algebraic equations. The effect of the Richardson number Ri (0.01- 100) and the location of the baffles within the cavity on the isothermal lines, streamlines distributions and the average Nusselt number (Nu) has been investigated. The result shows that the location opposite the baffles, close to the fluid outlet, is the optimal choice to be considered for industrial applications.

Despite the efforts to develop new solutions to achieve the objectives of positive buildings in energy, a few studies in this area has been performed using a porous media foam type. The aim of this paper is to present the behaviour transfers of flow through a multi-structured porous media and to achieve the influence of the porosity and the thermal conductivity properties of the skeletal phase, and the interaction with a cross flow in order to get the equivalent of a perfect insulator. Therefore, in a specially made device, a finite volume method was applied to study a flow through a porous media foam-type, which was simulated to characterize the properties of the equivalent medium in terms of permeability and thermal conductivity. The analysis demonstrates that the solid phase composition and the medium porosity, as well as the distribution of pore size, are preponderant characteristics to constitute a foam structured media. Furthermore, the thermal boundary layer given by a forced convection through the porous medium has demonstrated the important influence of the flow phenomenon in a thermodynamic coupling. Lastly, three optimum configurations for the construction envisaging a balance of depleted thermal and dynamic powers for a relative conductivity *=10 were found between the velocity 2 10-3 (m/s) and 4 10-3 (m/s).

For transient thermal performance of building envelops adequate parameters are needed to capture the time lag and decrement factor. It is surprising that, in the formal electrical analogy, "inertia" is not represented by same components in fluid mechanics and heat transfer. In Windkessel model for fluid flow in elastic tubes, the fluid inertia is represented by an electrical inductance while in thermal-electric analogy, thermal inertia is given by a capacitance. Some authors argued that the terminology of ''thermal inertia'' is used incorrectly in the literature. The aim of our communication is to provide some clarification about this controversy. We will show that the thermal effusivity which is the geometric mean of thermal conductivity and volumetric heat capacity plays the role of a "thermal mass". The revisited notion of inertia in mechanics will allow to show the analogy between: mechanical inertia (mass), thermal effusivity and electrical inductance. The three parameters show a tendency to keep invariant a certain physical quantity: velocity, temperature and current intensity respectively. However, the analogy is not complete, the capacitance used in the heat transfer seems to be similar to the one used in the Windkessel model which accounts for tube compliance and therefore to a local storage.

The development of positive-energy buildings is nowadays an important societal challenge and the research objective of many laboratories. Working towards this direction, we describe in the present report the development of active and reactive walls, by employing a multi-fiber, volumetrically structured porous medium. Flow and transfer characterization in such a foam structure is not fully understood due to the strong nonlinearities included. These are amplified by heterogeneities and porosity changes, where the local and global flow affect the thermal field and the resulting heat transfer. Thus, a finite volume method with immersed structure interfaces was implemented to study heat transfer through these media, with the aim of obtaining their ratio equivalent to fluid thermal conductivity (i.e. Nusselt number). Furthermore, our analysis shows that in such active wall constituted by two solid phases, under fixed weight constraints, the optimal value is difficult to predict a priori. Thus, different evolution laws of thermal gradient were studied, resulting in the change of the pore size distribution along some new anisotropic structures, in order to achieve the most one predictive.

The main purpose of our investigation is to providethe impact of some pertinent parameters,asthe thermal buoyancy and the geometryratio,on the oscillatory flow’stability of a Newtonian fluid which occurs within an annulus, found between a cold outer circular cylinder and a hot inner one, to come out at the end with critical conditions that couldpredict this phenomenon intosuch an industrial geometry. To do so, aphysical model is developed using the Lattice-Boltzmann approachside by side with the finite difference one. The validity of the latter is ascertained after comparison between our primary predictionsand various experimental & theoretical ones. By usinganunsteady-state regime, both Isotherms and velocity profiles of ourconvective fluidare widely inspected. Going far with its value, the use of a critical aspect ratio could die-out the impact of any investigated parameter on the oscillatoryflow. Then, only a conductive regime will take control intothe annulus. It is tonote that athree dimensions D3Q19model was adopted based on a cubical Lattice.

The present study is a numerical simulation of natural convection in nanofluids, within in a square cavity differentially heated, to identify the fluid flow and heat transfer by considering the Soret effect during which a temperature gradient in a binary mixture gives rise to a concentration gradient. The governing equations solved numerically using the finite element method following the use of COMSOL Multiphysics. The effects of various parameters, the Rayleigh number, the nanoparticle concentration and the type of nanofluid are analyzed. Our simulations reveal that the heterogeneity of the nanofluid, which is generated by the Soret effect, increases the heat transfer.

The present work is a numerical simulation of the mixed convection of an incompressible fluid in a horizontal channel under sun radiation partially filled with metal foam blocks. The Darcy-Brinkman model is adopted. The control volume approach is used to solve the motion and energy equations governing mixed convection. The study focuses on the effect of certain control parameters such as the Rayleigh number (Ra), the thermal conductivity ratio and the porosity on the flow structure and heat transfer. Indeed, the results for flow structures and temperature distribution are presented in the form of velocity fields with streamtraces and isotherms, while the average Nusselt number (Nu) is used to quantify heat transfer.

Air conditioning systems are seen as a crucial part of any structure because they are directly related to the comfort of the occupants. Finding a conditioning system that exhibits not only a high level of comfort, but also a decrease in energy consumption and cost of the system is now very much preferable, especially with the ever-increasing cost of energy. Mixed convection for different boundary conditions and different configuration is carried out. In addition, a flow is injected through a window and extracted through an opposite window. In this work we examine the influence of the value of the Rayleigh number on the flow structure. The numerical analysis was carried out using the ‘Fluent’ software. To deal with turbulence the RNG k-ε model was adopted in this study. The study of ventilation efficiency has shown that the intensity of the recirculation flow increases near the adiabatic wall with the increase of Rayleigh number.

In this paper, the thermohydraulic performance of a reciprocating room temperature active magnetic regenerator (AMR), with gadolinium (Gd) particles used as a magnetocaloric material (MCM) and water used as a working fluid, was numerically investigated. A two-dimensional transient flow model was developed using COMSOL Multiphysics, in order to determine the water flow distribution in two AMRs of cross and parallel Gd particles distributions for different water inlet velocities of 0.06 m.s-1, 0.08 m.s-1 , 0.1 m.s-1 and 0.12 m.s-1. The Gd particles have a radius of 1.5 mm and a distance from one another of 0.9 mm. Based on the simulations results of the first model, a two-dimensional transient coupled flow and heat transfer model was then developed using COMSOL Multiphysics, in order to characterise the convective heat transfer in the AMR of cross Gd particles distribution for the same water inlet velocities.

In this paper, a modelling investigation of water droplet evaporative freezing was conducted in order to better understand the snowmaking process and hence to optimise the design of the artificial snowmaking device. To this end, mass and heat transfer theoretical models of a single water droplet cooling in an air space were established and implemented in a numerical model developed using the software COMSOL Multiphysics. The effects of the air temperature, relative humidity and velocity and the water droplet initial diameter and temperature on this process were identified and analysed, and their appropriate ranges for the snowmaking were determined.

Porous foam metal has great application prospects in the field of compact heat exchangers. The characteristics of heat transfer and resistance for foam metal with random structure and different porosities (30%, 50%, 70% and 90%) were studied by finite element method in this study. The generated foam structures can be considered as homogeneous model and has better heat exchange capacity at higher inlet flow rate, and the boundary layer can develop well along the flow direction. The open–cell foammetal structure has a uniform heat transfer perpendicular to the flow direction. The bottom plate temperature of the low–porosity structure is more uniform at low flow rates. The intermediate porosities (50% and 70%) at high flow rates has a higher uniformity. As the porosity decreases, the internal pressure increases significantly and the pressure loss also becomes significantly larger. The corresponding optimal porosity is 57%, 66% and 76% at inlet flow rates of 0.001 m/s, 0.01 m/s and 0.1 m/s, respectively.

Cementitious materials are typical porous medium, which are widely used in civil engineering and thermal buildings. The thermal and hydrate properties of the material are fundamental to predict accurately the energy needs and the reliable duration of the structures in a long term. Due to the complicated coupling, the thermal capacity, conductivity and source term in energy equation are affected by the humidity distribution and the microstructure evolution of the porous materials. The coupling relation of thermal and hydrate properties are summarized in this work, the coupled drying model is discussed, and the experiment is performed to verify the simulation results for RH (Relative humidity) and ML (Mass loss). Two approaches are adopted to estimate the humidity/water content profile in the porous medium and to analyse the temperature effect. In addition, the equivalent hydrate capacity and conductivity are identified as function of humidity. The significance of this work lies in predicting the energy demand, the long-term thermal behaviour, taking into account the change of the thermal cementitious materials properties during their service time. Such inner structure is consequence of the system durability where the temperature, water content and humidity will act on the cracks settling within the material.

Abstract Convective heat transfer using different nanofluid types is investigated. The domain is differentially heated and nanofluids are treated as heterogeneous mixtures with weak solutal diffusivity and possible Soret separation. Owing to the pronounced Soret effect of these materials in combination with a considerable solutal expansion, the resulting solutal buoyancy forces could be significant and interact with the initial thermal convection. A modified formulation taking into account the thermal conductivity, viscosity versus nanofluids type and concentration and the spatial heterogeneous concentration induced by the Soret effect is presented. The obtained results, by solving numerically the full governing equations, are found to be in good agreement with the developed solution based on the scale analysis approach. The resulting convective flows are found to be dependent on the local particle concentration φ and the corresponding solutal to thermal buoyancy ratio N. The induced nanofluid heterogeneity showed a significant heat transfer modification. The heat transfer in natural convection increases with nanoparticle concentration but remains less than the enhancement previously underlined in forced convection case.