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Transient response of continuous composite material (CCM) fin made of high thermally conductive composite material is presented. The continuously varying effective properties of composite material such as thermal conductivity, heat capacity and density have been modelled using the Mori-Tanaka homogenization theory and rule of mixture. Additionally, temperature dependency of thermal conductivity, heat generation (composite materials) and convection coefficient (fluid properties) have also been incorporated. Different base boundary conditions are addressed such as oscillating heat flow, oscillating temperature, step-changing heat flow and step-changing temperature. At the other boundary, the fin is assumed to have a convective tip.

Lattice Boltzmann method is implemented using an in-house source code for obtaining the numerical solution of typical non-linear heat balance equation of the aforementioned problem under various transient base boundary conditions.

The effects of various thermal parameters such as material diffusivity ratio and conductivity ratio, area ratio and Biot number on transient response of fin and temperature distribution of fins are studied and interpreted. The heat transfer rate and time for attainment of steady state temperature of metal matrix composite (MMC) fin are found to be proportionally dependent on their diffusivity ratio. Additionally for higher values of area ratio and biot number, MMC fins are reported to dissipate the heat more efficiently in comparision to homogeneous fins in terms of time required to attain the steady state and surface temperature.

Response of transient fin associated with advanced class of material can facilitates the practicing engineers for designing high-performance and/or miniaturized thermal management devices as used in electronic packaging industries.

Studies of composite fin consisting of laminating second layer of material over the first layer have been reported previously, however transient response of CCM fin fabricated by continuously varying the volume fraction of two materials along the fin length has not been reported till date. Such material finds its application in thermal management and electronic packaging industries. Results are plotted in form of a graph for different application-wise material combinations that have not been reported earlier, and it can be treated as design data.

This paper aims to study the mechanism of heat generation in a screw, and investigates the heat flux in the connection screw pair under high frequent oscillation along the axial direction. Heat generated in the screw under high frequent oscillation could be observed in a lot of situations and was significant, and it could cause damage of screw joining and transmission.

A heat flux model in a screw pair under high frequent oscillation along the axial direction is established. Bulk temperature field in the connected parts is calculated by means of finite element methods. A testing device aimed to temperature rise measurement in a thread pair under high frequent oscillation is built. Temperature rises under different operation conditions are measured.

The heat flux generated in the screw pair because of friction between the contact surfaces of the screw thread is obtained. The effects of oscillating amplitude and frequency on heat flux are obtained. It is found that amplitude and frequency have a significant influence on the heat generated under high frequent oscillation. The numerical results show good agreement with the numerical results.

This study has some limitations; for example, the friction coefficient and the relative sliding displacement between the thread surfaces need further accurate research.

Heat generated in a screw under high frequent oscillation is very rarely mentioned in previous research papers. The methods used in this paper could be used to evaluate the heat flux and temperature under high frequent oscillations. The temperature could be used to calculate the thermal stress and expansion in the screw thread under high frequent oscillation. The screw connections need to be protected from the damage because of heat stress and from getting loose because of heat expansion of the connected parts.

The mechanisms of heat generation in the screw pair under high frequent oscillation are studied. The model of heat flux in the screw under high frequency oscillation is established, and it could be used to calculate the heat flux under different operating conditions. The transient temperature field of the connected parts is given. A test facility was built and the experiment to measure the temperatures of the bolt and nut was carried out. The results had good agreement.

The unsteady natural convection flow of a viscous dissipative fluid along a semi‐infinite vertical plate subjected to periodic surface temperature oscillation is investigated.

An electrical‐network model based on the Network Simulation Method is developed to solve the governing equations. The accuracy and effectiveness of the method are demonstrated.

The increasing of the viscous dissipation and the decreasing in the Prandtl number lead to a decrease in Nusselt number and an increase in the local skin‐friction. Also, it is found that the oscillations of the Nusselt number and of the local skin‐friction depend on the frequency and amplitude of the oscillating surface temperature. For Pr = 1,000 and ε = 0.005 (realistic case) the effect of the viscous dissipation is appreciable at large distances from the leading edge.

The inclusion of viscous dissipation in the energy equation, except of the theoretical interest, has applications in very special cases, for example, gases at very low temperature and also for high Prandtl number liquids.

The influence of the non‐uniformity of wall temperature on the heat transfer by natural convection along of the plate together with the viscous dissipation of the fluid are analysed by means of a new numerical technique based on the electrical analogy.

The purpose of this study is to simulate the temperature distribution during an electron beam freeform fabrication (EBF³) process based on a fully threaded tree (FTT) technique in various scales and to analyze the temperature variation with time in different regions of the part.

This study presented a revised model for the temperature simulation in the EBF³ process. The FTT technique was then adopted as an adaptive grid strategy in the simulation. Based on the simulation results, an analysis regarding the temperature distribution of a circular deposit and substrate was performed.

The FTT technique was successfully adopted in the simulation of the temperature field during the EBF³ process. The temperature bands and oscillating temperature curves appeared in the deposit and substrate.

The FTT technique was introduced into the numerical simulation of an additive manufacturing process. The efficiency of the process was improved, and the FTT technique was convenient for the 3D simulations and multi-pass deposits.

The purpose of the present paper is to model a cavity, which is equally divided vertically by a thin, flexible membrane. The membranes are inevitable components of many engineering devices such as distillation systems and fuel cells. In the present study, a cavity which is equally divided vertically by a thin, flexible membrane is model using the fluid–structure interaction (FSI) associated with a moving grid approach.

The cavity is differentially heated by a sinusoidal time-varying temperature on the left vertical wall, while the right vertical wall is cooled isothermally. There is no thermal diffusion from the upper and lower boundaries. The finite-element Galerkin technique with the aid of an arbitrary Lagrangian–Eulerian procedure is followed in the numerical procedure. The governing equations are transformed into non-dimensional forms to generalize the solution.

The effects of four pertinent parameters are investigated, i.e., Rayleigh number (104 = Ra = 107), elasticity modulus (5 × 1012 = E_T = 1016), Prandtl number (0.7 = Pr = 200) and temperature oscillation frequency (2p = f = 240p). The outcomes show that the temperature frequency does not induce a notable effect on the mean values of the Nusselt number and the deformation of the flexible membrane. The convective heat transfer and the stretching of the thin, flexible membrane become higher with a fluid of a higher Prandtl number or with a partition of a lower elasticity modulus.

The authors believe that the modeling of natural convection and heat transfer in a cavity with the deformable membrane and oscillating wall heating is a new subject and the results have not been published elsewhere.

The paper aims to introduce a new algorithm based on the boundary integral method developed to solve moving boundary phase change problem subject to all possible cases of cyclic boundary temperature.

In the present paper, the phase change problem with periodic boundary temperature, which may be above or below the phase change temperature, is analyzed. The analysis is based on applying the boundary integral method in a new numerical algorithm. There are two main topics of the analysis herein. The first one is to study the direct effect of the cyclic boundary temperature on the movement of the moving boundary for various Stefan numbers. The second one is check that the proposed method covers all possible cases of cyclic boundary temperature with respect to the phase change temperature.

When using the proposed method, it is found an easy mathematical manipulation and the results can be improved when fine time step size used.

The proposed method is a very new method, which can be applied to any case of moving boundary phase change problem subject to any case of cyclic boundary temperature. Also the proposed method takes into consideration different parameters that affect directly on the evolution of the moving boundary such as Stefan number, etc.

Numerical computations were performed for the heat transfer and fluid flow characteristics of natural convection with an internal vertical channel composed by a pair of parallel plates in a rectangular enclosure. The inner plates and the bounding wall of the enclosure were maintained at uniform but different temperatures. The plates were symmetrically arranged. Unsteady computation was performed to simulate the evolution process of the natural convection developing from the zero initial field. The cases of Ra = 2 × 10⁴, 2 × 10⁵ and 10⁶ were studied. A symmetrical steady solution was achieved for the case of Ra = 2 × 10⁴. For Ra = 2 × 10⁵ and 10⁶, time dependent asymmetrical processes were observed. The flow oscillating process seemed to be more complex at Ra = 2 × 10⁵ than that at Ra = 10⁶, which is quasi‐periodic with two frequencies.

This study aims to perform a numerical study of air convection in a rectangular enclosure with two isothermal blocks and oscillating bottom wall temperature under laminar flow conditions. The geometry of the enclosure contains two isothermal blocks placed equidistant along the streamwise direction. The top wall is assumed to be cold (low temperature). The bottom wall temperature is either kept as constant or sinusoidally varied with time. The vertical walls are considered as adiabatic. The flow is diagonally upwards and assisted by the buoyancy force. The inlet is positioned at the bottom of the left wall, and the outlet is placed at the top of the right wall. The parameters considered in this paper are Rayleigh number (104-106), Prantdl number (0.71), amplitude of temperature oscillation (0-0.5) and the period (0.2). The effects of these parameters on heat transfer and fluid flow inside the open cavity are studied. The periodic results of fluid flow are illustrated with streamlines and the heat transfer is represented by isotherms and time-averaged Nusselt number. By virtue of increasing buoyancy, the heat transfer accelerates with an increase in the Rayleigh number. Also, the heat transfer is intensive with an increase in the bottom wall temperature.

The momentum and energy equations are solved simultaneously. The energy equation (3) is initially solved using the alternating direction implicit (ADI) method. The results of the energy equation are updated into the vorticity equation. The unsteady vorticity transport equation is also solved using the ADI method. Dimensionless time step equal to 0.01 is used for high Ra (10⁵ and 10⁶) and 0.001 is used for low Ra (10⁴). Convergence criteria of 10⁻⁵ is used during the vorticity, stream function and temperature calculations, as the sum of error should be very small.

Numerical study of air convection in a rectangular enclosure with two isothermal blocks and oscillating bottom wall temperature is performed under laminar flow condition. The effect of the isothermal blocks on the heat transfer is analyzed for different Rayleigh numbers and the following conclusions are arrived. The hydrodynamic blockage effect is subdued by the isothermal heating of square blocks. Based on the streamline diagrams, it is found that the formation of vortices is greatly influenced by the Rayleigh number when all the walls are exposed to a constant wall temperature. The influence of amplitude on the heat transfer is remarkable on the wall exposed to oscillating temperature and is subtle on the opposite static cold wall. The heat transfer increases with an increase in the Rayleigh number and temperature.

Flow is assumed to be two-dimensional and laminar subject to oscillatory boundary condition. The present investigation aims to study natural convection inside the cavity filled with air whose bottom wall is subject to time-variant temperature. The buoyancy is further intensified through two isothermal square blocks placed equidistant along the streamwise direction at mid-height.

The authors have developed a CFD solver to simulate the situation. Effect of Rayleigh number subject to oscillatory thermal boundary condition is simulated. Streamline contour and isotherm contour are presented. Local and average Nusselt numbers are presented.

The purpose of this study is to investigate the two-dimensional unsteady inclined stagnation point flow and thermal transmission of Maxwell fluid on oscillating stretched/contracted plates. First, based on the momentum equation at infinity, pressure field is modified by solving first-order differential equation. Meanwhile, thermal relaxation characteristic of fluid is described by Cattaneo–Christov thermal diffusion model.

Highly coupled model equations are transformed into simpler partial differential equations (PDE) via appropriate dimensionless variables. The approximate analytical solutions of unsteady inclined stagnation point flow on oscillating stretched and contracted plates are acquired by homotopy analysis method for the first time, to the best of the authors’ knowledge.

Results indicate that because of tensile state of plate, streamline near stagnation point disperses to both sides with stagnation point as center, while in the case of shrinking plate, streamline near stagnation point is concentrated near stagnation point. The enhancement of velocity ratio parameter leads to increasing of pressure variation rate, which promotes flow of fluid. In tensile state, surface friction coefficient on both sides of stagnation point has opposite symbols; when the plate is in shrinkage state, there is reflux near the right side of the stagnation point. In addition, although the addition of unsteady parameters and thermal relaxation parameters reduce heat transfer efficiency of fluid, heat transfer of fluid near the plate can also be enhanced by considering thermal relaxation effect when plate shrinks.

First, approximate analytical solutions of unsteady inclined stagnation point flow on oscillating stretched and contracted plates are researched, respectively. Second, pressure field is further modified. Finally, based on this, thermal relaxation characteristic of fluid is described by Cattaneo–Christov thermal diffusion model.

The purpose of this paper is to model the convective flows in a room equipped by a glass door and a heated floor of length l = 0.8 × H and submitted to a sinusoidal temperature profile and mono alternative temperature profile.

The paper opts for a numerical study of convective flows in a large scale cavity using the Lattice Boltzmann Method (LBM) by considering a two dimensions (2D) square cavity of side H and filled by air (Pr = 0.71). All the vertical walls, the ceiling and the rest of the floor are thermally insulated, the hot portion of length l = 0.8×H is heated with two imposed temperature profiles of amplitude values 0.2 ≤  a  ≤ 0.6 and for two different periods ζ = ζ0 and ζ = 0.4×ζ0. One of the vertical walls has a cold portion θ_c = 0 that represents the glass door.

A systematic study of the flow structure and heat transfer is carried out considering principal control parameters: amplitude “a” and period ζ for Rayleigh number Ra = 10⁸. Effects of these parameters on results are presented in terms of isotherms, streamlines, profiles of velocities, temperature in the cavity, global and local Nusselt number. It has been found that an increase in amplitude or period increases the amplitude of the temperature in the core of cavity. The Nusselt number increases when the amplitude “a” of the imposed temperature increases, but this later is not affected by variation of the period.

The authors used LBM to simulate the convective flows in a cavity at high Ra, heated from below by tow imposed temperature profiles. Indeed, they simulate a local equipped by a solar water heater (SWH). The floor is subjected to a periodic heating: Sinusoidal heating (Case 1) for which the temperature varies sinusoidally (SWH without a supplement), and mono alternation heating (Case 2), the temperature evolves like a redressed signal (SWH with a supplement). The considered method has been successfully validated and compared with the previous work. The study has been conducted using several control parameters such as the signal amplitude and period in the case of turbulent convection. This allowed us to obtain a considerable set of results that can be used for engineering.