1,721,001 research outputs found
Numerical investigation of melting process for phase change material (PCM) embedded in metal foam structures with Kelvin cells at pore scale level
No full textThe present numerical study analyzes the melting process of phase change material (PCM) embedded in a metallic foam structure at pore scale level. The computational domain consists of two different sizes of 3D cubic boxes. The analyzed domain is filled with Kelvin cell-structures with different Cell Per Length (CPL) and constant porosity of 0.956. A constant temperature, higher than the melting temperature of PCM, is assigned to one external surface of the enclosure, while the other surfaces are adiabatic. The conjugate problem for the heat transfer between the PCM and the solid structure with Kelvin cells is developed. Enthalpy-porosity method is used to describe the PCM melting process. The finite volume method is used to solve the conjugate heat transfer problem at pore scale level by Ansys-Fluent code. A comparison of different CPL values is reported in terms of liquid fraction, average temperature of the PCM, and energy storage. The comparison is also considered between the two different volumes of the cubic boxes. The presence of the metallic structured Kelvin cells increases the overall heat transfer rate and decreases the melting time. Results for smaller cavity indicates that as the CPL number increases, the time required for the PCM melting process decreases. Furthermore, the total heat accumulation process takes a shorter time to reach the maximum value. The melting time and the duration of heat accumulation are worsened for the large cubic box (L = 4 inch) at CLP>6. This is due to the dominant viscous effect, which decreases the velocity induced by the buoyancy forces because of higher contact surface area. In these cases, heat transfer between liquid and solid phases of the PCM decreases substantially
Heat transfer of chemically reacting mixed convection fluid using convective surface condition: Non-Darcy model
No full textThis work reports the study of mixed convection of permeable fluid with Robin conditions in the vertical channel including the effects of chemical reactions. The fluid transport is designed by the Darcy-Forchheimer-Brinkman model. The series method is adopted for approximate solutions for governing equations considering the Brinkman number as the perturbation characteristic whose outcomes correspond to magnitudes of Brinkman number less than one. Adopting a numerical scheme followed by fourth order Runge–Kutta algorithm with shooting method, the solutions for bigger magnitudes of the Brinkman number are obtained. The present results for limiting cases are compared with the literature and good agreement is seen. For various values of thermal and mass Grashof numbers, porous parameter, inertial parameter, Darcy number and first order chemical reaction the problem is resolved for the same and distant Biot numbers reflecting the border temperatures symmetric and asymmetric. Finally, the outcomes are tabulated for wall friction parameters, Nusselt and Sherwood numbers for innovated parameters. It is noticed that enhancing buoyancy and dissipations, thermal Grashof number helps to improve the flow rate for all values of Biot number. The Schmidt and Soret parameters can improve concentration patterns. Nusselt number can be improved with thermal Grashof number and Brinkman number and it is dropped with inertia and porous parameters. The solutions have a very good agreement with Zanchini data without mass Grashof number
Effect of third size on natural convection of variable viscosity fluid in a closed parallelepiped
No full textThermal convection is one of the main mechanisms that are implemented in different cooling systems. Most often this phenomenon occurs in such practical areas as microelectronics, instrumentation and building construction. In this article, the numerical simulation of thermogravitational convection of medium having dependent viscosity inside closed enclosure with isothermal heating/cooling from vertical walls has been conducted. Other borders of the chamber are heat insulated. The control relations have been written employing non-dimensional vector potential functions, vorticity vector and temperature. The finite difference procedures are applied for solving of the considered differential equations. Obtained outcomes have been compared with numerical data for thermal convection within a differentially heated square cabinet. An influence of third coordinate, Rayleigh number and viscosity variation parameter on thermal distribution and flow structures combined with mean Nusselt number has been demonstrated. Obtained outcomes have shown that for the considered 3D problem an evaluation of the mean Nusselt number can be performed by employing 2D data when the aspect ratio is greater than or equal to unity
Three-dimensional natural convection of fluid with temperature-dependent viscosity within a porous cube having local heater
No full textA numerical simulation is conducted on the convective heat transfer of liquid having variable viscosity in a closed porous 3D enclosure under an influence of isothermal or heat-generating solid body. Two vertical surfaces of the chamber are considered at fixed low temperature while other surfaces are thermally insulated. The local energy source is placed on the lower surface of the chamber. The control equations are written using non-dimensional variables «vector potential functions – vorticity vector – temperature». The finite difference technique of the second order accuracy is used to work out the differential equations. The effect of control parameters including the Rayleigh number, Ostrogradsky number, Darcy number, viscosity variation parameter and time on the liquid flow structure and heat transfer inside the cavity has been studied. The obtained data show that the porous material and variable viscosity working fluid can be considered as good conditions for the heat removal from the heated element in a closed chamber. A comparison of 2D and 3D models for natural convection of fluid having temperature-dependent viscosity in chambers with local heaters of various types has shown the features of different spatial approaches and boundary conditions for heated elements
Cooling of periodically heat-generated element under the convective-radiative heat transfer in a rotating domain with a thermally conducting base plate
No full textConvective heat transfer under an influence of thermal radiation in a rotating chamber has been investigated numerically. The cavity has periodically heat-generating source, cooling vertical walls and heat-conducting bottom wall. Governing equations have been formulated using stream function, vorticity and temperature. The considered set of control equations has been worked out employing the finite difference procedures. Streamlines and isotherms for different angles of rotation have been shown and described in detail. The effects of emissivity, angular velocity and bottom wall thickness have been illustrated using the flow rate, average heater temperature, mean convective and radiative Nusselt numbers. The results demonstrate that lower wall thickness can significantly reduce the mean heater temperature
Transient free convection of variable viscosity liquid in an inclined cube affected by the temperature modulation on a vertical wall
No full textConvective energy transport can be found in various engineering and nature systems. From practical point of view this transport phenomenon within engineering cabinets can be progressed in the presence of temperature modulation. In this research, the transient natural convective heat transference of a temperature-dependent viscosity liquid inside an inclined cube in the presence of time-dependent temperature profile at one vertical bounded surface is investigated. The opposite vertical border is kept at permanent low temperature, whilst other surfaces are thermally insulated. Partial differential equations formulated using dimensionless non-primitive characteristics with appropriate restrictions are worked out by the finite difference technique. Impacts of the domain tilted angle, and wall temperature oscillation frequency on energy transport and flow structures are scrutinized
Convection in a vertical duct under the chemical reaction influence using Robin boundary conditions
No full textConvective flow with chemical reaction in a vertical duct using third kind boundary conditions is investigated. The heat is exchanged from the walls of the duct and the external fluid. The equations of balance are written in dimensionless form taking into account the effect of viscous dissipation. The inclusion of viscous dissipation reflects the transformation of original balance equations into nonlinear equations. Hence the closed form solutions are not possible. Therefore, the balance equations are resolved by the classical explicit Runge–Kutta method combined with shooting method which can be employed for various magnitudes of Brinkman number. The solutions obtained numerically are justified by solving the balance equations analytically using the perturbation technique which is applicable only for Brinkman numbers to be less than one. The flow profiles are shown graphically for different values of the thermal and solutal Grashof numbers, Biot numbers, Brinkman number, and chemical reaction parameter. The impacts of physical characteristics on the friction factor and Nusselt number are also evaluated and the results are tabulated. The solutions received by perturbation technique and Runge-Kutta method are equal when Br = 0 and as the Brinkman number increases, the error also increases
Convective-radiative heat exchange in a cube with a flat heated element under the rotation effect around coordinate axis
No full textThe production of a various engineering systems is accompanied by studies of liquid flow structures and thermal energy patterns. Many engineering systems in electronics and energy are affected by rotation and an important task becomes the description of physical phenomena under rotational effects. This investigation is dedicated to convective-radiative thermal and mass transport inside a rotating cube having a flat heated element placed on the bottom surface. The rotation of the cube around each of the axes of Cartesian coordinates has been considered. Governing equations based on mass, momentum and energy conservation laws are written employing the non-primitive variables. The set of control equations is resolved by the finite difference schemes. The influences of angular velocity, rotation axis orientation, and emissivity of surfaces on the intensity of heat transfer have been shown. Temperature patterns for various rotation angles are presented and described in detail. The results demonstrate that rotation around the vertical axis shows a steady-state of the Nusselt numbers, while rotation around the horizontal axis shows the periodic changes. It is interesting that similar heat exchange modes are formed during rotation around horizontal axes. More intensive convective and radiative heat exchange is observed in the case of rotation around an axis at which the cooling walls change their position
Double diffusion in a rectangular duct using metals or oxides suspended in a viscous fluid
No full textIn this study, double diffusive free convection of nanofluid within a confined rectangular duct is investigated numerically. The momentum and energy equations are placed in the form of difference equations and solved numerically. The left wall conditions for the concentration and temperature are lesser than those of the right wall and the upper and lower walls are insulated. Different nanofluids are considered such as mixtures with copper, diamond, silicon oxide and titanium oxide, suspended in water. Brinkman and Maxwell models are used to characterize the nanofluid. Tiwari and Das model is opted to define the nanofluid behavior. The simulations are conducted using different nanoparticles, thermal Grashof number 1 ≤ GrT ≤ 20, solute Grashof number 1 ≤ GrC ≤ 15, solid volume fraction 0 ≤ Φ ≤ 0.05, Dufour number 0 ≤ Df ≤ 1, Brinkman number 0 ≤ Br ≤ 2, and Soret number 0 ≤ Sr ≤ 5. Additionally, behavior of volumetric flow strength, skin friction, heat transport intensity and Sherwood number is also examined. The thermal Grashof number, Brinkman number, Dufour, Soret and Schmidt parameters accelerate the velocity and temperature and dwindle the concentration whereas the reversal effect was obtained for the solid volume fraction. The concentration Grashof number diminishes the velocity and temperature and intensifies the concentration. The silver nanoparticles produce the highest velocity whereas diamond nanoparticles cause the lowest velocity and temperature. The maximum temperature is attained with silicon oxide
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