Search results

The purpose of this paper is to study natural convective fluid flow and heat transfer inside a cubical cavity having a local heat source of constant temperature.

The cubical cavity is cooled from two vertical opposite walls and heated from the local heater mounted on the bottom wall, while the rest walls are adiabatic. The governing equations formulated in dimensionless vector potential functions and vorticity vector have been solved using implicit finite difference method of the second-order accuracy. The effects of the Rayleigh number (Ra = 1e+04 – 1e+06), heat source position (l/L = 0.05 – 0.35) and dimensionless time (0 < tau < 100) on velocity and temperature fields, streamlines, isotherms and average Nusselt number at the heat source surface have been analyzed.

It is found that the extreme left position of the heater (l/L = 0.05) illustrates more essential cooling of the cavity where the thermal plume over the heat source is suppressed by low temperature waves from the cold vertical walls.

The originality of this work is to analyze transient 3D natural convection in a cubical cavity with a heater of triangular shape and compare obtained 3D data with 2D results. It should be noted that for numerical simulation, the authors used vector potential function and vorticity vector that for transient problems allows to reduce the computational time. The results would benefit scientists and engineers to become familiar with the analysis of transient convective heat and mass transfer in 3D domains with local heaters, and the way to predict the properties of convective flow in advanced technical systems, in industrial sectors including transportation, power generation, chemical sectors, ventilation, air-conditioning, etc.

The purpose of this paper is to investigate natural convective heat transfer in a cubical cavity with the heat source of a trapezoidal form having a constant temperature.

The domain of interest is a cubical cavity with two isothermal opposite vertical walls, while other walls are adiabatic. A discrete heater of a trapezoidal shape is located at the bottom wall of the cavity. Governing equations formulated in dimensionless vector potential functions, vorticity vector and temperature with corresponding initial and boundary conditions have been solved numerically using a developed computational code based on the finite difference method.

The results show that the variation of geometric parameters, such as height, length and size of the local heater, significantly influences the evolution of a temperature field and fluid flow inside the enclosure. The effects of Rayleigh number and time on streamlines, isotherms and average Nusselt number have been studied.

The originality of this work is to explore three-dimensional (3D) natural convection in a cubical cavity with a local heat source of trapezoidal shape, to analyze the effects of heater geometric parameters and to compare obtained 3D data with two-dimensional results.

The performance of solid fins inside a differentially heated cubical cavity is numerically studied in this paper. The main purpose of the study is to make an optimization to reach the maximum heat transfer in the enclosure having the solid fins with studied parameters.

The considered domain of interest is a differentially heated cube having heat-conducting solid fins placed on the heated wall while an opposite wall is a cooled one. Other walls are adiabatic. Governing equations describing natural convection in the fluid filled cube and heat conduction in solid fins have been written using non-dimensional variables such velocity and vorticity taking into account the Boussinesq approximation for the buoyancy force and ideal solid/fluid interfaces between solid fins and fluid. The formulated equations with appropriate initial and boundary conditions have been solved by the finite difference method of the second of accuracy. The developed in-house computational code has been validated using the mesh sensitivity analysis and numerical data of other authors. Analysis has been performed in a wide range of key parameters such as Rayleigh number (Ra = 10⁴–10⁶), non-dimensional fins length (l = 0.2–0.8), non-dimensional location of fins (d = 0.2–0.6) and number of fins (n = 1–3).

From numerical methods point of view the used non-primitive variables allows to perform numerical simulation of convective heat transfer in three-dimensional (3D) regions with two advantages, namely, excluding difficulties that can be found using vector potential functions and reducing the computational time compared to primitive variables and SIMPLE-like algorithms. From a physical point of view, it has been shown that using solid fins can intensify the heat transfer performance compared to cavities without any fins. Fins located close to the bottom wall of the cavity have a better heat transfer rate than those placed close to the upper cavity surface. At high Rayleigh numbers, increasing the fins length beyond 0.6 leads to a reduction of the average Nusselt number, and one solid fin can be used to intensify the heat transfer.

The present numerical study is based on hybrid approach for numerical analysis of convective heat transfer using velocity and vorticity that has some mentioned advantages. Obtained results allow intensifying the heat transfer using solid fins in 3D chambers with appropriate location and length.

The purpose of this paper is to examine numerically the three natural convection of air induced by temperature difference between a cold outer cubic enclosure and a hot inner cylinder. Simulations have been carried out for Rayleigh numbers ranging from 103 to 107 and titled angle of the enclosure from 0° to 90°. The developed mathematical model is governed by the coupled equations of continuity, momentum and energy, and is solved by finite volume method. The effects of cylinder inclination and Rayleigh number on fluid flow and heat transfer are presented. The distribution of isocontours of temperature and isosurfaces of velocity eventually reaches a steady state in the range of Rayleigh numbers between 103 and 107 for titled inclination of 90°; however, for the remaining inclinations, Rayleigh number must be in the range 103-106 to avoid unsteady state, which is manifested by the division of the area containing the maximum local heat transfer rate into three parts for a Rayleigh number equal to 107 and an inclination of 90°. We mention that instability study is not included in the present paper, which is solely devoted to three-dimensional calculations. Results also indicate that optimal average heat transfer rate is obtained for both high Rayleigh number of 106 and high inclination of 90° for the two cases of the inner cylinder and cubical enclosure.

The manuscript deals with prediction of the three-dimensional natural convection phenomena in a cubical cavity induced by an isothermal cylinder at the center with different inclinations by simulating the flow using highly numerical methods such as finite volume method.

It is found that the local Nusselt number through active walls for titled inclination set at 90°, the symmetry of the flow is conserved and the area containing the maximum heat transfer is divided into three smaller areas situated near the upper portion of the wall, taking the maximum value. That may be due to the preparation of local occurrence of instabilities and bifurcation phenomena that appear for Ra > 107, which is not included in the present paper to save journal space. It was found also that an optimal heat transfer appears when the cylinder orientation becomes vertical (a = 90°). For this inclination, buoyancy forces act upward, corresponding to an aiding situation. In addition, heat transfer rate is increasing with Rayleigh numbers, so correlations of average Nusselt through the cubical cavity and the cylinder are established as function of two parameters (Ra, a). Comparisons of the numerical results with those obtained from all correlations show good agreements.

To the author’s knowledge, studies have thus far adressed three-dimensional cuboids enclosures induced by an inner shape which the location is changed. However, no study has examined three-dimensional natural convection between the inner isothermal cylinder and outer cooled cubical enclosure when the outer enclosure is tilted.

The purpose of this paper is to examine numerically the natural convection heat transfer in a cubical cavity induced by a thermally active plate. Effects of the plate size and its orientation with respect to the gravity vector on the convective heat transfer and the flow structures inside the cavity are studied and highlighted.

The numerical code is based on the finite volume method with semi-implicit method for pressure-linked equation algorithm. The convective and diffusive terms in momentum equations are handled by adopting the power law scheme. Finally, the discretized sets of algebraic equations are solved by the line-by-line tri-diagonal matrix algorithm.

The results show that plate orientation and size plays a significant role on heat transfer. Also, the heat transfer rate is an increasing function of Rayleigh number for both orientations of the heated plate. Depending on the thermal management of the plate and its application (as in electronics), the heat transfer rate is maximized or minimized by selecting appropriate parameters.

The flow is assumed to be 3D, time-dependent, laminar and incompressible with negligible viscous dissipation and radiation. The fluid properties are assumed to be constant, except for the density in the buoyancy term that follows the Boussinesq approximation.

The present work will give some additional knowledge in designing sealed cavities encountered in some engineering applications as in aeronautics, automobile, metallurgy or electronics.

This study aims to deal the numerical simulation on buoyant convection and energy transport in an inclined cubic box with diverse locations of the heater and coolers.

The left/right walls are cooled partially whereas the other walls are kept adiabatic. In the left/right walls, three different locations of the cooler are examined, whereas heater moves in three locations in the middle of the enclosed box. The governing models are numerically solved using the finite-element method.

The simulations are done on several values of the Rayleigh number and cavity inclination angles and different locations of the heater and coolers. The results are presented in the form of streamlines, isosurfaces and Nusselt numbers for different values of parameter involved here. It is recognized that the inclination of the box and the locations of the coolers strongly influence the stream and energy transport inside the enclosed domain.

The present investigation is conducted for steady, laminar, three-dimensional natural convective flow in a box for different locations of cooler and tilting angles of a cavity. The study might be useful to the design of solar collectors, room ventilation systems and electronic cooling systems.

This work examines the effects of different locations of cooler and tilting angles of a cavity on convective heat transfer in a 3D cavity. The study is useful for thermal engineering applications.

The purpose of this paper is to investigate numerically thermal convection heat transfer in closed square and cubical cavities with local energy sources of various geometric shapes.

The analyzed regions are square and cubical cavities with two isothermally cold opposite vertical walls, whereas other walls are adiabatic. A local energy element of rectangular, trapezoidal or triangular shape is placed on the lower surface of the cabinet. The lattice Boltzmann technique has been used as the main method for the problem solution in two-dimensional (2D) and three-dimensional (3D) formulations, whereas the finite difference technique with non-primitive parameters such as stream function and vorticity has been also used.

The velocity and temperature fields for a huge range of Rayleigh number 104–106, as well as for various geometry shapes of the heater have been studied. A comparative analysis of the results obtained on the basis of two numerical techniques for 2D and 3D formulations has been performed. The dependences of the energy transfer strength in the region on the shape of energy source and Rayleigh number have been established. It has been revealed that the triangular shape of the energy source corresponds to the maximum values of the velocity vector and temperature within the cavity, and the rectangular shape corresponds to the minimum values of these mentioned variables. With the growth of the Rayleigh number, the difference in the values of these mentioned variables for rectangular and triangular shapes of heaters also increases.

The originality of this work is to scrutinize the lattice Boltzmann method and finite difference method for the problem of natural convection in 2D and 3D closed chambers with a local heated element.

The main purpose of this work is to arrive at a three-dimensional (3D) numerical solution on mixed convection in a cubic cavity with a longitudinally located triangular fin in different sides.

The 3D governing equations are solved via finite volume technique by writing a code in FORTRAN platform. The governing parameters are chosen as Richardson number, 0.01 ≤ Ri ≤ 10 and thermal conductivity ratio 0.01 ≤ Rc ≤ 100 for fixed parameters of Pr = 0.7 and Re = 100. Two cases are considered for a lid-driven wall from left to right (V+) and right to left (V−).

It is observed that entropy generation due to heat transfer becomes dominant onto entropy generation because of fluid friction. The most important parameter is the direction of the moving lid, and lower values are obtained when the lid moves from right to left.

The main originality of this work is to arrive at a solution of a 3D problem of mixed convection and entropy generation for lid-driven cavity with conductive triangular fin attachments.

The purpose of this paper is to provide a solution for natural convection in a cavity with a partial heater in case of volumetric heating and analysis of the entropy generation.

The control volume method based on three-dimensional (3D) vorticity-potential vector was applied to solve governing equations of natural convection in a 3D cavity with a fin for different governing parameters as external Rayleigh numbers (103=Ra_E=106), internal Rayleigh numbers 103=Ra_I=106, partition height (0.25=h=0.75) and partition location (0.25=c=0.75). A code was written by using Fortran platform.

The edge of the fin becomes important on entropy generation. The ratio of the Ra_I/Ra_E plays the important role on natural convection and entropy generation. The variation of external Rayleigh number becomes insignificant for the Ra_I/Ra_E>1.

The originality of this work is to analyze the entropy generation and natural convection in a cubical cavity with volumetrically heating.

This paper aims to present the numerical models and experimental outcomes pertain to the performance of the parabolic dish concentrator system with a modified cavity-type receiver (hemispherical-shaped).

The numerical models were evolved based on two types of boundary conditions; isothermal receiver surface and non-isothermal receiver surface. For validation of the numerical models with experimental results, three statistical terms were used: mean of absolute deviation, R² and root mean square error.

The thermal efficiency of the receiver values obtained using the numerical model with a non-isothermal receiver surface found agreeing well with experimental results. The numerical model with non-isothermal surface boundary condition exhibited more accurate results as compared to that with isothermal surface boundary condition. The receiver heat loss analysis based on the experimental outcomes is also carried out to estimate the contributions of various modes of heat transfer. The losses by radiation, convection and conduction contribute about 27.47%, 70.89% and 1.83%, in the total receiver loss, respectively.

An empirical correlation based on experimental data is also presented to anticipate the effect of studied parameters on the receiver collection efficiency. The anticipations may help to adopt the technology for practical use.

The developed models would help to design and anticipating the performance of the dish concentrator system with a modified cavity receiver that may be used for applications e.g. power generation, water heating, air-conditioning, solar cooking, solar drying, energy storage, etc.

The originality of this manuscript comprising presenting a differential-mathematical analysis/modeling of hemispherical shaped modified cavity receiver with non-uniform surface temperature boundary condition. It can estimate the variation of temperature of heat transfer fluid (water) along with the receiver height, by taking into account the receiver cavity losses by means of radiation and convection modes. The model also considers the radiative heat exchange among the internal ring-surface elements of the cavity.