Analysis of combined radiation and convection heat transfer inside a porous medium with heat source electronic devices

In this study, a numerical study is performed on the cooling phenomenon of three heat source electronic devices. The electronic devices are cooled in the form of natural heat transfer by the airflow in a porous medium. Electronic devices are installed on the boundary walls of a square environment. Cooling simulations are performed by drawing flow lines and constant temperature lines. Our main goal is to find the highest cooling rate in different Darcy numbers and different Rayleigh numbers in our investigation. The range of Darcy numbers and Rayleigh numbers is between 0.0001 to 0.01 and 1000 to 100,000, respectively. Our investigation showed the maximum cooling is obtained at the Darcy number of about 0.01. And also, by decreasing the value of Darcy number, a higher cooling rate for the hot boundary walls is achieved.

Numerical Study of Heat Transfer by Natural Convection in Concentric Hexagonal Cylinders Charged with a Nanofluid

In this document, a numerical study of the natural convection of steady-state laminar heat transfer in a horizontal ring between a heated hexagonal inner cylinder and a cold hexagonal outer cylinder. A Cu - water nanofluid traverses this annular space. The system of equations governing the problem was solved numerically by the fluent calculation code based on the finite volume method. Based on the Boussinesq approximation. The interior and exterior sides from the two cylinders are maintained at a fixed temperature. We investigated the impacts of various thermal Rayleigh numbers (103≤ Rat ≤2.5x105), and the volume fraction from the nanoparticles (0≤ Ø ≤0.12) on fluid flow and heat transfer performance. It is found that in high thermal Rayleigh numbers, a thin thermal boundary layer is illustrated at the flow that heavily strikes the ceiling and lower from the outer cylinder. In addition, the local and mean Nusselt number from a nanofluid are enhanced by enhancing the volume fraction of the nanoparticles.The results are shown within the figure of isocurrents, isotherms, and mean and local Nusselt numbers. Detailed results of the numerical has been compared with literature ones, and it gives a reliable agreement.

Multicomponent mixing on the “diffusion – convection” transition boundary at elevated pressures

An experimental and theoretical study of three-component mixing at the “diffusion – convection” boundary at elevated pressures is carried out. It is shown that the pressure dependence of the dimensionless parameter α, defined as the ratio of the experimental values of the component concentrations to those calculated by the Stefan-Maxwell equations, has characteristic regions due to the interaction of structural formations moving towards each other, in which a transition from one critical motion to another occurs. Within the framework of a linear analysis of the stability of a ternary gas mixture for a vertical circular cylinder channel, it is shown that scale perturbations determining the transition from one type of flow to another correspond to a certain value of the perturbation mode n and the critical Rayleigh numbers.

Numerical Investigation of Heat Transfer with Natural Convection in a Regularly Heated Elliptical Cylinder Submerged in a Square Fence Loaded With a Nanofluid

During this first paper, numerical research from the natural convection of steady-state laminar heat transfer into a horizontal ring within a heated internal elliptical surface and a cold external square surface is presented. A Cu - water nanofluid, traverses this annular space. For different thermal Rayleigh numbers varying from 103 to 2.5x105 and different volume fractions from the nanoparticles. The arrangement from equations directing the problem was resolved numerically with the Fluent computational language founded on the finite volume approach. Based approaching the Boussinesq approach. The interior and exterior surfaces from the two cylinders are maintained at a fixed temperature. We investigated the impacts of various thermal Rayleigh numbers, the volume fraction from the nanoparticles, and the effect of the eccentricity of the internal cylinder on the natural convection. The results are shown within the figure of isocurrents, isotherms, and mean and local Nusselt numbers. The objective of this investigation is to examine the impact of different parameters on the heat transfer flow.

Pressure-Velocity Coupling Schemes for Bouyancy Driven Flow in a Differentially Heated Cavity Using F.V.M and Matlab

Numerical analysis of fluid flow is anchored on the laws of conservation. A challenge in solving the momentum equation arises due to the unavailability of an explicit pressure equation. To avoid solving the pressure term most researchers have eliminated it by cross differentiating the x and the y two dimensional momentum equations and subtracting them. This method introduces more variables to be solved in comparison to the primitive variables and is restricted to two-dimensional flows as streamlines do not exist in three-dimension. This method thus presents a serious limitation in analysis of fluid flow. In this study an equation for computing pressure has been developed using pressure - velocity coupling and used in solving the governing equations. The performance of three pressure velocity schemes namely; the Semi Implicit Method for Pressure linked Equation (SIMPLE), SIMPLE Revised (SIMPLER) and SIMPLE Consistent (SIMPLEC) for laminar buoyancy driven flow has been tested in order to establish the scheme that gives results consistent with bench mark data. The equations governing the flow are solved iteratively using finite volume method together with the central difference interpolating scheme. The solutions are presented for Rayleigh numbers of 103, 104, and 105. This resulted in the velocity profiles for the SIMPLE, SIMPLER, and SIMPLEC algorithm for a Rayleigh number of 104 and 105 converging to the same path. At a Rayleigh number of 103 however, SIMPLER algorithm undergoes a degradation in convergence with grid refinement at the baffle region. Results predicted by using the SIMPLEC algorithm are thus able to effectively compute the velocity of fluid flow in a differentially heated square enclosure with baffles for both low and higher Rayleigh numbers irrespective of the grid size.

Dynamics and length scales in vertical convection of liquid metals

Using complementary experiments and direct numerical simulations, we study turbulent thermal convection of a liquid metal (Prandtl number $\textit {Pr}\approx 0.03$ ) in a box-shaped container, where two opposite square sidewalls are heated/cooled. The global response characteristics like the Nusselt number ${\textit {Nu}}$ and the Reynolds number $\textit {Re}$ collapse if the side height $L$ is used as the length scale rather than the distance $H$ between heated and cooled vertical plates. These results are obtained for various Rayleigh numbers $5\times 10^3\leq {\textit {Ra}}_H\leq 10^8$ (based on $H$ ) and the aspect ratios $L/H=1, 2, 3$ and $5$ . Furthermore, we present a novel method to extract the wind-based Reynolds number, which works particularly well with the experimental Doppler-velocimetry measurements along vertical lines, regardless of their horizontal positions. The extraction method is based on the two-dimensional autocorrelation of the time–space data of the vertical velocity.

Numerical Analysis of Natural Convection Heat Transfer Inside an Inverted T-Shaped Cavity Filled with Nanofluid

This assessment is centered on the characteristics of natural convection heat transfer of Aluminium Oxide-Air nanofluid inside an inverted T-shaped enclosure with differentially heated sidewalls. The left edges of the enclosed cavity have been treated as a heated wall and are kept at a constant temperature. The right edges are also maintained at a constant temperature but lower than the heated wall. The top and bottom faces of the cavity have been considered adiabatic. The evaluation has been numerically investigated using ANSYS fluent. The effect of different significant parameters like volume fraction of nanoparticles, the shape of the enclosure, and Rayleigh number on the heat transfer characteristics inside an inverted T shape enclosure have been investigated. In this numerical analysis, a series of DNS simulations have been conducted for different Rayleigh numbers in the range of 103 to 106, the volume fraction of particles in the range 0≤ φ ≤0.1, and for the different aspect ratios for the inverted T shape have been conducted. The outcomes of this CFD analysis indicate a remarkable rise in the average heat transfer coefficient with the rising volume fraction of Al2O3 particles in the air. An increase of the average Nusselt number was also observed with the increase of Rayleigh number, but it drops slightly at a higher volume fraction of nanoparticles due to an increase in conductive heat transfer. For Rayleigh numbers ≥ 104, both the average Nusselt number and average heat transfer coefficient decrease up to a certain shape of the cavity aspect ratio. After that cavity aspect ratio, both the parameters value increase. But in the case of Rayleigh number = 103, both of the values decrease with the increase in the cavity aspect ratio.

Free Convective Heat Transfer in a Closed Gap between Concentric Semi-Hemispheres

Free convective heat transfer in the closed gap between concentric semi-hemispheres is quantified by means of a numerical approach based on the volume control method using the SIMPLE algorithm. The average Nusselt number is determined for several configurations obtained by varying the cavity’s aspect ratio between 0.15 and 1.5, while the Rayleigh number varies within the 5.33 × 103–4.50 × 108 range. The results show that the correlations available in the literature dealing with concentric whole spheres cannot be used for the configuration treated here. The new correlation between the Nusselt and Rayleigh numbers proposed in this work can be applied in various engineering sectors, such as in the electronic packaging considered in this present work, buildings, and architecture.