Interaction Of Natural Convection Research Articles

Impact of thermal radiation on free convection in a differentially heated rolling cubical cabinet

An interaction of natural convection and surface radiation in a rotating cubic cabinet is scrutinized in this article. The cavity has differentially heated walls, namely opposite heated and cooled walls, while the remaining boundaries are adiabatic. The key equations have been written employing the mass, momentum, and energy conservation laws combined with nonprimitive dimensionless variables including vector potential functions and vorticity vector. The resulting set of equations with the corresponding restrictions has been discretized and resolved employing the finite difference procedure employing a uniform grid. The outcomes have been analyzed for a wide range of key characteristics, including the surface emissivity and the Rayleigh and Taylor numbers. The temperature distributions have been shown during a complete revolution of the chamber. The influence of the governing parameters has been described by changing the mean convective and radiative Nusselt numbers. The results have shown that rotation and radiation can be used as key mechanisms to control the energy transport. Moreover, employing the Boussinesq approach the thermal centrifugal force can be neglected for moderate Rayleigh and Taylor numbers.

Numerical study of the coupled natural convection with surface radiation in a cylindrical annular enclosure

The interaction of natural convection with thermal radiation of black surfaces in a cylindrical enclosure filled with air has been numerically investigated. The steady-state continuity, Navier-Stokes and energy equations were discretized using the control volume method and solved numerically via the SIMPLER algorithm. Effects of Rayleigh number (Ra), wall emissivity (εp) and height ratio parameter (X) are studied. The result shows that surface radiation significantly altered the temperature distribution and the flow patterns, especially at higher Rayleigh numbers. The total average Nusselt number has also been discussed for valuating heat transfer through the enclosure.

Combined natural convection and radiation with temperature-dependent properties

This paper investigates the effects of temperature dependence of radiative properties of a medium on radiation and natural convection interaction in a rectangular enclosure. The radiative transfer equation is solved using the discrete ordinates method, and the momentum, continuity, and energy equations are solved by the finite volume method. Effects of the conduction-to-radiation parameter, Rayleigh number, and optical thickness are discussed. Results show that temperature dependence of radiative properties affects the temperature gradient, and hence the energy transport even in relatively weak radiation condition. On the other hand, temperature dependence of radiative properties has relatively insignificant effects on convection characteristics, even though it does affect the way that energy transfers into the system. As conduction-to-radiation parameter is decreased or Rayleigh number is increased, the effects of temperature dependence of radiative properties become more significant.

Non-Boussinesq convection in a square cavity with surface thermal radiation

The interaction of natural convection with surface radiation in a differentially heated square cavity filled with air is considered under large temperature differences. The study has been investigated by direct numerical simulations with a two-dimensional finite volume numerical code solving the time-dependent Navier–Stokes equations under the Low Mach Number (LMN) approximation. Calculations were performed for cases with strong non-Boussinesq effects. The results reveal that the fluid flow and heat transfer are influenced significantly by the surface radiation. At steady state, the top wall is cooled and the bottom wall is heated compared to the case without radiation. The air flow is reinforced near the horizontal walls and the thermal stratification at the core is reduced. The surface radiation reduces the convection heat transfer at the hot wall and increases it on the cold wall.Transition from steady to unsteady flow has also been investigated. By comparing the solutions in pure convection, the results in combined convection–radiation show that the radiation promotes the occurrence of instabilities leading to an early transition to the unsteadiness and contributes to the modification of the physical mechanism responsible for their onset.

Experimental and Numerical Study of Mixed and Natural Convection in an Enclosure With a Discrete Heat Source and Ventilation Ports

An experimental and numerical study has been carried out in order to investigate mixed and natural convection heat transfer in a two-dimensional enclosure. A discrete isothermal heat source is located at one of the vertical walls. Also, two ventilation ports are at the bottom and on top of the opposite wall. A forced flow condition was imposed by providing an inlet of air at the bottom port. A Mach–Zehnder interferometer was used to visualize the temperature field within the enclosure and to determine the local and average heat transfer characteristics of the heat source. Five heater positions on the vertical wall and different Rayleigh numbers (4.5 × 105 to 1.15 × 106) and Reynolds numbers (120 to 1600) were considered in the experiments. A finite volume code has been developed based on the SIMPLE algorithm and hybrid discretization scheme for the numerical study. It is observed that the interaction of natural convection with the forced flow leads to various flow fields depending on the Richardson number, Reynolds number and the heater position. Also, results show different trends for variation of the average Nusselt number with the heater position at low and high Reynolds numbers. An optimum position for the heat source, at which the maximum heat transfer is achieved, exists for high Reynolds numbers and has been found to be at the middle of the vertical wall.

Thermophoresis Particle Deposition: Natural Convection Interaction from Vertical Permeable Surfaces Embedded in a Porous Medium

Thermophoresis Particle Deposition: Natural Convection Interaction from Vertical Permeable Surfaces Embedded in a Porous Medium

Effect of Surface Radiation on Natural Convection in Parabolic Enclosures

The interaction of natural convection and surface radiation in two-dimensional parabolic cavities heated from below with insulated walls and flat top and bottom walls is studied numerically. The shape of the cavities arises from the design of non-imaging optics-based compound parabolic concentrators (CPC). A numerical model based on finite differences is developed to solve the mass, momentum, and energy equations. A coordinate transformation is used to map the parabolic shape into a rectangular domain where the governing equations are solved. The results show that surface radiation significantly changes the temperature distribution and local Nusselt number inside the parabolic enclosure. Solutions are obtained for two different parabolic geometries that correspond to two different levels of concentration.

Interaction of turbulent natural convection and surface thermal radiation in inclined square enclosures

Two-dimensional numerical studies of flow and temperature fields for turbulent natural convection and surface radiation in inclined differentially heated enclosures are performed. Investigations are carried out over a wide range of Rayleigh numbers from 108 to 1012, with the angle of inclination varying between 0° and 90°. Turbulence is modeled with a novel variant of the k–e closure model. The predicted results are validated against experimental and numerical results reported in literature. The effect of the inclination of the enclosure on pure turbulent natural convection and the latter’s interaction with surface radiation are brought out. Profiles of turbulent kinetic energy and effective viscosity are studied to observe the net effect on the intensity of turbulence caused by the interaction of natural convection and surface radiation. The variations of local Nusselt number and average Nusselt number are presented for various inclination angles. Marked change in the convective Nusselt number is found with the orientation of enclosure. Also analyzed is the influence of change in emissivity on the flow and heat transfer. A correlation relevant to practical applications in the form of average Nusselt number, as a function of Rayleigh number, Ra, radiation convection parameter, N RC and inclination angle of the enclosure, φ is proposed.

NUMERICAL ANALYSIS OF NATURAL CONVECTION WITH SURFACE RADIATION IN A SQUARE ENCLOSURE

The interaction of natural convection with thermal radiation of gray surfaces in a square enclosure filled with air has been numerically investigated. The effect of radiation on the flow field, temperature distribution, and heat transfer is predicted. The result shows that surface radiation significantly altered the temperature distribution and the flow patterns, especially at higher Rayleigh numbers. The average convection Nusselt number increases with the increase of Ra. The presence of surface radiation can change the value of average convection Nusselt number, but only little variation can be observed with the increase of emissivity. The average radiative Nusselt number rises quickly with the increase of emissivity, and radiation heat transfer plays an important part in overall heat flux at larger emissivity. The correlation of entire average Nusselt number has also been discussed for evaluating heat transfer through the enclosure,

THERMAL RESPONSE OF A HEATED VERTICAL PLATE FIN WITH NATURAL CONVECTION-RADIATION INTERACTION

ABSTRACT The interaction of natural convection with thermal radiation affects the transient response of a plate fin; this is studied analytically. The Rosseland approximation is applied to describe radiative heat transfer in the flow boundary layer. A cubic spline colocation method is used to perform the numerical computation. The important parameters of the problem are the aspect ratio, the convection-conduction parameter, and the radiation-conduction parameter. The results indicate that the time taken for the fin root to reach the specified temperature is almost independent of aspect ratio at large heat input. The surface heat flux is affected to a large extent by the convection-conduction parameter. The surface heat transfer rate increases with increasing radiative interaction. At large heat input, the temperature distribution at the base of the fin is nearly isothermal.

Interaction of Natural Convection and Gravity Segregation in Oil/Gas Reservoirs

Summary The distribution of chemical components in reservoirs can be significantly affected by diffusional segregation caused by gravity. This segregation, however, can be opposed by convective mixing. Parallel-flow solutions are presented that shed light on the interaction of these two processes. The solutions are used to explain results of numerical calculations of convection-diffusion in model rectangular reservoirs.

An interferometric investigation of the effect of separation distance and temperature imbalance on natural convection for two horizontal cylinders at moderate Rayleigh numbers

An experimental investigation has been carried out to study the natural convection interaction between a pair of horizontal cylinders located directly one above the other. It is found that the presence of the upper cylinder has negligible effect on the heat transfer rate from the lower cylinder, thus attention has been given on the heat transfer characteristics from the upper cylinder The ratio S/D of the center-to-center separation distance was varied from three to six by a step of one. The temperature imbalance ΔT1/ΔT2 was also varied independently. The experiments were conducted with Rayleigh numbers varying from 6300 to 13000. It was found that maximum enhancement of the heat transfer from the upper cylinder for a given ratio S/D depends primarily from the temperature imbalance ΔT1/ΔT2 and weakly from the Rayleigh number. The experimental results for the maximum enhancement, can be presented fairly well by the empirical formula (ΔT1/ΔT2)op=0.136(S/D)0.75 for 2≦S/D≦6, 1000≦Ra≦200000. The findings of this investigation agree closely with those previously reported in the literature.

Interaction of Natural Convection Wakes Arising From Thermal Sources on a Vertical Surface

A numerical study of the interacting natural convection flows generated by isolated thermal energy sources, such as electronic components, located on a vertical adiabatic surface is carried out. Of particular interest were the effects of the wake on the heat transfer from and the flow over a downstream heat source and the nature of the wall plume far from the sources. This consideration is related to the positioning of finite-sized electronic components and the relevant heat removal process. A two-dimensional flow is considered, without making the boundary-layer assumptions. The full elliptic equations governing the flow are solved numerically, employing finite-difference methods. The results are compared with the boundary layer solutions, obtained in earlier studies, in order to determine the nonboundary-layer effects. This is an important consideration in several practical circumstances that involve small heat inputs, sources of relatively small heights, and small separation distances between the sources. It is found that the flow downstream rapidly approaches the characteristics of an idealized wall plume due to a line source. A boundary-layer flow arises far from the heat sources and this flow provides the boundary conditions for the elliptic problem. The nature of the velocity and temperature fields is studied in detail for a wide range of governing parameters and the heat transfer coefficients for the heated elements determined. The relevance of the results obtained to practical systems is outlined, particularly for small Grashof numbers which necessitate a solution of the full equations.