Igor V. Miroshnichenko

Numerical simulation of turbulent natural convection combined with surface thermal radiation in a square cavity

Purpose – The purpose of this paper is to present transient turbulent natural convection with surface thermal radiation in a square differentially heated enclosure using non-primitive variables like stream function and vorticity. Design/methodology/approach – The governing equations formulated in dimensionless variables “stream function, vorticity and temperature,” within the Boussinesq approach taking into account the standard two equation k-e turbulence model with physical boundary conditions have been solved using an iterative implicit finite-difference method. Findings – It has been found that using of the presented algebraic transformation of the mesh allows to effectively conduct numerical analysis of turbulent natural convection with thermal surface radiation. It has been shown that the average convective Nusselt number increases with the Rayleigh number and decreases with the surface emissivity, while the average radiative Nusselt number is an increasing function of these key parameters. It has be...

Effect of surface radiation on transient natural convection in a wavy-walled cavity

ABSTRACT Transient natural convection in a differentially heated square cavity that has one vertical wavy wall has been studied numerically. The domain of interest is bounded by vertical isothermal walls and horizontal adiabatic walls. The governing equations formulated in dimensionless stream function, vorticity, and temperature, within the Boussinesq approximation with corresponding initial and boundary conditions, have been solved using an iterative implicit finite-difference method. The main objective is to investigate the effect of the dimensionless time 0 ≤ τ ≤ 0.4, Rayleigh number 104 ≤Ra ≤ 106, surface emissivity 0 ≤ ε < 1, undulations number 1 ≤ κ ≤ 6, and shape parameter 0.6 ≤ a ≤ 1.4 on fluid flow and heat transfer. Results are presented in the form of streamlines, isotherms, and distribution of average total Nusselt number at the wavy wall.

Radiation effect on conjugate turbulent natural convection in a cavity with a discrete heater

A numerical study of a conjugate turbulent natural convection with thermal surface radiation inside a square cavity with heat-conducting solid walls and a local heat source has been performed. Two-dimensional equations for conservation of mass, momentum and energy using k turbulence model with a heat conduction equation inside the solid walls and corresponding boundary conditions have been solved using the finite difference method. The developed numerical method can be widely used in some engineering problems, such as the simulation of heat and mass transfer in heat-generating elements in power engineering. Discrete heater has been simulated by a heat source of constant temperature centrally located on the bottom wall. Numerical solutions have been obtained for Ra=109 and different values of surface emissivity (0<1) and thermal conductivity ratio (10 1,2 1000). It has been found that an increase in surface emissivity and thermal conductivity ratio leads to a growth of the average total Nusselt number, while a rise of surface emissivity only illustrates a reduction of the average convective Nusselt number. The obtained numerical results are useful for predicting the convective and radiative heat transfer in domain similar to the one under consideration.

Unsteady conjugate natural convective heat transfer and entropy generation in a porous semicircular cavity

The problem of unsteady conjugate natural convection and entropy generation within a semicircular porous cavity bounded by solid wall of finite thickness and conductivity has been investigated numerically. The governing partial differential equations with the corresponding initial and boundary conditions have been solved by the finite difference method using the dimensionless stream function, vorticity, and temperature formulation. Numerical results for the isolines of the stream function, temperature, and the local entropy generation due to heat transfer and fluid friction as well as the average Nusselt and Bejan numbers, and the average total entropy generation and fluid flow rate have been analyzed for different values of the Rayleigh number, Darcy number, thermal conductivity ratio, and the dimensionless time. It has been found that low values of the temperature difference reflect the entropy generation, mainly in the upper corners of the cavity, while for high Rayleigh numbers, the entropy generation occurs also along the internal solid–porous interface. A growth of the thermal conductivity ratio leads to an increase in the average Bejan number and the average entropy generation due to a reduction of the heat loss inside the heat-conducting solid wall. [DOI: 10.1115/1.4038842]

Effect of Thermophysical Properties of Solid Walls on Turbulent Modes of Complex Heat Transfer in an Enclosure

Two-dimensional numerical studies were performed for investigation of the effect of thermophysical properties of solid walls on turbulent convective – radiative heat transfer in an air filled square cavity. The main attention was paid to the influence of thermal conductivity ratio1 ≤ κ1, 2 ≤ 1000 and an emissivity of internal surfaces of the solid walls 0 £ < 1 on velocity and temperature fields. Numerical results were obtained by means of the finite difference method. The effect of the governing parameters on the average Nusselt number has been defined. The obtained results provide better technical support for development and research of energy-efficient building materials

Effect of Surface Emissivity on Conjugate Turbulent Natural Convection in an Air-Filled Cavity with a Heat Source

The interaction of conjugate turbulent natural convection and surface thermal radiation in an air-filled square enclosure having heat-conducting solid walls of finite thickness and a heat source has been numerically studied. The primary focus was on the influence of surface emissivity on complex heat transfer. The mathematical model has been formulated in dimensionless variables such as stream function, vorticity and temperature using k-ε turbulent model. The effect of surface emissivity on the average total Nusselt number has been defined. The distributions of streamlines and temperature fields, describing characteristics of the analyzed fluid flow and heat transfer have been obtained. The results clearly show an essential effect of surface radiation on unsteady turbulent heat transfer.