Zhiyun Wang

Combined Heat Transfer by Natural Convection – Conduction and Surface Radiation in an Open Cavity Under Constant Heat Flux Heating

Combined heat transfer by natural convection-conduction and surface radiation in an open cavity heated by constant flux is studied here. The laminar flow is solved numerically by employing the SIMPLE algorithm with QUICK scheme. The numerical results show that both radiation and solid conduction increase the average total Nusselt number. The average total Nusselt number is a linear increasing function of emissivity when emissivity is larger than 0.2. The heat conduction of a conductive wall increases the total cooling effect, but its effect is close to a limit when the conductivity ratio exceeds 100. The increase due to radiation ranged from 54.1% to 64.0%.

NUMERICAL SIMULATION OF UNSTEADY NATURAL CONVECTION FROM HEATED HORIZONTAL CIRCULAR CYLINDERS IN A SQUARE ENCLOSURE

In this article, a 2-D numerical study is carried out to investigate the effect of this interaction on natural convection from two heated horizontal cylinders confined in a square enclosure with isothermal walls at the heat sink temperature. The simulations are carried out for Rayleigh numbers between 103 and 107, and dimensionless horizontal distances of cylinders between 0.1 and 0.4. The results show that the variation of the area-averaged Nusselt number strongly depends on the distance between the two cylinders if Rayleigh numbers are less than 104. In contrary, the effect of cylinder spacing on heat transfer was found to be nearly negligible when the Rayleigh number is between 104 and 107. It is also observed that steady state flow and heat transfer undergo periodical oscillation, and ultimately chaotic oscillation in special positions of cylinders can occur.

Numerical Simulation of Steady Mixed Convection Around Two Heated Circular Cylinders in a Square Enclosure

In this paper, a numerical study has been carried out to investigate the steady-state mixed convection around two heated horizontal cylinders in a square two-dimensional enclosure. The cylinders are located at the middle of the enclosure height and the walls of the cavity are adiabatic. Streamlines and isotherms are produced and the effects of cylinder diameter, Reynolds number, and Richardson number on the heat transfer characteristics are numerically analyzed. The average Nusselt number over the surface of cylinders and average nondimensional temperature in the enclosure are also presented. The results show that both heat transfer rates from the heated cylinders and the dimensionless fluid temperature in the enclosure increase with increasing Richardson number and cylinder diameter. However, the trend of average Nusselt number and nondimensional temperature variation is completely opposite when Reynolds number increases. In addition, by increasing the cylinders diameter and Richardson number, the left cylinder is less affected by the inlet flow than right one.

Oscillation and Chaos in Combined Heat Transfer by Natural Convection, Conduction, and Surface Radiation in an Open Cavity

Combined heat transfer by natural convection, conduction, and surface radiation in an open cavity is solved numerically by employing SIMPLE algorithm with QUICK scheme. The unsteady-state flow and heat transfer exhibited periodic oscillating or chaotic behaviors due to formation of the thermal plumes at the bottom wall. If the formation of thermal plumes is periodic, the oscillations of flow and heat transfer are also periodic. On the other hand, chaotic oscillations of flow and heat transfer can be observed when the formation of thermal plumes at the bottom surface is chaotic.

Numerical simulation of transient forced convection in a square enclosure containing two heated circular cylinders

Purpose – Unsteady simulation of forced convection of two heated horizontal cylinders confined in a 2D squared enclosure. The paper aims to discuss this issue. Design/methodology/approach – The finite-volume method is used to solve the transient heat transfer problem by employing quadrilateral mesh type. To solve the governing equations (conservations of mass, momentum and energy) on unstructured control volumes, a second-order quadratic upwind interpolation of convective kinematics scheme for the convection terms and the semi-implicit method for pressure-linked equations pressure correction algorithm were used. Findings – The results indicate that the variation of the area-averaged Nusselt number strongly depends on the Reynolds number. On the contrary, the effect of cylinders’ space on heat transfer was found to be nearly negligible for Re < 460. It is also observed that steady state flow and heat transfer shift to periodical oscillation, and ultimately chaotic oscillation in non-dimensional cylinders d...

A New Heat Transfer Correlation for Turbulent Flow of Air With Variable Properties in Noncircular Ducts

Turbulent flow and heat transfer of air with variable properties in a set of regular polygonal ducts and circular tube have been numerically simulated. All the ducts have the same hydraulic diameter as their characteristic lengths in the Reynolds number. The flow is modeled as three-dimensional (3D) and fully elliptic by using the finite volume method and the standard k-e turbulence model. The results showed that the relatively strong secondary flow could be observed with variable properties fluid. For the regular polygonal ducts, the local heat transfer coefficient along circumferential direction is not uniform; there is an appreciable reduction in the corner region and the smaller the angle of the corner region, the more appreciable deterioration the corner region causes. The use of hydraulic diameter for regular polygonal ducts leads to unacceptably large errors in turbulent heat transfer determined from the circular tube correlations. Based on the simulation results, a correction factor is proposed to predict turbulent heat transfer in regular polygonal ducts. [DOI: 10.1115/1.4027855]

Lattice Boltzmann Method Simulation of Natural Convection Heat Transfer in Horizontal Annulus

The lattice Boltzmann method is employed to simulate the stability and transitions of natural convection in a horizontal annulus with the Prandtl number varying from 0.1 to 0.7 and the Rayleigh number ranging from 103 to 5.0×105. Different flow patterns including steady upward flow, oscillatory upward flow, steady downward flow, and oscillatory downward flow are found for different values of the parameters. The flow pattern is very complex when the Rayleigh number is large. The critical Rayleigh number increases with the increase of the Prandtl number and with the decrease of the aspect ratio.

Numerical Study of a New Heat Transfer Correlation for Turbulent Air Flow in Noncircular Ducts With Variable Properties

Turbulent flow of air with variable properties in a set of regular polygonal ducts and circular tube have been numerically simulated. All the ducts have the same hydraulic diameter as their characteristic length dimension in the Reynolds number. The flow is modeled as three-dimensional and fully elliptic by using the finite volume method and the standard k-e turbulence model is adopted. The performances of the flow and heat transfer have been thoroughly investigated. The results showed that comparatively strong secondary flow can be observed with variable properties fluid. For the regular polygonal duct, the local heat transfer coefficient along circumferential direction is not uniform and there is an appreciable reduction in the corner region. The use of hydraulic diameter for regular polygonal ducts to determine turbulent flow heat transfer from circular tube correlations leads to unacceptably large errors. Based on the simulation results, a correction factor Cϕ is proposed to ameliorate the previous correlations, and the error in the prediction of turbulent heat transfer with the new correlation is within 6%.Copyright

Combined Heat Transfer of Natural Convection-Conduction and Surface Radiation in an Open Cavity Heated by Constant Flux

Combined heat transfer of natural convection-conduction and surface radiation in an open cavity heated by constant flux is studied in this paper. Flow model is laminar and SIMPLE algorithm and QUICK scheme are employed. The relevant parameters are as follows, Prandtl number is 0.7 and dimensionless solid thickness is 0.2, conductivity ratio rangs from 0 to 1000, Rayleigh number ranges from 103 to 109 , surface emissivity ranges from 0 to 1. The numerical results shows secondary circular formed as an effect of radiation which increased the average Nusselt number about from 54.1% to 100.3%.Copyright