Three-Dimensional Transient Natural Convection in a Horizontal Cylinder: A Numerical Analysis
Three-Dimensional Transient Natural Convection in a Horizontal Cylinder: A Numerical Analysis

Author: James A. Liburdy

Publisher:

Published: 1980

Total Pages: 39

ISBN-13:

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A mathematical formulation of the governing equations for transient natural convection in a finite length horizontal cylinder is developed and constructed in finite difference form. The boundary conditions consist of radial heat flux for a specified thermal resistance, axial heat flux from one closed end and three different conditions at the other end to represent exposure to a hot convecting gas environment. The formulation is expressed in terms of the vorticity equations, energy equation and a set of vector potential equations. Solution is by the alternating direction implicit method for the vorticity and energy equations and the successive over relaxation method for the vector potential equations. Numerical experiments were run using the model to determine the local wall heat flux and the local wall temperatures. A heat transfer correlation is presented in terms of the Nusselt and Rayleigh numbers. Steady state conditions are obtained for the nondimensional time approximately equal to .005. Circumferential heat transfer coefficient variations are shown with larger values occurring near the top of the cylinder. Axial coefficients vary within approximately 10 percent with the largest values occurring near the center of the cylinder. With respect to test conditions at the AEDC facility, the convective components appear to be less than 10 percent of the radiative heat flux to the cylinder walls when a high temperature gas (air) is enclosed in the cylinder.

Investigations of Turbulent Natural Convection in a Horizontal Cylinder
Investigations of Turbulent Natural Convection in a Horizontal Cylinder

Author: James A. Liburdy

Publisher:

Published: 1982

Total Pages: 42

ISBN-13:

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An experimental study examines the transient natural convective heat transfer in a liquid filled horizontal cylinder with a constant uniform heat flux. The transient and quasi-steady state response of the local and averaged Nusselt number is correlated with a modified Rayleigh number. The transient response is mapped against the stretch time scale represented by the product of the Fourier modulus and modified Rayleigh number. Internal fluid temperature probe measurements and flow visualization reveal boundary layer type flow along the side walls with increased temperature fluctuations near the wall. Unstable mixing zones occur neat the top and bottom of the cylinder which may be three dimensional.

An Experimental Study of Natural Convection Heat Transfer from a Horizontal Cylinder Array Vertically Aligned to and Confined by a Single Wall and Two Walls
An Experimental Study of Natural Convection Heat Transfer from a Horizontal Cylinder Array Vertically Aligned to and Confined by a Single Wall and Two Walls

Author: Thamir R. Al-Alusi

Publisher:

Published: 1989

Total Pages: 448

ISBN-13:

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Convection heat transfer was experimentally investigated for two different geometries. One case had three horizontal cylinders in a vertical plane placed between two vertical walls. The second case had three horizontal cylinders in a vertical plane with only one vertical wall. Several different cylinder center-tocenter spacings were investigated. The wall spacings for the two wall and single wall cases were also varied. The cylinders were placed in a still air medium at atmospheric pressure and were maintained at a constant heat flux. The modified Rayleigh number, based on the diameter of the cylinders, ranged from 6.2 x 104 to 1.2 x 106. A scale analysis was performed to predict the relationship between the Nusselt number and the modified Rayleigh number. A standard finite-difference code was employed to show the temperature distribution and velocity vectors distribution around the cylinders. The results showed that there was a maximum heat transfer from each cylinder at a specific wall-array spacing and a specific center-to-center spacing. Comparisons of heat transfer results with a single free cylinder and a free array of horizontal cylinders were made and discussed. Empirical equations were proposed to predict the effects of the experimental parameters on the heat transfer as expressed by the average Nusselt number of each cylinder or the average Nusselt number of the whole array. Flow visualization was accomplished using laser sheets. The resulting studies showed that the presence of a single wall or the asymmetrical placement of the array between the two walls eliminated the presence of the vortices in the spaces between the cylinders and displaced the stagnation points. The asymmetrical placement of the array between two walls created a reversed current between the two walls.