Natural Convection Heat Transfer From A Horizontal Cylinder Between Vertical Confining Adiabatic Walls PDF Download

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.