The Effect of Conductive and Non-conductive Flow Diverters on Free Convection Heat Transfer from a Vertical Array of Horizontal Isothermal Cylinders

In this paper a numerical solution method (finite volume) has been applied to investigate the effect of conductive and non-conductive flow diverters on the free convection heat transfer from a vertical array of horizontal isothermal cylinders. The cylinders vertical spacing (center to center distance =H) of 2D, 3D and 4D has been investigated, which D is the cylinder diameter. Rectangular plate diverters with thickness of 1.5 mm and different ratios of cylinder spacing to diverter width, defined as H/W (W is the width of diverter) have been placed between cylinders. Diverters are tilted at different angels φ with respect to horizon. The calculation has been done for various Rayleigh numbers in the range of 103 to104 . The results show that in the case of 2D cylinder spacing, applying both conductive and non-conductive flow diverters decreases the heat transfer rate of cylinders at low Rayleigh numbers (103 ≤ Ra ≤ 3×103 ). However, as the distance between the cylinders increases to 3D and 4D, adding non-conductive diverters leads to an increase in the heat transfer rate of the array. Also, in the cases of 3D, 4D spacing, the use of non-conductive flow diverters results in more increase in heat transfer rate in comparison with the rate of heat transfer resulted by applying conductive diverters while this result for the case of 2D spacing is vice versa. Also the results show that among these variety of configurations, the case of 3D spacing between the cylinders (H=3D), with H/W=1 and diverter's steep equals to 1( φ = 45o ), has got the most percentage of increase in heat transfer rate in comparison with that of the same spacing (H=3D) and without diverters. The obtained numerical results have been compared with the available experimental data and excellent agreement observed.

Keywords:

Free Convection , Horizontal tubes , constant temperature , conductive diverter , nonconductive diverter