An Experimental Study on Forced Convection Heat Transfer From An Embedded Horizontal Cylinders Array in A Porous Medium in Cross Flow

Abstract

An experimental study on forced convection heat transfer from an embedded horizontal cylinders array in a porous medium in cross flow was carried out under constant heated cylinder surface temperature condition. The study included the effect of Peclet number, heated cylinder location in array, and the spaces between cylinders on the heat loss ability from this cylinder, as well as the enhancement in heat transfer rate due to embedding the cylinders array in a porous medium. An experimental set-up was used for this purpose which consists of a blower, air duct, test section, and heating element which is represented by a copper cylinder with a diameter of (12.7 mm) heated internally by an electrical source, which represents transfer and heat loss element through this set-up. The experiments were done at the range of spacing ratios between (1.2 ≤ S / D ≤ 2 ) for the cylinders array consisting of five embedded horizontal cylinders in a porous medium consisted of Alumina granules with a particle diameter rate of (3.938 mm) in a turbulent flow at Peclet numbers between (15 < Pe < 56 ). The study showed that the ability of heated cylinder to heat loss is a function of Peclet number, its location in array, and the spaces between cylinders. This ability is increased by increasing Peclet number, and it was shown that this ability reaches maximum value at the third cylinder in array at a spacing ratio of (S/D=1.6) and also at the fourth cylinder in array at a spacing ratio of (S/D=1.4). Also, it was shown that the heated cylinder at any location in array for almost spacing ratios, there was an increase in the heat transfer as maximum (21%) in comparison with a single embedded cylinder in a porous medium. It was noticed that the maximum enhancement value of heat transfer from a heated cylinder in cylinders array (due to embedding it in a porous medium) was nearly five times the heat that transferred from the same free cylinders array or arrangement at the same flow velocity depending on available data from preceding experimental study.