Effect of Porous Media on The Performance Characteristics of a Concentric Vertical Annular Tube

Abstract

In this work, energy analyses were performed to enhance the characteristics and performance of forced convection into vertical annuli with and without porous media. Different sizes of porous media and porosities were used. A three-dimensional numerical simulation of an annular tube with and without porous medium was conducted using ANSYS Fluent software version 17.2. Water liquid was used for Reynolds numbers ranging from 100 to 600 and a wide range of wall heat flux. In the experiment, an annular tube consisting of two concentric cylinders 300 mm long was manufactured. The outer cylinder was made of Teflon, whereas the inner cylinder was made of copper. The inner cylinder had an outer diameter of 20 mm, and the outer cylinder had an inner diameter of 100 mm. Three different porous medium diameters (11, 16 and 25 mm) and three different porosities (0.65, 0.75 and 0.85) were used and tested under steady state to study fluid flow and the heat-transfer properties of the annular tube. Results of the energy analysis indicated that Nusselt number values increased with decreased porosity (i.e., by approximately 4.25, 4.2 and 3.5 times at the porosities of 0.65, 0.75 and 0.85, respectively) compared with those in the annulus without glass balls as porous media at the same glass sphere sizes. Accordingly, the best Nusselt number improvement occurred at the diameter of 16 mm (approximately 4.6 times) and at the lowest porosity of 0.65 (approximately 4.25 times).