Buoyancy Effects on Entropy Generation in the Entrance Region of Isothermal/Adiabatic Vertical Channel

Abstract

The entropy generation due to laminar mixed convection in the entrance of vertical channel between two isothermal/adiabatic parallel plates has been numerically investigated. The effects of the modified buoyancy parameter (Gr/Re) and other operating parameters such as the entrance temperature ratio (τ), Reynolds (Re), and Eckert (Ec) numbers on the entropy generation have been presented and discussed in this article. The optimum values of the modified buoyancy parameter (Gr/Re)optimum at which the entropy generation assumes its minimum has been obtained and found to be sensitive to the variation of the entrance temperature ratio (τ) while it is less sensitive to the variation of Re and Ec numbers. (Gr/Re)optimum was found to vary between 66.5 and 24 when τ varies between 1 and 2, respectively. On the other hand, (Gr/Re)optimum varies between 32 and 31 when Re number varies from 300 to 1500, respectively. The results revealed that the entropy generation increases with Ec that has almost no effect on the optimum value of the modified buoyancy parameter. The results also revealed that there exists an optimum value Re number at which the entropy generation assumes a minimum value. These values of Re number were found to be of minor independence on the buoyancy parameter since it varies between 480 for buoyancy-opposed flows and 490 for buoyancy-aided flows of Gr/Re = 90, respectively. The developments of other important parameters such as Bejan number have been also analyzed and presented.