Abstract
Numerical simulations of a two-dimensional laminar forced convection flow adjacent to inclined backward-facing step in a rectangular duct are presented to examine effects of baffle on flow, heat transfer and entropy generation distributions. The main aim of using baffles is to enhance the value of convection coefficient on the bottom wall. But the useful energy can be destroyed due to intrinsic irreversibilities in the flow by the baffle. In the present work, the amount of energy loss is estimated by the computation of entropy generation. The values of velocity and temperature which are the inputs of the entropy generation equation are obtained by the numerical solution of momentum and energy equations with blocked-off method using computational fluid dynamic technique. Discretized forms of the governing equations in the (x, y) plane are obtained by the control volume method and solved using the SIMPLE algorithm. Numerical expressions, in terms of Nusselt number, entropy generation number, Bejan number and coefficient of friction are derived in dimensionless form. Results show that although a baffle mounted onto the upper wall increases the magnitude of Nusselts number on the bottom wall, but a considerable increase in the amount of entropy generation number takes place because of this technique. For validation, the numerical results for the Nusselt number and entropy generation number are compared with theoretical findings by other investigators and reasonable agreement is found.
Highlights
Forced convection flows in channels with abrupt expansion or contraction are widely encountered in engineering applications, such as cooling passages of turbine blades, diffusers, combustors and heat exchangers
These results showed that the flow separation and subsequent recirculation result in very poor heat transfer performance in the region near the backward facing step
The main task of the present study is to investigate the effect of baffle on the entropy generation in laminar forced convection flow, the following results shown in Figures 6 to 10 are due to air flows over inclined step with 60 for three different locations of baffle, D H 1, 2 and 3, three different baffle’s height, hb H 0.2, 0.4 and 0.5, when the baffle’s width is equal to H/2
Summary
Forced convection flows in channels with abrupt expansion or contraction are widely encountered in engineering applications, such as cooling passages of turbine blades, diffusers, combustors and heat exchangers. Flow over a BFS with force convection heat transfer was conducted by other investigators by different numerical techniques [2,3,4,5,6,7] These results showed that the flow separation and subsequent recirculation result in very poor heat transfer performance in the region near the backward facing step. The main aim is to identify the irreversibilities and entropy generation due to baffle against its advantage which is enhancing the convection coefficient in the thermal system Toward this end, the set of governing equations consisting the conservation of mass, momentum and energy and the entropy generation equation are solved by CFD method in the Cartezian coordinate system using blocked-off method. The effects of baffle location and its height on the distributions of Nusselt number, entropy generation number and friction coefficient are explored
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