Numerical study of mixed convection and entropy generation in the Poiseulle-Benard channel in different angles

The issue of entropy generation and Nusselt number in Poiseuille-Benard channel flow are analyzed by solving numerically Navier-Stokes and energy equations with the use of the classic Boussinesq incompressible approximation. The Nusselt number is studied as a function of q. In addition variations of entropy generation and the Bejan number as a function of q and j are studied. The channel angle (q) and irreversibility (j) were changed from -25 to 30 and from 10-5 to 1, respectively, whereas Reynolds, Peclet, and Rayleigh numbers were fixed at Re = 10, Pe = 20/3, and Ra = 104. More over the positive and negative effect of buoyancy force on flow field, Nusselt number and entropy generation are discussed. Optimum angle for dif- ferent irreversibilities are specified by definition h as the rate of the Nusselt number to the entropy generation, the optimum angle was distinguished for different irreversibility. Results show that the Nusselt number changes very slightly and is almost constant when q changes from -10 to 10 and the Nusselt number decreases sharply when q increases from 20 to 30 or decreases from -15 to -25. Moreover it has been found that the entropy generation due to heat transfer is localized at areas where heat exchanged between the walls and the flow is maximum, while the entropy generation due to fluid friction is maximum at areas where the velocity gradients are maximum such as vortex centers. Consequently when q is decreased from -15 to -25 or is increased from 20 to 30 entropy generation for small irreversibilities decreases and increases sharply for large irreversibilities.