COMPARISON BETWEEN TWO METHODS FOR ENHANCING HEAT TRANSFER IN SEPARATED CONVECTION FLOWS-SECOND LAW ANALYSIS

In the present work, a laminar forced convection flow over a backward-facing step
(BFS) in a duct is investigated. This study concerns the practical application of entropy generation
analysis in separated convective flow for the first time. Two different methods, (i) attaching a
baffle to the channel top wall and (ii) employing suction for enhancing heat transfer performance,
are compared by the second law criteria. Entropy generation in the flow domain which indicates
the amount of irreversibilities in convective flow is computed numerically. Heat transfer and
viscous dissipation are the two sources of entropy generation in convective flow. The set of
governing equations defining conservations of mass, momentum and energy are solved
numerically to calculate velocity and temperature profiles which are needed for estimating entropy
generation. The SIMPLE algorithm is used to resolve the pressure-velocity coupling. Numerical
expressions, in terms of entropy generation number (Ns) and Nusselt number (Nu) are derived in
dimensionless forms. The total entropy generation is also calculated in different case studies for
comparing the amount of irreversibilities. Numerical results revealed that using baffles and
permeable walls with suction have considerable effects in enhancing heat transfer but the presence
of baffle produces more irreversibilities than the suction technique.