Second law analysis of curved rectangular channels

The thermodynamic performance of the curved rectangular channels in laminar flow is numerically investigated in terms of entropy generation. The classical Navier–Stokes equations are adopted, and water is selected as the working fluid. The results show that the geometric parameters have important influences on the heat transfer performance of the channel flows. For the channels with the same cross-section, the Nusselt number increases significantly as the curvature ratio increases at the expense of slight increase of pressure drop; the dimensionless total entropy generation generally tends to reduce as Reynolds number grows, and decreases as the curvature ratio increases at the same Reynolds number. The dimensionless total entropy generation lessens with the reduction of cross-sectional area at the same Reynolds number in the channels with the same radius of curvature. Despite the rapid drop of the Bejan number, we have not found the optimal flow regime for curved rectangular channel laminar flows. The local heat transfer and fluid friction entropy generations mainly occur in the narrow region near the walls, especially the outer wall. The field synergy principle provides an alternative way to explain the heat transfer enhancement mechanism for the curved rectangular channel flows.