HEAT-TRANSFER AND PRESSURE-DROP CHARACTERISTICS OF FLOW IN CONVERGENT AND DIVERGENT DUCTS

The heat transfer and pressure drop characteristics of the flow in convergent and divergent ducts of rectangular cross-section are obtained through the simulation of the flow by a three-dimensional parabolic model. The results show that in both convergent and divergent flows heat transfer decreases and pressure drop increases sharply near the entrance region of the ducts. Generally, the Nusselt number increases with increasing convergent/divergent angle, aspect ratio, or Reynolds number, and the pressure drop increases with increasing convergent/divergent angle or decreasing aspect ratio or Reynolds number in both flows. However, an increasing convergent/divergent angle may also result in a lower pressure drop owing to the recovery of static pressure from dynamic pressure. Furthermore, the pressure drop in a divergent flow is generally lower than that in a convergent flow except in the entrance region. For divergent flows with high divergent angle or high Reynolds number, flow separation may occur.