Influence of the Prandtl number on the thermal performance of tubes with the separation and reattachment enhancement mechanism

摘要

This paper demonstrates that the heat-transfer performance of an enhanced tube with transverse, rectangular disruptions can be predicted with a numerical modeling method, an accomplishment not previously achieved. This computer code is then used to determine the influence of the Prandtl number. The numerical simulation demonstrated that six distinct regions exist: the three rib surfaces, the upstream and downstream recirculation regions, and the boundary-layer development zone. Three zones dominate the thermal performance: the rib top and downstream faces and the downstream recirculation zone. The thermal performance at the rib region begins to dominate tile overall performance as the Prandtl number becomes large. The contribution from the downstream recirculation zone becomes more important and dominates for low Prandtl number fluids such as air. The Reynolds number dependence at the rib region and the downstream recirculation zone is similar to that for reattaching flows with exponents in the 0.65 to 0.75 range. The location of the maximum in the recirculation moves closer to the rib with increasing Reynolds and Prandtl numbers and is bounded upstream by the location of the maximum wall shear stress and downstream by the reattachment length. The high turbulence level near the surface in this region is responsible for the heat-transfer enhancement.