Numerical Investigations on Enhancement of Heat Transfer in a Compact Fin-and-Tube Heat Exchanger Using Delta Winglet Type Vortex Generators

摘要

Three dimensional flow and heat transfer in a compact fin-tube cross flwo heat exchanger have been modeled as the flow in a rectangular channel with built-in cylindrical obstacles. The flow past a tube bank has been simulated by a spacewise periodic fully developed flow in a computational domain consisting of a channel element with one tube. Flow and temeprature fields in this element and in another element with two in-line tubes have been computed forml the numerical solution of three dimensinal Navier-Stokes and energy equations. Comparison of results show that at low Reynolds number (～400) the Nusselt number in the neighbourhood of the seond tube of a two tube in-line configuration is close to the Nusselt number for spacewise periodic fully developed flow. Computatioanl results also shwo poor heat transfer in the wake region. In the presence of the winglet type longitudinal vortex generatiors int ehwake behind the cylinder, heat transfer in this region is enhanced signficantly. Results show increases in average Nusselt number due to the vortex generators can be between 20 and 50 percent in the Reynolds number rnage of 400 and 1200. A factor, defined as the ratio of increase in Nusselt number to increase in fricition factor, of 0.65 to 0.78 can be obtained, over the range of Reynolds number mentioned above.