Numerical investigations on enhancement of heat transfer in a compact fin-and-tube heat exchanger using delta winglet type vortex generators

Three dimensional flow and heat transfer in a compact fin-tube cross flow h eat exchanger have been modeled as the flow in a rectangular channel with b uilt-in cylindrical obstacles. The flow past a tube bank has been simulated by a space wise periodic fully developed flow in a computational domain co nsisting of a channel element with one tube, Flow and temperature fields in this element and in another element with two in-line tubes have been compu ted from the numerical solution of three dimensional Navier - Stokes and en ergy equations. Comparison of results show that at low Reynolds number (sim ilar to 400) the Nusselt number in the neighbourhood of the second tube of a two tube in-line configuration is close to the Nusselt number for spacewi se periodic fully developed flow. Computational results also show poor heat transfer in the wake region. In the presence of the winglet type longitudi nal vortex generators in the wake behind the cylinder, heat transfer in thi s region is enhanced significantly. Results show increases in average Nusse lt number due to the vortex generators can be between 20 and 50 percent in the Reynolds number range of 400 and 1200, A factor, defined as the ratio o f increase in Nusselt number to increase in friction factor, of 0.65 to 0.7 8 can be obtained, over the range of Reynolds number mentioned above.