Heat transfer enhancement mechanism of elliptical cylinder for minichannels with delta winglet longitudinal vortex generators

In order to improve the heat transfer performance in the minichannel with delta winglet longitudinal vortex generators and obtain the heat transfer enhancement mechanism, the flow and heat transfer of four basic models (CFD-I, CFD-V, CFU-I and CFU-V configurations) and four enhanced models with elliptical cylinders are numerically simulated in the range of Reynolds number from 2500 to 10,000. The friction factor, Nusselt number and thermal performance factor are evaluated, and the secondary flow intensity and entropy generation rate are analyzed. The main conclusions are as follows: compared with the basic models, the Nusselt number increase by 8.4-14.1 %, 6.1-12.0 %, -1.9-5.0 % and 11.0-14.9 % respectively after adding the elliptical cylinders, and the thermal performance factor of these four models with elliptical cylinders are within 1.05-1.25, 1.00-1.13, 0.97-1.16 and 1.03-1.22, respectively. Compared with the smooth channel, the Nusselt number of CFD-V and CFU-I configurations with elliptical cylinders increased by up to 61 % and 63 %, respectively, and the overall thermal performance increased by up to 25 % and 22 %, respectively. These two configurations are recommended because they make full use of the fluid accelerated by the elliptical cylinder and effectively improve the strength and influence range of the longitudinal vortexes.