Flow Symmetry and Heat Transfer Characteristics of Winglet Vortex Generators Arranged in Common Flow up Configuration

Abstract

The generation of longitudinal vortices is an effective method for promoting thermal performance with a relative low-pressure penalty in heat exchangers. The winglet pair can generate symmetrical longitudinal vortices on the cross-section of the channel. The heat transfer and pressure-loss characteristics of a pair of winglet vortex generators with different transverse pitches are numerically studied in this paper. The winglet pair arranged in a common flow up configuration generates a pair of symmetrical longitudinal main vortices with counter-rotating directions. The symmetrical flow structure induces fluid to flow from the bottom towards the top of the channel in the common flow region between the longitudinal vortices. The flow symmetry of the longitudinal vortices and the heat transfer performance are strongly affected by the transverse pitch of the winglet pair owing to the interaction between the longitudinal vortices. The optimal transverse pitch of the studied winglet pair with the best thermal performance is reported. The increments in the vortex intensity and the Nusselt number for the optimal pitch are increased by up to 21.4% and 29.2%, respectively.

Heat Transfer Enhancement in a Novel Annular Tube with Outer Straight and Inner Twisted Oval Tubes

“…The active techniques, such as using ultrasonic vibration [2] and magnetic fields [3][4][5], need external power. The passive techniques, such as tube inserts [6,7], turbulators [8], vortex generators [9][10][11] and special shaped tubes [12][13][14], can induce strong secondary flow, which has been proven to be beneficial to heat transfer [15][16][17][18][19]. These passive techniques with lower operating costs and higher stability and reliability are the main applied techniques in DPHE.…”