Augmentation of thermal performance of heat exchanger using elliptical and circular insert with vertical twisted tape

摘要

Present work deals with the experimental and computational investigation of thermal properties and fluid flow characteristics on circular tube with elliptical inserts. The major axis is taken equal to hydraulic diameter i.e. 6.81cm. A new parameter, height ratio (gamma = b/D) has been defined with three values - 0.45, 0.66, and 0.74. The test section is 1.5 m long which is provided with a constant heat flux of 1000 W/m(2) along with air as working fluid at Reynolds number ranging from 3,000 to 21,000. The results show that the augmentation in heat transfer was six times for case gamma = 0.74 and the maximum thermal performance factor (TPF) obtained is 2.43 for insert with gamma = 0.45 at Re = 3000 over the smooth tube. Computational fluid dynamics (CFD) investigation is also carried out for elliptical inserts, and the results are in good agreement with the experimental results where the maximum deviations in Nusselt number, friction factor, and TPF are +/- 9.39, +/- 8.68, and +/- 8.58%, respectively. CFD investigation for tube having circular inserts with vertical twisted tapes (CVTT) and elliptical inserts with vertical twisted tapes (EVTT) is also presented where the augmentation in heat transfer ranges 3-8 times for CVTT placed in full length and TPF is ranging 1.19-2.63 times for CVTT placed in TL length over to smooth tube.