Effects of spiral start number and depth ratio of corrugated tube on flow and heat transfer characteristics in turbulent flow region

Abstract

Influence of spirally-corrugated tubes on heat transfer (Nu), pressure loss (f) and thermal enhancement factor (TEF) characteristics was numerically investigated. The physical models of spirally-corrugated tubes and also a straight circular tube were built for the comparative study. The predictions were performed for the spirally-corrugated tubes with spiral start numbers (N) of 2, 3, 4 and 5 and depth ratios (DR = e/D) of 0.02, 0.04, 0.06, 0.08, 0.1, 0.12, 0.14 and 0.16 at Reynolds numbers of 5000, 8000, 14000 and 20000. The numerical results show that the spiral corrugated tubes created two types of flow structures: main swirl flows (appear around the core) and secondary swirl flows (appear near tube wall) which facilitate heat transfer between the fluid and the tube walls. The overall heat transfer depends on the competition between two effects: the positive effect of the stronger swirl intensity by increasing start number and the negative effect of the difficulty of fluid transfer into grooves by increasing depth ratio. For the investigated range, the corrugated tubes yield Nusselt numbers and thermal performance factors varying from 0.82 to 2.16 times and 0.66-1.2 times of the straight circular tube, respectively. The highest thermal enhancement factor (TEF) of 1.2 is achieved by using the tube with spiral start number of 4 having moderate depth ratio of 0.08 at Re = 5000.

Numerical study on heat transfer and flow resistance characteristics of multi-head twisted spiral tube

“…The heat transfer enhanced mechanism of twisted tubes are similar with spiral corrugated tubes [6][7][8][9][10][11] and threaded grooved tubes [12]. Secondary flow is generated by variety of tube shape, which periodically destroys the heat transfer boundary layer of the tube wall.…”

Thermal and swirl flow topologies in a twisted square duct with a multi-twisted tape installed

“…A spirally-coiled twisted-duct with twist-pitches, tp, of 0.05-0.15 m and coil-pitches, cp, of 0.015-0.035 m were employed. The maximum augmentation of the Nusselt number and friction factor were found by using the spirally-coiled twisted-ducts with tp = 0.05 m and cp = 0.015 m. Kongkaitpaiboon et al (2019) used corrugated tubes with various numbers of starts and depth ratios heat transfer enhancement. It was found that a corrugated tube generated swirl flow which improved fluid mixing and augmented heat transfer rate.…”