Mechanism Study of Heat Transfer Enhancement Using Twisted Hexagonal Tube with Slurry from Biogas Plant

Abstract

Waste-heat recovery from discharged slurries is important to improve the biogas production efficiency but still remains challenge duo to the special properties of slurries in anaerobic digestion process. In this work, numerical study was carried out to investigate the flow field, and heat transfer performance of slurry from biogas plant in the twisted hexagonal and other twisted tubes was simulated with computer fluid dynamic (CFD) for the first time. The numerical method was validated with experimental data from the literature. The heat transfer performance and flow resistance of twisted hexagon tube were calculated and compared with other types of twisted tubes. The enhancement factor of the twisted hexagonal tube reached to 2 and kept optimum at turbulence flow region compared to the twisted tubes with square and elliptical cross section. Meanwhile, the mechanism of heat transfer enhancement with different twisted tubes was further studied, and the optimal field synergy and minimum local circulation flow near the wall are the main reasons for the high performance and low flow resistance of the twisted hexagonal tube.