Research On Auto-cleaning Technology Of Self-rotating Spiral In Tube Of Cooling Crystallization Equipment

On the basis of analyzing fouling prevention and removal domestically and overseas, self-rotating spiral automatic-cleaning technique for crystallized fouling is mainly studied. Its technical principle is that inserts of heat transfer equipment are driven by flow kinetic energy of hot fluid, so fouling on heat transfer surface is cleaned automatically. At the same time with thermal boundary layer disturbed, heat transfer process through it occupying most in convective heat transfer, is intensified effectively. Thus it provides the new technique support for energy-saving of heat transfer equipment.Theoretical computation formula of spiral self-rotating kinetic moment is concluded through mechanical analysis. Therefore relationship between kinetic moment and basic technical parameters of spiral is clear, which has engineering guiding role.Numerical simulation on fluid field inside heat tube which installs self-rotating spiral is performed by software FLUENT, because of it has very close relation with heat transfer enhancement mechanism. The results of numerical simulation show that after self-rotating spiral is applied, stream lines near inner wall of heat tube are changed to spiral instead of straight lines. The radial and tangential velocity near inner wall is increased compared with that without inserts in them and thickness of boundary layer is decreased. Therefore, temperature gradient near inner wall of heat tube is reduced sharply, and it is beneficial to decrease salt crystallization rate near inner wall of tube.On the basis of theoretical analysis and numerical simulation, radial pressure model of self-rotating spiral auto-cleaning capability is proposed. There is a concordance between auto-cleaning capability and radial pressure that revolving spiral blade acts on inner walls of heat tubes. According to radial pressure model of auto-cleaning capability, experiment station is established and a lot of tests are performed. Its results show that self-rotating spiral twisted-tape has a minor cleaning effect on the condition that pressure revolving spiral cutters act on inner walls of heat transfer tubes is infinite in vertical tubes. In contrary, it has a significant effect in horizontal heat transfer tubes after blade acts pressure on inner wall of heat transfer tubes because the density of plastic spiral twisted-tape and spiral steel wire is much heavier than that of solution. The steady heat transfer coefficient is enhanced by 113 percent and 87 percent respectively in comparison with that of tubes without any inserts. The density difference between self-rotating spiral twisted-tape with steel wires and solution's is respectively 23 percent and 52 percent higher than the former. The steady heat transfer coefficient is respectively higher 25 percent and 34 percent than the former. Therefore, experiment results are consistent with radial pressure model of self-rotating spiral auto-cleaning capability. The research plays a reference role in developing of self-rotating spiral auto-cleaning capability.