| Shell-and-tube heat exchangers are widely used in many process industry fields and pronouncing tremendous waste of energy for remaining unresolved fouling problem.Tube side assembled rotors(TSAR) can achieve heat transfer enhancement and online cleaning,with flexible design of structures and materials to meet technical requirements of various shell-and-tube exchangers, lighting up the hope for conquering scale formation.Therefore,it is of great importance to study the performance,mechanism and structure modification of tube side assembled rotors.In this paper,many experimental methods were employed to investigate the disturbed flow characteristics,heat transfer and friction loss of TSAR to analyze its mechanism.Moreover,modified structures were put forward aiming for better performance.Visualization experiment,rotate speed measurement and PIV test gave an exhibition of disturbed flow field by TSAR from qualitatively to quantitatively. Rotate speed of rotors was theoretically deduced,considering geometrical, mass and viscous factors.A non-rotating flow velocity was believed to exist somewhere in the tube,which was primarily proved by PIV test.Axial flow velocity distribution of tube side combined with rotation of rotors,determined the flow state,such as radial mixing,turbulent intensity and vorticity.The interspace between two adjacent groups of rotors was named stagnant sect, flow characteristics in which were discussed in detail.To sum up the cold test of TSAR,several conclusions are reasonable as follows:(1) TSAR created swirl flow with different extent and even different direction,which intensified radial mixing and shear effect between fluid layers,attenuating the boundary layer.(2) A complicated flow state existed in the stagnant sect,inducing stronger turbulent intensity.(3) Longitudinal vortexes sometimes occurred in tube side.It is exciting that all these features are good for heat transfer enhancement.Principle for selecting characteristic length was advanced and validated based on heat transfer and friction loss experiment.Considering the physical significance of each characteristic number combined with experiment data,it was made concise that the inner diameter of the tube should be used in data deduction for dynamic tube side flow disturbing technique.Experimental results calculated in this way revealed actual heat transfer performance much better.Thus,experimental investigations were carried out to evaluate the heat transfer and friction loss performance of TSAR.The oil experiment indicated: In the laminar and transition region with Re=500-8000,TSAR augmented heat transfer and inevitably increased friction loss;Bigger rotor diameter hardly contributed to heat transfer enhancement but lead to much more friction loss; Greater rotor pitch angle brought about more remarkable heat transfer enhancement and also more friction loss;Experiment data concerned with rotors with biggest pitch angle displayed a dislocation,which was assumed due to kinestate mutation of rotors;Experiment data concerned with other four types of rotors were continuous,which might imply that these rotors were always at stationary state for their smaller pitch angle;Performance evaluation indicated that rotors with biggest pitch angle behaved best.It can be concluded that radial mixing of fluid should be the principal choice for enhancing laminar convective heat transfer.The water experiment indicated:In the turbulent region with Re=10~4-10~5,TSAR augmented heat transfer and inevitably increased friction loss;Bigger rotor diameter obviously contributed to heat transfer enhancement and lead to not much friction loss;Greater rotor pitch angle brought about almost nothing for heat transfer enhancement but gained more friction loss;Performance evaluation indicated that rotors with biggest diameter and smallest pitch angle behaved best.It can be concluded that attenuation of boundary layer should be the principal choice for enhancing turbulent convective heat transfer.Therefore,structure parameters of rotors should be determined according to the flow region of fluid(laminar,transition or turbulent).With regard to condensers of power plants,rotors with bigger diameter and smaller pitch angle are preferred providing installation condition permits,because the tube side flow was under fully developed turbulence.According to some insufficiencies of traditional rotors detected in anti-fouling performance,flow disturbing characteristic,heat transfer and friction loss performance,through-carved rotor,rotary-vane rotor and boundary layer shearing rotor were invented to fix the problem.Visualization experiment together with heat transfer and friction loss experiment with water as working fluid were launched to examine through-carved rotor and rotary-vane rotor.Visualization experiment indicated:Through-carved rotors provided better resistance against hard particle fouling than traditional rotors, but still stepped far behind the requirement of high concentration and long running;rotary-vane rotors avoided blockage of hard particle fouling successfully due to particular structure design.Heat transfer and friction loss experiment indicated:Through-carved structure reduced friction loss to some extent,but also weakened heat transfer performance for the influx of fluid to through-carved void,with an over-all property even inferior to traditional ones; rotary-vane rotors reduced friction loss while maintaining constant heat transfer performance,thus achieving much better over-all property.It can be concluded that attenuation of boundary layer should be the principal choice for enhancing turbulent convective heat transfer.For turbulent convective heat transfer,radial mixing of fluid hardly contributes to heat transfer augmentation but increases friction loss to no purpose.Consequently,boundary layer shearing rotor was promoted to settle the conflict.It was designed with a particular configuration which can transfer the kinetic energy of central fluid to the edge and margin,shearing,disturbing and attenuating boundary layer.
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