Numerical Simulation Of Enhanced Tube With Twisted Tape Or Conical Ring

The technology of convective heat transfer in tube is an energy-saving technique which is widely used in the industrial fields, such as energy, chemical industry,electronics,medicine,materials etc.Therefore, the development of new types of heat transfer enhancement technology and improving facilities' heat transfer efficiency have a great effect on energy-saving and economic development.We designed short-width twisted tape of alternate axes,center-cleared short-width twisted tape of alternate axes and center-cleared twisted tape of alternate axes on the basic study of short-width twisted tape,and numerical study was performed on the laminar heat transfer characteristics in circular tubes inserted with these types of twisted tapes.The results show that, for the case with short-width and center-cleared short-width twisted tape of alternate axes, the Nusselt number(Nu) increases with the increment of the dislocation angle under small Reynolds number(Re); but for large Re, the impact of dislocation angle grows negligible.While the friction factor(f) increases slightly with the increment of the dislocation angle,and the best PEC matches the dislocation angle of 90°.For the case with center-cleared twisted tape of alternate axes,the biggest value of Nu and f matches the dislocation angle of 60° and 90° each,and f differs each other greatly with different dislocation angle.PEC shows complex variation with different dislocation angle and gets the best value with a 60° dislocation angle.Heat transfer performance of twisted tape of alternate axes differs each other slightly with different dislocation angle under turbulent conditions,so numerical study was performed on the turbulent heat transfer characteristics in circular tubes inserted with short-width twisted tapes and center-cleared twisted tapes.The variation of Nusselt numbers,friction factors and performance evaluation criterion were presented,and the results were discussed with velocity field and temperature field.From the results we know that for theshort-width twisted tapes,the Nu ? f and PEC increase with the increasing width of the twisted tapes.While for the center-cleared twisted tapes,the Nusselt numbers are almost the same with smaller hollow size but decrease when the hollow size is big enough. When the hollow size gets bigger,the f decreases and PEC gets better.The heat transfer performance and performance evaluation criterion of the typical twisted tapes are better than that of the short-width twisted tapes and the center-cleared twisted tapes.At last,numerical study was performed on the turbulent heat transfer characteristics in circular tubes inserted with different types of conical rings.We find that when the small end diameter is fixed,the heat transfer performance is better when the gap between the big end diameter and the tube wall is smaller.When the end diameter ratio of the conical ring is fixed,the heat transfer performance is better when the gap is smaller for converging conical ring,while for diverging conical ring the heat transfer performance may be better at proper bigger gap.The f of the diverging conical ring is much bigger than that of the converging conical ring when at smaller gap,while the tendency of f changes when at bigger gap.The performance evaluation criterion of the diverging conical ring is better than that of the converging conical ring.