Abstract
Thermal-hydraulic characteristics in circular tubes with twisted tape (Y=4.762, 7.143 and 9.524) and wire coil (p=20mm, e=2mm) inserts were studied experimentally and numerically. It was found from experimental analysis that Nusselt number and friction factor in tubes with twisted tape inserts were 38%-57% and 148%-202%, respectively, higher than those of plain tubes .When wire coil was inserted in plain tubes, the Nusselt number and friction factor grew by 75%-94% and 685%-792%, respectively. In particular, Nusselt number and friction factor in tubes with twisted tape and wire coil inserts were 113%-139% and 836%-874%, respectively, greater than those of plain tubes. Furthermore,PECvalue of tubes with the twisted tape and wire coil inserts was larger than all others. Numerical analysis shows that a large tangential velocity can be generated after inserting a twisted band or coil in the tube. The angle between the temperature gradient vector and velocity vector was significantly less than 90°. So collaborative degree between temperature field and velocity field was improved.
Highlights
Heat transfer enhancement technology with the inserts inside tubes does not change the shape of heat transfer surface
The results demonstrate that the twisted-tape gives better heat transfer enhancement with reduced twist ratio
It is found that heat transfer coefficients and friction factors in the tube fitted with the broken twisted tape are 1.28-2.4 and 2-4.7 times of those in the tube fitted with the smooth twisted tape, respectively
Summary
Heat transfer enhancement technology with the inserts inside tubes does not change the shape of heat transfer surface. E. Smith [3] provided experimental data of heat transfer and flow friction in a circular tube fitted with regularly spaced twisted tape elements. Smith [3] provided experimental data of heat transfer and flow friction in a circular tube fitted with regularly spaced twisted tape elements Their studies suggest the larger twist ratio is, the bigger heat transfer coefficient becomes. The experimental results reveal that the tube fitted with the conical-ring and twisted-tape provides Nusselt number and enhancement efficiency are 4%-10% and of 4%-8%, respectively, higher than that with the conical-ring alone. Experimental or numerical analysis of circular tubes with twisted tape or wire coil inserts has not applied to actual production very well. It can be applied to actual production with providing a reliable basis for the design of heat exchangers
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