Experimental study was conducted to investigate fluidelastic instability in finned tube bundles with normal and parallel triangular arrays. Three arrays of each geometry type were studied experimentally: two arrays with serrated, helically wound finned tubes of different fin densities, and a bare tube array with the same base diameter as the finned tubes. The finned tubes under consideration were commercial finned tubes typically used in the fossil and process industries. For the purpose of the present investigation, the concept of "effective diameter" of a finned tube, as used to predict the vortex shedding, was used to compare the finned tube results with the existing bare tube world data and some theoretical predictions for fluidelastic instability. The finned tube arrays in this study have the same tube pitch and have been scaled to have the same mass ratio and tuned to have the same natural frequency. A low speed wind tunnel, Betz micro manometer and HP 35670a dynamic signal analyzer were employed to conduct the experiments. Experimental results for the triangular arrays show that the fin's structure strongly influences the fluidelastic stability of finned tube bundles and the fin pitch is demonstrated to reduce the difference in the fluidelastic instability between the tube arrangements as the fin density increases. The results also suggest that there might be an optimum fin pitch value at which the threshold reduced velocity for a finned tube array is much higher than the one for its corresponding bare tube array, due to the influence of fin geometry. In the appendix, an analytical model produces a new correlation of critical reduced velocity against mass damping parameter to predict the fluidelastic instability of tube bundles. Its predictions are in reasonable agreement with the experimental data. Since negative damping is one of the mechanisms of fluidelastic instability of a tube array, "Lift effect" was applied to explain the negative damping in an inviscid flow. An experiment is suggested to test the relationship between the pitch flow velocity and a tube velocity dependent "lift effect". Accordingly, two duct structure designs are suggested which may alleviate the negative damping by using the energy of oncoming flow to reduce the "lift effect" on the tubes. / Thesis / Master of Applied Science (MASc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/22410 |
| Date | 20 November 2017 |
| Creators | Wang, Jing |
| Contributors | Weaver, D. S., Mechanical Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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