Flow-rate limitation in a uniform thin-walled collapsible tube, with comparison to a uniform thick-walled tube and a tube of tapering thickness

摘要

Previous experiments on a tapered-thickness tube showed qualitatively different behaviour from that exhibited by a uniform thick-walled tube. To understand whether the taper or the thinner wall was responsible, similar aqueous flow-limitation experiments were conducted on a uniform thin-walled tube of the same material, with all other experimental set-up the same. As in the thick tube, there was a dramatic reduction in flow-rate when collapse and flow limitation started, but during external pressure reduction, the limited flow-rate progressively increased, so that as in the tapered-thickness tube, there was little flow-rate increase when collapse ceased. Hysteresis was thus a prominent feature of the relationship between flow-rate and pressure drop along curves of constant upstream transmural pressure. Flow-rate limitation was mainly accompanied by large-amplitude self-excited oscillation for both increasing and decreasing external pressure, to an even greater extent than in the tapered-thickness tube. Clusters of points sharing the same pair of upstream transmural pressure and upstream driving pressure values were found, indirectly implying as in the tapered-thickness tube that the flow-limited flow-rate for a given pressure drop was not uniquely determined by upstream transmural pressure. Negative effort dependence was observed in all three tubes, but in the thin tube, as in the tapered-thickness tube, it was obscured for some values of upstream transmural pressure where low-frequency single-collapse-per-cycle oscillations occurred. Thus, the qualitatively unique properties of the tapered-thickness tube appear to be confined to the relative lack of hysteresis, and the oscillatory regime in which collapse ceased before the downstream end. The rest of the observed behaviours seem to be characteristic simply of more compliant tubing.