INVESTIGATION ON FLUID FLOW IN FLEXIBLE AND COLLAPSIBLE TUBES

Abstract

An investigation was carried out on steady air flow in a compliant tube subjected to varying pressure drop and transmural pressure differences. The experimental results were presented in non-dimensional parameters, Q/(AoCo) and (P - Pe)/Kp, and compared with theory. Two main types of cases were considered, one with upstream stagnation pressure fixed and another with upstream static pressure fixed. In the first case, when the transmural pressure difference is positive, reducing the downstream pressure will cause a sharp increase in flow rate as in previous studies. When the transmural pressure is negative, further reduction of downstream pressure causes: (i) partial tube collapse and a slight increase in flow rate if the stagnation pressure is substantially higher than the external pressure, e.g. (Po - Pe)/Kp =130.5; or (11) complete tube collapse and a reduction in flow rate if the stagnation pressure is only slightly higher than the external pressure, e.g. (Po - Pe)/Kp = 18.6. These findings differ from previous studies where the flow rate remained constant with downstream pressure reduction. With a fixed external and downstream pressure there is an optimum stagnation pressure to attain the maX1num flow-rate. The experimental measurement of the flow rate based on the optimum stagnation pressure compared favourably with theory. With the upstream static pressure fixed, reducing the downstream pressure causes drastic increase in flow rate initially for positive transmural pressure as in previous studies. When the transmural pressure becomes negative, further reduction of downstream pressure causes: (1) a partial tube collapse and an increase in flow-rate if the upstream static pressure is much -higher than the external pressure, e.g. (Pl-Pe) /Kp - 53.3 , or (11) a complete tube collapse and decrease in flow-rate, if the upstream static pressure is slightly higher than the external pressure, e.g.(Pl - Pe)/Kp ~ 10.7. With upstream static pressure maintained fixed at the external pressure, the flow was measured at two Reynolds number ranges. The general trend of the experimental data, for Reynolds number between 1000 to 1400, shows satisfactory comparison with the theory. At the low Reynolds number range, Re from 200 to 900, the experimental results was curve fitted to the theory. A numerical constant relating to the friction loss is found to be 7800 for the present experiment.