Pinching mechanism

Adhesive tapes are also extensively employed for protection of pipes with curvilinear and corrugated surfaces used in chemical industry, gas and oil held developments. The problem of lining convoluted pipes is solved [116] by rolling the tube over a roller base wrapped in a poljuner tape (Fig. 3.45a). Roller axes are arranged at a pitch equal to the distance between crimps of the pipe. For this purpose, pinch mechanisms can also be used [117] made as a sprocket and having a roller on each beam (Fig. 3.45 ). 

Fig. 3.45. Diagrams of devices for hning convoluted pipes (a) with a roller base, (b) with a sprocket pinch mechanism (1) pipe, (2) adhesive tape, (3) base, (4) drive, (5) roller, (6) shaft, (7) sprocket, (8) spindle...

The pinch mechanism is tested by having the patient form an "O" with his thumb and index finger as the examiner hooks his fingers into the "O" and tries to pull it apart. 

Figure 6.22a-e show breakup by shedding off small droplets from the bulbous ends ( end-pinching mechanism Stone and Leal, 1989) for 0.05

combined action of instabilities and end-pinching for /i = 1 and L/R = 14. Apparently, the time scale of the end-pinching mechanism is less than the time scale of the instability mechanism in cases where end-pinching prevails. 

J ct Spra.y, The mechanism that controls the breakup of a Hquid jet has been analy2ed by many researchers (22,23). These studies indicate that Hquid jet atomisation can be attributed to various effects such as Hquid—gas aerodynamic interaction, gas- and Hquid-phase turbulence, capillary pinching, gas pressure fluctuation, and disturbances initiated inside the atomiser. In spite of different theories and experimental observations, there is agreement that capillary pinching is the dominant mechanism for low velocity jets. As jet velocity increases, there is some uncertainty as to which effect is most important in causing breakup. 

Illustration Satellite formation in capillary breakup. The distribution of drops produced upon disintegration of a thread at rest is a unique function of the viscosity ratio. Tjahjadi et al. (1992) showed through inspection of experiments and numerical simulations that up to 19 satellite drops between the two larger mother drops could be formed. The number of satellite drops decreased as the viscosity ratio was increased. In low-viscosity systems p < 0(0.1)] the breakup mechanism is self-repeating Every pinch-off results in the formation of a rounded surface and a conical one the conical surface then becomes bulbous and a neck forms near the end, which again pinches off and the process repeats (Fig. 21). There is excellent agreement between numerical simulations and the experimental results (Fig. 21). 

Now let s see what happens when we want to reduce the flow. Control valves don t work too well when they are less than about 10 percent open. They can become mechanically unstable, shutting off completely and then popping partially open. The resulting fluctuations in flow are undesirable. Therefore, we want to design for a minimum valve opening of 10 percent. Let s see what the minimum flow rates will be in the two cases considered above when the two valves are pinched down so that/J, = 0.1. 

This author has previously suggested that the mechanism of flux enhancement might be due to the "tubular pinch effect" ( ). The lower density (0.94 g/cc) MMA beads show less tendency to... 

Figure 3 shows some topography of surfaces illustrating the pinch-off mechanism here T = 0.56 r , and = 64a. At time U, a layer of the sinusoid has relaxed away exposing a pair of terraces with relatively straight steps. At time U, a single pinch-off event has occurred and at time t, all relevant pinch-offs have been nucleated. By time u the layer has relaxed away. 

Figures. Snapshots of a surface obeying/-kinetics illustrating the pinch-off mechanism. T= 0.56 Tb, = 64a. toVo= 1.75x10 (no pinch-off), /,Vo= 2.62x10 (firstpinch-off),t2v0= 3.78x105 (steady-statepinch-off), tsVo = 5.24x10 (terrace dissolution virtually complete).

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