Tubeless column

Now let us take a look at a recent NMR imaging experiment of Fano flow, in which the local velocities in the tubeless column were mapped out quantitatively and nondestructively [20], For such a set-up, the weight force of the column is balanced by the extensional stress difference azz - axx associated with the vertical velocity gradient (dvz/dz), as... 

Another type of experiment involves a fluid filament being drawn upward against gravity from a reservoir of the fluid (101,213,214), a phenomenon often called the tubeless siphon. The maximum height of the siphon is a measure of the spinnabiUty and extensional viscosity of the fluid. Mote quantitative measures of stress, strain, and strain rate can be determined from the pressure difference and filament diameter. A more recent filament stretching device ia which the specimen is held between two disks that move apart allows measurements ia low viscosity Hquids (215). AH of these methods are limited to spinnable fluids under small total strains and strain rates. High strain rates tend to break the column or filament. 

Fig. 4.3.1 (a) Photographs of a tubeless siphon formed by dissolving 0.5%w/v poly (ethylene oxide) powder in tap water, where a Fano column can be seen between the tip of the glass pipette at the top and fluid reservoir at the bottom, (b) Excess fluid can be seen just below the fluid entrance, (c) A large amount of excess fluid eventually flows downwards outside and along the Fano column, which can disturb the vertical location of the column. These figures illustrate the fact that there is an optimum volume flow rate for a particular flow system. 

Example of (mainly) longitudinal shear flows (a) conveigent duct, (b) the tubeless siphon. With dilute (10 polymer solutions one can often arrive at a column 10 cm high. 

A nearly i al situation of this type is found with the tubeless siphon of Fig. VI. 10b. (This ascending column is easily obtained with polymer solutions because of their ability to thread.) The interest of this geometry, from the present point of view, is to provide us with a simple convergent flow (not perturbed by walls) in the bulk of the fluid behw the siphon. (Chain behavior inside the siphon has been studied in experiments at Naples, but the analysis ignored possible elongations before entry.)... 

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