Rotating cylinder technique, liquid

As noted above, the mass transfer kinetics of temperature gradient loops are usually described with reference to dissolution in the hot leg. It is possible to quantitatively study the dissolution step using the rotating cylinder technique. Unlike loop studies, this technique allows one to study dissolution in a system where the hydrodynamic conditions are fully defined. Experimentally, solid cylinders of the test material are rotated at various speeds in an isothermal liquid-metal bath. Changes in the concentration of solid in the liquid and changes in the cylinder radius are determined as a function of time. With these data it is possible to determine the mass transfer coefficient and the rate-controlling step for dissolution. 

Princen ) has extended the spinning drop technique to the case that the rotating cylinder contains a liquid (Lj) emd an air bubble (G) dispersed in another liquid Lj. When drop L2 and bubble G do not touch each other, the surface tension y and the Interfacial tension can be simultaneously determined. However, under certain conditions bubble and drop adhere to each other. Then, as well as the two tensions, the three three-phase contact angles can be simultaneously measured. 

In the first of these techniques an approximation to uniform rate of shear throughout the sample is achieved by shearing a thin film of the liquid between concentric cylinders. The outer cylinder can be rotated (or oscillated) at a constant rate and the shear stress measured in terms of the deflection of the inner cylinder, which is suspended by a torsion wire (Figure 9.2) or the inner cylinder can be rotated (or oscillated) with the outer cylinder stationary and the resistance offered to the motor measured. 

The first forced-flow planar liquid chromatographic technique was achieved by means of centrifugal force (3). Hopf (69) introduced a centrifugally accelerated apparatus, called the Chromatofuge, for the separation of substance groups on a 100 mg scale. The main parts of this instrument were a special perforated cylinder, filled with support material, and a central tube, down which sample and mobile phase were introduced. In this system, the radial forced-flow migration of the mobile phase was solved by rotation around the axis of the basket. Heftmann et al. (70) modified this apparatus, making it more suitable for preparative separations. The parallel development of TLC... 

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