Velocity shear origin

Dispersion will be discussed in the subsequent section. At this point we only mention that dispersion always occurs in fluids with a distinct direction of advective flow. It originates from the velocity difference between adjacent streamlines. This effect is called velocity shear. 

The parameters for the model were originally evaluated for oil shale, a material for which substantial fracture stress and fragment size data depending on strain rate were available (see Fig. 8.11). In the case of a less well-characterized brittle material, the parameters may be inferred from the shear-wave velocity and a dynamic fracture or spall stress at a known strain rate. In particular, is approximately one-third the shear-wave velocity, m has been shown to be about 6 for various brittle materials (Grady and Lipkin, 1980), and k can then be determined from a known dynamic fracture stress using an analytic solution of (8.65), (8.66) and (8.68) in one dimension for constant strain rate. 

In a drop extractor, liquid droplets of approximate uniform size and spherical shape are formed at a series of nozzles and rise eountercurrently through the continuous phase which is flowing downwards at a velocity equal to one half of the terminal rising velocity of the droplets. The flowrates of both phases are then increased by 25 per cent. Because of the greater shear rate at the nozzles, the mean diameter of the droplets is however only 90 per cent of the original value. By what factor will the overall mass transfer rate change ... 

In 1971 Mizushina (M9) reviewed the limiting-current method with particular emphasis upon shear-stress and fluid-velocity measurements. Mass-transfer measurements, that is, limiting-current measurements in the original more restricted sense, are documented fairly extensively. The electrochemical analysis of limiting-current measurements is touched upon, but not elaborated. 

Droplet Formation in Water Atomization. In water atomization of melts, liquid metal stream may be shattered by impact of water droplets, rather than by shear mechanism. When water droplets at high velocities strike the liquid metal stream, some liquid metal fragments are knocked out by the exploding steam packets originated from the water droplets and subsequently contract into spheroidal droplets under the effect of surface tension if spheroidization time is less than solidification time. It is assumed that each water droplet may be able to knock out one or more metal droplet. However, the actual number of metal droplets produced by each water droplet may vary, depending on operation conditions, material properties, and atomizer designs. 

In the original model, the gas-liquid interface was assumed hermetic to momentum transfer (shear-free boundary) and the interfacial gas velocity was zero [30], This assumption implies that the gas flow does not influence the liquid flow. However, the experimental studies have shown that the gas flow has a considerable influence on the hydrodynamics of TBR, especially at high operating pressure [31-41],... 

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