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Experimental Results
In the first figure results of the diameter determination of fixed toluene droplets by RBR are compared with results obtained by a digital processing of CCD images. The results are in a good agreement.
The next figure illustrates the results of the sphericity determination for rising toluene droplets of 2.0 to 4.0mm diameter in a continuous water phase. For a droplet diameter up to 3mm (Reynolds nuber Re=299) the dominant frequencies are nearly identical. Therefore, the rising droplets are spherical in this diameter range, since the difference between the two calculated droplet diameters is close to zero . For a larger diameter Re>300 the shape of the droplets becomes oblate. Thus the diameter value obtained from receiver 1 is larger than the result obtained from receiver 2. Hence the difference between the two droplet diameters is unequal from zero. In addition, the standard deviation of the results for different measurements taken under the same conditions increases.
The position j of the first maximum of the monocromatic rainbow is a direct function of the refractive index m, which correlates linear with the concentration of Acetone in the droplet.
During the instationary mass transfer process concentration gradients which result in gradients of the refractive index emerge within the droplet. These gradients decrease from inital high values to zero after reaching the equilibrium. In the last figure j-t-data are shown. These were measured for the process of diffusion from the aqueous phase to the a determined droplet (d=2mm) for different concentration of Acetone in water. After an increase, that can be reduced to very steep inital refractive index gradients at the beginning of mass transfer, j approaches the corresponding value for the equilibrium concentration of Acetone.
