A HYDRODYNAMIC MECHANISM FOR THE COALESCENCE OF LIQUID DROPS (thesis)
The coalescence of liquid drops at planar interfaces was studied theoretically and experimentally. The mechanism of coalescence was found to occur in two parts. In the first part, the drop (phase 1) approaches the interface through the continuous medium (phase 2) and deforms the interface by creating a spherical depression in it. The thin spherical shell of phase 2 material between the drop and the interface rs slowly squeezed out under the combined action of surface and gravity forces. The phase 2 film becomes thinner at a rate inversely proportional to the cube of its thickness. When the film becomes sufficiently thin, the second part of the mechanism occurs. Because a denser liquid always overlies a less dense liquid at one of the interfaces of the film, the interface is inherently unstable with respect to long-wavelength disturbances (Taylor instability). lf such a disturbance is introduced into the proper interface, the disturbance will grow exponentially in time until the film disintegrates, causing coalescence of the drop. A sufflciently intense disturbance of any wavelength can also rupture the metastable film, causing coalescence. The ease of rupture of the phase 2 film increases with decreasing thickness of the film. The disturbances can originate from any source yielding a fluctuating pressure at the interface, i.e., mechanical vibration, thermal convection currents, Marangoni instability, or other. Drop rest-times were predicted to decrease with decreasing drop radius, decreasing phase 2 viscosity and decreasing frequency of disturbance. The effect of density difference and interfacial tension depends upon whether film thinning or film rupture is the ratedetermining step in coalescence. Coalescence measurements were made in an all-glass thermostatted cell. The two-component systems water-benzene, water- anisole, ethylene glycol-benzene, tributyl phosphate-water, and water-Aroclor 1248 were studied. Both artificial sonic and artificial subsonic disturbances were found to decrease the drop rest-times. Measurement of the natural sonic pattern present in the coalescence cell by means of a special microphone showed the presence of intense but short-time disturbances. Studies with surfactants showed that concentrations of less than 0.02 mM of surface-active agent ln the water-benzene system could increase coalescence times by a factor of 2. Experimental changes in drop size and system properties agreed with the theory, qualitatively. Because of the microscopic nature of the theory and the macroscopic nature of the experimental results, exact experimental verification of the theory is not possible. (auth)
- Research Organization:
- Calfornia. Univ., Berkeley. Lawrence Radiation Lab.
- DOE Contract Number:
- W-7405-ENG-48
- NSA Number:
- NSA-16-025956
- OSTI ID:
- 4814162
- Report Number(s):
- UCRL-10097
- Resource Relation:
- Other Information: Orig. Receipt Date: 31-DEC-62
- Country of Publication:
- United States
- Language:
- English
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