On-line monitoring of drop size distributions in agitated vessels. 1. Effects of temperature and impeller speed

Abstract

Transient drop size distributions in a batch stirred tank were measured by a laser diffraction technique. Ita short measuring time permitted on-line analysis with minimal possible instrumental, sampling, and dispersion errors. Comparison with the previously used photographic technique showed increased sensitivity in measuring the small diameter drops. In this study, the effecta of temperature and impeller speed were investigated for a system of 1% styrene in water stabilized with 0.1 g/L poly(viny1 alcohol) (PVA) as a suspending agent. The system assumed characteristic bimodal distributions within a very short time. Further stirring only reduced the drop sizes without substantially affecting the shape of their distribution. Increasing the agitation rate caused a shift of both peake to smaller diameters since higher turbulence intensity is more effective in breaking the drops. An increase in temperature resulted in a size reduction and narrowing of the large-size peak of the distribution. Finally, the minimum time required for the system to reach steady state at different conditions was found to depend on the Weber number of the main flow. An increase of agitation rate or a decrease of interfacial tension caused a reduction of the minimum transition time, thus allowing the system to approach equilibrium much faster.

Influence of Physical Properties on Drop Size Distribution of Stirred Liquid‐Liquid Dispersions

“…(4) shows that the Sauter diameter depends solely on the power input per unit mass. A further dependency on the geometrical size of the apparatus should not exist.…”

Representative drop sizes and drop size distributions in A/O dispersions in continuous flow stirred tank

“…Some of these studies are summarized in Table 1. Majority of them (Vermeulen et al, 1955;Rodger et al, 1956;Weinstein and Treybal, 1973;Mlynek and Resnick, 1972;Fernandes and Sharma, 1967;Brown and Pitt, 1974;McManamey, 1978;Calabrese et al, 1986a,b;Wang and Calabrese 1986;Nishikaw et al, 1987a,b;Laso et al, 1987;Chatzi et al, 1991;Zhou and Kresta, 1998;Pacek et al, 1999;Ruiz et al, 2002;Desnoyer et al, 2003;Giapos et al, 2005;Sechremeli et al, 2006) have been done on batch vessels. Only few of them have been done on continuous flow stirred tanks (Wienstein and Treybal, 1973;Fernandes and Sharma, 1967;Quadros and Baptista, 2003).…”

Steady‐state drop‐size distributions in high holup fraction dispersion systems

“…As the interfacial tension decreases (PVA concentration increases) the drop-size distribution shifts to smaller sizes. At low agitation speeds (400 and 500 rpm), the drop breakage is the dominant mechanism affecting the drop-size distribution developments (Chatzi et al, 1991a). At high agitation speeds (700 rpm) drop coalescence becomes important, especially at lower PVA concentrations.…”