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where C d is the drag coefficient, is the density of the fluid, v is the velocity of
2
flow, and g c is a conversion factor (lbmft/lbfsec2) (lbm)(ft)/(lbf)(sec ).
Second, energy is used in the formation of ‘‘surface energy,’’ which
occurs as a result of the separation of the molecules at the plane of
cleavage. This surface energy is related to the surface tension, which
involves the creation of an enormous area of interface with attendant free-
surface energy. Energy contained per unit area is referred to as ‘‘surface
tension,’’ having the units of dynes/cm.
The drops attain the spherical shape, which involves the least energy
contained for a given volume. This is in accordance with the fact that all
energetic systems tend to seek the lowest level of free energy [4]. Because the
surface tension is defined as ‘‘the physical property due to molecular forces
existing in the surface film of the liquid,’’ this will cause the volume of a liquid
to be contracted or reduced to a shape or a form with the least surface area.
This is the same force that causes raindrops to assume a spherical shape.
A schematic presentation of energy utilization in emulsion formation is
given in Figure 3. A crucial question that can be asked now is the following:
Can the plant designer prevent emulsion formation? Well, the best he can do
is to reduce its extent of formation based on the fact that the liquids initially
are not emulsified. From the design point of view, primarily reducing the
flowing velocity of the fluid and minimizing the restrictions and sudden
changes in flow direction could minimize formation of emulsion.

5.2.2 Emulsifying Agents
If an oil emulsion is viewed through a microscope, many tiny spheres or
droplets of water will be seen dispersed through the bulk of oil, as depicted

Figure 3 Forms of energy participating in emulsification.

Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.