ECH 141—Fluid Mechanics
Exam 1 (Closed book, no notes)
(20 pts.) An object that is denser than water weighs A in air and weighs W when completely
submerged in water.
What is its specific gravity?
Explain your answer.
An emulsifier is a device that is used to disperse oil droplets in water.
(Similar devices are used in
bioprocessing to “disrupt” or break up cells in order to harvest target proteins inside them.)
Typically a mixture of oil and water flows at velocity U through a channel and up to a plate, and
then is forced at high pressure through a small gap with height h.
The density and viscosity of the
In order to create small drops from large ones, they must be
stretched until they break, and the oil/water interfacial tension
opposes this extension.
property used to evaluate the performance of an emulsifier is the mean diameter D of the oil drops
exiting the device.
It has been found that D is insensitive to the much larger diameter of drops in the oil/water mixture
entering the device.
In addition, although the ratio of the oil viscosity to the water viscosity is a
dimensionless group that obviously impacts performance, that ratio changes by so little in practice
that it is not of interest here.