Investigation of surface and interfacial tension requires a viewable environmental
chamber, temperature and pressure control and observation equipment. The IFT cell
operates to 10000psig at 350°F. Within this range most reservoir conditions can
be accurately and safely simulated. This allows conducting experiments in an oxygen-free
environment as opposed to normal room-condition IFT measurements. It is important
to measure the interfacial tension at the reservoir temperature because it changes
dramatically with temperature. The IFT cell is heated by band heaters and insulation
jackets (instead of placing the cell in an oven), so that the valve is not heated.
The cell is leveled on a vibration-free table that reduces the interference of constant
low-frequency vibration. A drop phase is created and put in contact with the external
phase through a needle tip, located in the cell at reservoir conditions. The IFT
pendent drop visual cell includes a light source to illuminate the drop phase in
its glass-windowed Chamber and a low power video microscope connected to a computer.
Measurement of the drop dimensions and fluid densities enables calculation of interfacial
tension. The low power video camera is used to capture the drop and embedded algorithms
in the software to compute the interfacial tension. As part of the interfacial tension
measurements, the program performs a numerical integration of the drop profile to
determine the volume and surface area. This opens several possibilities for additional
or complimentary use of the program. A 2-step process determines interfacial tension
as follows. First, size parameters Ro and β are determined from the drop profile.
Secondly interfacial tension is calculated from these parameters by the equation:
Δρ g Rο2 / β
By convention, Δρ is defined such that Δρ and β is negative for pendant drops.
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