Interview conducted by Matthew Rafferty
What is Viscosity?
Viscosity is a measure of the resistance of a fluid to flow due to its molecular makeup. This molecular makeup creates an internal friction that resists gradual deformation when a shear or tensile stress is applied, that is, when a fluid comes in contact with solid boundaries. Most equate the viscosity of a fluid to its thickness. Thicker fluids have a higher viscosity compared to relatively thinner fluids. For example, at the same temperature, honey will typically have a higher viscosity than water. There are two measures of viscosity: dynamic (absolute) and kinematic viscosity. Dynamic viscosity is the ratio of the fluid’s shear stress to the shear rate applied to it. Kinematic viscosity is related to dynamic viscosity by the fluid’s density. Kinematic viscosity is equal to the dynamic viscosity divided by the density of the fluid.#
Image credits | shutterstock.com/g/fluids
Why Should You Measure Viscosity?
Understanding how a fluid will behave is important for designing machines with moving parts, applying fluids to structures, transporting fluids through pipes, filling containers, etc. It is important to remember that for liquids, the kinematic viscosity decreases with higher temperature. For gases, the kinematic viscosity increases with higher temperature.
What Industries use Viscosity testing?
Any industry for which it is important to know the flow properties of a fluid to estimate how to efficiently store or handle such fluids. Industries that test for viscosity include oil and chemical, pharmaceutical and cosmetics, paints and coatings, paving, food and beverage, and others.
What are the different types of viscometers?
Almost any way to measure a fluid’s resistance to flow can be used as a viscometer. It is the comparison to another fluid with a known resistance that gives the measure meaning for its application. Some viscometer types include orifice, capillary, falling piston, rotational, falling ball, vibrational, constant pressure, etc. The hydrocarbon processing industry values direct kinematic viscosity measurements as the kinematic viscosity value is used to classify most chemical products, such as lubricants, greases and fuels.
What is different about constant pressure viscometers?
Constant pressure viscometers use a constant driving force rather than simple gravity to measure the fluid resistance through a straight tube. A constant pressure viscometer designed and manufactured by Phase Technology does not use breakable glass as with traditional capillary viscometers. There is no liquid bath to control temperature and the equipment has a relatively small footprint compared to other viscometers.
Why are they key for the hydrocarbon processing industry?
There are many ways to measure viscosity. The most popular are those instruments that can measure kinematic viscosity directly. However, these are usually lower throughput instruments, though they have a high degree of precision. Other types of viscometers may have higher throughput, but typically have lower degrees of precision. The constant pressure viscometer offers high sample throughput as well as good precision, both factors valued by hydrocarbon processing customers.
What does PAC offer to fulfil these needs?
PAC offers viscosity instrumentation designed to meet the full range of customer requirements. PAC glass capillary viscometers directly measure kinematic viscosity. PAC’s constant pressure-based viscometers include the JFA-70Xi with jet fuel viscosity measurement at both -20°C and -40°C and the DFA-70Xi with diesel fuel viscosity measurement at 40°C.
What type of materials does this work with?
The viscosity of almost any liquid can be measured using constant pressure viscometers. If the liquid can be introduced into the instrument, its viscosity can be measured.
How does the PAC Phase system benefit the end user?
The Phase constant pressure viscometer (CPV) has many end user benefits. The CPV has a small benchtop footprint; it offers above average precision compared to other non-glass capillary viscometers; it is easy to use and doesn’t require much training time. The CPV delivers quick test results; it features a fast, self-cleaning system; and it is designed to maximize uptime and reduce downtime.
What areas of research are PAC investigating to further develop viscometry?
PAC is highly committed to ongoing R&D efforts in the development of new, innovative, high-value solutions for our customers.
About Dr Larry Spino
Dr. Larry Spino is Global Product Manager for PAC’s Diesel and Lubricants portfolio. He has more than 20 years of experience in manufacturing, sales, market development and product management.
Larry has earned several advanced degrees with a PhD. in Chemistry from Texas Tech University, an M.B.A. in Finance from the University of Houston and a B.S. in Chemistry from West Virginia Institute of Technology. He is a published author and holds several patents.
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