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What Is an Ostwald Viscometer?

By Doug Bennett
Updated May 21, 2024
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An Ostwald viscometer, also known as a viscosimeter, is a device used to measure fluid viscosity under one type of flow condition. This fluid viscosity represents the fluid’s resistance to flow. It can be thought of as the fluid’s friction, often referred to as internal friction or thickness.

The Ostwald viscometer is also known as a U-tube viscometer or capillary viscometer. The device utilizes direct or reverse flow of the test fluid through a U-shaped tube to measure the fluid’s viscosity. The measurement is determined by noting the time required for the fluid to flow a certain distance through tubing of a specific diameter.

Each side of an Ostwald viscometer consists of different size of tubing. The side with smaller tubing is referred to as the capillary. For a direct flow viscometer, a bulb is located toward the top of the capillary side. On the wider diameter side, a slightly larger bulb is located toward the bottom.

Two marks are placed on the tubing at a known distance apart. These marks are placed above and below the smaller bulb. For reverse flow viscometers, the bulb on the wider side is located above the bulb on the capillary side.

To measure the rate of flow, or Ostwald measurement, suction is used to draw the fluid up the narrow tubing until it rises above the upper mark. The fluid is then released, and the time required for the fluid to pass between the two points is measured. The Ostwald viscometer flow rate is then used to compute the fluid’s viscosity using Poiseuille's equation.

In addition to the Ostwald viscometer, there are several other types of viscometers in use. These include falling sphere viscometers, falling piston viscometers, vibrational viscometers, rotating viscometers and bubble viscometers. Instead of measuring the movement of the fluid, some of these other types measure the movement of an object through the fluid, such as a falling sphere, a falling piston or a rising air bubble. The uses and accuracy of different types of viscometers can vary.

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Discussion Comments

By arindammanga — On Oct 23, 2014

Which type of Viscometer is perfectly related to Oswald Viscometer?

By arindammanga — On Oct 23, 2014

Which type of of viscometer is more beneficial and reduces cost consumption?

By Certlerant — On Mar 02, 2014

When you dip that French fry in ketchup, who wants runny ketchup that just makes the fry all wet. This is why we need this tool.

A very important part of keeping customers coming back to your particular product is consistency. The last thing anybody wants is having the reputation of making some bottles of ketchup or applesauce different from others. This tends to make your customers think you don't care about them.

A lot of the different foods you eat contain a certain texture. Texture is certainly a part of the way we taste a food. If you get an ordinary bottle of ketchup or mustard you never even notice that it is sculpted to be just like the time you had it the last time. Tests are consistently run on batches of product to check the making of that item. If you got some mustard that was thick like molasses, you would probably avoid that brand again. It might be a small part of quality control, but it is important.

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