Explain centistokes

[Tron1]

Can someone explain which oil flows better at 40 C and why:
cST @40 C =78 or cST @ 40=100 I am guessing the 100 number flows better at 40. Can anyone help me understand the principle involved here. Thanks.

 

[d00df00d]

Lower number = thinner = flows better.


As I understand (someone correct me if I'm wrong), those measurements are taken as follows:

1. Fill a tube of a certain size with the oil.
2. Bring it to the appropriate temperature (40 or 100 C).
3. Put a ball of a certain size in at the top and see how fast it falls.

The faster the ball falls, the thinner the oil must be.

 

[addyguy]

Resistance to flow. Centistrokes, AFAIK, is how much resistance there is to a fluid flowing through a channel. The higher the number, the more resistnace there is to flow, so the oil flows slower.

 

[jstutz]

1 cSt = 1 mm2·s−1 . Water has a viscosity of about 1 cSt at 20C. So if a fluid is thicker, then the time it takes to flow is longer so for the equation to stay balanced, cSt will also increase. So for your case the situation where cSt=78 will have less viscosity than the one that has cSt=100 and would therefore flow better.

 

[scurvy]

In engineering lab, we used a simple Ostwald viscometer to measure kinematic viscosity. It has a bulbous reservior of fluid and a longish, thin tube with another bulb at the top of it. There are two marks along a gauge section of the tube, one above & below the second bulb. You clamp the whole thing square, fill the resevior with the fluid you want to check and submerge that end in an ice or warm water bath. It looks like this, which I found on the interwebs:

After it has come to equilibrium, you use a suction bulb to draw fluid up past the top mark, then time how long the meniscus takes to drop from one line to the next. Each viscometer has a factor that you multiply by the time observed to get kinematic viscosity, i.e., there is a direct correlation between how long it takes to flow through the gauge section and the kinematic viscosity of the sample.

Simple.

 

[Y_K]

Stokes is a large unit of measure, so they use 0.01 or 1/100 of it and call it a centiStoke. Named after a prominent scientist.
He was also titled a Senior Wrangler - the highest honour for the top-score math student in Cambridge. Later he had to resign his fellowship at the Uni after he married: fellowship was considered a true monastic dedication to Science, marriage to Science was the only way.

Anyway, he derived several Stokes Laws. One of them states that attenuation of the sound in a [newtonian] fluid is proportional to the [dynamic] viscosity. Another law mathematically described the friction force (drag force) exerted on spherical object by a stream of continuous viscous fluid. The CGS unit of kinematic viscosity was named "stokes" after his work. The importance of Stokes' law is illustrated by the fact that it played a critical role in the research leading to at least 3 Nobel Prizes. Swimming microbs and sperm, drifting clouds and snowflakes - all use his theory.

 

[Tom NJ]

The most common tubes used for kinematic viscosity are the Canon-Fenske tubes, shown here along with a good description of the procedure:

http://baervan.nmt.edu/research_groups/petrophysics/group/viscometer.pdf

In essence, you just time how long it takes for the fluid to flow between two lines under its own weight. Thicker fluids take longer to flow and therefore read a higher viscosity.

Tom NJ

 

[Tron1]

Glad we got that issue resolved.....

 

[Tron1]

Thank you....

Originally Posted By: Tom NJ
The most common tubes used for kinematic viscosity are the Canon-Fenske tubes, shown here along with a good description of the procedure:

http://baervan.nmt.edu/research_groups/petrophysics/group/viscometer.pdf

In essence, you just time how long it takes for the fluid to flow between two lines under its own weight. Thicker fluids take longer to flow and therefore read a higher viscosity.

Tom NJ