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What is Redwood Viscocity

I just got a really embarassing experience as chemical engineer. Sometimes we deal with a really complicated problem and we can handle that. On the other hand, we handle a simple problem, but we can’t handle that. How if a chemical engineer can not convert the kinematic viscosity expressed in Redwood second into dynamic viscosity? That is my problem. It happened about two days ago. My boss apparently was really disappointed.

Honestly, I think this is the first time I heard about kinematic viscosity expressed in Redwood second. I checked the properties of Marine Fuel Oil (MFO) and Industrial Diesel Oil (IDO) for instrumentation purpose and I found they used Redwood second to express kinematic viscosity.

The very first question come from my mind is what Redwood viscosity is and why it should be expressed in thay way? I will share to you the answer to my questions and hopefully it would give you full understanding of Redwood viscosity.

What is Viscosity and Redwood Viscosity

capillary viscometer

Viscosity is a measure of fuel resistance to flow. When expressed in seconds Redwood at 100 degrees Fahrenheit, it is the time it takes for a fixed amount of fuel to pass through an orifice of fixed size at 100 degrees Fahrenheit. The viscosity of petroleum oil increases when oil is cooled and decreases when it is heated. For this reason, the value of oil viscosity must always be accompanied by temperature at which the viscosity was determined.

How to Measure Viscosity

PT Pertamina (Persero) uses ASTM D-445 to measure the kinematic viscosity of both marine fuel oil and industrial diesel oil. Actually there are several common methods to measure viscosity, such as the Saybolt (ASTM D-88) and the Kinematic viscosity (ASTM D-4235). In this post, I will limit the topic into ASTM D-445.

Video below illustrates how to measure viscosity using ASTM D-445.

The test is relatively simple. The oil is placed into a calibrated glass viscosity tube, which is placed inside a constant temperature kinematic viscosity bath set to 40 degrees Celcius. The time it takes for a fixed volume of liquid to flow under gravity through the capillary of the viscometer is measured. Using the calibration constant of viscometer and the time, the kinematic viscosity is calculated.

How to Convert Redwood Viscosity to Other System

If you find the viscosity expressed in Redwood second, you may need help to convert it into other system (such as to centiStokes or centiPoise). This link will help you to convert Redwood viscosity to other system. And this link will help you to convert Static viscosity to dynamic viscosity.

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