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Tuesday, July 30, 2019

Determination of viscosity of oil by 'Redwood Viscometer' - Thermodynamic Practical

What is Viscosity? : It is a measure of the resistance offered by one layer of fluid to the other layer of the same fluid during motion. It is expressed in Pa.s unit

Redwood Viscometer is normally used for the determination of the viscosity of petroleum products.

'Redwood Viscometer' determines the viscosity in terms of seconds (which are terms as Redwood seconds), a time taken by oil to pass through a standard orifice and collection of the same oil in 50 cc flask.

Originally Redwood Viscometer was developed for the measurement of viscosity of petroleum products.

'Redwood Viscometer' are of two types:

1. Redwood Viscometer No.1 (For fluid having viscosity corresponds to Redwood seconds less than 2000)
2. Redwood Viscometer No. 2 ( For fluid having viscosity corresponds to Redwood seconds greater than 2000)

or Redwood Viscometer No. 1 & 2 is used depending on the time of oil flow through an orifice at the desired temperature is greater or less than 2000 seconds. Normally viscosity of highly viscous fluids is determined by the use of Redwood Viscometer 2.

 Buy and Know more about Viscometer

The difference between Redwood Viscometer 1 & 2 is the difference of orifice diameter.

Formula to convert Redwood seconds to kinematic viscosity unit i.e. centistokes.

= At-B/t  (Where A = 0.26 and B = 171).

The absolute viscosity is found by measuring the density of the fluid whose viscosity is being measured. Thus, Absolute Viscosity = Kinematic Viscosity x Density


1. Fill the oil cup with oil to the required oil level indicated by marker point
2. Heat the water at a uniform temperature.
3. When the required temperature of the oil is attained, lift the ball above the orifice hole.
4. Allow the oil to pass through it (start the stopwatch) and collect 50 CC of oil in the volumetric flask.
5. The measured seconds are in terms of viscosity of oil measured.

To know more about the Redwood viscometer, refer to the following best book on
thermodynamics by PK Nag


  1. Replies
    1. For Redwood viscometer 1, A=0.26 and B=171
      The equation: At-B/t, t=Redwood seconds

  2. In Redwood Viscometer in order to find Kinematic Viscosity,V= ((A x t)-(B/t) ) how the values of constants A & B are taken? How do we determine viscometer constant?? Can anyone help me with a convincing solution.

    1. The value of A and B are determined from design of experiments and can be obtained by calibration of the apparatus. A=0.26 and B=171

  3. Does we use redwood viscometer now a days on field?

  4. For red wood no.1 and redwood no.2, is same formula to be used?

  5. Where at-b/t equation have which unit


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