Redwood Viscometer is normally used for determination of viscosity of petroleum products.
'Redwood Viscometer' determines the viscosity in terms of seconds (which are terms as Redwood seconds), a time taken by an oil to pass through a standard orifice and collection of the same oil in 50 cc flask.
Originally Redwood Viscometer was developed for 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 time of oil flow through orifice at desired temperature is greater or less than 2000 seconds. Normally viscosity of highly viscous fluids is determined by use of Redwood Viscometer 2.
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
2. Heat the water at uniform temperature.
3. When required temperature of oil is attained, lift the ball above the orifice hole.
4. Allow the oil to pass through it (start the stop watch) and collect 50 CC of oil in the volumetric flask.
5. The measured seconds is in terms of viscosity of oil measured.
To know more about the Redwood viscometer, refer to following best book on thermodynamics by P K Nag