Lab 8: Viscosity vs. Temperature using Redwood Viscometer

🎯 Objective

To determine the effect of temperature on the viscosity of a given oil sample using a Redwood viscometer No. 1 and plot viscosity–temperature curve.

📖 Principle / Theory

Viscosity is the resistance of a fluid to flow due to internal friction between layers. In the Redwood viscometer, the time (in seconds) for 50 mL of oil to flow through a calibrated orifice at a given temperature is measured. This time (in Redwood seconds) is used to calculate kinematic viscosity.

Viscosity decreases with increasing temperature (for liquids) following the Andrade equation: log η = A + B/T

Kinematic viscosity (cSt) ≈ 0.26t − 179/t (for t > 100 s Redwood) or 0.247t − 50/t (for t 34–100 s)

🧰 Apparatus Required

Redwood viscometer No.1, thermometer, stop watch, oil bath, heating coil, measuring flask (50 mL).

🧪 Chemicals Required

Given oil sample (engine oil / lubricating oil), distilled water for the oil bath.

⚗️ Procedure

Level the Redwood viscometer on a flat surface. Clean the inner tube and place the oil sample.
Set the water bath to the desired temperature (40°C). Wait for 10 minutes equilibration.
Remove the ball plug and start the stopwatch simultaneously. Collect 50 mL of oil in the measuring flask.
Stop the watch when 50 mL is collected. Record time t (in Redwood seconds).
Repeat at temperatures 50°C, 60°C, 70°C, and 80°C.
Calculate kinematic viscosity at each temperature using the formula.
Plot kinematic viscosity (cSt) vs. Temperature (°C).

📊 Observations & Calculations

ℹ️

Record time at each temperature. Kinematic viscosity (cSt) = 0.26t − 179/t (Redwood formula). Note: Viscosity decreases with temperature.

Temperature (°C)	Time (Redwood sec) T1	Time (Redwood sec) T2	Mean Time (sec)	Kinematic Viscosity (cSt)
40	______	______	______	______
50	______	______	______	______
60	______	______	______	______
70	______	______	______	______
80	______	______	______	______

Kinematic Viscosity Formula (Redwood):
ν (cSt) = 0.26t − 179/t (for t > 100 Redwood sec)
ν (cSt) = 0.247t − 50/t (for t = 34–100 Redwood sec)
Plot ν (y-axis) vs Temperature °C (x-axis) to show the viscosity–temperature relationship.

✅ Result

Kinematic viscosity at 40°C = ______ cSt, at 50°C = ______ cSt, etc. Viscosity decreases with increasing temperature as expected for a liquid.