PHYSICS OF OIL SANDS EXPERIMENT
Investigating Stokes’ Law
Comparing two different ways of separating two liquids
Take-Home Experiment
Purpose
The purpose of this experiment is to investigate Stokes’ Law, and to compare two different ways of
separating canola oil and water.
Background
Canada has one of the largest petroleum reserves in North America. It is found in the oil sands of Alberta;
this fuel is also known as bitumen. Due to its viscosity, bitumen has to be extracted by unconventional
methods. The oil sands are first shovelled and then sent to a crusher. The crushed ore is then mixed with
water and chemicals. It travels through a hydrotransport pipeline where the bitumen is separated from any
solid particles. The bitumen finally arrives to a gravity-separation vessel where the bitumen floats to the top
and is collected. The separation of the bitumen from the rest of the slurry inside the gravity separation
vessel involves fluid-particle physics. We can analyze particles settling in a fluid using Stokes’ Law, and we
can observe what happens inside the gravity separation vessel by doing a simple experiment.
The Challenge
Part A: Conduct an experiment to determine the terminal velocity of a water droplet falling in canola oil and
to find the viscosity of canola oil. From here, you can check if theory matches reality by calculating if the
buoyancy force and the drag force are equal to the force of gravity.
Stokes’ Law:
Fd = 6πμav; where Fd is the drag force acting on the water droplet, μ is the viscosity of the canola oil, a is the
radius of the water droplet (assuming it is a sphere) and v is the water droplet’s velocity.
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vt = ((ρp – ρf) ga2)/μ; where vt is the particle’s terminal velocity, ρp is the particle’s density, ρf is the fluid’s
density, g is the gravitational acceleration, a is the radius of the water droplet and μ is the viscosity of the
canola oil.
To calculate the terminal velocity of a water droplet falling in canola oil, inject a water droplet with a syringe
into a graduated cylinder almost full of canola oil, and film the water droplet falling inside the oil with a
digital camera. Terminal velocity is reached once the water droplet is falling at a constant speed. Plot graphs
of position vs. time from the data you collect by analyzing your video. You can calculate the radius of the
water droplet by calculating its approximate volume using the formula for the volume of a sphere. You can
calculate the volume of a water droplet by counting how many water droplets you can squirt out of a needle
with a certain amount of water in it. After analyzing your video of the water droplet falling inside the oil, you
can determine the viscosity of the canola oil. With this information, you can know calculate the magnitude
of the drag force that was being exerted on the water droplet.
Part B: Compare two different methods used to separate water and canola oil.
Use the graduated cylinder you already have from part a. Add food colour to 100 ml of water and dump into
the graduated cylinder. Cover the top of the graduated cylinder with a rubber stopper and shake it. Place
the cylinder on a horizontal surface so that the cylinder stands vertically upwards. Take pictures of the
cylinder every 10 minutes until the water and the oil are completely separated. Once both liquids are settled
repeat the procedure, but this time tilt the graduated cylinder by attaching it to a stand that can hold it at an
angle.
Plot graphs of volume (of water) settled vs. time for each test to compare which way of separating the water
and the canola oil is the fastest.
Key Concepts
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The drag force acting on the water droplet can be calculated using the viscosity of the canola oil and
the terminal velocity of the water droplet
There is a difference between the two different methods used to separate water and oil.
Skills
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Data collection and experimental design
Graphical analysis and curve fitting
Spreadsheet calculation methods
Video analysis
Materials
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Syringe
Graduated Cylinder
Water
Canola oil
Food colour
Digital camera
Stand (to hold tilted graduated cylinder)
Rubber stopper
Suggested assigned time: One week
Questions to think about:
1. Which of the two methods did you think would have been the fastest?
2. How is this experiment related to process of extracting bitumen from the oil sands?
Chris Waltham, Edson Sanchez 2011/03/30