Determination of Viscosities of Different Fluids

Determination of Viscosities of Different Fluids

Introduction

Viscosity refers to the resistance to flow of fluids. It can be defined as the speed of the flow, which depends on the thickness or thinness of the fluid. Viscosity can thus be described as the friction between the molecules in the fluid, which like friction between solid objects, determines the energy required to make a fluid flow. Viscosity in fluid becomes apparent when a layer of fluid is made to move in relation to another layer. It is simply the friction between these layers when they are caused to move against each other.

Methods of Measuring Viscosity

Various methods can be adopted in the measurement of viscosity. These methods include:

1. Viscosity Cup: This is a small container with a handle and a small hole in the bottom. The time taken to empty this cup through the hole is related to the viscosity of the fluid. Common types of viscosity cups include Ford cups and Zahn cups.

2. Capillary Viscometer: This methods uses capillary tubes to measure the flow fluids and the time it takes for a given volume of fluid to pass through a length of the tube is related to viscosity.

3. Falling Sphere Viscosity: Here, a sphere of known density is dropped in a fluid sample and the time it takes for the sphere to fall to a specific point is recorded.

4. Vibrational Viscometer: This method measures the damping of an oscillating electromechanical resonator immersed in a fluid.

The method described in this procedure is the Viscosity Cup method. However, because of the large volume of fluid needed for the experiment, special buckets with controlling valve (for opening and closing) at the bottoms are used in place of the cups.

Objectives of the Experiment

The aim of the experiment is to find out the volume flow rates of water, engine oil, and kerosene, and to compare their viscosities based on these volumes of flow.

Apparatus and Materials

• Stopwatch
• Fluids : Water, kerosene and engine oil
• Measuring cylinder and engine oil
• Funnel

Procedure

1. Fill the bucket with water to the brim
2. Place the measuring cylinder at the outlet of the tap of the bucket
3. Open the tap and immediately start the stopwatch.
4. When the time equals 2 seconds, close the tap and measure the volume inside the cylinder
5. Record the volume. 
6. Refill the bucket and repeat the procedure for three more times to get precise values
7. Refill the bucket and repeat the procedure for 4, 6, and 8 seconds, repeating 3 times too for each.
8. Repeat procedures 1-6 using the other fluids. For increase in accuracy, different buckets and cylinders should be used for different fluids.

Results and Calculations

The volume of each measurement is tabulated as shown below:

1. For Water

Where Average = (Vol. 1 + Vol. 2 + Vol. 3) / 3

2. For Kerosene

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Where Average = (Vol. 1 + Vol. 2 + Vol. 3) / 3

3. For Engine Oil

This image has an empty alt attribute; its file name is mechanical-determination-of-viscosities-of-different-fluids-pic1.jpg

Where Average = (Vol. 1 + Vol. 2 + Vol. 3) / 3

Discussion and Conclusion

A higher volume flow implies less internal friction, that is less viscosity. It should be noted that this has nothing to do with the density of the fluid. They are two different concept of fluids. Density is the measure of the molecular weight of the composition while viscosity is the measure of the intermolecular forces and molecule shapes. Therefore, that one fluid is denser than another does not necessarily guarantee its being more viscous.

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