Question

• Comment on the validity of Bernoulli’s equation Comment on the comparison of the calculated and measured total heads in this experiment.

• Discuss your results, referring, in particular, to the following:

• Energy loss and how it is shown by the results of this experiment, and the components of Bernoulli’s equation  

• Indicate the points of maximum velocity and minimum pressure with venture tube  

• Suppose mercury instead of water was used as the manometer fluid. How would this affect the accuracy of the measurements?

Answer 1

The fluid must be incompressible, Frictionless flow, No heat transfer from the fluid to the surroundings or the walls of the tube, No change in elevation of tube these are to be validated.

But coming to experimental results no fluid is incompressible, There will slightly heat transfer to the surroundings due to the motion of fluid as flowing on the walls of the tube, No change in elevation can be achieved.

So the input and output conditions in the ideal equation cannot match with the experimental result but then there will be some difference between the heads.

The ideal height would be greater than the experimental height.

Energy Loss

The major thing which causes energy loss is friction between the fluid and the surface of the tube wall and the compressible nature of the fluid no fluid is incompressible in nature.

The components involved in Bernoulli's equation are

Energy, Pressure, Velocity, head level etc.

Bernoulli's Principle can be simply stated as Static Pressure + Dynamic Pressure = Total Pressure

This is a diagram of Venturi Tube.

As we know that pressure is defined by force per unit area and here decreases pressure needs to be increased and pressure and velocity are inversely proportional to each other.

So, the point 2 has maximum velocity and minimum pressure.

When we use mercury instead of water in manometer

The density of mercury is 13600 kg/m³  and water is 1000kg/m³. So it can exert more pressure than water.

For one atmosphere pressure, the length of the water column required is far higher than the length of the mercury column.

Mercury is more sensitive than water. So it can give a more accurate measurement.

Mercury does not evaporate so easily.

Mercury has very low vapour pressure compared to water.

So mercury is widely used in manometers.