Mechanical Engineering - Hydraulics and Fluid Mechanics - Discussion

The liquid used in manometers should have a high density so that the height of the column can be reduced. Because the manometers are used for high-pressure measurement, it is important to make the column height within a practical limit.

Most of case, for gauge pressure measurements, mercury is widely used as manometric fluid because it has non-evaporating quality under normal conditions, sharp meniscus and stable density. For some pressure differences and low-level vacuum, water can be considered as the working fluid in the manometer.

Important Points:

Manometric fluid should have a low surface density to have higher accuracy in the reading.
∴ Low surface tension is one of the desirable properties but the most important property is the property of being highly densified.

@All.

Some people say high surface tension is the correct option. No, it is incorrect as it will reduce the efficiency of the manometer.

Low surface tension and high density.

It should be low surface tension due to surface there will be rise or fall of liquid depending upon the contact angle and reading may be less accurate.

Only two property high,

1. High density.
2. High boiling point.

Other than all property should low.

Surface tension should be high because higher surface tension gives low vapor pressure (i.e. No vapor formation takes place of manometric fluid) and also high surface tension prevents the unnecessary rise of fluid in Fluid column due to adhesion during pressure measurement.

Why low surface tension is required? Please explain in detail.

@Ahmed.

The Liquid should Stick the walls of tube-- represents high surface tension.

Manometric fluids should have the following properties

* High density (for high-pressure measurement the rise of liquid will be within reasonable limits)
* Low Surface tension.
* Low Viscosity (As high viscosity will slow down the sensitivity or responsiveness of fluid movement).
* Low Vapour Pressure (Because, if Vapour pressure is greater than the fluid pressure to be measured then the problem of cavitation will arise.).
* High Boiling point.
* Low Freezing Point.
* Chemically Inert.
* Distinct Interface.

Low surface tension and high density.

Desirable properties of good manometric liquid should have;
-> Low-freezing point.
-> High boiling point.
-> Non-wetting characteristics.
-> Low surface tension.
-> Chemically inert.
-> Clear visible interface.
-> Ability to maintain density at various temperatures.