Mechanical Engineering - Hydraulics and Fluid Mechanics - Discussion

Should have high density to decrease the column height and due to which we can measure more range of pressure.

It should be of high density.

Should have liquid surface tension so that unnecessary rise can be avoided. Am I correct please comment.

Should have high density so that the height of column can be reduced. Because the manometers are used for high pressure measurement so it is important to make the column height in practical limit.

Characteristics of liquid used in U-tube Manometer:

1. Low viscosity.
2. Low surface tension.
3. Liquid should have a high boiling point and should not get vaporized.
4. The liquid should stick to the walls of the tube.

Should have low surface tension. But density should be high in order to decrease column length.

It should be low surface tension.

Density of fluid selection depends upon the pressure of the liquid system. If we choose low-density fluid we can measure small changes in pressure. If we choose high density we can measure larger pressure difference.

Although the increase in density leads to the reduction in accuracy of the manometer.

Low surface tension is a desirable property.

Yes, 100 % correct @Pvdatt.

One thing, I would like to add is if the manometer liquid has high surface tension then the liquid surface in a tube will be in a shape of the dome it wouldn't be flat so we can't measure a correct reading that's why liquid should have low surface tension.

@Nadim.

The diameter of the tube is large enough to avoid the capillary effect. The Surface tension of the liquid in large diameter tube has nothing to do with the capillary effect.

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.