The need to store liquids has led us to design and build large containers which are widely used in industry with enormous volumetric capacities. The design of each tank depends on the liquid that it must store, having open, closed and vented tanks among others, but what they all have in common for any process is that we must know the level of liquid present to avoid spills or unnecessary activation of pumps as required by the process. In today's delivery I would like to mention the level measurement.
By Bubbling
It consists of a tube immersed in the liquid through which air is bubbled by a rotameter with a built-in flow regulator.
The air pressure in the pipeline is equal to the hydrostatic pressure exerted by the liquid column, i.e. the level. The flow regulator allows a constant flow of air through the liquid regardless of the level (a flow rate of 150 N1/h is normal); if this did not exist, there would be a large difference in the required air flows from the minimum to the maximum level, with the disadvantage of undue air consumption. The bevelled tube allows for easy formation of air bubbles.
It consists of a diaphragm in contact with the tank liquid, which measures the hydrostatic pressure at a point on the bottom of the tank.
As far as operation is concerned, in an open tank the pressure is proportional to the height of the liquid at a point on the bottom of the tank and its specific weight. That is: P = H.y.g in which:
P = pressure
H = height of liquid above the instrument
y = density of the liquid
g = 9,8 m/s2
The diaphragm is part of a pneumatic, electronic or digital differential pressure transmitter similar to diaphragm flow transmitters.
In the most commonly used type, the diaphragm is fixed to a flange that is mounted flush with the tank to allow for the measurement of fluid levels, such as paper pulp and liquids with suspended solids, without difficulty. It can even be mounted overhung so that the diaphragm completely flush with the interior walls of the tank, as is the case with extremely viscous liquids in which no bends are allowed.
Hydrostatic Pressure
DEFINITION
It is a fundamental characteristic of any fluid at rest, since the force exerted on any particle of the fluid is the same in all directions. If the forces were unequal, the particle would move in the direction of the resulting force.
MEASUREMENT UNITS
Pressure is usually measured in atmospheres (atm); in the International System of Units (SI), pressure is expressed in newton per square metre; one newton per square metre is a pascal (Pa). The atmosphere is defined as 101,325 Pa and is equivalent to 760 mm of mercury in a conventional barometer. It is also measured in psi pounds/inches squared (lbs/in2) and in bar.
This concludes another installment that I leave for you with much affection hoping that I can be of use to you and sincerely thanking you for the time you have taken to read my article.
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