WHAT IS ROTAMETER AND HOW DOES IT WORKS ?

In previous posts, we discussed orifice meter and venturi meter. If you had not gone through it , you can read by clicking on below links.
In orifice and venturi meter , the variation of flow rate through a constant cross sectional area and variable pressure drop or difference. Today we are going to discuss about another class of meter called area meters. They includes devices with constant pressure drop or difference and cross sectional area of fluid flow varies with flow rate. The area is related through proper calibration to the respective flow rate.

In these class of meters, most important area meter is ROTAMETER.

ROTAMETER:

Credit : Automationforum

Construction:

Rota meter devices is basically a plain conical tapered tube I.e smaller cross section in bottom and larger cross section at top.Made up of glass or any other transparent material with proper calibrated scale.fluid is supposed to flow in upward direction .
Apart from these it includes a float for indication.This float is suspended in tube.
This tube is directly connected , parallel with axis of pipe.
Float can be constructed of material of different density like aluminium, glass , Stainless steel or even plastic.
Shape of rotameter may be different for different application.

Working:

The entire fluid stream flow through rota meter which is connected to pipe. Due to float in rotameter , it makes annular space between float and tube.
Fluid while flowing through this annular space , raises the float to certain elevation, because fluid applies drag force to float.The tube is marked in divisions and calibrated to read from scale at edge of float.

But in some cases the fluid to be measured are opaque or at high temperature and pressure in this case glass can not be used , so metal tube are used and reading of float is transmitted with help of electronic devices.
Drag force: Force in direction of fluid flow.