flow sensors: How it is works


What is flow sensor

 flow sensor is a device which is used to measure the flow of any fluid.it is nothing but a small device which is used in flow meter as a sensing element.as we know about the traditional methods of measuring the flow of the fluid.the measuring of the flow rate of the liquid involves devices that are based on the throttling process.throttle means drop in pressure.so As the fluid passing through a construction pipe then due to the losses there is drop in pressure and this pressure drop can be calculated through the bernoulli’s equation and also we can find out the  flow rate of the working fluid.
bernoulli’s expression 

 Image result for bernoulli's theorem

 Image result for continuity equation

 We know that there are two types of flow  rate
1.volume flow rate 
2.mass flow rate

volume flow rate 

                               volume flow rate is defined as the volume of the fluid that is passing through a  cross-section per unit time.

Image result for volumetric flow rate

mass flow rate
                                 mass flow through a given cross-section per unit time is known as mass flow rate.

Image result for mass flow rate

 the most common principle for the fluid flow measuring 

1.differential pressure flowmeters
2.velocity flowmeters
3.positive displacement flowmeters
4.mass flowmeters
5.open channel flowmeter

differential pressure flowmeters
                                                      these are the common flow measure device and also based on the bernoulli’s theorem.with the help of these measuring devices we can measure the flow rate.the calculation of the fluid flow rate by reading the pressure drop.

 there are some differential pressure flowmeters
1.orifice plate
2.flow nozzle
3.venturi tubes
4.variable area rotameter

orifice plate 
                    it is simply a disc with central hole which is placed in a tube through which the fluid is flowing.As the   fluid passing through a pipe adjusted with orifice plate then pressure is decreases at the downstream and it become minimum at the vena contracta and the velocity of the fluid at this point become maximum.this pressure drop can be easily calculated by the bernoulli’s expression and through this result we can calculate the flow rate of the fluid.some times it does not give the real value of  flow of discharge due to the pressure drop at the point of orifice plate so to reduce the unwanted pressure drop the edge of the kept  sharp which result minimum surface contact  with the fluid.

flow nozzle
                      flow nozzle is a simple device to measure the flow rate of the fluid .it is simply a cone type  device through which the fluid is flow which flow rate has to be measure.A nozzle is a device which is used to control the characteristic of the fluid (increase the velocity of the fluid and decrease the pressure of the fluid).it is nothing but a venturi meter (diversing type).

working process of the flow nozzle
                                                           the working principle is similar to the orifice meter. the nozzle is  situated between a construction passage or a pipe. the fluid is flowing that passage(measured fluid).As it crosses the nozzle , the pressure of the fluid may varies depending upon the assembly.this variation of pressure can be measured with the help of  differential pressure sensor(u tube menometer or differential pressure gauge) and this results to flow rate of the fluid.

flow nozzle arrangement

from the above schematic  we can also understand the process the of flow nozzle
when the fluid whose flow rate has to be measured  is passage through the nozzle the pressure of the fluid become minimum at the section called throat this results to increase the velocity of the fluid. form above designation before entering in the nozzle the pressure of the fluid is p1 and as it crosses the nozzle the pressure become p2.the pressure difference between the p1 and p2 can be measured by the differential flow sensor.after that we can easily find out the value of the flow rate using the bernoulli’s and continuity equation .

flow sensor  is mainly used for high pressure and temperature steam flow.it is also used to measuring the flow rate at atmosphere pressure.


                  installation is easy and is cheaper when compared to venturi meter
                  it has high coefficient of discharge. 

                      maintenance cost is much higher than the orifice meter.it is difficult to install.

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