School of Technology, Energy and Apprenticeship
Instrumentation Control & Electrical Technology (ICET)
ICS3305 – F2013

1

Process Instrumentation I
Unit 4

Review Of Most Common Process Variables

4.1

Review the definition of continuity equation

4.2

Define pressure in fluids and its relation with the density weight

4.3

Explain how pressure transmitter can be used to infer the values of level and flow rate

4.4

Explain direct and indirect temperature measurement 1

School of Technology, Energy and Apprenticeship
Instrumentation Control & Electrical Technology (ICET)
ICS3305 – F2013

4.1

2

Review the definition of continuity equation

Continuity Principle
For steady fluid flow, where the velocity of the fluid is high its pressure is low, and where the velocity is low the pressure is high

Equation of Continuity A1v in
This results  v out

 A1 
 v in  
 A2 

= A 2 v out
2

School of Technology, Energy and Apprenticeship
Instrumentation Control & Electrical Technology (ICET)
ICS3305 – F2013

3

Example 1:
Water flows through a garden hose of internal diameter 1.5 cm at a speed of 2.0 m/s. With what speed does the water escape from the nozzle if the opening is reduced to a diameter of 0.5 cm?

A1 =  r1

2

=  (0.75)2= 1.77 cm 2

and A2 =  r2

2

=  (0.25)2= 0.196 cm 2

As equation of Continuity A1v in

= A 2 v out

A 
 1.77  so, v out  v in  1  = 2.0 
 = 18 m/s
 0.196 
 A2 

3

School of Technology, Energy and Apprenticeship
Instrumentation