Technical information - SF Pressure Drop Help

SF Pressure Drop
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Principles
Technical Information

Pressure drop:

Pressure drop in pipes is caused by:

1.) Friction
2.) Vertical pipe difference
3.) Changes of kinetic energy


 

Calculation of pressure drop caused by friction in  circular pipes
First we calculate the Reynolds-Number:


If Reynolds number < 2320, than we have laminar flow, else we have turbulent flow.
Now we calculate the pipe friction  number:

Pipe friction number at laminar flow:


Pipe friction number at turbulent flow:


Now we can calculate pressure drop in circular pipes:


 

Calculation of pressure drop caused by friction in  fittings etc.
To calculate pressure drop in fittings we use resistance coefficients normally. The resistance  coefficients are in the most cases found through practical tests. If the  resistance coefficient is known we can calculate the pressure drop:

 

Calculation of pressure drop caused by vertical pipe  difference
Pressure drop caused by vertical pipe difference we calculate with the  formula:


 

Calculation of pressure drop caused by changes of kinetic  energy
Pressure drop caused by changes of kinetic engergy we  calculate with the formula:

The element "Dyn. pressure  change" calculates these pressure changes. Normally you input the dimension  of begin and end of the whole pipe.

 

Pressure drop in gases and vapor
Compressible fluids expands caused by pressure drops (friction) and the  velocity will increase. Therefore is the pressure drop along the pipe not  constant.

SF Pressure drop calculates these pressure drops with an approximate equation  (pressure drop at arbitrary heat transfer):


We set the pipe friction number as a constant and calculate it with the  input-data. The temperature, which is used in the equation, is the average of  entrance and exit of pipe.

You can calculate pressure drops of gases with the same formula as liquids  if the relativ change of density is low (change of density/density =  0.02).
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