Pipe flow calculators

Pressure drop calculator


Calculator Description

Pressure drop calculator helps you to calculate fluid flow rate through closed pipe. The calculation includes pipe friction factor f and local losses with resistance coefficient K calculation. It can be used for non-compressible flow like liquids as well as for low velocity, short distance gas stream.

  • Calculate:

    • Pressure drop
    • Flow rate
    • Friction coefficient
    • Flow velocity
    • Reynolds number
  • Input:

    • Pipe diameter
    • Fluid density
    • Pipe roughness
    • Local resistance coefficient K

Calculator Features

  • Darcy-Weisbach equation based
  • Laminar and turbulent flow regime
  • Round and rectangle pipe
  • Incompressible flow only

You can use the Pressure drop in pipe calculator for all Newtonian fluids that have constant density (non-compressible fluids) and viscosity, either in a closed round or a rectangle pipe. It is possible for one to calculate the flow rate or the pressure drop in a pipe as well as the friction coefficient – f for laminar or turbulent flow conditions. It can be even used for compressible gases if pressure difference of gas stream is not too high (Dp < 5%), so stream can be treated as non-compressible, with minor difference in relation to exact results.

Information required in calculating pressure drop is the internal pipe diameter, volumetric or weight flow rate, stream velocity, pipeline length, fluid density and viscosity. In order to calculate the flow rate, it is required that the pressure on both the start and also the end of pipe is known in addition to the pipe diameter, pipe length, fluid density and viscosity being known as well.

Calculator is suitable for the closed round and rectangle pipes. For the rectangle pipes, the hydraulic diameter instead of a pipe diameter should be used.

You can use this calculator for both laminar and turbulent flow conditions and it will calculate and present the actual Reynolds number.

Friction factor and local resistances factor

Calculator is based on Darcy-Weisbach equation for calculating head losses due to friction. Darcy-Weisbach shows relation between pipe diameter, stream velocity, pipe length and friction factor and how those values are affecting head loss due to friction.

For streams with low Reynolds number and laminar flow conditions, friction factor can be precisely calculated like f = 64/Re. For high Reynolds number and turbulent flow (Re > 4000) the Colbrook and White equation (1937) is used for the friction factor calculation.

Check various equations for friction factor.

For calculating head losses due to local resistances, you should insert in the calculator the local resistance factor K for valves, fittings, pipe contractions and enlargements.

The calculator itself actually includes various values of local resistance factor K for some of the fittings (tees, elbows, and reducers). If you can't find right value for your application, you can use the Resistance coefficient calculator to calculate resistance factor K value.

This version of calculator doesn’t however include pressure difference in pipe that results from a different fluid height level, even though the flow rate can still be calculated by entering the head of fluid height difference in the calculator as the head loss.


Please tell me what do you think about this calculator

Q: Calculate pressure drop in round pipe with flow of 5 m3/h, pipe length 100 m, internal pipe diameter of 25 mm and pipe roughness of 0.1 mm. Flowing fluid is water with density of 1000 kg/m3. Local resistance can be negligible K = 0.

A: Calculation setup:
Calculate for: pressure drop
Select pipe shape: circular pipe
Input one from following two:
p1 - absolute pressure on pipe start
q - volume flow rate
nu - kinematic viscosity
Enter values:
q = 5 m3/h
L = 100 m
d = 25 mm
p1 = 6 bar (irrelevant)
rho = 1000 kg/m3
nu = 1.006 mm2/s
K = 0
kr = 0.1 mm

Q: Calculate flow rate of water through closed round pipe with internal diameter of 25 mm, pipe length of 100 m. Pipe line connecting reservoir on the elevation of 20 m above the pipe exit with water flowing to open atmosphere. Reservoir is under atmospheric pressure. Pipe roughness is 0.1 mm.

A: Calculation setup:
Calculate for: flow rate
Select pipe shape: circular pipe
Input one from following two:
p2 - absolute pressure on pipe end
nu - kinematic viscosity
Enter values:
L = 100 m
d = 25 mm
p2 = 101325 Pa
p1 - p2 = 20 mWS
rho = 1000 kg/m3
nu = 1.006 mm2/s
K = 1 (fluid exit from open pipe)
kr = 0.1 mm

Q: Calculate pressure drop of 2000 m3/h of air flowing through closed rectangle chanel to open atmosphere. Chanel width is 400 mm and height is 250 mm. Chanel is with surface roughness of 0.01 mm. Local resistance coefficient is line is 3.5. Chanel length is 85 m.

A: Calculation setup:
Calculate for: pressure drop
Select pipe shape: rectangle pipe
Input one from following two:
p2 - absolute pressure on pipe end
q - volume flow rate mu - dynamic viscosity
Enter values:
L = 85 m
H = 250 mm
W = 400 mm
p2 = 101325 Pa
rho = 1.293 kg/m3
mu = 17.3 x 10 -6 Pas
K = 3.5
kr = 0.01 mm

Equation used for pressure drop calculation

Read more about used theory on pipe flow theory page.

If you experience problems with calculator start try to find answers on instructions page.

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