In industrial fluid systems, flow rate determines everything — pipe diameter, pump size, valve selection, and energy consumption. Getting it wrong means inefficient systems, water hammer, or insufficient pressure at the point of use.
Flow Rate Fundamentals
Volumetric flow rate (Q) = velocity × cross-sectional area. For pipes: Q = v × π × r². Doubling the pipe diameter quadruples the flow capacity at the same velocity.
Recommended flow velocities: water supply 1–2 m/s, HVAC chilled water 1–3 m/s, industrial process lines 2–4 m/s. Too fast causes erosion and noise; too slow allows sediment buildup.
Pipe Sizing for Flow Rate
For a required flow of 100 L/min (1.67 L/s): at 2 m/s velocity, you need a pipe area of 0.000833 m², which means a 32.5 mm internal diameter — so you'd select a DN40 (1.5") pipe.
Pressure drop increases with the square of flow rate. Doubling the flow quadruples the pressure drop (and roughly octuples pumping power). This is why oversized systems waste enormous energy.
Pump Selection
Pump power = (flow × pressure) ÷ efficiency. Moving 100 L/min at 3 bar pressure through a 70% efficient pump requires: (0.00167 m³/s × 300,000 Pa) ÷ 0.7 = 715 W.
Centrifugal pumps are used for high flow, low pressure. Positive displacement pumps handle high pressure, viscous fluids. Always select a pump near its best efficiency point (BEP).
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