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Calculate Flow from Pressure Measurement Cheat Sheet (DRAFT) by [deleted]

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Introd­uction: Flow in a Pipe/Tube

Several factors determine the pressure drop that occurs in fluid flow applic­ations including laminar versus turbulent flow, the flow velocity, kinematic viscosity and Reynolds number of the fluid, internal roughness of the inside of the pipe as well as its diameter, length and form factor. Orifice plates, Venturi tubes and nozzles simplify the situation. In these cases (refer to Figure 1), the flow is related to ΔP (P1-P2) by the equation:


For fluid flow measur­ements, orifice plates, venturi tubes and nozzles simplify the use of differ­ential pressure (ΔP) sensors to determine the flow rate. In these cases, the flow is related to ΔP (P1-P2) by the equation


The most common use of pressure sensors to calculate another parameter is flow.

This technique is also used to measure air flow of blowers, air flow through filters, vent hoods, gas boilers, or in heating ventil­ation and air condit­ioning (HVAC) variable air volume (VAV) contro­llers.

In medical applic­ations, drug delivery (liquid flow) uses differ­ential pressure sensors to measure flow rates of 0.5-10.0 microl­ite­rs/min.

Many gas flow measur­ements are also made with pressure sensors.

Elements of a ΔP flow measur­ement

Pitot tubes

Use the difference between total pressure and static pressure to calculate the velocity of the aircraft or fluid flowing in the pipe or enclosure. A Pitot-­static tube for measuring aircraft velocity is shown above'