Know Your Flow! – Selecting the right FlowMeter.

When trying to select the right flow meter for your specific needs, it is important to remember that all fluids and gases behave differently when flowing through a pipeline. How much a fluid resists flow – it’s viscosity – affects the velocity of flow through the pipeline.


Profiling the flow of a particular gas or fluid and understanding how it behaves through a pipeline is pivotal to narrowing down the large variety of flowmeters on the market, to ensure you select one best able to handle your specific conditions and application.


A fluids flow profile will vary depending on whether it is Newtonian or non-Newtonian.


Newtonian Fluids – such as milk, water, sugar solutions and mineral oils have a tendency to ‘stick’ to the walls of the pipe they pass through, resulting in the liquids moving faster through the middle of the pipe than closer to the sides. This causes Newtonian liquids to have a directly proportionate relationship between the pressure pushing the liquid through the pipe and the resistance.


Non-Newtonian Fluids – such as paints, shampoos and yogurt type substances are harder to predict they don’t have a proportionate relationship between pressure and resistance. The flow of these fluids can vary over time as the viscosity affected by resistance caused by the collision of two different velocities.


Selecting the right flowmeter for your application requires calculation of the Reynolds Number. This figure represents the ratio between inertial forces (resistance) against viscosity, and can be calculated using the minimum or maximum flow and viscosity figures of the application.


7741.92 x ID x V
ID = the pipe inside diameter in inches
V = the flow velocity in feet per second
Cst = the fluid viscosity in centistokes


Once you’ve calculated the Reynolds Number, you can match that against a particular flowmeter’s Reynolds range, to help select a flowmeter that is suited to meet the demands of your application.


For any further questions about selecting the right flowmeter, contact the professional precision instrumentation suppliers at DG Instruments today.

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