How does a calorimetric flow switch work?

If the current presence of flow in a piping system should be monitored, a calorimetric flow switch ? also called a flow monitor ? is often used. But so how exactly does a calorimetric flow switch actually work? The following post explains this in greater detail.
Calorimetric flow switches, which are often also referred to as thermal flow monitors, use the physical laws of heat transport in flows. A distinction is actually made between two technical solutions: continuous and regulated heating.
Schematic illustration of a measuring probe for a calorimetric flow switch
Continuous heating
A flow switch which is in line with the calorimetric measuring principle includes a measuring probe with two temperature sensors integrated into it (see illustration). One of the sensors is heated continuously with the aid of a built-in heating element (wire-wound) with a continuing heating power and measures the temperature at the heating element. The second sensor determines the temperature of the medium in the pipe. Consequently, a temperature difference occurs between the two sensors, which is registered by the electronics. The bigger the flow velocity of the medium in the pipeline, the smaller this temperature difference is. The basis for this is the cooling aftereffect of flowing media. The molecules in the medium, which are flowing past the probe tip, collect ?packages of heat? and transport them away. The more molecules flow past, the greater the cooling effect. The number of molecules passing by increases continuously with increasing flow velocity.
Regulated heating
The measuring probe is actually identical in design: You can find two temperature sensors in the medium, among that can be heated. In this technical solution, the heating power is regulated in order that the temperature difference between the two temperature sensors is kept constant throughout. Consequently, as the flow velocity increases, the heating power must be increased to keep how big is the temperature difference constant. The applied heating power is thus a direct way of measuring the flow velocity in the medium.
Note
Do you have further questions on the measuring principle behind the calorimetric flow switch or do you want help with the selection of this type of product? In Better , WIKA includes a calorimetric flow switch for monitoring the flow of liquid media (model FSD-3). Your contact person will be happy to help you.

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