If the current presence of flow in a piping system must be monitored, a calorimetric flow switch ? also referred to as a flow monitor ? is often used. But so how exactly does a calorimetric flow switch actually work? The following blog post explains this in more detail.
Calorimetric flow switches, which are often generally known as thermal flow monitors, utilize the physical laws of heat transport in flows. A distinction is basically 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 that is in line with the calorimetric measuring principle consists of a measuring probe with two temperature sensors built-into it (see illustration). Among the sensors is heated continuously with the aid of a built-in heating element (wire-wound) with a constant 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, small this temperature difference is. The foundation for this may be the cooling effect 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 amount 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 which may be heated. In this technical solution, the heating power is regulated so that the temperature difference between your two temperature sensors is kept constant throughout. Consequently, because the flow velocity increases, the heating power should be increased in order to keep the size of the temperature difference constant. The applied heating power is thus a primary measure of the flow velocity in the medium.
Note
Do Piranha have further questions on the measuring principle behind the calorimetric flow switch or do you want help with selecting this type of product? In Still , WIKA includes a calorimetric flow switch for monitoring the flow of liquid media (model FSD-3). Your contact person will undoubtedly be happy to assist you to.g