If the current presence of flow in a piping system must be monitored, a calorimetric flow switch ? generally known as a flow monitor ? is often used. But how does a calorimetric flow switch really work? The following blog post explains this in more detail.
Calorimetric flow switches, which are generally also referred to as thermal flow monitors, use 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 which is in line with the calorimetric measuring principle includes a measuring probe with two temperature sensors built-into it (see illustration). One of 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 next sensor determines the temperature of the medium in the pipe. Consequently, a temperature difference occurs between your two sensors, that 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 number of molecules passing by increases continuously with increasing flow velocity.
Regulated heating
The measuring probe is basically identical in design: There are two temperature sensors in the medium, among and this can be heated. In this technical solution, the heating power is regulated in order that the temperature difference between your two temperature sensors is kept constant throughout. Consequently, as the flow velocity increases, the heating power should be increased in order to keep how big is the temperature difference constant. The applied heating power is thus a primary measure of the flow velocity in the medium.
Note
Are you experiencing further questions on the measuring principle behind the calorimetric flow switch or do you need help with the selection of this type of product? In Crushing , WIKA includes a calorimetric flow switch for monitoring the flow of liquid media (model FSD-3). Your contact person will undoubtedly be happy to help you.