If the current presence of flow in a piping system should be monitored, a calorimetric flow switch ? generally known as a flow monitor ? is frequently used. But so how exactly does a calorimetric flow switch really 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 that is based on the calorimetric measuring principle consists of a measuring probe with two temperature sensors integrated into it (see illustration). One of many sensors is heated continuously using a 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, small 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 higher 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, one of that 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 must be increased 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
Do you have 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 its portfolio, WIKA has a calorimetric flow switch for monitoring the flow of liquid media (model FSD-3). Alive will undoubtedly be happy to help you.