2022-09
21Why do laminar differential pressure principle mass flow meters and controllers not require preheating?
Why do some flow meters need preheating?
The mass flow meter (MFM) and controller (MFC) need to be preheated before use, which is a characteristic of the thermal principle MFM/FMC product. Why?
This is determined by the thermal principle measurement method, and a small bypass pipe, usually called a capillary tube, needs to be opened in the product flow channel. The capillary tube is heated to a certain temperature and the flow rate is calculated through a certain formula. The newly turned on thermal product needs to be heated to the predetermined temperature after the pipeline is ventilated, as the capillary temperature has not yet reached the required temperature for normal measurement. This heating process is the preheating process, which usually takes 5-30 minutes.
Schematic diagram of thermal flowmeter
As is well known, one advantage of laminar differential pressure principle flow meters is that they do not require this preheating process. Why is that?
The principle of laminar differential pressure is to calculate the flow rate through the "Hagen Poiseuille formula":
image
Under certain conditions, it is only necessary to measure the fluid differential pressure to calculate the fluid volume, and the generation of differential pressure only requires the fluid to pass through the flow channel without bypassing the capillary tube, so there is no process of heating the capillary tube. So, after the flowmeter based on laminar differential pressure principle is turned on, it can start working normally without preheating.
This is a major characteristic advantage of the laminar differential pressure principle flowmeter, which allows users to test it at any time without the need for debugging or waiting. For production enterprises, it can save time and improve efficiency.