Regarding the measurement of exhaust gas from air ducts, all shipmates are welcome to discuss it
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For measuring exhaust gas in air ducts, we used insert-type target flowmeters in the past, but their performance was not good. The pipe diameter is DN400. Dear colleagues, what kind of flowmeters do you usually use for measuring exhaust gas flow in your systems? Except for thermal mass flow or barometric flow meters, due to cost considerations.
If medium-induced pressure loss is not an issue, then an orifice plate can be used; however, accuracy and price are inversely related – it depends on how much budget is available
Remember it, and just say it once. Generally, only three types of flow meters are allowed for flue gas measurement: differential pressure type, thermal type, and ultrasonic type. The latter two types are less commonly used; for example, the thermal type has many limitations and can be tricky to work with. So, honestly, choose the differential pressure type; for a cheaper option, go with a pitot tube, and for a more expensive one, opt for a Bourdon tube type.
If cost is a concern, go for an orifice plate; don’t expect high precision from it
Theoretically, there’s no problem with the engine; what needs to be checked is whether the exhaust gas is dry and how dusty it is. Bar-type flowmeters require the medium to be clean. Thermal types are also acceptable; they’re just more expensive and have higher installation requirements. It’s hard to talk about ultrasonic waves without having used them.
Currently, domestic thermal types are also quite mature; they are not expensive, and can be chosen when the moisture content in the exhaust gases is low. With proper calibration, they work without any issues
Can exhaust gases and smoke be free of water? Therefore, using a thermal method is a problem – a problem that cannot be resolved.
Some thermal flow meter manufacturers claim that they can be calibrated for different moisture contents. . . It is estimated that this approach is suitable only in situations where the water content does not change much. The differential pressure of the exhaust gases is generally low, so integrated gauge types are sufficient; however, maintenance can be inconvenient as it requires working on large pipes. . . . . Liver tremble hehe
The pitot tube differential pressure type is commonly used, and it should be possible to install it for a DN400 diameter； Thermistive types can also be considered (however, this type requires one of the two probes used for insertion to be heated; safety considerations must be taken into account regarding whether the exhaust gas could reach the LEL level)
You’re right; the pressure in the exhaust pipelines is very low, and it’s unstable as well. Generally, the exhaust pipelines are under slight negative pressure. Barye flow meters are also not very useful. Currently, the only viable option is thermal flow meters. However, thermal flow meters have limitations regarding the rate of change in moisture content; this range generally shouldn’t exceed 5% of the gas composition (this is an empirical upper limit). Yet, it’s quite difficult to determine the composition of exhaust gases. Therefore, choosing an appropriate flow meter is quite challenging. Ultrasonic waves can also be used, but they have limitations regarding the gas components and calorific value; therefore, it is still necessary to know the gas components in order to choose this method.