At my new job at a chem plant they take the impulse lines and heat them to keep the liquid a vapor.... Has anyone ever seen this.... How does this work?
It is generally easier to let the lines condense or fill them with liquid and calibrate accordingly. Not sure why you would want to maintain vapour in the impulse lines - I assume it is chemical specific.
Well during the winter the chemical will condense in the lines at 80*. During the summer it will remain a vapor, so to keep it constant they will just keep the lines steam traced..
If the fluid flowing by is already a 2-phase mixture, your flowmeter is giving you garbage output anyway.
If the fluid flowing by is a liquid, this strategy won't work and is unnecessary. In that case you want both impulse legs full.
In the vapour case, all the heat tracing does is to prevent condensation and later evaporation of liquid in the impulse legs which shifts the zero of the instrument. The same strategy is sometimes used on the negative leg of a DP pressure transmitter used to measure level, in an attempt to keep this leg empty- with varying degrees of success of course depending on the application.
The impulse line is a "dead end". The only differential pressure between the pipe and the meter is a hydrostatic difference - if the meter is located at a different elevation than the pipe where the impulse line "starts".
So the fluid in the impulse line dosnt move, and even if some liquid gets into the line and evaporate - then the gas will just expand into the pipe - because you cant have different pressures (at same elevation) without flow. Once the pressure is the same then flow will stop.
Acutally if the impulse line is full of liquid and the meter sits at a different elevation than the error will be large with a fluid. SInce its a dP meter that is, however, inconsequential.
