Determine if valve is passing by temperature

[NovaStark]

Hi all,

I've been tasked to determine if a valve is passing but the only information I currently have is the temperatures upstream and downstream the valve.

I am told that the temperature difference across the valve would tell me if it's passing or not. However I am not sure what the temperature difference had it not been passing would be as a comparison. Is there any way to estimate what the temperature of the piping downstream the valve would be if it wasn't passing ? If I try to use fourier's heat transfer law for conduction where Q= -kA(dT/dx) what would I use for the area A , the area of the spot I measured or the surface area of the piping, etc ?

(Also I don't have FEA or CFD or any complex software to check this)

 

[Compositepro]

If there is no flow, it will be at ambient temperature.

 

[LittleInch]

This only works well for gas due to the JT cooling effect, but estimating flow is not easy as the temperature you monitor from the outside is affected by lots of things (ambient air, size of the valve, mass of the valve etc etc.

Try measuring temperature on the first bit of pipe, but you are correct, you need to know if there is a temperature change normally or not.

small leaks you won't find, but bigger ones you can see a temperature difference higher than there should be.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[georgeverghese]

Talk to a mechanical or piping maintenance engineer about using an acoustic sensor that picks up noise through a valve body or a pipe wall as gas hisses past a leaking valve.

 

[NovaStark]

Thanks for the replies.

With the temperature difference if I don't know what the temperature of the pipe downstream the valve is supposed to be when not passing then I won't know how it compares.

For the acoustic sensor, it's a high temperature line which is completely insulated, there are just small ports cut in to measure the temperatures.

 

[georgeverghese]

There wont be much of a JT effect for a high temp gas stream.

Yes, the portable acoustic probe ( less than 5mm dia ?) should be in direct contact with the valve body wall to pick up this noise.

 

[racookpe1978]

Are the pipes and valves well-insulated across this vavle?

A single "temperature point" - two actually, one upstream and one downstream - will be unlikely to tell you anything. Too random a position, too little delta T information unless it is a severe leak.

Instead, try an IR camera continuously focused on the entire valve and a short length of pipe upstream and downstream. Close the vale, watch the IR recording over a 1 minute, 5 minute, and 15 minute interval (use a fast motion camera at intervals of a few seconds for the longer times. ) You will see the normal pattern, then the static condition as the whole assembly cools down, then - if there is any leakage, the result of that leakage after 10-30 minutes.

If it is a single time test, do it with the insulation removed. For continuous long-term monitoring? Not sure of a better way.

 

[gerhardl]

You 'have the information of temperature upstream and downstream of the valve'. How is this determined, and where is the temperature measurement points located? What amount of leakage is critical/ are you expected to be able to detect. Is there a history of measurements and previous experience here? Since temperature ports are existent, there is obviously some reason behind this.

Depending on the answers on the questions above, you might probably be able to say 'something' on an approximate level for larger leakages. Except for this I would have gone for racookpe1978s' answer, or acoustic measurement or combination. Insulation must be removed in sufficient degree.