JT effect 1

[JollyStNic]

I am not an engineer, so forgive my ignorance. I need to know if there is a formula for determining the delta T when taking a pressure drop across a valve. Specifically, what information do I need other than the inlet/outlet pressures, specific gravity (this is natural gas) and inlet temperature? Thanks for your help.

 

[TD2K]

Usually, I use a Mollier chart (or similar thermodynamic chart) for methane for something like this (the GPSA data book has a copy if there is one around, so will Perry's as will many other books). For less than 10% of C2s and heavier, the Mollier chart still gives you a reasonable dT compared to something like Pro/II.

You find the starting pressure and temperature and then drop straight down (assuming the x axis is enthalphy, otherwise you follow a constant enthalphy line) to your outlet pressure and read off the resulting temperature.

I don't remember seeing a simple equation like you are hoping to find and nothing is popping out of some of my engineering textbooks.

 

[JollyStNic]

TD2K, thanks for your help. I was hoping to find a formula to put in a spreadsheet. BTW, what section of Perry's are these charts. I couldn't find it. Thanks.

 

[TD2K]

They are in section 2 of the 6th Edition.

 

[MortenA]

A very rough rule of thumb is half a degree cel. pr bar of pressure drop. But its surpricingly accurate anyway for most appl. up to 100 bar and no condensation.

Best Regards

Morten

 

[sos]

dear sir:
i want to know what is the effect of heat transfer by conduction , by convection and by raiation . and thank you

 

[MortenA]

You will propably never read this beeing a visitor and all but a few pieces of advice:

1) Dont ad a question to a random tread - create a new tread
2) Your question is mush to general.Best advice to expect will be a number of references to good text books.

Best Regards

Morten