5 replies to this topic

[keby9vam]

Hi all,

Is it possible that when a liquid stream, mostly water flows through a valve the temperature would increase? Before the valve, the pressure is about 120 bar and is let down to 65 bar. Hysys is showing a temperature increase, but why? Thank you for your time.

Regards

keby9vam

[latexman]

How much of a tempeature increase? Is it really worth worrying about? What is the temperature going into the valve?

Edited by latexman, 25 July 2012 - 06:59 AM.

[keby9vam]

it's going in at 50C and the increase is by 3 degrees celcius

[MrShorty]

For whatever reason, we do tend to assume that a fluid temperature will decrease as the pressure decreases. However, this is not always true. If we approximate your expansion through a valve as if it were like a Joule-Thompson experiment, then the direction of temperature change will be determined by the sign on the JT coefficient. NIST says that the JT coefficient for liquid water at 50 C is <0. If they are using the same convention as my old P-chem book, which says, "when the JT coefficient is positive, the [fluid] will cool upon expansion," then it would be natural to see liquid water warming upon expansion.

[PaoloPemi]

if it may help to understand the problem Prode Properties with the IAPWS 1995 model calculates (adiabatic flash operation)
Pin 120 Bara
Pout 65 Bara
Tin 50 C
Tout 51,1342 C
as you see the IAPWS 95 model predicts a little increase in temperature,
by the way Joule Thomson is not constant in this range of pressure

[latexman]

The friction from the pressure drop through the valve will heat the water, so a small temperature increase seems reasonable.