Steam Dryness

[steris]

Does anyone know of any instrument or device that can measure steam dryness and superheat? I've been looking at test kits like (

http://www.steamquality.co.uk

) but kits like this are very dependent on the user's procedure to gain any measure of repeatability. I was hoping for something more automated that wouldn't take as much training and finesse to achieve accurate & repeatable results. Any help that anyone can provide would be greatly appreciated.

 

[ash9144]

Are you trying to test at various points within a steam distribution header?
Usually you can determine steam quality based on temperatures and pressures through the header.

 

[steris]

We are trying to choose a small scale steam generator & superheater. There are a bunch of units from various manufacturers that we have in house. We want to perform the same test on all of them to have an accurate performance benchmark. As part of this we want to measure the dryness and degree of superheat out of the systems.

 

[ione]

Throttling calorimeters could be an option. Steam sample is taken at pressure of interest P1 and then throttled to a atmospheric pressure P2.
The transformation through the throttling valve is isenthalpic (well not precisely isenthalpic as the enthalpy is not constant from the beginning to end of the process, but the initial and final enthalpy is the same) so h1 = h2.

Now:

h1 = hf1 + x*hfg1

Where:
hf1 = enthalpy of water at pressure P1 (known)
x = dryness (unknown)
hfg1 = enthalpy of evaporation at pressure P1 (known)


You can measure h2, knowing P2 and T2 (this temperature should be above the saturation temperature Ts2 at reference pressure P2).

h2 = hf2 + hfg2 + cps*(T2 – Ts2)

hf2 = enthalpy of water at pressure P2 (known)
hfg2 = enthalpy of evaporation at pressure P2 (known)
cps = specific heat of steam is state 2 (known)
Ts2 = saturation temperature at pressure P2 (known)
T2 = temperature of steam in state 2 (measured)

Being h1 = h2 and solving for x

x = [hf2 + hfg2 + cps*(T2 – Ts2) –hf1] / hfg1

I also suggest:

ASME Performance Test Code 19.11 Steam and Water Purity in the Power Cycle

 

[steris]

Thank you for the reference Ione, that article is a good read. I've read posts similar to the equations you listed in other threads that describe methods of making these measurements. I'm not looking for a procedure as much as an automated device that will do it. The kit I linked to does exactly what you posted however the results are very sensitive to the user's procedure (or rather how careful and attentive they are). I'm trying to remove human errors from the process.

If anyone else knows of a device or sensor that does this please let me know. As always, thanks for the help!

 

[ione]

Steris,

I'd try to contact Spirax. Those guys have a wealth of experience with steam.

http://www.spiraxsarco.com/us/

 

[steris]

Unfortunately Spirax doesn't have a solution in house. When needed, they use the Shuttleworth kit. They do have a steam separator but that does not provide any measurements.