At 11:34 PM 6/22/2011, Finlay MacNab wrote:
If the relative humidity sensor measures
capacitance then the dielectric constant of
steam and the dielectric constant of steam plus
water would be very different and yield very different readings.
A quick google search for capacitance
measurement of steam quality yields several
papers and a multitude of patents on the subject
so it would seem that a measurement of steam
quality from capacitance values is possible. A
quick literature search for the dielectric
constant of steam results in an avalanche of
data about the dielectric constant of steam at
various temperatures and pressures. There is even data at 100.1C and 1 atm.
Then again I am just a lowly chemist so what do I know?
About as much as anyone else outside their specialty. Maybe a little more.
Saying that a Google search leads to this or that
without providing the actual search, and without
showing what results you looked at, is less than helpful.
I did this search:
http://www.google.com/search?q=capacitance+measurement+of+steam+quality&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a
I found papers, for example, on the measurement
of steam quality using capacitance. The RH meters
in question are not designed to use that
approach. If they were, they would surely
advertise it! (This is a valuable application.)
You want to measure steam quality, see
http://www.thermochem.com/Geo_On-line_Steam_Quality_Measurement_Equipment
The equipment described is far more complex than
these RH meters. I've suggested here a simple
possibility for steam quality measurement or at
least estimation, involving light passing through
a glass tube containing the steam flow. I see
this from Thermochem: "New Laser-Based Steam
Quality Meter is under Development and soon to be
Commercial." It's pretty easy to guess what they
are doing and, in fact, I've been involved in the
design of equipment that does something like this
with smoke particles in air (in wind tunnels).
They are simply observing the water droplets,
directly, with lasers. My own suggestion was much
simpler, it would detect dry steam but would not
catch really large water droplets as much. My
guess is that with some experimental work to
calibrate it, it could set an upper bound on entrained water.
But for the gross measurements being done, seeing
that steam is transparent, visibly, and with the
tests suggested used by experienced steam
engineers, should be enough. Has anyone thought
of inviting an actual steam engineer to the
demonstrations? That is *not*, apparently,
Galanatini, a chemist from every piece of
evidence I've seen. His company, touted as
evidence of his expertise, does mostly chemistry
with some environmental analysis, the kind that
will use an RH meter. So he'd have a meter, but
nothing there indicates steam quality measurement experience.
