Different question about heater bars

[Farrell]

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"This humidity thing is always fun... and dont worry... even if I am =
blowing air out of my better end,,, I still enjoy the conversation.. =
grin."

Me also!........But. Look at Dampp-Chaser marketing propaganda. All =
their graphs about soundboards. Now I don't really think that they =
truely represent the results of any particular experiment, but rather =
trends they are trying to exemplify (although I do believe they should =
state that some of the data in their brochure might be a bit idealized). =
Anyhow, as the RH decreases in air in a piano, the soundboard Moisture =
Content also declines. Moisture content is water in wood. Lower moisture =
content means less water in wood. That means the water left the wood. It =
is no longer there. It does not have anything to do with the amount of =
water the wood may be able to hold (like RH). This is a central issue in =
wood technology - manipulating the moisture content of wood.

It really, really is true. You can trust me! I is edgeekated. I got me a =
deegree in Forestry (two lives ago)! So there! Top that!   ;-)


  Terry Farrell
  Piano Tuning & Service
  Tampa, Florida
  mfarrel2@tampabay.rr.com
  ----- Original Message -----=20
  From: Richard Brekne=20
  To: pianotech@ptg.org=20
  Sent: Wednesday, October 18, 2000 6:21 PM
  Subject: Re: Different question about heater bars


   =20
  Farrell wrote:=20

    Gee whizz Richard. You of course know that it pains me to an =
unimaginable=20
    extent to suggest that my thoughts might be more valid and someone =
else may=20
    be, er, a, less than correct, BUT.....=20
    =20

  You isolate the system far too much, and over simplify the situation =
as such... grin... Number one.. you cannot discount the back side of the =
piano.. or the exterior of the piano otherwise... Equilibrium will =
always take the easiest path. And the easiest path is air ... from =
wherever it leaks in...=20

  That being said..... you will have to some degree the affects as you =
describe them below... But on the other hand, you will also have the =
affects as I describe them. Raising the temperature does indeed also =
lower RH in the interior of the wood... whats good for the goose is =
usually (and in this case as well, good for the gander.=20

  Your Kiln example is a much more isolated system to begin with. And if =
it was completely and totally isolated... where on earth do you think =
these water molecules would migrate to ??? You put a panel into an oven =
that is already dry inside... thats how it draws out water.. this isnt =
exactly the same process as damp chaser creates.. tho admitedly some of =
the same functions are at work.=20

  I think you would aggree that takeing a panel and puting it into a =
kiln which has the same moisture content in the air as the panel does in =
the wood, sealing the kiln and turning it on wouldnt have exactly the =
same effect.. now would it.=20

  This humidity thing is always fun... and dont worry... even if I am =
blowing air out of my better end,,, I still enjoy the conversation.. =
grin.=20

    =20
    Lets say the RH of air in vertical piano interior is 70%, =
temperature is 70=20
    degrees F and soundboard moisture content is 10%. Equilibrium =
conditions=20
    exist (water molecules are evaporating from the soundboard surface =
at the=20
    same rate that water molecules from the air are imgrating into the=20
    soundboard surface). Turn on heat inside piano. Raise temperature =
to, say,=20
    90 degrees F. The RH in piano interior immediately drops to perhaps =
50%.=20
    Immediately, the air inside the piano is capable of holding much =
more water=20
    vapor than previously. Water molecules will then migrate from the =
soundboard=20
    surface from within the wood and evaporate into the air inside the =
piano at=20
    a rate exceedingthe migration of water molecules migrating from the =
air into=20
    the soundboard wood. Hence there will be an net decline in the =
number of=20
    water molecules in the soundboard (and a net increase in the amount =
of water=20
    molecules in the air within the piano - untill it leaks out and =
mixes with=20
    room air). That is what is meant by soundboard moisture content. =
That is the=20
    absolute amount of water "trapped" within the wood. It is not a mere =

    artifact of heating the wood and the air wihin the wood pores having =
a lower=20
    RH. A net volume of water will continue to escape from the =
soundboard until=20
    a new equilibrium is established between the RH of the piano =
interior and=20
    the water content of the soundboard. (We are or course neglecting =
the fact=20
    that the soundboard is also exposed to the outside air on the =
backside, but=20
    this does not change the course nor end point of this discussion.)=20
    This is why when one dries a soundboard before installing into a =
piano or=20
    before shimming, the soundboard shrinks - because the board has an =
lower=20
    absolute volume of water within it. You can prove this to yourself =
by=20
    weighing a piece of wood before and after heating for a long time. =
It is why=20
     a freshly cut log is real heavy, but one of the same size and =
species that=20
    has dried for a year is much lighter - because water has been "drawn =
out"=20
    from the wood!=20

    I think. I'm having fun watching language at work. I truely hope you =
are=20
    also. :-)=20

    Terry Farrell=20
    Piano Tuning & Service=20
    Tampa, Florida=20
    mfarrel2@tampabay.rr.com=20

    ----- Original Message -----=20
    From: "Richard Brekne" <Richard.Brekne@grieg.uib.no>=20
    To: <pianotech@ptg.org>=20
    Sent: Wednesday, October 18, 2000 2:33 PM=20
    Subject: Re: Different question about heater bars=20

    >=20
    >=20
    > Farrell wrote:=20
    >=20
    > > > Moisture is not exactly "drawn out" of=20
    > > > the piano... rather the relative humidity is reduced.=20
    > >=20
    > > No and yes. Assuming that the air inside the piano is at some =
elevated=20
    > > reletive humidity and the soundboard is in equalibrium with =
those=20
    > > environmental conditions. Now turn on the Dampp-Chaser heat =
rod.The=20
    relative=20
    > > humididy in the interior of the piano is indeed reduced. That =
sets up a=20
    > > non-equilibrium condition between the reletive humidity in the =
piano=20
    > > interior and the moisture content of the soundboard wood. =
Because the=20
    air=20
    > > has less reletive humidity and can now hold more humidity, there =
will be=20
    a=20
    > > net movement of water from the soundboard to the air. So, it is=20
    reasonable=20
    > > to say that "moisture is drawn out of the piano and into the =
air.=20
    >=20
    > Grin... How fun it is to watch language at work. I'll buy your=20
    interpretation of=20
    > the words "moisture is drawn out of the piano and into the air" in =
this=20
    > connection. Its actually what I was saying. Still, from the other=20
    standpoint..=20
    > absolute humidity remains the same within the wood as it does =
within the=20
    air..=20
    > expanding the air surrounding air, and thereby decreasing Relative =

    humidity does=20
    > indeed create the non-equilibrium you describe, but as to whether =
or not=20
    one=20
    > describes the equalizing of this in terms of "drawing out =
humidity" or=20
    rather=20
    > that the soundboards air content also expands, retaining the same =
volume=20
    of=20
    > absolute humidity is ...grin.. up for discussion... I would choose =
the=20
    > latter.... for ..... clarity...hehe..=20
    >=20
    > Keith.... sorry to be so picky...:)=20
    >=20
    > >=20
    > >=20
    > > Terry Farrell=20
    > > Piano Tuning & Service=20
    > > Tampa, Florida=20
    > > mfarrel2@tampabay.rr.com=20
    >=20
    > --=20
    > Richard Brekne=20
    > RPT, N.P.T.F.=20
    > Bergen, Norway=20
    >=20
    >=20
    >

  --=20
  Richard Brekne=20
  RPT, N.P.T.F.=20
  Bergen, Norway=20
   =20


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