This is a multi-part message in MIME format. ---------------------- multipart/alternative attachment "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 ---------------------- multipart/alternative attachment An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/pianotech.php/attachments/77/e4/b3/4c/attachment.htm ---------------------- multipart/alternative attachment--
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