I’m in the middle of writing a piece that brings in discussion of atmospheric Absolute Humidity (AH) and atmospheric Relative Humidity (RH) and how they affect wood moisture content (MC.)
Of various ways of measuring AH and RH I’m interested in two in particular:
1. Grains per cubic foot (where 1 grain = 1/7,000 lb.)
2. Grammes per cubic meter.
I know for instance that at sea level and at 70ºF a cubic foot of air can hold a maximum of 8 grains of water vapour, and at 49.3°F a ft³ of air can hold 4 grains. Similarly at 100°F air can hold ~20 grains per ft³. I’ve got a rough idea of how many grains per ft³ air can hold at temperatures ranging from -20ºF to 120ºF. What I could use would be a chart that breaks Fahrenhit down into, say, 10º increments from minus 20 up to say 140ºF with a figure next to it say how many grains of water vapour air can hold at that temperature.
I’m looking for the same information in grammes per M³ of water vapour (at sea level) that can be held in temperatures ranging from about -15°C to about 45 or 55ºC in 5º increments.
I’ve scratched around and looked for a long time and can find loads of information on the topic, especially if I get into text books and websites dealing with psychometrics, where there’s really too much information, ha, ha. I just haven’t found those two (simple?) charts (or the numbers I seek to make my own charts) to illustrate the text I’m writing.
Can anybody out there help? Slainte.
Edited 7/4/2006 3:26 am by SgianDubh
Replies
Did you try the bible of wood - Understanding Wood by Bruce Hoadley. If not, the DNR might have somethign to help you out.
Thanks. Yes, I have that book and that's where I got the numbers from. What, or who is the DNR? Now, it's 5 am and this has been bugging me since ~7 pm last night (as well as for a few days before) so it's time for bed. 'Til tomorrow. Slainte.Richard Jones Furniture
You might give a ring to your local tele meteorology department or contact the meteorology department at one of the UK universities and explain your predicament. An e-mail to the Weather Channel in the U.S.A. owned by Landmark Communications based out of Norfolk, Va.: but head-quartered in Atlanta, Ga.
I would think that as puzzling as it is to the non-meteorologist, it should be "meat and potatoes" as they advance up the learning scale towards Ph.D. The buried treasure is out there somewhere, perhaps cornering one in the know outside the net might produce better results.
And if ya do... give those cute "weather babes" my best regards... ha.. ha...
SARGE.. g47
Well Black knife, Try a google of "Water saturation tables", There was some info there, but not broken down as far as you want, but a start. Used to have three feet of books of thermodynamics and steam engineering, And gladly gave them away when I retired. Now it's three+ feet of WW books.
Work Safe, Count to 10 when your done for the day !!
Bruce S.
Here you go, Sgian. This is from "Dry Kiln Operator's Manual". Since detail is important I'm leaving this as a large attachment. I can give you the formulas as well if you want them but I suspect they will fall squarely into that "too much information" category.
Lee
Thanks for all the help everybody. There are some very useful pointers and you've all caused me to delve into the subject even more. This has helped expand my knowledge on the subject. Certainly it might be a very good idea to contact my local yooni. They have departments there that would almost certainly be able to help.
The ultimate goal of course is to get down in a few words for woodworkers aided by a simplified chart or graph the essence of AH and RH as it relates to air. It doesn't, (I feel) need to be too detailed as long as the concept is understood. I hope I can find a way of creating a simple chart or table to illustrate the general idea.
I've got other tricks up my sleeve that I will use to illustrate points. F'rinstance I shall use as props three beer glasses, two Imperial pint beer glasses and a 1/2 Imperial pint beer glass. I'll fill the 1/2 pint to the brim and pour the liquid into the pint glass. Then I'll fill the 1/2 pint to the brim again. Lastly I'll fill the other 1 pint glass to the brim, line up all the glasses and get my camera out.
I think I can use these props to graphically illustrate the concept of 50% RH of air at a specific temperature followed by subsequent cooling of the air (analagous to the glass shrinking) to a point where water condenses (liquid spills over the rim.) Finally the pint pot filled to the brim could be used to illustrate the maximum water vapour air could hold at a specific temperature.
Anybody see anything insuperably wrong with this graphic means of illustration and, more importantly, has anybody got any good suggestions for a suitably photogenic liquid? I've already tried gin, but that didn't seem to photograph too well, but I forget why now-- in fact the afternoon and evening I tried the exercise is all a bit of a blur. Slainte.
Richard Jones Furniture
My immediate thought would be Scotch, But a viewer may confuse that with another similarly coloured liquid. Go for Cola ;.)Work Safe, Count to 10 when your done for the day !!
Bruce S.
Sounds like an excellent idea that WW'ers could relate too. Now, are you going to use the beautiful American amber or that UK stuff that looks like burnt motor oil? Whichever, best to keep a spare keg on hand in case the alcohol evaporates before the camera can get into full swing.
Good luck and keep us updated on the proceedings...
SARGE..g47
At http://docs.lib.noaa.gov/rescue/mwr/066/mwr-066-06-0178.pdf I found four pages from from the MONTHLY WEATHER REVIEW (JUNE 1938) that have most of the information you're looking for.
Unfortunately, the reference doesn't cover all the temperatures you wanted, so I grabbed the Goff-Gratch equation from Wikipedia (at http://en.wikipedia.org/wiki/Water_vapor ), and put together an Excel spreadsheet to see if I could work up the rest of them. The spreadsheet results that overlap with the reference agree fairly well, so I think it should be OK. But if you want to have someone cross check it, I certainly have no objection.
I haven't tried attaching a spreadsheet before, so if it doesn't work on this try, my apologies in advance.
Slainte,
Dan
Looks like the spreadsheet made it but the carriage returns didn't (again). Very strange.
Edited 7/5/2006 2:22 am ET by DanG
Dan, Wow. I am almost overwhelmed by the generosity you've shown through the time you must have put in to do the research and create that spreadsheet. My spreadsheet skills incidentally are, er, hmm-- nil.
The small charts at the end are just the sort of thing I was looking for! It will serve the purpose perfectly but, as you suggest, I perhaps ought get a professor over at Leeds Yooni to run his or her eyes over it.
You have been an angel. Many, many thanks. Slainte.Richard Jones Furniture
You're most welcome, Richard. I've enjoyed your many contributions to the Knots community for a while now, and since it appeared that what you were getting was close but not quite there, I was happy to be able to reciprocate in a very small way.It wasn't that difficult once I had the parentheses in the Groff-Gatch equation properly allocated. The fellow who did the charts in the June 1938 pdf reference probably had to make do with slide rules and nomographs, so I feel pretty lucky.Slainte,
DanIt occurs to me that I should have mentioned: this probably would serve as a problem for about a second year chemical engineering class, so if they have something like that at Leeds, or maybe mechanical engineering or meteorology, those would be the people you'd want to talk to about it.
Edited 7/5/2006 5:55 pm ET by DanG
Anyone working in or studying thermodynamics would be fluent in the topic. Chemical or mechanical engineering departments would be full of grad students and profs who could help you.Be seeing you...
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