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Thermal resistance of plywood

Discussion in 'Electronic Design' started by Jim Thompson, Aug 1, 2009.

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  1. Jim Thompson

    Jim Thompson Guest

    Several years ago, as an aside to another thermal question, I asked...

    "Brings to mind a thing I've been pondering... what's the thermal
    resistance of 3/4" plywood ?:)"

    Never saw a response.

    More specifically, a closed plywood box, inside dimensions of 8" x 11"
    x 18".

    Outside ambient of around 77°.

    How many watts of dissipation inside of box to raise interior air
    temperature to 95°F? (I might use a fan to circulate the air.)

    If I made one wall of the box 1/8" glass (8" x 18" side), how much
    change?

    ...Jim Thompson
    --
    | James E.Thompson, P.E. | mens |
    | Analog Innovations, Inc. | et |
    | Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
    | Phoenix, Arizona 85048 Skype: Contacts Only | |
    | Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
    | E-mail Icon at http://www.analog-innovations.com | 1962 |

    I love to cook with wine Sometimes I even put it in the food
     
  2. It is called R factor.

    There are exterior panels that are made specifically for this purpose.
    The best in the world are made from hemp fiber in a country that grows
    thousands of acres of non-drug hemp strains because the fiber is very
    strong (the strongest plant fiber) The best exterior home construction
    panels are hemp.

    They also mean that:

    "No pine tree forests were cleared in the making of these homes".

    America is stupid sometimes. Hemp laws are one such example.
     
  3. What do you think the "R factor" value is based on?

    We call it science regardless of the discipline.
     
  4. Jim Thompson

    Jim Thompson Guest

    Shucks! That was what was giving me the pain and agony... converting
    Btu's per fortnight, etc ;-)

    ...Jim Thompson
    --
    | James E.Thompson, P.E. | mens |
    | Analog Innovations, Inc. | et |
    | Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
    | Phoenix, Arizona 85048 Skype: Contacts Only | |
    | Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
    | E-mail Icon at http://www.analog-innovations.com | 1962 |

    I love to cook with wine Sometimes I even put it in the food
     
  5. In case that this is not a troll, look at it (using a fixed width font
    like Courier New):

    W
    0.13 ----------
    m K



    Paul
     

  6. Idiot. NOTHING "milli" uses a capital M. It was also inappropriate to
    be the first word in your non-sentence, if not for that reason alone.

    Perhaps "Are you saying milli-Kelvin?"
     
  7. I have some liking to page 1572 of the 43rd edition of the "CRC
    Handbook", "Thermal Conductivity of Wood Across the Grain at Various
    Moisture Content Values".

    The moisture content values vary mainly with type of wood tested, mostly
    from 9 to 14 %. Thermal conductivity in BTU/hour through 1 inch thickness
    of 1 square foot with 1 degree F temperature difference has 90% of figures
    in the range of .73 to 1.39, and I would like to say as a result
    moderately-conservatively .8, more-usual .9.

    This box, with inside surface area (assuming above dimensions are
    external) of 6 * 6.5 * 9.5 * 16.5 /12^3) about 3.54 square feet, with 3/4
    inch thickness, has thermal resistance (within itself, as opposed to
    thermal resistance of adjacent air) of maybe 3/4 divided by 3.54 divided
    by .8-.9 watts/F, or roughly (give or take) 1/4 degree F per watt.
    Thermal resistance drops bigtime, to extent where I consider likely the
    thermal resistance of the air inside and just outside the box.

    I know someone who, at my advice, did an experiment measuring
    temperature of a metal-cased device in open air and in a "largish
    shoebox", with readings taken over time to verify temperature
    stabilization. As best as I remember at this moment, the "largish
    shoebox" including air stagnated near its inside and outside surfaces
    had thermal resistance around 2-2.5 degrees F per watt, probably closer to
    2 - apparently mostly from impairing convection of air around the device
    that was tested. The device being tested had overall dimensions close to
    those of a "double thickness cigarette pack".

    - Don Klipstein ()
     
  8. Larkin = dope.
     
  9. On Sun, 02 Aug 2009 03:04:14 -0700, Archimedes' Lever


    Archie = Celibate asshole
     
  10. Better is the wrong word. PROPER is the right word.

    Placing it right next to the K makes it a "milli" prefix in ALL
    circles. So if it is not written right, it will not get read right. It
    has nothing to do with what someone "thinks".
     
  11. Artemus

    Artemus Guest

    "Jim Thompson" wrote
    I hope you can see this post as I've never gotten any acknowledgement on any other
    post I've made in this group.

    From: http://www.performancepanels.com/?content=app_pp_atr_therm
    For most practical purposes it is neither necessary nor feasible to determine the
    actual species makeup of the plywood panel. For determining the overall coefficient
    of heat transmission (U value) of a construction assembly, APA publications use k =
    0.80 for softwood, as listed by the American Society of Heating, Refrigerating and
    Air Conditioning Engineers (ASHRAE). Use of this single value simplifies
    computations, and produces only insignificant differences in resulting design heat
    losses.

    The table below shows thermal resistance, R, for several plywood panel thicknesses,
    based on k = 0.80. Thermal resistance represents the ability of the material to
    retard heat flow and is the reciprocal of k, adjusted for actual material thickness.
    (for a 3/4" panel R = 0.94)

    The definitive authority on wood properties is R. Bruce Hoadley and his book,
    "Understanding wood: a craftsman's guide to wood technology", is considered by many
    to be the holy bible on wood properties.

    I hope this helps.
    Art
     
  12. Except by those who know enough physics to know what units of heat
    conductivity are - power per (area cubed * temperature difference / linear
    distance), which simplifies to power per (linear distance unit *
    temperature difference). People who know this and metric units as used in
    physics are familiar with watts per meter-kelvin and recognize that w/mK
    stated as a unit of thermal conductivity meant this.

    It appears to me that you went quite a ways on a spelling flame.

    - Don Klipstein ()
     
  13. Except that ANYONE that does know such a thing would also know how to
    express it properly, DIPSHITS!

    So... IMPROPERLY expressed means invalid at the start. Stop trying to
    attack those that 'read' it. Put the fucking blame where it fucking
    belongs, dumbfuck.

    Lower case m in front of a figure that represents a unit of measure,
    ALWAYS means milli.

    Without the dash, your shit is weak. Learn to express it right.
    Doesn't matter what ANYONE's familiarity with ANY segment of physics is.

    You do not pull that dumb ASSumption crap just like you do not top
    post.

    Those that know enough physics know how to express a fucking formula
    without fucking it up royally.
     
  14. Jim Thompson

    Jim Thompson Guest

    Neeeerp! Conductivity is proportional to AREA and inversely
    proportional to THICKNESS.

    ...Jim Thompson
    --
    | James E.Thompson, P.E. | mens |
    | Analog Innovations, Inc. | et |
    | Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
    | Phoenix, Arizona 85048 Skype: Contacts Only | |
    | Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
    | E-mail Icon at http://www.analog-innovations.com | 1962 |

    I love to cook with wine Sometimes I even put it in the food
     
  15. nospam

    nospam Guest

    Thermal conductivity is proportional to area (m^2) and inversely
    proportional to thickness (m) which leaves you with just m.

    0.13 W/mK is 0.13 W/K across a 1m cube.

    --
     
  16. Jim Thompson

    Jim Thompson Guest

    NymNoNuts is dippy 100% of the time.

    ...Jim Thompson
    --
    | James E.Thompson, P.E. | mens |
    | Analog Innovations, Inc. | et |
    | Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
    | Phoenix, Arizona 85048 Skype: Contacts Only | |
    | Voice:(480)460-2350 Fax: Available upon request | Brass Rat |
    | E-mail Icon at http://www.analog-innovations.com | 1962 |

    I love to cook with wine Sometimes I even put it in the food
     
  17. GregS

    GregS Guest

    I learned R-1 = 1 inch of dry wood.
    R-12 = 12 inches of wood.
    Plywood has glue so its less.

    I learned in my basement, I used two sheets of foil/foam/foil and I get
    a lot more insulation than what the stuff specifies. It about 3/16 inch
    thick. On a cinderblock wall, which itself is R 3.5, I lay a sheet against the wall.
    Out from the wall about 1 inch I put another layer of the foiled sheet.
    Its almost as good as 2 inches of fiberglass.


    I am getting an insultion value of over double what the foil specifies. The foil
    adds almost R1.5 for the reflective addition, but I am seeing more.

    In the garage, I stapled porous aluminum on polyethelene sheeting to the joists
    on the ceiling. The results are far better than the R value. You cannot feel
    any radiated energy from the roof compared to before. Even in the winter
    its helps insulate mostly from reflective energy. The higher the differential
    the more reflective coatings play a role in heat transfer.


    greg
     

  18. I'm sorry, but the only 2x4s in MOST of the nation are PINE.

    Pine is the predominate construction media in the US.

    Pine grows at a wide spacing, at two feet per year. Hemp grows, even
    tightly spaced, at two feet per month.

    An acre of hemp can produce far more material than an acre of ANY tree
    species.

    The fibers are also more manageable, and there are other products that
    can be derived as well.
     
  19. Rich Grise

    Rich Grise Guest

    http://www.sizes.com/units/rvalue.htm
    http://www.allwallsystem.com/design/RValueTable.html
    etc.:
    http://www.google.com/search?hl=en&q=R-value+of+plywood

    Hope This Helps!
    Rich
     
  20. You're a goddamned retard as usual, Thompson. You don't even know what
    he was talking about.

    You are as clueless as it gets every time you jack off and enter a
    thread you only partially participate in.

    You are about as stupid as it fucking get, you retarded motherfucker.
     
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