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Convection wind tunnel

  1. won't work because

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  2. will work but not efficient

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  3. will work but not economic

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  4. will work and have some suggestions

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Multiple votes are allowed.
  1. Jul 11, 2007 #1
    POWER FROM A CONVECTION LOOP:

    this is a scaled down version of the solar tower
    updraft system planned for austrailia, or the SHPEGS
    project with water/silica jell adsorption instead of
    ammonia absorption, or the water spray downdraft
    'culvert on a hillside', proposed for hot dry
    climates.... or is it a solar hot, creek water heat
    sink, stirling motor with gravity/adsorption/psi
    assist?

    MY SMALL SCALE PLAN:

    I have a 10 acre property in bc, canada, with a very
    cold, (7C seasonal avg), creek water intake ~ 80'
    uphill, reaches my waterbox at ~40 psi, the overall
    grade is about 35%.

    a wind turbine, (kicks in at 5m/s, out put at 8m/s =
    10Kw), with 6m span is the basic buy;

    a blown in place cement loop, consisting of two ~
    500m3 chambers and two 30 meter long x 2 meter diam ducts,
    (see monolithicdome.com), and a very large solar batch heater are the basic builds:

    the top chamber is under ground, sloping downhill. in
    the 2 meter duct preceding this chamber 20, or so,
    cold creek water misters, pointing down hill, spray cool the dry, hot air. excess water is collected, and supplies the domestic hot water tank. as humid air
    is lighter than dry air the next step is a silica gell
    adsorbent wheel. the air is warmed by this, so a
    copper pipe heat exchanger, filled with cold creek
    water, recools the airstream to 10C before it falls
    into the upper chamber.
    a buried 2 meter air duct runs 50m down, (drop = 12m)
    to the wind turbine, which sits in the mouth of
    the hot air chamber, (at the lowest point therein).


    HEATING CHAMBER:
    a blown in place cement tube,(nickel or carbon black
    outside surface, selective thermal topcoat), contains
    another blown in place cement tube. this forms a one
    meter 'jacket' filled with heat transfer fluid, the
    smaller diam inside inclosure is the lower hot air
    chamber. this section runs back uphill, smoothly
    enters a 2m air duct that connects with the spray down
    and desiccant wheel duct. this hot return section is spray
    foam insulated and buried in a perlite trench.

    this large volume of htf enables:

    domestic heat,(did i mention that the system will
    provide all domestic heating and removal of heat?).

    fluid to circulate in the interior heat pipes: to stay
    out of the airflow, these are put, infloor heating
    style, on the bottom of the inner cylinder, (this adds
    to seasonal thermal storage as well).

    diurnal storage: i have sized the htf volume and
    aperture for 7 hrs exposure = the btu's it takes to
    heat my house for 24 hours when it is 20c below, PLUS
    the amount of heat loss from 24 hr wind tunnel
    operation. these kind of cupped cylinder, black body
    collectors convert a healthy percentage of solar
    energy into btu's. even if i only get 50% of the
    energy falling in 7 hrs on 100 square meters, (10
    meter by 10 meter collector area @ ~~1000 watts/sq
    meter) into btu i have lots. even in this dead of
    winter, worst case scenario, there is a cold air bonus
    available. by use of a venturi valve the cold water at
    50psi can draw in outside air: you can tune these as
    to how much air but, due to nucleation issues, the
    water would not freeze until minus 7C, or colder.(i
    have tried to make snow this way...it does not work).
    thus, when solar is at low ebb, some delta t can be
    maintained.

    seasonal thermal storage: sizing this big will give
    tons of heat in the summer. the black tube sits very
    close to bed rock so, with little effort and a minor
    cost, shallow, vertical heat pipes are bored directly
    below the hot section, (ten meters deep x one every
    few feet). very small retrieval cost as the tube sits
    right in the hot plume.

    the look of the entire solar collector is very close
    to a scaled up solar batch heater. anodized aluminum
    parabolic troughs cup the black cylinder and bring the
    width of apertue out to 10m. a cable tensioned ETFE
    membrane covers the 10x10 meter aperture. a second
    desiccant wheel draws geo temp
    air into the bottom of this envelope and hot dry air
    is vented at the top of the ETFE skin. although this is a parasitic drain on the collector, this space must be temp and humidity controled, (the envelope must be vented in any case), this hot dry air can be put to use regenerating the desiccant wheel.

    if it seems all this water removal is costing to many btu, consider this: the the htf CANNOT impart more than a fraction of its energy to the air in the heating chamber, no matter the surface area of heat exchange. by moving some work to desiccant regeneration, MORE of my btu can be brought to bear ON the objective.

    this is NOT a million dollar build:

    100 sq meters ETFE foil = $15,000
    cable tensioned ETFE support structure = $10,000
    10 Kw wind turbine = $20,000
    200 feet of 2 meter blown in place air duct, trench,
    perlite = $50,000
    many gallons of heat transfer fluid = $10,000
    two, (well, three really), blown in place cement
    chambers = $100,000.
    10 6" by 10 meters deep boreholes; 60 meters @
    $300/meter = $18,000

    GRAND TOTAL $223,000


    my stirling question is this: if this thing just laid
    flat, ie - no drop at all, it looks like a sterling
    setup with potential,
    but no potentiator. the air would still want to move
    from the high pressure to the low pressure chamber,
    but would probably form loops in both air ducts; ie it
    has no direction. but, aided by that 50' drop and
    nudged again by the nozzles, flow is established and
    no air goes the wrong way. therefore, one should get
    at least the output predicted by stirling formulas
    that take swept volumes and delta T as inputs. i have
    seen this formula somewhere online, plug and play
    style. my own Fermi estimate is that, at summer solar
    max, with the hot air at ~ 160C and cold at 10C, there
    may be too much wind for a 10Kw turbine.

    assume 500m3 air in each chamber.
    cold dry air at 10C has a density of ~ 1.2 Kg/m3
    hot dry air at 150C has a density of ~ .8 Kg/m3

    so, we have a 600 Kg air chamber displacing a 400Kg
    air chamber. to do so, it falls 12 meters. it seems to
    me that you have the potential energy of 200 Kg falling 12
    meters, or 200 x 9.8 x 12 = 23520 ...... but are these mega joules or what?am i on the right track at all here? how to translate that in to Kw? it
    seems to me that you would need at least a 10Kw motor
    to lift 200Kg 12 meters in the time it takes for any object to fall 12 meters.

    i am aware that the friction loss needs to be accounted for, this is one reason for the large diam connecting ducts, i may need help quantifying this later but, as a 10 kw only needs 5-7 m/s flow to run, and is useless beyond 10m/s, i will probably have to size down. this is only because i cannot find a suitable air motor that would take higher velocity air from a smaller duct...ie the wind turbine is off the shelf.


    ok, let the torrents of 'yeah but's loose. i am
    posting here to put this idea up against rigorous
    thinking, but help full suggestions very welcome too.

    regards duke
     
  2. jcsd
  3. Jul 11, 2007 #2

    brewnog

    User Avatar
    Science Advisor
    Gold Member

    Any chance of a diagram?
     
  4. Jul 11, 2007 #3
    good idea, a diagram. i will have one up in a day or so ... have to get it into a pdf as attachment i guess. why, does it look like a Kline bottle in your minds eye?
     
  5. Jul 12, 2007 #4
    working on diagram... can someone please just tell me what units does 9meters drop x 9.8m/s/s x 200 kg come out in and how can i get to kw/h or cfm or even horse power?
     
  6. Jul 12, 2007 #5

    Astronuc

    User Avatar

    Staff: Mentor

    kg m2/s2 = Nt-m = J

    mgh or hgm = gravitational potential energy.

    200 kg * 9 m * 9.8 m/s2 = 17.64 kJ
     
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