View Full Version : convection/adsorption wind tunnel

09-07-2007, 09:16 PM
this is a scaled down version of the solar tower updraft system planned for austrailia, or the SHPEGS project with water/silica jell,(or cacl) 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?

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 18 foot span is the basic buy;

two blown in place cement chambers, (see monolithicdome.com), are the basic build:

the top chamber is a 10' diameter by 10' long cylinder, under ground, sloping downhill. 20, or so, cold creek water misters, pointing downstream, form a ring around the hot air inlet. excess water is collected at the lower end; can pass as preheated domestic, or be ambient cooled and let back into a smaller creek that i have nearby.
a buried 2' air duct runs 150' down, (drop = 50') to the wind turbine, which sits in the the mouth of the larger, 18' diameter by 30' long, hot air chamber. BUT... this humid air would be very hard to heat and lift, AND when it got back to the top, almost saturated, the cooling effect of the spray would be severely reduced.

so, after the turbine, in the bottom of the solar collector i have a desiccant bed/wheel ... um .... er ...of some sort. this absorption bed begins the heating cycle by removing the water. i have two ideas for this:
1 a silica gel desiccant wheel --- these exist for
smaller diam ducts, scale up and build. the saturated
part of the wheel is regenerated by the hot air trapped between the black cement collector, (get to that in a sec), and its ETFE skin. might have airflow issues, but..... here is a question that vexes me: is not heat the end product of the airflow issues? is not more heat a good thing anywhere after the turbine? same question for the interior heat transfer pipes inside the black tube that may be called for: is not
friction here at least breaking even, as it adds heat?

2 fill the bottom third of the hot cylinder say, 2 feet deep with rock cacl as the adsorbent. at the lowest point, a drain takes the cacl/water mixture out to a reservoir. a pump circulates this up to a solar evaporator bed, running back down to the base of the lower chamber. (again, hot air from the trapped space can be used here). the recrystallized cacl gathers at the base of the black tunnel, and a chute periodically dumps this back in. the only energy cost here is pumping the same volume of water that you remove, (yes, its denser), up 35feet. i think a couple liter/min is optimistic, as heating any amount of water up 100C, (this is my 24/7/365 projected AVERAGE delta T... read on) would take more energy than pumping it up 25 feet. in fact the more water, the better for my prospects, right?
a blown in place cement tube,(nickel or carbon black outside surface, selective thermal topcoat), with inside diameter 20', length 30', contains a blown in place cement tube with outside diameter 18'. the two foot 'jacket' is filled with heat transfer fluid. the 10 meter long inner section runs back uphill, smoothly enters a (shorter) air duct that connects with the spray down chamber. this hot return section, again 2' diameter, 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)

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 out to 10 meters . a cable tensioned ETFE membrane covers the 10x10 meter aperture.
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' air duct, trench, perlite = 8,000
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 $182,000

my stirling question is this: if this thing just laid
flat 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.
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