What a concept.Every day there are new innovations and more opportunities to cash in on alternate power generation. This looks like one in the works if they can get through the regulators. It is real and it is a billion dollar enterprise.
Energy Innovation: Massive Solar Downdraft Tower Proposed in Arizona
The specific volume and possibly the pressure drop with the initial misting but what's the rest of the thermocycle?
Because of the higher density the pressure at the bottom of the tower is greater than outside the tower, maybe 6% at most. So the next step is an adiabatic expansion step, same expansion as in a Brayton [gas turbine] thermocycle.
Unless you wanted to "send the air over a mountain" to dry it out again the addition of heat would then be the third and last step to complete the cycle.
Not that Carnot efficiencies have any effect on the operational costs of renewable energy but the developer claims 70 - 80% Carnot efficiency.
Triangular thermocycles intrinsically have low Carnot efficiencies.
You can make a lighter than air balloon in the desert work with water vapor if the fabric is filmy enough.
100% r.h. air has maybe 1 - 2% lower density at the same pressure and same 40 C temp. In the downdraft tower the absolute temperature of the misted air, however, is 7% lower so the density might be 6% higher than outside the tower.
delta p = rho g h = 0.06 X g X 600 meters.
That's significant but at $2/watt, the downdraft idea is at least 5X the price of PV.
From Bernoulli's eqn., delta gravity head + delta velocity head + delta pressure head = 0
Since the gravity delta is only about 1 kPa the venturi effect must be responsible for most of step 2. That would explain the diffuser shaped tower.
Otherwise, if they are just using the velocity head with wind turbines, then the best they can do is a little over 40% of Carnot efficiency -- 10% at best -- and the overall efficiency would be considerably less than 4%.
Efficiency plays a role in the capital cost of a renewable power plant.
They probably have their calculations correct but first run some tests with an idle cooling tower from the Palo Verde or other nuke plant.
They'll just string thousands of misters across the top. No Aspen pad is necessary as everything can be monitored and tweaked so that all the mist evaporates in the first 20 m or so.
Just misting the air at the top will cause a powerful downdraft because the abs temp drops by 10% and the density increases by 10%.
If the turbines really are expanding the air then the exhaust will be even cooler than ordinary swamp cooled air. A pleasant outdoor summer retreat, now impossible in Yuma, could be designed around the base of the tower.
With an additional heat exchanger -- this would be many acres of tubing -- this could be done near a binary geo thermal plant to precool the dry air going into the cooling tower. Getting the cold side down a degree is more valuable than getting the hot side up a degree, Carnot = 1 - Tc/Th. Ormat will definitely be interested as the high voltage power lines are already in place.
Good design of any movement of air or water has to assure the intake doesn't start pulling in the exhaust.
For most systems the volume of the flow is a small part of the local region, with things like this tower, the volume of the flow is a big part f the region.
And the situation is worse than other types of systems because the flow is great and the only difference between the exhaust and the needed inflow is moisture saturation of the air.
As long as the exhaust does not become a substantial part of the in flow, everything is fine.
The proof of the pudding is .........
Frankly I think the size for the working prototype is too large, and the fact that they are asking for investors is a problem with me, they should be just establishing that it will work, and develop a solid business plan and get bank loans to build a working prototype, why are they so anxious to give away a big part of the pie to get the thing started?
What do you think the smallest possible positive proof working prototype could be?
I am more interested in systems for the individual home or business, the market is bigger, the need is greater because grid power isn't available everywhere, and why create things that make the public dependent on big money projects if user-owned, smaller ones would work.
I am perfectly willing to go along with AGW prevention technology if the results are such that it costs less than fossil fuel within the next ten years and which can replace fossil fuel when oil and coal become very scarce.