Evaporative Cooler / -Refrigeration Engine for Vehicles

This will only work during the day in the desert on a moving vehicle,
preferably on abandoned RR tracks or little used back roads because of
the low power density.
Water needs to be added every few miles but it's actually solar-low
humidity powered.
At the front of the vehicle a small amount of liquid water is sprayed
on a hot roadbed, the flow rate adjusted so that the water evaporates
by the time the vehicle passes. High humidity air leaving a cooling
tower is blown under the vehicle to help keep the liquid water
consumption down.
The hot humid air from the road then condenses on and warms the
evaporator of a centrifugal compressor refrigeration system running
backwards. The cooling tower cools the condensor.
The delta T in such an engine might be 100 F so a 75 ton ac
refrigerator system might put out a few hp.
Bret Cahill
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Bret Cahill
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Dear Bret Cahill:
Desert: no water Evaporating water, high dispersion rate... lots of loss.
No water available.
Hunh? You want the sprayed water to evaporate, saturating the air, and a cooling tower needs to put water into the air or it doesn't cool.
But will consume lots of water, and 10-20 hp just to operate... so you get a net loss.
David A. Smith
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Desert =3D low humidity, not no water.
Skirts would channel the humid air under the vehicle.
Canals provide acrefeet of water in some deserts.
It will evaporate rather quickly when it hits the 200 degree F pavement.
Dry air feeds the cooling tower.
And the temperature difference causes the vaned diffuser centrifugal compressor to run backwards.
The parasitical losses aren't any different than any other organic fluid rankine cycle plant.
Bret Cahill
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Bret Cahill
Dear Bret Cahill:
NO water. Just because you are having monsoon at this moment, you have 11 months out of the year with no rain.
No, it would rise above the skirts. Note that it is hotter than air, and with a molecular weight lower than "air".
Actually, it doesn't. The pavement doesn't carry that much heat, and the latent heat of vaporization is quite high. Throw a cup of water per mile, you are right. Throw a cup of water per foot, and your speed had better be < 1 mph.
So you just want supersaturated air...
No, it doesn't. If it doesn't run forwards, the evaporator doesn't get cool. If the evaporator doesn't get cool, your process stops. You aren't generating power, you are distilling water.
Except that this one doesn't work for generating power.
David A. Smith
Reply to
If the speed is 5 mph, a 1 - 2 hp output engine will require at least ten 1 gallon/hr misters.
That's 30 - 50 cups/mile.
A 100 micron droplet only lasts about one second in the desert air. It evaporates even faster sprayed onto moving hot pavement. If the evaporator is even a few feet behind the misters the water on the pavement has already evaporated.
That's 300 gallons/mile. It's not practical for a low hp vehicle to carry several tons of water.
Actually a higher speed will utilize more hot pavement at a higher rate. That was the whole point of the project:
To identify the one and only technically feasible way to get significant work from passive solar thermal.
The overall efficiency of conversion of sunlight to work will be in the tiny fraction of a percent range simply because so much area is required.
Close to sat. air to heat the evaporator as much as possible wasting as little water as possible.
You don't cool the evaporator in a power plant.
The heat flows are reversed in engine mode and so is the direction of the impeller.
The only difference from any other low-intermediate temp. ratio binary geo thermal power plant is the primary mode of heat transfer to the evaporator is by condensation.
Everything else is the same.
Bret Cahill
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Bret Cahill
Dear Bret Cahill:
The droplet lasts much longer than this when the second and subsequent vehicles try it. Additionally, during our monsoon, it lasts much longer anyway.
Why are you worried about practical *now*?
You need a temperatrure difference. You won't have one, despite your naive expectation.
There is an underground cavern with a small vent opening outside of Prescott. It blows out really hard in the morning, and draws in slowly during the night.
Lots of passive solar energy storage, starting with "solar hot water heaters".
What you propose does not work.
You don't get condensation withotu a cool surface. Process stops.
=2E.. which doesn't help you.
The magical theodynamics fairies will heat your evaporator with the latent heat of vaporization of a few droplets of water, and then will cease condensing. Your process stops.
David A. Smith
Reply to
Obviously this won't support heavy traffic using similar systems.
=2E . .
_You_ suggested the impractical cup / foot which is over a ton/mile.
A few gallons/mile is proper sizing for something that will _actually_ work.
The point was to demonstrate that significant mechanical work from unconcentrated solar was possible.
This has never been done before.
1. What is the cooled water temp. from the evaporative cooler?
2. What is the temperature of the roadbed?
=2E . .
You'll need to show that the cooled water temp. from the evaporative cooler minus the temperature of the roadbed isn't significant.
It's actually close to 100F.
"Cool" is any temp. below the dew point.
You get condensation anytime the surface temperature is cooler than the dew point.
=2E . .
Help me what?
The heat from the road bed will continue to be transferred to the evaporator just as the heat from geo thermal water is transferred to the evaporator.
Bret Cahill
Reply to
Bret Cahill
Dear Bret Cahill:
So it only helps one person. One-off solutions, aren't solutions.
_You_ suggested an impratical process that won;t work, and could only work for "one vehicle per hour", and then only in the daytime.
Infernal combustion.
NOT possible, with this process.
And I have been trying to tell you why.
Dewpoint of the inlet air. As you approach saturation (your goal) it becomes =3D ambient.
If you could capture the steam, and derive work from that, then you'd have a solar steam turbine. But that would not be interesting. You have to invoke a refrigeration cycle you clearly don't understand.
All the available work has been spent in displacing atmosphere when steam was made. Anything you try to do stops as soon as the evaporator reaches ambient... a few seconds at best.
Which is a few seconds.
Thank you. Sometimes the obvious is worth pointing out. This is not one of those times.
Generate power from hot roadways. One car per hour. During daylight hours. When there is no monsoon. Using water vapor from water you don't have in the desert (except during the monsoon).
You tell me, and we'll both know. This process won't work, and you can't see why.
*No*. *Just* to the atmosphere.
No. The "condensor" in this case must be dumping heat to something less than ambient.
David A. Smith
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