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Go Back   SailNet Community > On Board > Gear & Maintenance > Solar chimney
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Thread: Solar chimney Reply to Thread
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Topic Review (Newest First)
05-01-2012 09:42 PM
MedSailor
Re: Solar chimney

Thanks for the tip on the perpetuum mobile word. I can now say I've learned something here. I was afraid all that there was going to be in this thread was ridicule and your favorite "laughing at you" icon.

So when the sun goes behind a cloud for a few minutes is it suddenly not scorching down below in the boat anymore? Really? Is this the part where I'm supposed to pipe up and say "obviously not a weatherman" ?

I still don't get what you don't like about the water jacket. Do you think it would make the device work less well? Do you think that consistency of flow is not a useful feature? Perhaps where this differs is in ideal concepts vs how the device is expected to perform in the real world. You don't disagree with the basic concept, as you recommend fins for heating the chimney yourself.

Does air flow up a fireplace chimney after the fire is out? Answer: yes. Why? The bricks retain heat. Why would retaining heat (and air draft) in the chimney not be a useful feature in the real world?

Since you don't disagree with the solar chimney idea posted by the OP you can continue to think that I'm trying to design a perpetuum mobile, but I don't think you get what I was designing or its purpose and I think you're a little too attached to ideal models. That might have been my poor explanation, and if so I apologize for any confusion. If you want to feel that you "called BS" and that my explaining what I meant further is me weaseling my way out of things, then knock yourself out.

I'm growing tired of this "discussion" though and will cease posting to this thread. I'll let you have the last word and another chance for the icon.

MedSailor

PS Thanks for the perpetuum mobile word though. That's coming out next time I play scrabble!
05-01-2012 01:54 AM
MedSailor
Re: Solar chimney

Quote:
Originally Posted by Chris12345 View Post
Sorry, I think I see what you are trying to do; but no, you did not get the convection principle, and you are still full member of the perpetual motion fraternity with your concept.
Which is disjunctive from the physics fraternity.

Convection works by actually heating the air, not moving it past a hot surface without heat transfer.
Any draft the chimney will produce comes from having heated the air in the chimney. No heating, no draft.
Which is what you are suggesting: Less heating, same draft.
Your water jacket somehow magically multiplies the energy by storing it.
It does not.

If you don't believe me, just build it. If it works, I will buy you a beer.
You will of course be able to afford your own beer, because you will be obscenely rich from just having solved the world's energy issues.

Ooops, you won't: The US patent office requires a working model for filing patents for perpetual motion machine. Not for any other kind of machine, but for perpetual motion ones.
Seems they got sick and tired of having the same conversation that we are having now long ago.

One of three things is happening here. Either I am REALLY bad at explaining what I propose or you are REALLY bad at interpreting it, or you're intentionally mis-reading what I'm saying just to stir the pot. I'm putting my money on #3 and yet somehow feel compelled to post against my better judgement.

Get off the perpetual motion machine thing. I get it, what I propose has nothing to do with it. No magic multiplier, only a more consistent flow. Besides the sun is the energy input so there's nothing perpetual here. I'm glad that now you can spell it though, that's an improvement.

For starters do you take issue with the OP's concept of a black sun-heated chimney moving air itself or do you take issue with the addition of thermal mass that I proposed?

So how exactly do you (or the OP) propose the air gets heated? Sun right? That's why it was proposed to be black right? Sun heats tube, tube transfers heat to air, hot air moves up. Yes? With such an obvious addition of energy into the system I don't get where you're getting hung up on the perpetual motion idea.

My point is that if there is a larger reservoir of heat in the tube (as provided by the sun) it would be less affected by the cooling effect of the necessary transfer of heat to the air in the chimney that will soon be gone. A hot chimney works better than an ambient temperature one and while it would take longer for the sun (heat input to system) to heat it up to working temperature it would also take longer for it to fizzle out. I was proposing that it would be a more consistent flow.

If the chimney is built out of 1 atom thick material, the materiel would be heated, it would transfer heat to the air, the air would move up and be displaced by cooler air from below. The cooler air would cool the chimney and any disruption of sun energy heating the system would now interrupt flow until the sun heated the material again and it transferred its heat to the air again. If the chimney had a lot more than 1 atom of mass it would take a lot longer for the thermal input of the sun to heat it and for the convection to start, but as the chimney did it's job and was moving cooler air from below it would take longer for it to cool the chimney and smooth out disruptions of energy input and outflow to the system.

This would act to add consistency to the airflow as forces acted on the chimney to cool it. What if a slight wind came up at the anchorage and began to cool the chimney from the outside? Which would be better the more massive water jacket chimney or 1 atom chimney? What about when the sun goes behind the cloud for a minute?

MedSailor
04-29-2012 09:33 AM
captbillc
Re: Solar chimney

up here on lake superior i have a solar fan to get rid of moisture. the cold water keeps the hull cold . i am happy to feel a warm breeze now and then.
04-28-2012 11:18 PM
MedSailor
Re: Solar chimney

Quote:
Originally Posted by Chris12345 View Post
Well, for the convective cooling: The transport of the air MUST use the (solar) energy available for it; otherwise, he would have invented a perpetuum mobile that would suck boat, crew, and lake int the stratosphere.

The water jacket does not change the amount of energy that is captured and available for air transport. It just delays the time when the the energy is available.
Which is counter-productive, he wants venting when the sun is the hottest.
I see, though you didn't recognize the reason I suggested the water jacket. I proposed that the airflow through the chimney might cool it some thus decreasing its effectiveness. Yes if air is moving though it, it must be hot enough to work, but the cooling of the convection would not be helping. Having the greater thermal mass heated would reduce the effect of the air convection cooling on the inside of the chimney (where you need it most) and thus keep the flow (in theory) more steady. Yes it would delay it's start up time, but in my experience with sun showers on a hot day, they don't take too long to get hot.

Your criticism of the water jacket is valid in my opinion in so far as it may be counterproductive to the intended use, though I would still disagree and argue that it is a useful addition. It doesn't look like your criticism has pointed out any major flaws in the physics of the application though, so I guess I will get to keep my membership to the physics fraternity for now.

MedSailor

PS I propose that if the OP's solar chimney is a success that he should call it the "perpetuum mobile", assuming that Chris12345 would be wiling to license this most original name.
04-27-2012 03:30 PM
SlowButSteady
Re: Solar chimney

Quote:
Originally Posted by LakeSuperiorGeezer View Post
I have a brother who works for the National Park Service. The Park Service has tried the solar chimney on both chemical and composting toilets. Engineers tried testing this to see what was going on as it did seem to work. What they found was that the wind accounted for the air movement. If you are going to do this, I would suggest testing it out first.Maybe a really tall chimney would work, but the boom and/or sails could be a problem. You would probably be better off with a battery powered fan with solar charging of the battery.
Looking through this thread I think that LSG has pretty much nailed it. On anything but a PERFECTLY calm day the Venturi/Bernoulli effect at the opening of the chimney is going to pull far more air than the "solar" effect. And on calm days a solar vent will move more air (and far less obtrusive) than your solar chimney.

If you want a passive vent, go with one of these:

or a more traditional vent, like this (but you have to keep the opening properly oriented):


If you want ventilation 24/7, even without any breeze, go with something like this:
04-27-2012 02:00 AM
MedSailor
Re: Solar chimney

Quote:
Originally Posted by Chris12345 View Post
Clearly not a physicist.
Care to correct my error(s)? I'm always happy to learn.

MedSailor
04-26-2012 12:51 AM
Frogwatch
Re: Solar chimney

#1 90 degrees is not hot, it is nice Fall temps.

Some engineer here (I am a physicist and can do nothing practical, hey, it's an excuse) should look into absorption refrigeration (air cooling) using zeolites. Humid air blown thru zeolites cause the zeolite to absorb humidity. So, then you heat em more to drive off the absorbed water. Heat em via a solar concentrator. Next, cool em with seawater flowing thru coils in contact with the zeolite. Repeat. The less humid air is cooler because the zeolite absorbs heat from the heat of vaporization of the water vapor.

Somebody else design the zeolite heat exchanger thingy and I'll design the solar concentrator optics (Optics are my gig) and we'll share in the results.
04-25-2012 06:01 PM
hellosailor
Re: Solar chimney

"They would probably be easy enough to build."
I agree with you. Like the recipe for Gypsy Chicken Soup begins, "First, steal a chicken."

First, obtain a radiator's worth of cupronickel tubing. Or maybe, just a junkyad radiator, cheap enough to replace when it clogs or rots out. After all, pinhole leaks could just be epoxied.

And a cheap well pump that doesn't mind a 20' head on the water.
04-25-2012 04:20 PM
ebs001
Re: Solar chimney

Years ago I saw A/Cs adverised that used cold water pumped from below then through through a heat exchanger with a fan. I had forgotten about them until I saw this thread. I tried to google them but came up with nothing. They would probably be easy enough to build.
04-25-2012 03:58 PM
hellosailor
Re: Solar chimney

"Passively".
And that's where the perpetual motion schemes fall apart,nothing happens passively contrary to entropy.
"Swamp coolers" are old technology but you need yards and yards of piping or terracotta or whatever your heat exchange material will be on the "swapping" end. And then you need an active pump to haul up the water, and a way to clean the marine life out of the plumbing, or maintain filters to do that, and if the water is salty you'll need cupronickel or something else besides copper or aluminum.

Still, if you're in fresh water, don't have zebra mussels, and do have a power supply, water misting and swamp coolers both work. Might invest in a reflective awning or something simpler first though.
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