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darryl
05-28-2012, 09:55 PM
Lots going through my mind today- I was looking at thermal expansion of liquids and noticed that kero has one of the highest thermal expansion ratios. It should be possible to cycle fixed amounts of it through a solar extraction cell, where the contained fluid soaks up concentrated solar energy and then expands to do work. The contained volume would then be valved out and a fresh charge of fluid enters the chamber and the cycle repeats. Controls would be needed of course.

Offhand it seems like it would need to be a very high pressure system, since the expanded volume would have nowhere to go except to push against a piston or something. This force-over-distance is where you extract the energy mechanically.

It would seem to me that at least one part of the system would be highly efficient, that where the suns energy is imparted to the contained volume of kerosene. As it expands, the volume change does work, but of course the exiting liquid charge would still retain some of the temperature that it was heated to. I'm wondering if there's a way to capture at least 20% of the influx as mechanical energy. Anybody have any facts, or an opinion?

jkruger
05-28-2012, 11:19 PM
Perhaps you could harness the contraction of the kero as well? Solar expansion and pre-heating water for the cooling side?

The Artful Bodger
05-28-2012, 11:53 PM
The theory has certainly be proven. Google 'naptha engine' or as someone termed them "boats running on boiling petrol".

darryl
05-28-2012, 11:58 PM
Well, I'm thinking that the pressure side would be used at several kpsi at least, in order to take great advantage of the expansion. In contrast, using the contraction process could only take advantage of 15 psi at best- such a small percentage that it may not be practical. Cooling is one thing that I would add however, if it would be practical to use a cooling medium such as flowing water.

The 'expansion chamber' in this idea would be a network of small diameter pipes, which would serve to absorb the concentrated solar energy. Being small the energy transfer would be fairly quick, plus small piping is better able to withstand pressures for a given wall thickness than larger diameter piping. It would be arranged in some appropriate pattern at the focal point and painted flat black to be a good absorber. The controller would take into account the measured solar influx, and would cycle at a time when the right amount of mechanical energy has been given up by the charge in the chamber at that time. In other words, it would be calibrated to work over a range of influx levels. Below a certain level it would cease to cycle. The working fluid, the kerosene, would be in a closed loop of which one part could be the cooling arrangement. If there was a piston with a compression ring involved, any leakage past the ring would remain within the system. Of course you'd design for minimum leakage, and you might use leverage to multiply the stroke and divide the force if that makes it easier to use the mechanical push given.

tdmidget
05-29-2012, 12:03 AM
Nope. Expansion of a fluid is miniscule compared to it's heat of evaporation. That's why steam is king as a medium of energy.

The Artful Bodger
05-29-2012, 12:12 AM
I have a copy here of Model Engineer 18 May 1979, Mr Peter Cosier wrote about simple solar powered liquid expansion pumps and engines utilising acetone.

He showed three diagrams, the first two are similar in principle to a Stirling engine where a displacer moves the working fluid between hot and cold ends of a cylinder and the power it taken by a piston which he said could be sealed with "O" rings. In one the displacer is moved by an external magnet and the other by an internal mechanical linkage between the power piston and the displacer.

His third diagram shows an enclosed cylinder with power piston and a water pipe passing through the cylinder. In this scheme the power piston opens and closes a valve that controls cold water flow to contract the working fluid.

Using acetone he predicted that a 1/4" piston would give about 2cm movement if 40cc of acetone are raised by 10 deg C and produce a pressure of 1000p.s.i.

darryl
05-29-2012, 02:10 AM
Very interesting. I've just been comparing the various liquids for coe. Acetone will expand about 43% more than kerosene for the same temperature rise. Ammonia will expand more than twice as much as kerosene. Pure ammonia I'm sure would be a handling hazard, so acetone seems like a pretty good fluid to use in an application like this- better than kerosene.

One thing I'm not sure about is the compressibility. Should be very low and thus not significantly affect the operation of the mechanism using it. I know it has a very low viscosity and thus it might be difficult to seal against it under pressure.

The Artful Bodger
05-29-2012, 02:24 AM
Maybe it would be practical to extract the energy of expansion via a metal diaphram bearing on piezo electric devices?

jkruger
05-29-2012, 02:42 AM
Very interesting. I've just been comparing the various liquids for coe. Acetone will expand about 43% more than kerosene for the same temperature rise. Ammonia will expand more than twice as much as kerosene. Pure ammonia I'm sure would be a handling hazard, so acetone seems like a pretty good fluid to use in an application like this- better than kerosene.

One thing I'm not sure about is the compressibility. Should be very low and thus not significantly affect the operation of the mechanism using it. I know it has a very low viscosity and thus it might be difficult to seal against it under pressure.

Maybe this is why a lot of old refrigerators used ammonia for refrigerant?

darryl
05-29-2012, 03:41 AM
Ammonia is probably the best refrigerant, but it's not something you'd want to play around with. Apparently it's not particularly toxic, but it damages skin and lung tissue even at low concentrations. Corrodes zinc, copper, etc but not steel. But steel rusts-

A friend used to work at a food processing plant. They had a 'cold room' 5 times larger than my entire house. It was an ammonia system, and they had a leak one day on his watch. He had to rush in and drag a guy out. Nobody died, but they both ended up in hospital. Makes me wonder about all those ammonia system fridges in motor homes and trailers-

philbur
05-29-2012, 03:57 AM
The expansion value is at constant pressure. You will need to subtract the loss of expansion due to the compressibility of the liquid.

This must be a very inefficient use of heat to produce mechanical work. Most of the heat remains in the liquid after expansion (due to the specific heat of the liquid) and needs to be removed before the next cycle.

The reason gases are used in reciprocating engines is because they have high expansion for a relatively low specific heat.

An interesting concept though. Do you have any links or photos.

Phil:)

philbur
05-29-2012, 04:01 AM
You could cycle hot and cold water over an auto engine bellows type thermostat.

Phil:)


Maybe it would be practical to extract the energy of expansion via a metal diaphram bearing on piezo electric devices?

darryl
05-29-2012, 04:51 AM
Somehow, most of the heat would have to be lost to expansion while the pressure remained high enough to do useful work. Maybe a triple expansion ammonia engine would be able to extract the bulk of the energy. Maybe the liquid phase could be used in the first and smallest cylinder, then as the pressure is dropped and the ammonia gassifies, it can further expand in larger cylinders.

I don't know- it just seems like too much mechanical stuff with all the attendant losses- equating to much lost efficiency anyway. There has to be a more efficient process somehow-

How about a high temperature solar cell? Only begins to work when it gets way up there in temperature- then it remains at that temp as the drawing off of electricity keeps it from heating further-

Frank46
05-29-2012, 05:45 AM
I don't know about kerosene for useful work, but we had a gas refrigerator in our trailer. Light off was done with pilot light and a match. Only thing you had to watch was were you set the temp controls. Too high and you ended up with everything in the fridge frozen. As we only had two 30lb bottles on board the trailer we did use it for heating, cooking and the fridge. I catually think we went backwards when we had problems keeping the burner going on the fridge. As we had two children with us I figured it was safer to get an electric refrigerator. Frank

darryl
05-29-2012, 03:44 PM
Kind of ironic how you get cooling from heat.

I had a lady come to me once to see if I could decipher her rv fridge. All seemed to be working except it wasn't cooling. That's the first time I ever messed with one of those three-way fridges. I learned that it's an ammonia absorption cycle which does the cooling, and it first has to 'charge'. This can take hours. Basically the heat makes water separate out of the ammonia, and the components go into their separate tanks. Once that is done, the water and ammonia can re-combine, which is what absorbs heat and produces cooling.

Seems odd at first, since it seems like the thing is running but not getting cold.

The Artful Bodger
05-29-2012, 04:49 PM
Depending on the design there may be a 'procedure' to go through to re-start a fridge that has stopped working.

"Two hours lying face down, overnight lying on the right side..." that sort of thing but without the procedure for the particular fridge there is not much you can do but hope for it to come right of its own accord.:(

Guido
05-29-2012, 05:37 PM
http://i126.photobucket.com/albums/p86/Guido_album/250px-Icy_ball_top.jpg

Only one we've ever seen: Andy Devine Museum, Kingman, Az---Just down the street from Saltmine's digs.

Machine shop owner back home played with pulling/using the heat via inner passages fabbed into exhaust manifold of a six cylinder Stovebolt. Played with but never perfected for auto airconditioning, about 1950, or so. Then came DuPont and their Freon system.

G--

Bob Fisher
05-29-2012, 09:42 PM
Had an ammonia fridge in a motor home some years ago that was not working properly, was told by the local RV parts guy to pull it out, turn it upside down overnight and re-install it. Worked perfectly after that. Bob F.

darryl
05-29-2012, 10:56 PM
I did that trick with an rv fridge, and it didn't come back to life. The thing worked one season, then the next season it didn't work.