Ringbom-Rice conversion?

[Tom Booth]

I've been working on various conversion attempts, air compressors and generators without much success so far.

It seems that the greatest expansion and contraction is realized where the working fluid approaches phase change, as in the so called "rice" engine.

I've wondered for years, ever since reading
William Beale's account of the great increase in power he realized by adding a few drops of water to his engine, if most of the power in an atmospheric air type Stirling is not derived primarily from the water vapor in the air alternately condensing and evaporating imperceptibly as a kind of vapor mist. Perhaps that could explain the sometimes finicky behavior of Stirling engines, if their operation depends on the humidity in the air from one day to the next.

Anyway, the "rice" engine seems to prove IMO and observations that if water vapor is entirely substituted as a working fluid for air, the result is a very simple and yet quite powerful engine.

A Ringbom conversion from an IC engine or compressor is also very simple, in theory. Just add an external displacer chamber. Almost nothing to it.

Generally though, a conventional displacer does not really generate the necessary pressure differential to overcome the friction and inertia in an IC engine or a compressor.

What about a "rice" type engine add-on?

Ringbom-Rice-Stirling-Engine.jpg (241.13 KiB) Viewed 1578 times

Even simpler, and with fewer moving parts than a conventional Ringbom type conversion. No flammable gas or liquid. No large boiler. No difficult to contain gases.

Likely the water vapor in the condenser could be isolated completely from the engine section, or the whole thing could be Stainless steel to avoid rust.

Maybe something worth experimenting with.

[Tom Booth]

The idea basically is that the pressure differential between the compression and expansion strokes, instead of inducing a displacer to move to increase the temperature and expand the working fluid, the pressure changes induce condensation and evaporation. Similar to the "cloud in a bottle" demonstration.


https://youtu.be/G70y90BVes4?si=TeC9iZsyMOuQ8Tnw


The rice takes the role of the smoke. Something for the water vapor to nucleate around.

BTW, apparently the upgraded forum dropped the media plugin ? No more inline videos.

[Tom Booth]

So how would this work?

In the video squeezing the bottle causes the cloud to disappear (evaporation). Releasing the bottle, low pressure/expansion causes the cloud to form (condensation).

It doesn't take much of a pressure differential to make this happen, just a squeeze. But this is also not a full "saturated vapor" as it would be with all steam. In the video demonstration the space is still occupied by mostly ordinary air, some smoke and very little water vapor.

With a pure "saturated vapor" the effect is more dramatic (theoretically at least).

Compression (piston moving inward) causes high pressure and "heat of compression" heat resulting in evaporation. Evaporation means the water droplets turn into a gaseous vapor expanding up to 1,600 times.

The expansion pushes the piston back out which results in lower pressure, cooling and condensation.

Condensation means the gaseous water vapor contracts back into a liquid form onto whatever nucleation medium is present forming a vacuum that "pulls" the piston back inward.

The inward motion of the piston causes compression, heating and evaporation so the water again changes phase to a gas and expands pushing the piston back out.

As the piston moves out the water vapor expands and cools causing it to again condense back into a liquid so the piston is drawn back in.

This oscillation then continues on and on.

If the piston also does external work on expansion of the water droplets to the gaseous phase then the additional cooling (from energy lost to work output) causes more rapid condensation and more forceful "contraction" and so some form of heat addition is necessary to be supplied to compensate for the work output to drive a load and ensure evaporation will take place to continue the cycle.

[Tom Booth]

I'm thinking I'll try making a miniature "rice engine" canister to power one of my small model engines using this small eye dropper bottle:

mini-rice-engine-chamber.jpg (415.61 KiB) Viewed 1552 times

[Tom Booth]

Some additional ideas and possibilities:

I have some used, or more or less "broken" or barely functional model engines kicking around that I have an idea I might be able to convert to phase change "rice" engines.

And of course, some cans, mason jars and lots of other stuff I've been getting together over time for this project. (Or, just for experimenting generally with this "wet" phase change Stirling concept).

https://youtu.be/bw7izz9fUT8?si=s6sEcHcrKSyyNWU3

I've never built one of these "rice" engines before, so I figure it's probably best to get a feel for it by putting together and/or converting small models before graduating to the big power generating engines and conversions.

What I like about this concept is with a phase change expansion/contraction ratio of 1:1700 the potential power density is off the charts.

This provides a lot of margin or leway for experimentation.

There seems to be a relationship between power potential and the ratio of air to phase change vapor. The engines will run with some air. For more power, increase the proportion of vapor, (add a few more drops of water).

Also the potential is there for using different liquids with different phase transition temperatures. The possibilities seem virtually unlimited.

[Tom Booth]

Well, I've completed my first ordinary or conventional so-called "rice" engine.

https://youtu.be/FhcpAm3lomk?si=kEmj6wZghLdoy5Ix

It worked first try using aquarium gravel.

The gravel is about 2/3rds deep in the upper can.

First run it was self starting and I did not need to remove the screw to let out any steam, the engine just started right up when it got hot enough.

I never saw any visible steam at any time, but I only had the stove burner on low with very little water in the bottom of the engine.

The upper part of the engine never got hot and remained easy to handle without gloves or anything.

I did try wrapping a cold wet washcloth around the top of the engine and the engine slowed down and/or stopped running when I did this.

I also wrapped a dry washcloth around it to insulate or hold in the heat. If anything that seemed to cause the engine to run a little stronger.

After these initial tests, I then shut off the stove and went to get my phone and tripod to record the above video.

I think while sitting, heat rose up through the engine to the top, as this time while making the video the silicone mat ballooned up right away and I had to take out the screw to relieve the excess pressure, and the engine did not quite self-start.

I can't say the engine had tremendous power. It could be stopped fairly easily but I was also being very cautious with this first effort, shutting off the heat or turning it down as soon as the engine showed signs of running.

For the upper can that holds the gravel I just punched holes in the bottom using a hammer and a small finishing nail.

At this point, judging by the fact that I never saw any steam at all, I probably did not use enough water, but I did not make any provision for adding more once the engine was already assembled.

[Tom Booth]

Opening the engine back up and adding a little more water did make a big improvement.

I was able to press my finger down rather firmly on the magnets and the engine kept on running.

https://youtu.be/yQobz7aMQJ4?si=AdzvLRK7gMDL4ng7

Just an additional observation after a few runs, so far at least, with plain water, this engine has not started until after I could hear the water boiling. The first run with less water I only heard a sizzle that lasted a little while but then stopped, but the engine still ran, but not as strong as with more water.

This time I could here boiling continue, but the engine seemed to run stronger with the water just at a slow simmer rather than a full boil. At times the engine ran better after turning off the heat to slow down the boiling.

There is some controversy about how these engines actually operate, but my guess or theory is that if the water temperature gets too high, the water vapor cannot condense. Then the pressure builds up and the diaphragm starts ballooning out.

Opening the "valve" to reduce the pressure will usually at least get the engine running again, but if the heat is not reduced to slow the boil down to a simmer also this will keep happening over and over and the engine will not run steady state.

At a slow simmer it seems to be able to run indefinitely.

However if the engine is stopped, the diaphragm will start ballooning out again.

I'm thinking that with a linear generator or a crankshaft for some actual power output, more heat could be applied.

I think now, with the addition of more water, this engine could probably turn a crankshaft. Before I don't think it could have put out enough power.

[Tom Booth]

I also want to try various thermally inert materials as "condensation medium".

Aquarium gravel is very dense and heavy. I think it is just gravel with some plastic coating.

The gravel works, but requires a long period of pre-heating before the engine will run.

At least, in my tests so far, it seems to take an extraordinarily long time to bring a few tablespoons of water to an audible boil.

I imagine the gravel becoming coated with condensation and absorbing heat until it (the gravel) reaches a temperature of 100°C, at least on the bottom layer of the gravel, so that there is some surfaces near to the phase change temperature where rapid evaporation and condensation can take place.

Until the gravel gets hot, it seems, the water in the bottom of the container will not be able to reach the boiling point.

My theory or experimental objective is to isolate the condensation/evaporation (surface area) component of the medium from the thermal properties, to see, or get a better idea what is a actually going on and what properties are most essential.

If the engine runs with plastic beads or Perlite as a condensation medium, these materials are basically thermally inert. So that would be evidence that surface area for condensation is more of a factor than heat conductivity or heat capacity.

I happened to have some of these plastic spacers left over from a tiling job.

non-thermal-medium.jpg (363.15 KiB) Viewed 1460 times

They should provide a lot of surface area but have very low thermal conductivity. But heat capacity of plastics is still rather high.

If that works, or even if it doesn't, I also have some Perlite.

Perlite is very absorbent though, so at some time I may try coating the perlite with something similar to the aquarium gravel.

That would have a plastic surface similar to the gravel but very low heat capacity and low conductivity.

[Tom Booth]

This is one of the weirdest things I've ever seen in a long time.

https://youtu.be/KBtv3skwfDw?si=ERtnPAMnkI7nvjuo

Copy,/paste from my YouTube description:

All the "wet thermoacoustic" or so-called "rice" heat engines I've seen have been made of metal.

I wanted to see what was going on inside, so made a glass engine, however, I didn't leave enough room in the bottom and added too much water.

also the only heat resistant beaker I had had a spout at the top and no rim to stretch the diaphragm over, so it was difficult to seal. I tried taping down the edges, but the tape did not hold or seal completely, so I never got the engine to run, but I may try again.

before the tape came loose though, as the engine was heating up, I noticed something strange.

The water level appeared to be rising higher and higher. I had only added water to just below the top of the perforated tuna can. As the water rose, the diaphragm would rise and balloon out also, then suddenly both would "fall".

the water level would drop down to the bottom and the diaphragm would drop. It seemed the pressure would suddenly turn into a vacuum and the diaphragm that was ballooning out under pressure would suddenly drop down.

this reminded me of taking the lid off a pot of water that is boiling over; the foam all disappears and the vigorous boiling slows down or stops.

I thought this might be due to changes in pressure, temperature or both, but not really sure what was going on. I found however that the phenomenon was controllable by raising and lowering the diaphragm on the engine manually.

Pushing down, increasing pressure a little lowered the apparent water level and stopped the boiling.

Raising the diaphragm lowering the pressure slightly, raised the apparent water level and. caused vigorous boiling to resume

[Tom Booth]

One of the main reasons I wanted (and still want) to construct a working transparent "rice" engine is,

Many times in videos of people running these engines water is injected into a VERY hot engine on a stove, or otherwise pre heated and the water SIZZLES.

In experimenting myself I've noticed that I don't see the engine running if there is too much water. If the water all evaporated so no boiling can any longer be heard, the engine will still run quite well, but hearing an initial "sizzle" as the last bit of water evaporates, seems to be the Hallmark that indicates the engine is ready to run.

This indicates to me that these engines work best when at least some of the steam is superheated.

So I'm curious to see what is actually going on or what happens between futile thumping on the diaphragm on an engine that won't start, and the point when the engine often is self-starting or ready to run.

So far it seems like the engines run best when a relatively small amount of water is superheated and the bottom of the engine is actually DRY, with all the water having evaporated.or, so to speak. All the water vapor has become "airborne" but is hotter than mere steam down near the heat source.

Anyway, it's impossible to know what's going on inside the bottom of a tin can.

I'm also interested to see if there is actually any "cloud in a bottle" type effect. That is a cloud or mist appearing and disappearing.

[Tom Booth]

A problem with the clear beaker is it has printed on the side "not for stovetop use".

How far I can go with heating water to a "sizzle" before the glass cracks I don't know.

When I get a chance I have a few large borosilicate test tubes I've boiled water in over an open flame without a problem, so maybe I can make a transparent test tube "rice" engine.

The weirdest thing about the last video/experiment is it LOOKS LIKE, or before I started recording, looked like, the water itself was expanding.

The water level started out below the gravel and slightly below the top of the metal can.

While first being heated, BEFORE the water came to a visible boil the apparent water level started gradually rising up through the gravel.

This seemed bizarre as I never imagined that water could actually expand when heated so much.

Maybe air bubbles were getting trapped in the perforated tuna can, displacing the water, but that seemed unlikely, as I made a lot of holes in the can.

But the visible "water level" would rise and fall all the way from the bottom, to nearly the top of the gravel, with scarcely any visible sign of actual boiling (bubbles).

I imagine maybe zillions of microscopic "bubbles" forming within the liquid water, or maybe the water is in a kind of weird superfluidity sort of state where it expands and contracts like a gas?

The gravel, taking up most of the space tends to exaggerate the appearance of expansion and contraction of the water as it moves up and down between the bits of gravel, but...

Could water actually expand and contract that much when near or at the boiling point? Or is the apparent rise in water level just due to bubbles forming and displacing the water.

Of course visible bubbles do form and the water begins to boil, but the water level seems to rise before boiling begins.

[Tom Booth]

Another interesting aspect of this apparent water expansion which I unfortunately, did not capture on video, was that the extreme or exaggerated rising and falling of the water line was at first, happening by itself.

That is, the water level would go up and up and up and up...

At the same time the diaphragm would gradually balloon out but not a lot.

Then suddenly the water level, or apparent water level would drop all the way back down to the bottom and the diaphragm would collapse as well.

This appeared to be a kind of "implosion". Not at all gradual like the slow expansion.

It seemed like the gradual "expansion" reached some critical point, then boom, the whole thing would fall.

I kept thinking that maybe the seal on the diaphragm "burped" letting a lot of air/steam escape all at once, and perhaps that WAS what was happening, over and over again....

But personally, I don't think so.

It could possibly be that the gravel was still cold, so the "water" level went up higher and higher through the gravel but then the gravel took away so much heat that the expansion reversed.

Or maybe the water beginning to boil caused "bubbles" of steam to get trapped inside/under the tuna can. Then...

Why the repeated sudden "implosions"?

Maybe the trapped gas/vapor in the can at the bottom suddenly all escaped at the same time and rising up from the bottom into the cooler gravel suddenly all condensed back into liquid?

Maybe all an illusion caused by trapped air bubbles?

But then, it was "controllable" once the engine, (or wannabe engine) heated up more, appearing to be the result of applied pressure variations.

Overall, it reminded me of the somewhat more erratic behavior of a pot coming to a boil on the stove with a lid on the pot. The lid may sometimes jump around or up and down in a rather violent and noisy manner alerting the cook to remove the lid and stir the contents.

Removing the lid brings an end to the chaos.

But in this case it seemed like the diaphragm ballooning out past some critical point had an effect similar to removing the lid on a pot of boiling soup. The boiling would stop and all the "foam" subside or collapse, but all WITHOUT actually removing the diaphragm and apparently without it leaking, but I guess I have to verify that.

[Tom Booth]

Another rather strange and/or unexpected result is that when I'm lifting up the diaphragm, pulling upward, I can feel the "vacuum" inside the engine pulling back, or atmospheric pressure pushing down.

So the water begins boiling vigorously...

Normally, with some enclosed container with boiling water inside, like a pressure cooker, the pressure inside the pressure cooker, of course, goes up. And it goes up continually. If not released it will blow the lid off.

But in this case the boiling water, with the water boiling very vigorously, there is no reduction of the partial vacuum. The downward pull on the diaphragm, in opposition to my upward pull remains constant.

Presumably the evaporation (boiling) and re-condensing stays in perfect balance.

Likewise when pushing downward to stop or slow the boiling. The outward pressure does not change when the water vapor condenses, or boiling stops.

Maybe that is unremarkable.

I've always wondered why those "hand boilers" do not explode in people's hand when boiling. Why don't they build up pressure inside the hand boiler, like a pressure cooker?

I guess it is the same situation. The substance in the hand boiler is in a vacuum or "saturated vapor" so the internal pressure never goes above atmosphere. The rate of boiling/evaporation and condensation are in balance in spite of appearances.

But what seems strange to me is the ”vacuum" is so slight, and the water is on a hot stove and was already at the boiling point. Also the pressure is very slight. I'm only pretty gently lifting and pushing down on a silicone membrane, but I can start and stop the boiling of a beaker of water simmering on a hot stove?

Seems very very strange to me.

[Tom Booth]

To try to overcome the problems I had with the glass engine; (the spout got in the way of securing down the diaphragm, lack of a lip on the rim allowed the diaphragm to slip off too easily, and no easy way to let out excess steam through a glass beaker, other than putting holes in the diaphragm.)

I like having an actual "valve" to let out the steam that can be opened or plugged closed as needed, which was lacking.

I finally came up with a plan

rice-engine-modification.jpg (388.9 KiB) Viewed 1391 times

If I can find something that fits as a new rim, I can attach it to the flask, or if not, just build up a new rim with a lip out of epoxy.

By inserting a tube through the spout I can get rid of the interference from that, but use the opening as a valve.

I don't really want to try drilling through the glass to make a steam valve.

Possibly I could make the new rim out of wood or something on the lathe if necessary. I'm not sure how well epoxy will stick to the glass or how hard it might be to form it into the desired shape.

If I can find a metal can or something with a rim that might simplify the operation. Just snip off the rim from the can and glue it onto the beaker.

Down on the bottom I need to get rid of the tuna can, or cut out the perforated bottom and put it up on stilts or a spring or something so we can see what's happening under there. If a lot of air/vapor bubbles are getting trapped, displacing water, or not.

How is this water volume actually rising and falling?

I want to determine that before making other modifications or changes, like probably using less water and raising the screen higher so the water stays below the gravel.

Also I want to see if the engine can run while there is still water in the bottom or if it runs better if it all evaporates.

Possibly it is just that enough steam has to be generated to push out all the ordinary air to leave a "saturated vapor" and water in the bottom makes no difference, or does the steam need to be "superheated" or what?

Having a clear view of the bottom will help to answer all these questions.

[Tom Booth]

I found a section of left over PVC pipe that happened to be the same diameter as the flask, so I cut a 1" section and glued it on with epoxy.

Instead of using the spout I decided to just drill a hole in the PVC and installed a small steam bleeder valve such as used on old cast iron radiators, just filling the south area with epoxy.

Resize_20240328_181903_3781.jpg (30.8 KiB) Viewed 1384 times

On the bottom I just cut most of the side sections out of the tuna can, leaving just enough to hold up the gravel.

Resize_20240328_181902_2475.jpg (26.21 KiB) Viewed 1384 times

Eventually I probably want to leave more room on the bottom, but we'll see how this works.

With the PVC pipe top I can use a hose clamp to hold the diaphragm securely without worrying I might get the clamp too tight and crack the glass.

Now I just have to wait for the epoxy to fully cure.