It works perfectly, it is simple, it is fairly inexpensive. Except for one detail, it would be nearly perfect. More on that later!
It was similar to the ancient steam-driven spinning device invented by Hero thousands of years ago.
Inside the firebox of any furnace, woodstove or fireplace, a small water reservoir (between a quart and a half gallon capacity) is mounted such that it is (ideally) 6" above the flames. (Closer than that and the presence of the 'cold' tank would affect the burning of the fire.) The tank needs to be extremely sturdy, either 1/4" steel or of thinner stainless steel construction.
The tank has two 1/2" pipe connections. One is low on an end wall. This one is connected through TWO series check valves to the water supply line of the house. The other is on top, and this represents a steam escape line. This one has a temperature-pressure relief valve, where the pressure rating is 10 PSI higher than the highest house water supply pressure.
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The steam that leaves is sent to a simple steam turbine, potentially as simple as Hero's of 2000 years ago. As the steam is forced through a very narrow nozzle in that turbine, it achieves very high speed, which allows it to drive the turbine wheel to turn a shaft.
That is all that is involved in the device!
As long as there is water in the reservoir, steam is generated and the shaft is turned. AFTER all the water in the reservoir is boiled away, steam can no longer be created. At this point, the pressure in the reservoir begins to fall. At some point, the pressure in the reservoir drops below the T-P pressure setting and that valve closes. If a small amount of water was still present in the reservoir, pressure might briefly increase again enough to open that valve to release the pressure but it will soon close. With no water in the reservoir, the pressure would continue to drop. At some point, it will drop below the pressure of the house water supply and the check valves will open to allow additional water to enter the reservoir. This substantial addition of water will generally briefly cool the tank down well below boiling. This allows the tank to be filled as it originally was, to about 3/4 full. The reservoir condition is now as it was to begin with, and the cycle will repeat.
If the fire is extremely intense and/or the water supply provides the water very slowly, the hot walls of the reservoir could prematurely cause boiling of the water and creation of steam. This is not the intended result, but it represents a rapid cycling mode of operation, and it still works. The blower would then blow air much more intermittently.
Notice that everything about the operation is automatic. The cycling is a natural sequence of events and does not depend on or need any external control mechanisms.
Depending on the capacity of the reservoir, the heat from the fire, the surface area of the reservoir, and the rapidity of water supply availability, the cycling rate will vary, as well as the percentage of time that useful steam pressure is being generated. My experimental evidence indicated that around 80-85% of the time, substantial steam pressure will be produced, with the remaining 15-20% being that re-filling and re-heating part of the cycle. Some experiments gave about 15 minutes of steam generation followed by about 3 minutes of no steam, and then a repetition, as long as the fire and the water supply was present.
A variation of the device involved a second water chamber being connected to the boiler chamber by a large diameter (say 1.5" diameter connector pipe. The fill line is attached to this second chamber, which is located OUTSIDE the firebox, and very slightly ABOVE the boiler chamber, with the connection pipe slightly HIGHER yet. The advantage of this configuration is that a 'fill' cycle would occur very rapidly, just transferring water from the one chamber to the other through the large connector pipe. Everything else works exactly as before, but now any 'false cycling' is eliminated and the boiler tank gets a complete fill each time. Another variation we experimented with was a similar arrangement where a fairly constant 'dribble' of water passed from the one chamber to the other, which tended to extend the productive stage of the cycle.
This design has a wonderful characteristic. If just a small fire was present in the JUCA stove, only a limited amount of steam was produced and the blower turned slowly. When a more intense fire was built, more steam was generated, which turned the shaft faster, which made the blower circulate more air. The blower was an automatically variable speed blower! Without even using any electricity at all! It only spun as fast as necessary to distribute whatever heat the stove was creating at the time!
That represents a substantial production of electricity, and could provide the electricity for all of a home's lights and some appliances. As an automatic and natural 'accessory' to our wood-burning stove, a constant and reliable source of 800 watts of electricity was always available. In principle, a house could be provided with a set of electrical circuitry and lights for 12 volt operation, very much like travel trailers are. Or, it could be converted to 100 volts AC using a standard power converter, but that involves a loss of overall efficiency.
The problem is sound. Do you know how a teakettle sounds? That sound is created when fairly low pressure steam is emitted at moderate speeds. For these applications, where a substantial portion of a full horsepower is desired, both the pressure and the exit velocity must be far higher than for a teakettle. Imagine 10,000 teakettles. No, that probably wouldn't be as loud as this thing was! Even with earmuffs, it was painfully loud. I later estimated that it was around 130 decibels, comparable to the sound of a jet engine at around 10 feet away!
The concept seemed so beneficial in so many ways that I did a number of experiments to try to minimize or muffle the sound. I put the turbine outdoors, with the rotating shaft coming through a hole in the wall. Barely quieter. That horrible high pitched sound seemed to penetrate everything! I surrounded the whole thing with a foot thick of sound insulation. With this arrangement, it WAS possible for people to shout to each other to communicate!
The sound is SO incredibly loud that I cannot imagine any application where it could be used, except in a house of totally deaf people!
An alternative that I did NOT investigate, and which would have been substantially quieter, would have been to drive a steam ENGINE rather than a steam turbine. There may have been some future in that approach.
In ALL cases, if someone was intending to do further experimentation with this concept, it is critically important to realize the incredible pressures that steam can produce. A faulty or weak reservoir could burst and explode, sending shrapnel and boiling water over a large area. For this reason, it is critical to use a very sturdy reservoir and to add one additional feature to the piping, a branch pipe with a second T-P relief valve, set to a somewhat higher pressure than the one in the steam line. In case the nozzle clogged up, where steam could not escape, this valve would eventually open, releasing the pressure to keep the reservoir from exploding. This is the concept of the standard T-P valve on EVERY domestic hot water heater.
The invention STILL seems to me to be an excellent one! But the incredible sound-level problems never permitted us to ever use it in any products. Those experiments were done in a very rural location, where the nearest neighbor was half a mile away. They later asked what the loud whistle they heard was. They had had to turn their TV up, half a mile away! I always wondered why the windows on my house didn't shatter!
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C Johnson, Theoretical Physicist, Physics Degree from Univ of Chicago