Wallace MINTO

Freon Power Wheel

E. F. Lindsley: Popular Science (March 1976) ~ Wally Minto's Wonder Wheel
The Minto Wheel (Construction manual)
Wallace L. Minto: US Patent # 3,636,706 ~ Heat-To-Power Conversion Method and Apparatus
W. Minto & Leonard J. Keller: British Patent # 1,301,214 ~ Prime Mover System

Popular Science
(March 1976) ~

Wally Minto's Wonder Wheel

by E. F. Lindsley


I'd just finished shooting pictures of Minto's solar-powered, Freon engine/generator set (P.S., Feb. 1976) and I wasn't quite sure if he was kidding about this newest engine. Four used propane bottles were hose-clamped to the ends of two pieces of aluminum angle, each about four feet long.

The angles crossed at 90° at the center and were mounted on a central hub like a skinny four-blade windmill with bottles to swing in the breeze.


While I gazed in disbelief, Wally explained how his incredible power wheel works (see diagram below).




"Try holding onto the shaft," he said. I grabbed the shaft firmly --- it was if I'd tried to stop some eerie, irresistible force: no sound, no evidence of power, just pure twist.



For example, a practical 33 ft. diameter wheel running on a temperature difference of as little as 3.5° F and producing several horsepower could pump irrigation water, grind grain, or saw wood. The materials could be scrap pipe, and no machining or skills are needed to build it.





Minto has outlined construction details in a two-sheet paper entitled "The Minto Wheel." There are NO restrictions on building or experimenting with the wheel.

Sun Power Systems, Inc.
1121 Lewis Ave.
Sarasota, Fla 33577



Gravity does the rest:

The heavy bottle starts down; --- the lighter bottle floats up.


The Minto Wheel

( Transcribed by Bruce Hegerberg from a booklet published by Minto ( 4/30/97 );
Posted by Jerry Decker ~ KeelyNet/www.escribe.com)


Our forefathers used waterwheel to produce power, power which changed man's way of life and increased productivity. Today, when we know that our supply of energy from fossil fuels (including uranium) is exhaustible, every consideration should be given to tapping renewable energy sources.

Wallace Minto, a scientist internationally-known for his development of a pollution-free automobile engine, has developed a practical version of an engine that runs on small temperature gradients to produce useful power. Such small temperature gradients are plentiful almost everywhere on earth, or can easily be produced from solar energy.

The engine consists simply of a wheel with a series of sealed containers fastened around its rim. Diametrically opposite pairs of containers are connected by tubes. A low-boiling liquid, like propane, butane, carbon dioxide or Freon is sealed into the bottom container and subjected to a very mild increase of temperature. This causes a part of the liquid to vaporize, producing a higher pressure on the surface of the remaining liquid. This pressure forces the liquid up the connecting pipe until it spills into the opposite container at the top of the wheel.

This shift of mass causes the top container to become heavier while its opposite number at the bottom of the wheel becomes lighter, and the force of gravity causes the wheel to turn, in the same manner that water turns a water wheel. As the filled container nears the bottom of the wheel, it is in turn subjected to the influence of the heat source, and it then discharges its liquid into the original container which is now empty at the top of the wheel, having cooled as it traveled upward. This cycle is repeated indefinitely with no loss of the contents of the sealed chambers and the wheel keeps turning as long as there is an adequate temperature difference between its bottom and top.

No significant power can be produced from ordinary fluids that have relatively high boiling points, such as water or alcohol. Their vapor pressures are too low at temperatures near ambient. In addition, it takes too much heat energy to vaporize a pound of their liquid. However, today we have available liquids that vaporize to produce high differential pressures at very modest temperature differences. The use of these fluids is what makes the Minto wheel practical as a power source. Units of modest size could perform such tasks as pumping water for irrigation, grinding food grains and generating small amounts of machine power on a farm-by-farm basis. A temperature gradient of as little as two degrees Celsius (about 3½° F.) will drive a wheel ten meters (33 feet) in diameter. Such small temperature differences are abundant almost everywhere in nature: such as the temperature difference between water and cooler air, or even the difference between direct sunshine and shade.

The wheel turns relatively slowly, but produces enormous torque, or twisting effect on a shaft; this can be geared up through gears or belting to produce any speed desired at the final output shaft.

The Minto wheel is simple and inexpensive to build and is virtually maintenance free. When constructed of suitable materials and supplied with heat, a single unit can keep grinding out power for generations.

The wheel is simple to construct because no precision machine work is required. It is designed to be built from those materials most readily at hand in your community. The drawings herewith are intended to serve as a guide, or an example of such construction, but the exact dimensions given need not be followed closely. We suggest full exercise of your ingenuity in substituting parts available on most farms, from automobile junkyards, or your local refrigeration and air-conditioning serviceman.

Certain basic considerations in the design of a wheel are:

1. The main body of the working liquid should be heated as little as possible. Side arm tubes, for example, could be used to heat and vaporize only that portion required to pressurize the chamber.

2. The power output capability of the wheel depends upon the temperature differential available to drive it.

3. Extended surfaces should be employed to facilitate heat transfer.

4. Heat transfer to structural parts, particularly main container walls, should be minimized. Minimize the weight of the structural parts heated.

5. Higher density liquids maximize horsepower output from a given wheel operating at a given RPM.

6. Dual liquid fillings can be employed for special purposes. For example, using mercury as the shifting mass, powered by propane as the volatile fluid, tremendous torque can be generated with a relatively small diameter wheel.

7. The choice of working fluid is governed by optimum compromise among these factors, at the temperature range to be used.



Latent heat of vaporation of liquid

Specific heat of fluid

Viscosity of liquid


Vapor pressure

Ratio of the specific volume of the vapor to that of the liquid

Liquid density


The tanks around the rim are the most difficult part, so they should be made first. They are conveniently fabricated from pipe, (such as aluminum irrigation pipe) by welding, brazing or soldering. If you do not have the facilities to make hermetically-sealed tanks, you can get assistance from that modern-day equivalent of the village blacksmith --- your local welding shop. Or you may be able to improvise from surplus oxygen flasks or vacuum reservoirs from an auto junk yard. Throwaway freon tanks in 25 pound sizes make excellent tanks that are often available very cheaply from your local refrigeration and air conditioning service-man. Aluminum is desirable because of its lightness and durability, but steel is easier to weld, braze or solder.

On the other hand, welded joints are not essential. Carefully threaded and doped joints are satisfactory. If slip-on end caps are used, they may be applied with a good epoxy adhesive to form a hermetic seal.

After each tank is fabricated with a short side tube, we recommend it be tested with compressed air, applying soapy water liberally to all joints to check for leaks. You can fit a tire valve stem to the side tube and use a tire pump or take it to your local service station.

If you are concerned about the strength of your tanks, we recommend that you fill them with water before pressurizing. You can even pressurize them solely with water from your domestic supply. Since the compressibility of water is small at these modest pressures, this removes any danger from rupture on testing.

The number of tanks around the rim is not crucial, except that it must be an even number. We recommend at least eight tanks, or four pairs to get a reasonably-smooth power flow. The larger the tank diameter, the greater the developed torque. But larger tanks have a smaller relative area for heat transfer.

If you are using larger tanks, such as old freon containers, it is preferable to silver solder or braze on several copper U-bends to the outer side of the tanks. The volatile liquid can then flow into the copper tubes and vaporize in them to produce the pressure needed to force the bulk of the liquid up the radial tubes and into the opposite tank, Similarly, these tubes will enhance condensation of vapor in the top tank.

If you are fabricating tanks from pipe, we recommend that you insert in each tank a rolled-up piece of corrugated aluminum sheet to make a multiplicity of small channels next to the tank wall, This will improve heat transfer and tend to vaporize the fluid next to the wall with less heating of the main liquid mass.

Alternate ways to join the side arm tube to the tank:

1. Purchase brass adapters which are threaded with standard ½ inch Iron Pipe Thread on one end and ½ inch tubing compression fitting on the other end. Bore these out so that the ½ inch tubing slides all the way through. A thick walled tank may then be drilled and tapped to accept the ½ inch I.P. end, which is installed using Permatex or other good pipe dope. The side arm tube is slid into final position with its brass grommet and nut in place and tightened down. A little smear of Permatex on the tube before tightening will insure a leak-proof tube joint.

2. A brass plug threaded for 1/2; inch or 3/4 male IPT may be drilled through to accept a short length of 1/2; inch copper tubing, which is then soft-soldered into proper position. The brass plug is installed in the tank wall as in #1 and the radial tube connected to the opposite tank by solder sweat fittings.

3. If the tank has a thin wall, a short length of tubing may be soldered or brazed in position. If the tank is steel, use copper tubing and braze, silver solder or hard solder in place. If the tank is aluminum, use an aluminum tube and special aluminum solder to make the joint. You can also solder a copper tube through an aluminum tank using a special solder. These special self-fluxing aluminum solders are available from dealers listed in the appendix. Follow directions carefully and try soldering some scrap pieces until you get the knack of using these special alloys.

4. Of course, a good Heliac welder can do a quick and secure job of fastening on the end caps and stub tubes. If you and your friends were going to make a number of wheels, you might negotiate a reasonable mass-production price at a well-equipped welding shop.

5. If you are working with thin-walled tubing, the connecting tube may be brought through a thick end cap by threading in a street ell, or welding on an ell fitting. In that case, you may choose to use a fairly sturdy pipe as the crossover tube between tanks, which can also do double duty as a spoke of the wheel.


If you make the tanks from thin steel pipe (Schedule 20 or 10), their fabrication should be well within the capabilities of an ordinary electric welding machine or a flame brazing torch.

It must be emphasized that all joints must be made with care to be permanently leakproof under pressure. If this is done, the Minto wheel can produce power for generations, since there is no way for its working fluid to escape.

Once your tanks have been fabricated and tested, you have finished the hardest part. The next most important component is the central support hub and axle.

We have shown how to construct the central support hub and axle on a bare-bones basis, using a short length of 3 inch pipe, some square steel plates and a home-made bearing. But here a little browsing at an auto junk yard can give inspiration to your ingenuity. A rear axle and differential housing provides an excellent bearing assembly, with the added advantage that the former drive shaft will run at higher RPM than the wheel mounted on the axle. Of course, you will have to stop the other axle from turning --- or mount another Minto wheel on it to double the power output at the drive shaft. (Make sure you mount them so both turn the same way.) Also remember that the lubricating oil will run out of some differentials unless the drive shaft is horizontal.

A pair of old front wheel suspensions, complete with steel wheels, can also solve your bearing and hub assembly problems.

If none of these options is open to you, then make the bearing assembly as shown in the prints. The piece of 3 inch iron pipe should be polished with emery paper or any available abrasive.

The pillow-blocks may be of wood, jigsawed, rasped or carved to a reasonable fit with the pipe axle. It is preferable, but not essential, to line the wood with a sheet of copper or lead. Or pour molten babbit, plumber's solder or similar soft metal in a wooden

form to a level half way up the diameter of the axle, to make a long-lasting bearing. After pouring, remove the axle from the solidified metal and scrape the alloy lightly to smooth it. Occasional greasing will let it run for decades, especially if you protect the axle from weather by tacking a piece of old tire or tube over the bearing-axle junctions.

We have shown the spokes made from aluminum angles, since these are light and durable. However, any other material or shape of adequate strength will do. Aluminum channel, pipe or tubing is fine, or even steel pipes will suffice at a cost of added maintenance to retard rusting. Heavy walled plastic water pipe will give excellent durability, but the number of spokes should be doubled to compensate for the lesser rigidity.

The blueprints show a minimum number of spokes to minimize labor. You may find it desirable to add cross bracing to these, particularly if you build a larger wheel or use heavier tanks.

A taut lacing of wire or light cable, in the manner of the spokes on a bicycle wheel, will also improve rigidity.

The Support Stand:

The support stand is shown as made from ordinary two by four lumber. This will last longer if pressure-treated lumber is used. But it is more durably fabricated from steel angles or galvanized pipe, bolted or welded together. Either one should be supported off the ground on masonry, rocks or cement blocks to prolong its life. There is lots of room for improvisation here. Just remember to build with triangles, not rectangles.

Triangular framing provides stiffness and rigidity with a minimum of materials used.


Since there are so many uses for power, we can only give some general guidelines and a few illustrations. These facts should be kept in mind: The Minto wheel likes to work; like its ancestor, the water wheel, it is a high-torque, low-speed mechanism. It operates most efficiently just below its maximum torque-capability. Of course, its output can be converted to higher RPM by gears, chains, and sprockets, cable or rope drives, belts and sheaves, etc. But, it is most effective at jobs which use high torque at low speed, such as irrigation or grinding grain.

1. Always remember that horsepower is Proportional to the product of torque times RPM. A given wheel, operating across a given temperature gradient, will provide a particular maximum horsepower when fully loaded. If loaded less than that maximum, it will provide the output needed to drive its given load. It is self-regulating up to its maximum or stall torque.

2. The power take-off drive train should be designed to match your power requirements at the RPM of the final driven device. If you are pumping water, a low speed piston or well pump is easily driven with a simple crank arm fixed to the axle of the wheel. Two or more pistons have a smoother demand for power, and a wheel will more efficiently drive them if they are phased oppositely.

The wheel can easily drive a drum which hoists an endless series of pails to lift water from a well. Similarly, you can drive an air-compressor, such as an old piston refrigeration compressor or an air-conditioning compressor from a junked automobile (Ford type is best). The compressed air can be stored in a tank to drive any air motor to do anything.

You can pump water uphill into a pond or other reservoir and use this stored power to drive a small Pelton wheel to produce power on demand.

3. If you require a higher RPM in a directly driven device, it should be realized that ordinary V-belts and sheaves can not transmit the high torque of a Minto wheel, at least in the primary stages of gearing up to higher RPM.

For the first and possibly second stage of speed multiplication, use sprockets and motorcycle chain, or cable or rope drives, or gearing.

Here, mounting the wheel on an old automotive differential is advantageous, since the output will be geared up at least 3 to 1, depending upon the assembly chosen. If the original differential drive shaft is coupled to an automotive transmission (manual type) a further step up in speed will be obtained, along with the versatility of a variable speed output. After going through these speed multiplication gear stages, ordinary V-belts and sheaves should handle the probable torque demands of later higher-speed power requirements.

On the other hand, if you choose the simple axle and sleave bearing mounting, you can easily convert an old steel auto-wheel to a drive sprocket. Just weld or bolt studs on the rim, carefully spaced to coincide with the holes in the sprocket chain to be used. You do not need a stud per hole: eight or ten around the rim is usually adequate. But they must be set on a circumference of the wheel that is an integral multiple of the distance between adjacent holes in the chain.

A convenient method is to use bicycle sprockets and chain, fastening the pedal sprocket to the wheel axle and the small sprocket to a pulley shaft. For higher torque, use two or three bicycle sprockets and chains working in parallel. Or use the stronger sprockets and chain from a motorcycle. Another alternative is to fasten the output end of an old car transmission (manual type) to the wheel axle.



Many fluids are available for this purpose. Your choice will depend primarily upon a trade-off between cost and efficiency, as well as the temperature gradients available to you. The man-made fluids, represented by the freon family, have relatively high liquid densities and very low heats of vaporization. Therefore, they are most efficient as working fluids, producing the most horsepower for a given design of wheel. However, they are more expensive than the readily-available hydrocarbons, like butane, or liquified "bottled-gas".

A third class of fluids consists of solutions of one substance in another, such as carbon dioxide dissolved in washing soda solution (essentially "club soda"), or propane dissolved in kerosene. We recommend that the solution type of fluid be used only by more sophisticated constructors who have the expertise to deal with the more complex factors involved in desorption and re-sorption. However, these can yield excellent efficiencies because the heat of solution is lower than the heat of vaporization.


The fluid is put into each pair of tanks by means of a fill valve on each connecting tube. Of course, the fill valve can be on one tank of each pair. You can conveniently improvise a fill valve with the valve from a bicycle tube or a metal valve stem from an automotive inner tube. Other choices are to use fill valves available at an air-conditioning supply store, or the valves that come on freon tanks. The latter is a logical choice if you use the one-way freon tanks available from your local air conditioning shop.

In filling the tanks, it is very desirable to remove as much air as possible from each pair before filling and sealing.

The presence of air reduces the pressure differential attainable at a given temperature gradient, cutting down the power output.

There are a number of ways to remove most of the air, depending upon what equipment is available to you - or even without equipment.

Some Choices are:

1. Your refrigeration service man usually has an old compressor which will pull a decent vacuum through the fill valve.

2. An automotive air conditioning compressor from a junk yard can be directly-driven by an electric motor to evacuate the tanks.

3. You can obtain a "water aspirator" from a chemical supply house (or drug store) for several dollars which will pull a decent vacuum when hooked up to a garden hose, even at low domestic water pressure.

4. If you have no source of vacuum, merely admit some of the working fluid of your choice into the system through the fill valve, wait a few minutes for mixing, turning the wheel by hand, then vent the mixed gases. Three or four repetitions of this flushing will adequately remove air from the system. If you choose to fill the tanks with freon, we suggest you flush with "bottled gas", since that is cheaper and entirely compatible with the freon.

When most of the air is removed from the system, each pair of tanks is filled With enough working fluid to fill one tank with liquid and its opposite with vapor. Since the exact amounts are not critical, simple measurement of the tank dimensions will enable you to calculate the volumes of the tank. The tables in the appendix will allow you to estimate the weight of fluid to be put in the fill tube.

The most direct way to determine the weight of fluid placed in each pair of tanks is to weigh the supply tank. If the supply tank is connected to the fill valve with a flexible tube, you can continuously monitor its weight on a bathroom scale.

If that is not readily available, make a simple equal-arm balance from a length of lumber and hang the supply tank on one end and a bucket on the other. Fill the bucket with water until balance is achieved, then remove from the bucket a measured amount of water equal to the weight of fluid you wish to put in. A pint is a pound and a liter is a kilogram. The beam will balance again when the correct weight of working fluid has entered the system.

If you do not have a bucket big enough, hang the supply cylinder at some measured shorter distance from the pivot point and use the appropriate factor in determining the amount of water to be removed.


The Minto Wheel is designed to utilize relatively small temperature gradients to produce useful mechanical energy. A hot spring or solar heated water will drive it nicely. Be very careful to chose a liquid which will not produce a pressure too high for your tank walls. Do not try for very high temperature differences unless you are familiar with analysis of mechanical strength of the tanks. We advise against using high-temperature heat sources (such as flames) to drive the system, unless you are qualified to make the required analyses of stresses.


Do not be too ambitious in the size of tanks used. As the diameter of the tank is increased, its liquid capacity goes up as the square of the diameter, but the area available for heat transfer increases only linearly with the diameter. Heat transfer determines the op wer output. A wheel with small tanks will develop less torque, but will run faster. Remember that the power output is proportionate to torque times RPM.

Usually, tanks with diameters of from three to eight inches are most satisfactory. The length of the tank can be varied to suit the diameter of the wheel. Any variation in the length of the tank varies the volume and area in the same ratio. A long slim tank is better than a short fat one.

We recommend that at least eight tanks per wheel be used, but more than sixteen becomes somewhat complicated by the large number of crossover tubes threading through the hub area. Layout is simplified by using an even number of pairs, rather than an odd number of pairs. In other words, use eight, twelve or sixteen tanks (four, six or eight pairs) rather than ten or fourteen tanks (five or seven pairs).


To determine the weight of fluid needed to fill your chosen tanks: If they are cylinders, take the inside diameter of the tank and multiply it by itself, then multiply the product by 0.7854 to get the cross-sectional area. Multiply this number by the length of the tank to get its volume. Be sure that all measurements are made in the same units. If measured in inches, the result will be in cubic inches. If in centimeters, the result will be in cc. or ml. The tables in the appendix are given in English units of pounds per cubic foot, so your cubic inch result should be divided by 1728 to read out in cubic feet. Our metric friends only need to move the decimal point three places to the left to get liters, or six places to get cubic meters.

Remember that the total weight of fluid put into each pair of evacuated tanks should be equal to one tankful of liquid plus one tankful of vapor, at the probable operating temperature. The tables in the appendix will supply the necessary data to calculate the desired weiqht from the known volume of your tanks. This is not a critical matter but leads to maximum efficiency of operation. It is similarly desirable, but not essential, to have an equal weight of fluid in every pair of tanks on the wheel.

Operation of the wheel:

The power output of the wheel is proportionate to the rate at which heat is transferred into the liquid at the bottom and out of the vapor at the top,

For a given temperature difference, a hot water bath will transfer heat to the bottom tanks at a rate about forty times faster than hot air will.

So, we recommend that you use hot water to heat the bottom tanks, when feasible. The water may be heated by solar radiation, as with a solar collector below the bath level to heat it by convection. If you have a geothermal spring, your worries are over, and it need be only twenty degrees or so warmer than the air to give a reasonable power output.

Similarly, if you are using the wheel to pump water, arrange to have a few drops dripping on the top of the wheel to cool the upper tanks by evaporation. This increases the temperature difference across the wheel and increases power output. Even if you have no cool water, a bucket with a wick siphon dripping on the top of the wheel will help greatly, especially in hot, dry climates.

We have mentioned that the wheel likes to work and should be loaded to maximum torque for best efficiency. The optimum speed is easily determined for your particular wheel and heat source by putting into one of the crossover lines a small "bulls eye" type sight glass. These are available at your local air conditioning service man. Only one need be built into one cross-over line if all your tanks are similar.

The load should be adjusted so that liquid starts to spurt up the cross-over line when the bottom tank of that pair is horizontal. Bubbles of vapor should start to show in the sight glass as the tank trailing behind this one becomes horizontal. By adjusting the load on the power take off, and the depth of the water bath, this ideal may be approached.

Power output of the wheel:

Of course, you can just build a wheel and load it until it is working at maximum efficiency, then see whether it will do the job you hoped it would. But it is not difficult to calculate how much power it should turn out. The basic rules were worked out by Lazare Carnot (1753-1823) for water wheels, the major prime movers of his day, which were pure gravity engines. It is interesting that his son, Sadi Carnot, (1796-1832) is the author of the Carnot Theoreum of modern thermodynamics. Sadi took his father's formulae for power development by water wheels and converted it to the potential power output of heat engines. Sadi likened the "caloric fluid" to water, and the temperature through which it dropped to the height through which the water dropped. Today, we know that Lazare Carnot was correct, since the amount of water coming out the bottom of a waterwheel is the same as the amount of water going into the top. We also know that the amount of heat coming out of a heat engine is less than the amount of heat going into it. But in Sadi Carnot's day, the efficiency of steam engines was so low that he could not detect the difference between the "caloric fluid" going into the engine and the amount coming out. So he incorrectly applied his father's water wheel formulas to heat engines in 1824.

I do not wish to digress with this historical diversion, but it should be realized that this wheel is a synthesis of both the Carnots, father and son. It is a gravity engine operating on the principles of the water wheel, driven by a temperature gradient.

Back to our calculations:

If a weight of any substance falls through a vertical distance, its potential energy may be converted into kinetic energy. If one pound of weight falls one foot, it can develop one foot-pound of energy. Power is the rate of delivery of energy. It has been established that one horsepower is the equivalent of delivering 33,000 foot-pounds of energy per minute. Or 4500 kilogram-meters per minute.

To calculate the horsepower output of your wheel then, it is only necessary to know its diameter, and the weight of liquid transferred from bottom to the top tank each minute. The product of these two, divided by 33,000 will give you the horsepower. This is Lazare Carnot, upside down.

Well, its easy enough to measure the diameter of the wheel, but how much weight will transfer per minute? Here is where Sadi Carnot's theorem takes over. The greater the temperature difference, the higher the efficiency. Put Lazare and Sadi together and you get a "snowball effect".

Let's state it this way: The greater the temperature difference between the bottom and top of the wheel, the greater is the power output and efficiency of conversion of heat to power.

Let us get back to calculating how much weight will be transferred per minute.

To determine this, let us look at what happens. In the bottom tank, we must vaporize a quantity of liquid to fill that tank with vapor. The vapor displaces almost a tankful of liquid into the upper tank. You already know the volume of the tank, so you must calculate the weight of vapor it takes to fill it, at your probable operating temperature. This number you can get from the tables given herein. Then you read out, on the same line, the heat of vaporization per unit weight. This gives you the amount of heat you have to put into the bottom tank to empty it. {Pounds of vapor times heat of vaporization per pound.}

Now you know how much heat (measured in British Thermal Units, BTU's) you have to put into the tank to empty it and drive the liquid into the top tank.

But power depends upon the rate of heat flow. Knowing how many BTU's have to flow into the tank, you must next figure out the rate of heat flow. The heat flow rate depends upon the temperature difference between the water bath and the contents of the tank. For each degree Fahrenheit of temperature difference between the water bath and the working fluid in the tank, about 5 BTU's will flow per minute per square foot of tank wall area.

If you are not familiar with thermodynamic calculations, this may seem like a big chunk to swallow. But if we cut it up into little pieces, it is not hard to digest. And you would really like to make a reasonable prediction of what your wheel can turn out~ So let's take an example, step by step, to illustrate the principles:

Let us say that we make the tanks from three lengths of aluminum irrigation pipe of four inch diameter. If we cut each length into five foot sections, we will get about four tanks per piece of pipe, giving 12 tanks for our wheel. If the wheel is somewhat over 60 feet in circumference, it will be about 20 feet in diameter. Those are the basic facts.

We can calculate that each tank has a heat transfer area of 4 x 3 14 ( ) square inches per inch of length, multiplied by 60 inches of length gives about 754 square inches. Since there are 144 square inches in a square foot, the 754 square inches converts to 5.24 square feet per tank, We will ignore the area of the end caps as a little "fudge factor" in our favor,

Now we put in the 5 BTU per minute per square foot per degree Fahrenheit. So we know each tank can transfer 5 times 5.24 or about 26 BTU's per minute for each degree temperature difference between its contents and the water bath.

Next we will assume the ideal case, where we heat up and vaporize only the weight of fluid required to fill the tank volume.

We can calculate that the volume of one tank is:

4" x 4" x 0.7854 x 60" = 754 cubic inches

or 754/1728 = 0.436 cubic feet

If we are using freon-12 as our working fluid, and pick a reasonable intermediate temperature of l00° F, reference to the tables in the appendix show that its vapor has a density of 3.135 lbs/cu. ft. at that temperature. Therefore the weight of F-12 that has to be vaporized to displace the liquid in the lower tank is:

0.436 x 3.135 lbs = 1.37 lbs.

From the same table on the same line, we see that it takes 57.46 BTU to vaporize one pound, so the amount of heat to be transferred into the tank is:

1.37 lbs x 57.46 BTU = 78.54 BTU

How much mass is transferred? Well, we started with a tankful of liquid. Our tables tell us that liquid F-12 at 100° F weighs 80.11 lbs per cubic foot, and we know that a tank holds 0.436 cu ft.

80.11 x 0.436 34.93 lbs per tank

Of course, we are going to convert 1.37 lbs of the liquid into vapor, so the net transfer of liquid will be:

34.93 - 1.37 : 33.56 lbs

Since our wheel is about 20 feet in diameter, each tankful will provide nearly:

33.56 x 20' = 671 foot pounds of energy

In our example, twelve tanks will empty per revolution; we will get:

12 x 671 = 8050 ft lbs/revolution

If this work was used for hoisting water with an endless bucket chain, we can readily calculate that the 8000 ft. lbs of work per revolution is equal to that required to raise 95 gallons of water ten feet for each revolution of the wheel. In practice, somewhat less would be raised because of friction and other losses, but we are merely trying to approximate the magnitude of the useful work to be realized from the conditions of this example.

Let us continue by calculating how many revolutions per minute would be expected.

We said earlier that the rate of doing work is a function of the rate of heat flow. The rate of heat flow is governed by the area and the temperature difference. In our example, the tanks have an area of 5.24 square feet and a heat transfer coefficient of about 5 BTU per minute per square foot, so each tank will transfer 26 BTU per minute per degree Fahrenheit difference from the water bath. If the bath has water heated by solar panels, it might easily have an average temperature of 140° F, or 40°more than the tank.

So, our heat flow rate would be:

40 x 26 BTU = 1040 BTU/min/tank

We have already calculated that, under ideal conditions, it takes 78.54 BTU to empty the tank. Therefore a tank ideally should empty in:

78.54/1040 = 0.0755 min or 4.5 seconds

Since there are twelve tanks on the wheel, it would ideally make about one revolution per minute and hoist 95 gallons of water per minute through ten feet.

Remember that this is a theoretical calculation and your wheel will produce work at a somewhat lesser rate than the theoretical. If your specific embodiment produces half the theoretical work output, it would be equivalent to hoisting a 50 gallon drum of water up ten feet every minute. This is considerably more work than a man can perform on a sustained basis.

The wheel does not produce a high RPM, high power intensity output. If you have need for high intensity output, such as driving an electrical generator, then consider another innovative approach. Like the Minto wheel, this is also a gravity engine driven by a thermal gradient. But a different sequence of actions occur.


This prime mover is useful in more special circumstances. It uses a moderately-high temperature gradient (achieving greater Carnot efficiency) and a substantial difference of elevation, such as a mountain or high building. The basic principle involves the vaporization of a low-boiling liquid at modest pressure, such as a hot spring can produce. The vapor flows upward through a well-insulated pipe to some higher elevation, doing work against gravity. At the highest point it flows into an air-cooled condenser, wherein it gives up its heat and reverts to liquid form. The liquid flows back downhill through a pipe to produce a substantial hydrostatic head. The high pressure liquid drives an hydraulic motor. The exhaust of the motor flows into the vaporizer to close the cycle. The example gives details for one set of circumstances.

This form of prime-mover requires some precision-built machinery in the hydraulic motor. But it has a greater intensity of power output. (High torque at high RPM) Nonetheless, the components are durable and not expensive. If the necessary sources of altitude and heat are available, it has a very high cost effectiveness and excellent durability. Like the wheel, once built, it can turn out power for generations to come without consuming irreplaceable fuels.

US Patent # 3,636,706
( Jan. 25, 1972 )

Heat-To-Power Conversion Method and Apparatus

Wallace L. Minto

US Cl. 60/36, 55/459
Intl. Cl. F01k 25/04


USP # 3,358,451 ~ Feldman, et al. ~ US Cl. 60/108

Abstract ~

A fluorocarbon compound possessing a low-specific heat and a low-latent heat of vaporization is forced in the liquid state through a heat exchanger and heated to within 50 F of, but not exceeding its critical temperature, while being maintained at a pressure exceeding its vapor pressure, to produce a liquid containing vaporous nuclei which is then injected through a nozzle or other pressure-reducing device tangentially into an expansion chamber, which chamber is at a pressure below the liquid’s vapor pressure, whereby a portion of the liquid evaporates and separates from the remaining liquid. The vapor fraction is withdrawn from the chamber to drive a vapor engine, the engine’s exhaust vapor is condensed to a liquid which is then raised in pressure and mixed with the liquid fraction from the separation chamber and recirculated through the heat exchanger.

Background of the Invention ~

The present invention is directed generally to improvements relating to the thermodynamic cycle and it relates particularly to an improved method and apparatus for converting heat into motive power.

The use of steam as a drive medium or working fluid in vapor driven engines possesses important drawbacks and disadvantages. Among these disadvantages are susceptibility to freezing, the high weight-to-power ratios and the low maximum achievable efficiency, the latter being due to the high heat of vaporization of the water and the consequent high energy losses in the condenser. The use of other working fluids in place of steam as the drive medium overcomes many of the drawbacks accompanying the use of steam. Many of the fluorinated carbon compounds, particularly the fluorinated carbon compounds such as trichloromonofluormethane (R-11) and other of the fluorocarbons possess highly desirable properties and characteristics as drive fluids. They have low heats of vaporization so the condenser energy losses are low and their pressure-enthalpy characteristics are highly desirable.

However, the use of fluorinated carbon compounds is accompanied by important practical drawbacks when embodied in the conventional cycles. These compounds are subject to decomposition on being heated to excessive temperatures, have small enthalpies, and under conventional conditions possess low heat transfer properties. Consequently under conventional conditions accompanying the heating and vaporization of these fluorinated compounds attendant to their use as working fluids, localized heating or hot spots occur which promote and accelerate their decomposition. Moreover, the size of the boilers and heat exchange units are large relative to their heat transfer capacity when employed with the fluorinated compounds, and the conventional heating and vaporizing procedures and apparatus otherwise leave much to be desired.

Summary of the Invention ~

It is a principal object of the present invention to provide an improved method and apparatus for the conversion of heat into motive power.

Another object of the present invention is to provide an improved method and apparatus for producing a high-pressure vapor.

Still another object of the present invention is to provide an improved method and apparatus for the production of high-pressure vapors of condensable fluorinated compounds in which any heat decomposition of these compounds is eliminated.

A further object of the present invention is to provide an improved method and apparatus of the above nature characterized by their efficiency, reliability and versatility and the compactness, ruggedness and adaptability of the apparatus.

The above and other objects of the present invention will become apparent from a reading of the following description taken in conjunction with the accompanying drawing which illustrates a preferred embodiment thereof.

In a sense the present invention contemplates the provision of a method and apparatus for the production of a pressurized vapor from a liquid which vapor is employed as the drive medium in a vapor engine wherein the liquid is pumped through a heat exchange and is there heated to a temperature below its critical vapor pressure so that the liquid phase is maintained in the heat exchange unit, the heated liquid being discharged into an expansion chamber at a pressure below its corresponding vapor pressure to vaporize a fraction of the injected heated liquid. The vapor and liquid fractions are separated in the chamber, the liquid fraction being returned to the heat exchange unit and the vapor fraction being used to drive a vapor engine, the expanded vapor output of which is condensed and the condensate returned to the heat exchanger.

Advantageously, the working fluid is a low boiling point fluorocarbon compound having a low heat of vaporization, preferably a boiling point at atmospheric pressure of [ ? ]° F., to 250° F., and a heat of vaporization of 20 to 300 BTU per pound at atmospheric pressure. Examples of highly suitable liquids are R-11, R-113, R-114, R-115, R-216, perfluoro cyclic ethers and amines, and R-21.

The temperature and pressure of the liquid in the heat exchange unit is advantageously such that the liquid is in a nucleated state, that it, the pressure and temperature is such that a portion of the fluid is present in the form of minute vaporous nuclei but is characterized by the absence of any formation of bubbles of significant dimensions. The heat transfer rate to a liquid is found to be highest when it is in such a state of nucleated boiling, however, the rate of heat transfer from the wall to the fluid drops sharply if conditions are such that bubble formation occurs, and furthermore, there is a great danger of boiler tube burnout in the event that heat transfer from the tube wall to the heated fluid drops and the tube is not adequately cooled thereby. Moreover, the above conditions are highly conducive to the local overheating of the fluid with the resulting decomposition thereof. The system described herein obviates these difficulties and improves the efficiency of heat transfer, thereby substantially reducing the physical size of the vaporizer.

The heat exchange unit conduits are advantageously of such design and dimensions and the flow rate of the liquid therethrough are such as to produce turbulent flow in the heat exchange conduits. In addition, the surface-to-volume ratio of the heat exchange conduits should be such as to effect a temperature gradient between the external heating fluid or hot gases and the conduit wall far greater than between the conduit wall and the heated liquid.

Advantageously, the expansion chamber separating receiver is of cylindrical shape with a depending conical bottom wall, the heated liquid being injected into the chamber through a tangential nozzle to form a vortex in the chamber, the vapor fraction being obtained through a coaxial nozzle conduit in the top of the chamber and the liquid fraction being drawn from the bottom of the chamber.

In order to increase the entrance velocity and produce a pressure differential, the minimum cross-sectional area of the tangential nozzle leading into the cylindrical expansion chamber is advantageously less than, and preferably less than half of, that of the conduit leading from the heat exchanger to the nozzle. The diameter of the expansion chamber is advantageously 3 to 10 times that of the conduit leading to the nozzle and the height of the chamber is advantageously 4 to 12 times the conduit diameter, and the height of the depending conical section is preferably between 2 and 5 times the conduit diameter. The chamber coaxial vapor outlet conduit projects into the chamber a distance of one to 4 times and is of a diameter of one to 4 times the diameter of the conduit leading to the nozzle.

The vortex produced in the chamber causes a rapid separation of the liquid and gaseous fractions with minimal entrainment each of the other. Further, centrifugal action produces a pressure gradient across the radius of the vessel so that any small droplets of liquid entrained in the gas tend to evaporate.

The subject method and apparatus produces a pressurized vapor from a low boiling point fluorocarbon in a highly efficient and reliable manner with the obviation of any decomposition or deterioration of the fluorocarbon, and the apparatus is compact, simple and rugged.

Brief Description of the Drawings ~

Fig. 1 is a flow diagram of a heat to motive power conversion system embodying the present invention; and

Fig. 2 is a front elevational view, partially in section, of the fluid expansion and separation section thereof.

Brief Description of Preferred Embodiment ~

Referring now to the drawing which illustrates preferred embodiment to the present invention, the reference numeral 10 generally designates the improved heat to motive power conversion system which includes a heating unit 11, a vapor separator 12, a vapor engine 13, a condenser 14, a feed pump 15, and a burner 16 in a typical operation the low boiling fluid and would be circulated by pump 17 through the heat exchanger 18 which typically would be comprised f a multiplicity of coiled pipes constructed of a material that is heat and corrosion resistant. The heated fluid would then pass through a pressure reducing valve 19, which is optional, and thence through nozzle 20 into the vapor separator unit 12. The liquid portion of the heated fluid would then return via conduit 21 and reservoir 22 to the pump 17 for recirculation, whereas, the vapor portion of the heated fluid would exit separator via conduit 23, pass to the engine 13 through throttle valve 24 which controls the engine 13. Exhaust from engine 13 would pass via conduit 25 into an injector 26. Within the injector 26 the exhaust vapor from the engine thereby raising the pressure in condenser 14 and providing a much greater surface for the vapor to condense upon, as well as a higher pressure within the condenser, thereby making the heat transfer much more efficient. A portion of the liquid from pump 15 travels via check valve 29 back into the heat exchanger vapor separation system 11, 12. Fuel supplied to the burner 16 is controlled via valve 32 which, in turn, is actuated by network 33 of known construction. Network 33 is controlled in turn by the sensor 30, which is responsive to the temperature of the heated fluid within the heat exchanger coils and also to the sensor 31, which is responsive to the vapor pressure inside the vapor separator 12. Temperature sensor 30 is preset to turn down the duel supply or turn it off entirely if the temperature exceeds a preset value below the critical temperature of the working fluid. Pressure sensor 31 is arranged so as to reduce or cut off the fuel supply via network 33 if the pressure exceeds the preset value.

The expansion chamber and vapor liquid separator 12 includes a vertical cylindrical wall 40 provided with a depending conical bottom wall 41 which terminates in the dependent coaxial conduit 21. The top of chamber 12 is closed by a wall 42 through which inlet conduit 20 projects to a point below top wall 42. A preferably rectangular inlet nozzle 34 communicates with the upper part of chamber 12 through cylindrical wall 40 in a direction tangential to the cylindrical wall 40. The nozzle 34 is preferably of greater height than width and upon the flow of liquid therethrough into chamber 12 a rotating liquid and vapor vortex is produced.

The system 10 is charged with a low boiling point fluorocarbon compound for example, R-11. Under normal operating conditions with R-11, pressure regulator sensor 31 is adjusted to 500 pounds per square inch, absolute, fuel control network 33 adjusted for a liquid outlet temperature in pipe 18 of 380° F.

Under normal operating conditions the pressures and temperature are as above set forth. The conditions of the working liquid in pipe 18 are such that it is in a state of nucleated boiling with a highly efficient heat transfer from the pipe to the liquid. The hot pressurized liquid issues from nozzle 20 effecting the vaporization of about 10-20 percent by weight of the liquid discharged therein under the above conditions. By reason of the strong centrifugal force accompanying the vortex the liquid fraction and vapor fractions rapidly and efficiently separate, the liquid fraction traveling to the wall 40 and separating downwardly through funnel 41 and conduit 21 and the vapor fraction flowing upwardly through conduit 23. The vapor flows through and drives engine 12 the exhaust of which is liquefied in the pressurized condenser 14 and recirculated through heat exchange unit 18 by pump 15. The liquid fraction, on the other hand, flows into tank 22 from which it is withdrawn by pump 17 and recirculated through heat exchange unit 18.

A drop in demand of pressurized such as accompanies the closing down of throttle valve 24 results in an increase in the pressure in chamber 12 which in turn reduces the delivery rate or fuel to the burner 16 to return the pressure therein to the regulated value. Any tendency for the temperature in pipe 18 to drift from the preset temperature is overcome by the regulating system including network 33 and sensing element 30 which automatically varies the fuel control valve.

According to a specific example of the improved apparatus the diameter of vapor discharge conduit 21 is 1.5 inches, the conduit 23 projecting 3 inches into chamber 12. The diameter of chamber 12 is 5 inches and its height is 8 inches and the height of conical wall 41 is 4 inches. The nozzle transverse cross section is one inch high and 1/4 inches wide and the inside diameters of pipes 18 and 20 are one inch each. The engine 12 is a 5-cylinder reciprocating piston engine of a total displacement of 150 cubic inches and is capable of delivery with the present system about 125 shaft horsepower.

Examples of other working fluids which may be employed and their preferred operating parameters are as follows:

The working fluid is advantageously a nonflammable compound having, at atmospheric pressure, a boiling point of 0° to 250° F., and heat of vaporization at room temperature of 20 to 300 BTU per pound. It should preferably have a critical temperature of 200 to 600° F., and a critical pressure of 400 to 1000 psi absolute. The temperature to which the liquid is heated in heat exchanger 18 should be within 40 F., of the critical temperature and the pressure should exceed the saturation pressure by about 10 to 100 psi. The pressure in the expansion chamber should be between 10 and 200 psi less than the critical pressure.

While there have been described and illustrated preferred embodiments of the present invention it is apparent that numerous alterations, omissions, and additions may be made without departing from the spirit thereof.

I claim: [Claims not included here]

British Patent # 1,301,214

Prime Mover System

Wallace L. Minto and Leonard J. Keller

The present invnetion relates to prime mover systems.

In US Patent # 3,479,817 and in British Patent Specification No. 1,251,484 there are described external combustion engine systems employing as a drive medium in a closed sealed circuit, fluocarbon compounds having low latent heats of vaporization and desirable boiling points. While the systems described in the aforesaid British and US patents are in many respects superior to the conventional prime mover systems employing steam as the drive medium, the use therein of conventional vapor engines, as typified by the turbine and reciprocating engine is accompanied by numerous drawbacks and disadvantages. These drawbacks and disadvantages are consequent to the operating and flow characteristics of the conventional engines particularly when employed with the fluocarbon drive medium, whose properties in many critical areas are radically different from that of steam. In addition to the usual drawbacks of the reciprocating engine, including high inertial losses, poor torque speed characteristics, high friction and high maintenance requirements, the high losses and inefficiencies attendant to the operation of that engine due to the numerous changes in the direction of flow of the drive medium through the engine are aggravated by the use of a fluorocarbon drive medium because of its relatively high specific weight. The turbine, on the other hand, is a low-torque engine which in many applications requires the use of expensive energy consuming speed reducing transmissions, is inefficient at low speeds, requires relatively high inlet-exhaust pressure difference, and has a relatively high size to torque ratio. Thus the use of reciprocating engines or turbines with fluorocarbon drive medium leaves something to be desired.

The object of the present invention is to provide a prime mover system which has a high efficiency, ruggedness, simplicity, excellent torque and speed characteristics, low maintenance requirements, and great reliability, adaptability and versatility.

According to the present invention there is provided a prime mover system comprising a closed sealed circuit containing a drive medium having a latent heat of vaporization of less than 100 gram calories per gram ad a boiling point less than 95° C atmospheric pressure, said closed sealed circuit comprising:

A vapor engine including at least two male and female members defining oppositely pitched helical screws intermeshing along a longitudinally extending area of engagement and extending from a leading input end to a trailing outlet end, a casing housing the screws and having faces in substantially fluid tight engagement with the peripheries of the screws and an inlet communicating with the trailing end of the female screw, the female screw having chamber defining grooves and the male having helical lobes engaging the chambers along the intermeshing area, the screws rotating in predetermined opposite directions under the influence of a pressurized fluid introduced through the input port;

Means including an input and an output for heating and vaporizing the drive medium;

Means including a condenser having an input and output for cooling and liquefying the drive medium;

Means for injecting liquid drive medium from the cooling and liquefying means into the heating and vaporizing means input;

Means connecting the output of the heating and vaporizing means to the input of the engine; and

Means connecting the output of the engine to the input of the cooling and liquefying means.

An output drive shaft is connected to one or both screws and projects by way of suitable seals or glands through the casing. It should be noted that more than two intermeshing rotor screws may be employed, for example two female rotors engaging a common male rotor. Examples of mechanisms which may be employed and modified for the present purposes are described, in among others. US Patents Nos. 1,696,802 No. 2,578,196, and No. 3,016,842.

The drive medium should be a fluorocarbon compound, preferably having at least two carbon atoms and three fluorine atoms per molecule, and in addition may contain hydrogen, oxygen, silicon and chlorine atoms in any desired combination to obtain the optimum thermodynamic properties desired. Mixtures and azeotropes of two or more of the above compounds may be employed as the drive medium and there may be added a suitable compatible high boiling point lubricant which is liquid at normal temperatures, preferably a fluorosilicone lubricant. The above fluorocarbon compounds are characterized by their high lubricity, stability, vapor range and non-inflammability as well as their low heat of vaporization.

Preferably the engine is provided with means for controlling the vapor cut-off to the successive helical screw chambers and hence the chamber expansion ratio and engine torque. Expansion ratio of 1:1.5 to 1:20 are employed to advantage, the preferred range being 1:3 to 1:10 for operation without simultaneous liquid injection. Increasing the expansion ratio increases the engine’s conversion efficiency, while decreasing the ratio maximizes output torque. By adjusting the expansion ratios the need for variable speed transmissions or torque converters is obviated, and such adjustment is achieved by varying the point at which communication between successive rotor chambers and the engine input is cut off, and this may be accomplished by providing peripherally-spaced input ports and controlling the communication between the ports and the heated vaporized drive medium. The engine vapor is advantageously directed at the leading faces of the helical chamber grooves so that the inertia of the input vapor is also converted to mechanical energy with a resulting increase in engine efficiency, particularly at high engine speeds.

A further increase in efficiency is achieved by injecting or admixing with the engine inlet vaporized drive medium, medium in the liquid state. Unlike most substances the fluorocarbon compounds suitable for use as drive media tend to superheat upon isoentropic expansion from the saturated vapor. The superheat enthalpy may be used to vaporize additional liquid drive medium within the engine, increasing the volume of vapor and furnishing additional work of expansion. The pressure required to inject the liquid into the engine may be supplied by the boiler feed or other pump. The temperature of the liquid may be as low as that of the condenser outlet, or as high as that of the hot saturated liquid in the boiler in equilibrium with the saturated vapor being used to drive the engine, or any intermediate temperature.

The proportion of liquid to be injected is readily calculable from the relative enthalpies of the liquid injected and that of the exhaust vapor that would occur without admixture of liquid. In this calculation, allowance should be made for the fact that expansion of the vapor in the engine is not truly isoentropic, hence the enthalpy and superheat of the exhaust is greater than it would be is expansion was truly isoentropic. The proportion of liquid injected into the engine should be such that the resultant exhaust, after admixture, contains a minimum of superheat. Indeed, it is preferable that the exhaust condition be within the saturation line at condenser pressure, say at 80% or 90% quality. The presence of liquid droplets suspended in the vapor materially improves sealing across lines of approximation of the surfaces of the moving engine parts and assists in lubricating them to minimize wear and tear. By such admixture of liquid with the engine inlet vapor, a greater total volume of gas passes through the engine, and the work output of the engine becomes a larger fraction of the net heat inputs to the boiler, resulting in improved thermal efficiency of the system. It is to be noted that this advantageous result can only be obtained with substances which superheat upon expansion of their saturated vapors.

The admixture of liquid and gas should preferably take place within the engine expansion chambers, although may take place at any point prior thereto, since it will require a finite period of time to reach equilibrium, which will occur under the turbulent conditions of flow within the engine. It is advantageous to inject a portion of the liquid at relatively low temperature into the engine by such means as to cause it to flow through the bearings, thereby cooling and lubricating them. The liquid injected into the bearings at the high pressure end will admix with the vapor in the engine, increasing its efficiency as outlined above.

The fluorocarbon lubricant is admixed with the original charge of fluorocarbon drive fluid, in which it is soluble, particularly at elevated temperatures. Since the fluorosilicone is soluble therein, ebullition of the fluorocarbon in the boiler results in a vapor containing entrained microdroplets of fluorosilicone, which are carried into the engine and lubricate its moving parts. The fluorosilicone droplets dissolve in the fluorocarbon liquid in the condenser and the resultant solution has higher lubricity than the fluorocarbon alone, lubricating the boiler feed pump, circulating pump seals and all other moving parts in the system. The fluorsilicone is unaffected by the relatively low boiler temperatures required to vaporize the fluorocarbon drive medium (less than 250° C). Hence it circulated freely and unchanged throughout the entire system. We have found that less than 1 percent of fluorosilicone is adequate, and 0.2% by weight is out usual proportion.

The prime mvoer system of the present invnetion employing as a drive medium the specified fluorocarbon compound and helical screw engine is far superior to a system using a fluorocarbon drive medium and conventional vapor engines in its lower cost, high efficiency, versatility and adaptability and its improved torque speed characteristics, great reliability and low maintenance. Moreover, the improved system is far superior to a corresponding system employing steam as a drive medium for similar reasons, including the poor lubricity of steam and its tendency to condense on expansion.

Referring to the accompanying drawings:

Figure 1 is a schematic diagram of a prime mover system embodying the present invnetion;

Figure 2 is a top plan view partially broken away, of the vapor engine forming part of the improved system;

Figure 3 is a left hand end view thereof; and

Figure 4 is a right hand end view thereof.

The reference numeral 10 designates a helical screw rotor engine which forms part of a closed vapor liquid circuit of the nature described in US Patent No. 3,479,817 and British Specification 1,251,484. The engine 10comprises a housing 11 (Figure 2) including opposite end walls 12 and 13 and a peripheral wall 14 having a transverse cross-section delineated by intersecting circles.

A pair of mating, helical screw, male and female defining rotors 16 and 17 respectively are located in the housing 11 and are provided with axial end shafts 18 which are journaled in corresponding pairs of axially aligned bearings mounted on end plates 12 and 13, at least one of the shafts 18, for example that connected to female rotor 17, projecting by way of a suitable seal through one of the end plates and defining the engine drive or output shaft.

The rotors 16 and17 fit in the casing 14 to close tolerances to minimize any leakage between the rotors and the peripheral and end faces of housing 11. The female rotor 17 has a plurality of similar helical chambers or cylinders defining grooves 19 formed therein, each of which extends for somewhat less than 360 degrees about the rotor 17 from the leading to the trailing end thereof, example 6 grooves 19 in the illustrated embodiment. The male rotor 16 includes a plurality of similar helical piston defining lobes 20, four in number in the illustrated embodiment. Successive lobes 20 register with successive grooves 19 along a longitudinally-extending intermeshing zone and form a rolling fluid tight engagement therewith with the opposite concurrent rotation of the meshing rotors 19and 20. Thus the lobes 20 define pistons which slide along cylinder or chamber defining grooves 19 so that these successive chambers expand from the leading or input end proximate end plate 13 at the rotor intermeshing zone with the rotors 16 and 17 rotating clockwise and counterclockwise respectively as viewed in Figure 3. The lobes 20 disengage respective grooves 19 in less than one revolution and before the leading end of the respective groove again reaches the intermeshing zone.

A pair of pressurized vapor inlet conduits A and B respectively extend through corresponding openings in leading end plate 13 providing communication with the leading end of housing 11 and grooves 19 at a point shortly following the rotor intermeshing zone in the clockwise direction therefrom wherein the chamber in the communicating groove 19 is expanded a small predetermined amount by the mating lobe 20, and at a point further removed in the clockwise direction from the first point where the chamber in the groove 19 registering therewith is further expanded by the mating lobe 20. Thus the engine expansion chamber defined by mutual engaging groove 19 and love 20 is greater when communicating with conduit B than with conduit A and receives a greater volume of pressurized vapor in the former case, that is when the pressurized vapor is fed to the chamber by conduit B or by both conduits A and B, than by conduit A alone.

A pair of exhaust conduits C and D, respectively, provide communication with the grooves 19 through the trailing end plate 12 and are positioned in a manner similar to conduits A and B. Thus successive grooves 19 maintain their pressure even after they have been disengaged by corresponding lobes 20 by reason of the closure of opposite ends thereof until their trailing ends reach exhaust conduit C through which the pressurized vapor in the corresponding grooves is discharged. It should be noted that pressurized vapor may be fed to conduits C and D and conduits A and B connected to exhaust under which conditions the rotors 16 and 17 will be rotated in a reverse direction to that when the pressurized vapor is fed through conduits A and B.

The conduits A and B as well as the conduits C and D extend in a direction toward the leading face 21 of the respective groove in registry therewith, preferably perpendicular thereto. Thus, the pressurized vapor fed by any of the conduits A, B, C, or D into the engine impinges on the corresponding leading groove face 21 to impart torque to the rotors as a consequence of the momentum of the inflowing vapor.

As seen in Figure 1 of the drawing the conduits A and B are connected respectively to the outlet ports 22a and 22b of a valve 22 having an inlet port 22c and the conduits C and D are connected respectively to the outlet ports 23a and 23b of a valve 23 having an inlet port 23c, the valves 22 and 23 each having actuators or spindles for selectively connecting the inlet ports to both respective outlet ports or the leading of the respective outlet ports that is ports 22a and 23a or to cut off the outlet ports. The valve inlet ports 22c and 23c are respectively connected to the outlet ports 24a and 24b of a valve 24 having inlet ports 24c and 24d which are alternatively respectively connected to the outlet ports 24a and 24b or 24b and 24a.

A drive medium heater or heat exchange unit 26 of any suitable type is heated in any suitable manner, for example by a conventional oil or gas burner, to raise the temperature of the liquid drive medium therein to close to the coiling point thereof, preferably to its nucleated boiling point, at the pressure I the heater unit, the inlet to the heater unit 26 being connected to the outlet of a condensate pump 28 which may be driven by engine 10 or by any suitable auxiliary drive means. The inlet to condensate pump 28 is connected to the outlet of a liquid drive medium reservoir tank 29 whose inlet is connected to the outlet of a heat exchange condenser unit 30 which may be suitably cooled by air or water. The inlet to condenser 30 is connected to valve port 24d.

The outlet of heater 26 is connected to the inlet of an expansion chamber 32 of the structure described in the abovementioned British Patent Specification, the vapor outlet of which is connected successively through a selectively operable throttle valve 34 to valve port 24c. The liquid outlet of expansion chamber 32 is connected to the inlet to heater 26 and through a throttle valve 37 advantageously adjustable with throttle valve 34 to the inlet of throttle valve 34.

The circuit illustrated in Figure 1 is closed and hermetically sealed and is charged with a fluorocarbon drive medium of the nature specified above, for example R-113, R-114, R-216 or other fluorocarbon compounds with like properties and mixtures thereof. In addition the drive medium may have advantageously admixed therein, preferably less than 1 percent by weight, for example 0.2 percent of the drive medium, of a lubricant which is stable and inert in the drive medium and liquid at the pressures and temperatures encountered in the network, for example, the fluorosilicone lubricants. The pressures and temperatures are regulated to the desired values in the manner described in the above identified British and USA patent specifications.

Considering now the operation of the prime mover system described above, under normal forward low torque operating conditions the valve 23 is adjusted to provide communication between only ports 22a and 22c, the valve 23 is adjusted to interconnect ports 23a, 23b and 23c and valve 24 is adjusted to interconnect ports 23a, 23b and 23c and valve 24 is adjusted to interconnect valve ports 24a to 24c and 24b to 24d. The drive medium is heated just to the point of nucleated boiling in heater 26 and expanded in chamber 32 to produce vapor and liquid fractions. Part of the liquid fraction is recirculated by pump 36 to the heater 26 and part through valve 37 where it is admixed with the vapor from chamber 32 flowing through valve 34. It should be noted that the flow of the liquid drive medium from chamber 32 may be completely returned to the heater 26 and none admixed with the vapor. The drive vapor, with or without any drive medium liquid enters engine 10 through conduit A, and causes the rotation of rotors 16 and 17, by reason of the pressure and expansion of the vapor, assisted by the evaporating liquid, as earlier explained, and the reaction to the inlet flow to the drive medium. Since there is an early cut of the inlet of conduit A a relatively small amount of the drive medium enters the successive engine cylinders with a resulting high expansion ratio and low torque. The engine exhausts through conduits C and D and the exhaust flows through valves 23 and 24 and is cooled and liquefied in condenser 30 and stored in reservoir 29 from which it is pumped by pump 28 to the input of heater 26. If a greater engine output torque is desired valve 22 is adjusted to open ports 22a and 22b so that drive medium is delivered by conduits A and B to delay the vapor cut off point to a larger engine expansion and deliver a greater amount of drive medium to successive chambers and hence reduce the expansion ration and increase the engine output torque. The engine rotation is reversed merely by adjusting valve 24 so that ports 24a and 24b communicate with ports 24d and 24c respectively, the engine 10 operating reversely in a manner similar to its forward operation except that conduits A and B are now exhaust and C and D feed conduits. The engine speed may be varied by adjusting the throttle valve 34. The lubricant carried by the drive medium is circulated as described earlier.

The optimum operating parameters of the drive medium throughout the circuit and the engine expansion ratios depend on the specific drive medium and the use of liquid drive medium with the vapor. Thus expansion ratios of 1:1.5 to 1:20 are highly effective with expansion rations of 1:3 to 1:10 being preferred in the absence of injected liquid drive medium. Where employed, the optimum ratio of liquid drive medium to the vapor drive medium and the optimum engine expansion ratios depend on the particular drive medium employed and other parameters and may be readily determined.

Advantageously the drive medium temperatures and pressures are 90° C to 325° C and 45 psia to 1000 psia at the engine inlet, 25° C to 150° C and 5 psi to 250 psia at the engine exhaust, 25° C to 150° C and 5 psia to 250 psia at the condenser outlet and 25° C to 150° C and 45 psia to 1000 psia at the heater inlet. The following is given by way of illustration of specific operating parameters which may be employed with the working fluids or drive mediums specified:

The desired operating parameters may be achieved in the manner described in the above identified British and US patent specifications.


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