CA1261636A - Method and equipment for converting thermal energy to mechanical energy - Google Patents

Abstract

Abstract of the Disclosure Method and equipment for converting thermal energy to mechanical energy by means of a thermal power machine. A member of metal alloy contained in the thermal power machine is heated to a certain temperature, whereat its physical properties are changed. This physical change is used as the mechani-cal drive power of the thermal power machine. The metal alloy member of the thermal power machine is heated by means of heat which is transferred by means of one or several heat pumps from an external medium that contains heat. The heat pump is operated by means of part of the mechanical energy generated by the thermal power machine, and the rest of this mecha-nical energy is used for other purposes, for example for moving a vessel.

Description

, The present invention is concerned with a thermal power machine and a method for converting thermal energy to mechanical energy, wherein a member of metal alloy contained in it is heated to a certain temperature, whereat its physical properties, in particular its elastic constant, are changed and this physical change is used as the drive power of the thermal power machine. The invention is also concerned with equipment for converting thermal energy to mechanical ener~y, the said equipment comprising a thermal power machine which includes one or several lS metal alloy members, which change their physical pro-perties, in particular their elastic constant, at a certain temperature, whereat this physical change pro-vides the thermal power machine with drive power.
Several metal alloys are known in which the so-called memory phenomenon occurs. The patent claims refer to all of these so-called "memory alloys". One of such "me~ory alloys" is an alloy of titanium and nickel, known by the name Nitinol*. After an object of such a material has been brought to a certain shape by means of an appropriate heat treatment, it always tends to return to this shape when it is heated to its transition temperature. On the contrary, below its transition temperature, the material is readily deformable. Thereat, the material can be deformed by means of a substantially lower force as compared with the force that is generated by it at a higher temper-ature when it retuns to its heat-treated shape. The ; transition temperature can be adjusted by varying the composition of the alloy, and it may vary within the 35 range of about -90C to 150C, most commonly about 40 to 90C.
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Different applications of thermal power machines are known that are based on the ability of Nitinol to convert thermal energy to mechanical en-ergy. One thermal power machine of this sort is described in the U.S. patent 4,275,561 ~Finnish patent application no. 79-2398). The apparatus described therein is based on the tendency of a Nitinol loop t~ becorne straight at a temperature of, e.g., about 50C. When such a loop has been fitted around two wheels placed side by side and when one of the wheels is heated, e.g., by keeping it in warm water, the Nitinol loop tends to be straightened and to move at this wheel, making the wheel revolve by means of friction. The power can be taken out of the apparatus from the shaft of the unheated wheel.
Such an apparatus has proved highly reliable and durable in operation.
Thermal power machines have also been developed that are based on easy extensibility of a Nitinol wire below the transition temperature and on the force gen-erated by its shrinkage at the said temperature. Sucha reversible elongation in the case of Nitinol is about 6 per cent. The power re~uired for extending is consid-' erably lower than the force generated by the shrinkage.
Applications in which the shrinkage force is used for rotating a crankshaft, which again extends Nitinol el-ements, have been described in the U.S. patents 3,937,019 and 4,086,769.
The object of the present invention is to pro-vide further applications for the conversion of thermal energy to mechanical energy by means of a memory alloy.
According to the present invention, there is provided a thermal power machine for converting thermal energy provided from a heat source to mechanical energy comprising at least one oblong metal alloy member being Trademark ~;26~636 provided in a predetermined length which expands below a predetermined temperature and contrac-ts to the prede-termined lengt~ at-a certain transition temperature set by a composition of said alloy member, said member being stretchable below the predetermined temperature, wherein the machine is provided with a heat exchange cooling face ! the metal alloy member being alterna-tely brought into and out of contact with the cooling ~ace while the metal alloy member moves.
Thusj the internal energy of the metal alloy can be converted to mechanical energy with maximum effi-ciency by using the heat energy supply of an external medium as the primary source of anergy. In appropriate circumstances, the machine may operate so that it does no-t require an external electric mo-tor or combustion en-gine at all. In such a case, the machine can be applied,e.g., as a motor for a boat or for a ground vehicle, which is independent Erom distribution and supply of energy.
The machine is completely free from pollution, because no combustion waste is produced in the form of solid par-ticles or gases, nor does it produce noise.
Preferably, in accordance with the invention,there is provided a thermal power machine for converting thermal energy to mechanical energy, the said thermal power machine comprising two or more oblong metal alloy members placed side by side, which members change their length at a certain temperature to a certain length that was given to them earlier and which members are, at lower temperatures, relatively easily extensible, whereat the said metal alloy members are, at one end, attached pivot-ably and eccentrically to a rotary member revolving arounda shaft perpendicular to the said metal alloy members, and the shrinkage of the metal alloy members causes a movement of rotation of the rotary member while the rotary member, at the same time, extends a second metal alloy , ~Z6~L~i36 - 3a -member, characterized in that the other end of the metal alloy members is also attached pivotably and eccentrically to a second rotary member revolvlng around a shaf-t per-pendicular to the said metal alloy members.
According to the present invention, there is also provided a combination of a thermal power machine ; and a heat pump, the thermal power machine including a metal member having physical properties which change de-pendent on temperature of said metal member, the ¢hange of the physical properties providing a driving power out-put from the thermal power machine, the heat pump con-nected to the thermal power machine so that said metal member is heated by a heat containing medium external of said heat pump and transferred by said heat pump to sai.d metal member, the thermal power machine driving -the heat pump by means of mechanical energy ~enerated by the thermal power machine, comprising a pair of metallic heat exchange faces provided in the thermal power machine, one of said faces heated by the heat transferred from the heat pump, the other of said faces having a lower temperature than said one face, said metal member posi-tioned between said pair of faces so as to alternatingly contact said pair of faces, the metal member being pro-vided in a predetermined length which e~pands below a predetermined temperature and contracts to the predeter-mined length upon an increase in the temperature.
The invention and its specific features will be described in more detail in the following with refer-ence to the attached drawings, wherein Figure 1 shows an operational diagram of a ther-mal power machine based on -the deformation of a memory alloy, Figure 2 shows the use of a thermal power ma-chine in itself known in the equipment in accordance with - 3b -the invention, Figure 3 is a schematical presenta-tion of the use of an equipment in accordance with the invention as a power machine for a vessel, Figure 4 is an axonometric view of a particular embodiment in accordance wi-th the invention of a memory-alloy thermal power machine, Figure 5 is a cross-sectional view of the equip-~ ment shown in figure 4, ~

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Figure 6 is an axonometric view of a second particular embodiment of a memory-alloy thermal power machine, Figure 6a is a sectional v:iew of the Nitinol*
wire used in the apparatus shown in Fig. 6, Figure 7 is a sectional view of the apparatus shown in Fig. 6, Figure 7a shows a detail of Fig. 7, , Figure 8 is a schematical presentation of the connecting of the apparatus shown in Fig. 6 with a heat pump, Figure 9 shows an alternative wiring diagram for the connecting of the apparatus shown in Fig. 6 with a heat pump, Figure 10 shows a detail of an additional improvement of the apparatus shown in Fig. 6, and Figure 11 shows the heat exchanger faces of the apparatus shown in Fig. 9, as viewed i.n the direction of the Nitinol*strip.
Like for all thermal power machines, an operational diagram can also be derived for a machine based on the deformation of a memory alloy. Now, it is, however, purposeful to replace the pressure-volume system of coordinates by a stress-elongation system of coordinates. Such an operational diagram is shown in Fig. 1, wherein the x-axis illustrates the elon-gation (or compression) of the material and the y-axis illustrates its stress. The principle of operation shown in Fig. 1 will be described in the following.
Step 1: The material is deformed at a tem-perature lower than the transition temperature.
Step 2: The temperature of the material rises and reaches the transition temperature.
Step 3: The deformation of the material is returned to the original form.
Step 4: The temperature of the material is * ( Trade mark) ~iL26~36 lowered to a level below the transi-tion temperature. Hereupon/ s-tep 1 takes place again.
In view of the efficiency of the operation of the machine, the important steps are step 3, wherein the machine performs the mechanical work, as well as step 2, wherein the machine receives the quan-tity of heat re-quired by the change in phase.
The following is known about the opera~ion of the machine:
1. For a machine operating by means of the loop principle, an efficiency of 7 ~ 2 per cent has been obtained within the range of 25 to 60 experimentally.

2. The machine is not a Carnot machine. By means of calculations, it can be established that the efficiency of the machine is better than the efficiency of the Carnot process of circulation.

3. The quantity of heat required for the change in phase is 4150 joules per mole.
;~ 4. The other necessary physical properties are known sufficiently accurately so that it has been possible to perform the calcu-lations of the order of magnitude.
Figure 2 shows an equipment in accordance with the present invention, in which a thermal power machine 1 operating by means of the loop principle, in accord-ance with the U.S. Patent 4,275,561, is utilized. The thermal power machine is provided with two wheels 2 and 3 fitted side by side, around which one or several parallel Nitinol* loops 4 are fitted. The smaller wheel 3 is placed in a medium tank 5 covered by a layer of -~ thermal insulation, the medium, e.g. water, in the said tank 5 being heated by means of a heat pump 6. The heat pump is coupled by means of an appropriate trans-mission (not shown in the drawing) with the shaEt 7 * (Trade mark) ~26~63~

of the larger wheel 2 in the thermal power machine 1.
Moreover, an auxiliary motor is connected with the heat pump, which motor may be either a combustion engine or an electric motor (not shown in the drawlng).
When the heat pump 6 is started by means of an auxiliary motor, the pump transfers heat from the medium surrounding the pump into the medium in the tank 5. Heat is conducted from the medium in the tank 5 to the wheel 3 of the thermal power machine 1 and to the part of the Nitinol loop 4 surrounding the wheel 3.
When the temperature of the Nitinol* loop reaches its transition temperature, e.g. 50C, it tends to become straight, whereat the wheel 3 starts revolving. The movement is transmitted further to the wheel 2, from whose shaft 7 the power is taken off. Part oE the power obtained from the shaft 7 is used for driving the heat pump 6, but all of the output power is not needed for this purpose. The excess of the power may be used for any desired purpose.
In stead of an auxiliary motor, the starting may also be performed by means of an auxiliary heater, operating, e.g., by means of electricity or fuel. In such a case, the medium in the tank 5 is first heated to the transition temperature by means of the auxiliary heater, which can be turned off thereinafter.
Fig. 3 shows an embodiment for the utilization of the mechanical energy in this way produced. The thermal power machine 1 and the heat pump 6 are fitted on a boat 8. The heat pump transfers heat from the surrounding water 9 through a pipe system 10 into the water tank associated with the thermal power machine, keeping the temperature of the water contained therein, e.g., at about 50C. Some of the energy generated by the thermal power machine is distributed for the drive ` 35 of the heat pump and some of it for driving the propeller 11 of the boat.

* (Trade mark) Figures 4 and 5 show an alternative embodi-ment for the thermal power machine 1 operating by means of the loop principle shown in Fig. 2. This embodiment comprises a medium tank 5 between whose side walls several spring-like Nitinol* strips bent to an arc form are attached by means of compression springs 15. Every other strip is bent downwards and every other upwards.
To the middle of each strip, a connecting rod 13 is ; attached whose opposite end is attached rotably to a crankshaft 14, alternatingly to its opposite crank parts.
When the temperature in the tank 5 rises to the transition temperature of the Nitinol* strips, the downwardly bent strips 12, at their transition temper-ature, tend to be straightened to the position that was given them in the heat treatment. Thereby, the con-necting rods 13 start rotating the crankshaft 14. When the strips become straight, they rise out of the medium.
At that time, no more thermal energy is transferred to them. When they cool down, they again become flexible, and the connecting rod 14 causes them to be bent upwards this time. At the same time, the strips that were originally bent upwards, have been forced to be bent downwards, and they come into contact with the warm medium. Thereinafter they again convert some of the thermal energy contained in the medium to kinetic energy.
The transfer of heat to the Nitino~ springs in the apparatus shown in Figures 4 and 5 can take place either out of a liquid of low surface tension or out of a heating contact face or as any other energy impulse, e.g. by means of electricity, heat radiation, or laser. In the springs, it is possible to make use of the resonance phenomenon.
In apparatuses in accordance with the inven-tion, constructions of low weight are obtained, and possible materials are, e.g., nylon, fibreglass, etc.
The temperature of operation of the apparatus may be, e.g., 40C. Machines can be built in view of ma~.ing * (Trade mark) ~Z6i~.3~

them best suitable for certain temperature circum-stances to be determined separately.
The medium from which, according to the invention, energy is transferred by means of a heat pump may be, e.g., soil, water or air.
In the embodiment shown in Figures 6 to 8, Nitino~ wires 21 of flat cross-section have been fixed by means of articulated joints between two crankshafts 24 placed side by side symmetrically to each other. At temperatures below their transition temperature, the Nitinol wires are readily extensible, but when the temperature rises to a certain value, they shrink back to their original length.
In the apparatus, there are two chambers 22 and 27 between the crankshafts, placed one above the other. The chambers 22 and 27 are provided with rnetallic heat exchange faces 23 and 26 facing each other, the distance between the said faces being equal to, or smaller than, the diameter of the path of move-ment of the crankshafts 24. Fig. 7a is a more detailedview of the construction of the lower heat exchanger face, as a section in the longitudinal vertical plane.
It is provided with channels 32 placed side by side for the pipe system of the heat pump. Between the channels 32, in the top face, there are grooves 33 for the Nitino~ wires 21~ The construction of the upper heat exchanger face 26 is similar, except that the wire grooves 33 are placed at the bottom face. ~lost appropriately, the heat exchanger faces 23 and 26 are convex towards each other in such a way tha-t, in the middle portion, the distance between them is shorter than the diameter of the crankshafts.
Between the heat exchanger faces 23 and 26, there is an insulation layer 28 in which there are vertical grooves parallel to the grooves 33. Most appropriately, the insulation layer 28 extends to all sides of the chamber 27. The apparatus is enclosed * (Trade mark) ~ ~;26~E;3~i in a steel box 30, out of which the medium has been removed as completely as possible close to the vacuum.
The heat pump 6 is connected between the pipe systems 32 in the heat exchanger faces 23 and 26 so that it transfers heat from the upper heat exchanger face 26 either to the environment or to the lower heat exchanger face 23. The medium present in the lower chamber 22 may be additionally heated by means o~ an ; external source of heat 34, or, e.g., waste heat from 1~ a nuclear power plant ~water of about ~50C) may be passed into ito An external source of heat is, however, not necessary if the heat pump 6 trans~ers heat from an outside medium, e.g. from t4C water surrounding it, to the lower heat exchanger face 23.
When the lower heat exchanger face 23 is heated, the Nitinol* wires in contact with it are heaked to their transition temperature. On reaching their transition temperature, the Nitinol wires shrink and make the crankshaft 24 cranks at the lowest position, to which the wires 21 are attached, pull themselves ~ towards each other, whereat the wires 21 rise apart - from the face 23 and start cooling down. At the same time, the Nitinol*wires that are attached to the ; crankshaft 24 cranks in the upper position and in con-tact with the upper cooling face 26 are extended as the crankshafts revolve in opposite directions. The movement goes on further so that the wires that were, at the initial positio~, in contact with the heating face 23 come into contact with the cooling face 26 and are at that stage cooled efficiently. Thereinafter, the same movement is repeated after the wires have exchanged their positions. After the apparatus has been started, the crankshafts revolve constantly sym-metrically in opposite directions and the Nitino~ wires are alternatingly shrunk when reaching contact with the face 23 and extended as being extended by the crank-shafts 24.
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The output powers W1 and W2 of the shafts 24 can be combined by means of a common loading shaft (no-t shown in the figures) Part (W3) of this power can be used for driving the heat pump, whereat the net power W4 is obtained for any other, desired purpose.
If necessary, the position o the crankshafts 24 may be adjusted by shifting the shafts in the directions x and y denoted in Fig. 7. The apparatus, of course, also operates so that the lower face is the cooling face and the upper face the heating face. In such a case, the crankshafts revolve in the opposite direction. Of course, it is also possible to place the entire apparatus so that the wires 21 are not in the horizontal direction.
According to the invention, it is preferable to use a minimal difference in temperature between the faces 23 and 26. In such a case, the loss of heat is at the minimum and, correspondingly, the efficiency of the Carnot pump used for heating the face 23 and for cooling the face 26 is at the maximum.
It is also possible to use several thermal power machines as connected in series so that each machine operates at a slightly lower transition temper-ature relative the preceding machine. In such a case it is possible to make use of very little differences in temperature between adjoining temperature ranges.
Depending on the circumstances, it is also possible to utilize just some smaller portion out of such a series.
The output P of the thermal power machine described in Figures 6 to 8 can be calculated theore-tically. When the following values are used:
o ~rest length of Nitinol* wire) 5,000 mm r (radius of Nitinol* wire) 1 mm R (radius of crankshaft) 25 mm n (speed of rotation of crankshaft) 300 rpm z (number of Nitinol*wires) 100 ; ~K (internal diff. in temp. of machine) 1 to 3K, * (Trade mark) J ~
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as the output is obtained P 150 kW (without heat pump).Max. torque per wire is then 150 Nm.
Fig. 9 shows schematically how the liquid cooled in the evaporator of the heat pump 6 is circulated first via the heat exchanger 27 prov:ided with a cooling face, whereat the temperature of the cooling face is lowered efficiently. It is only thereinafter that the liquid is passed through the medium 9 used as the source of heat, where its temperature rises to the same level with the temperature of the medium 9. Thereupon the liquid circulates back to the evaporator of the heat pump, where it delivers heat.
The liquid passing through the heat exchanger 22 provided with a heating face is circulated through the condenser of the heat pump 6, where it is heated and thereby lceeps the temperature of the heating face sufficiently high.
Figures 10 and 11 show an additional improve-ment for the apparatus shown in Figures 6 to 8. In the 2Q apparatus, flat, band-shaped Nitinol*strips 21 are used, whose width is, e.g., about 10 mm and thickness, e.g., about 0.25 mm. The length of a strip may be, e.g., 100 cm. Rods provided with articulated joints are attached to the ends of the strips. The strips are fitted so that the long side of their cross section is placed vertically. Fig.10 shows one end of a Nitinol*
band as well as the articulated rod related to it and the crankshaft 24. The articulated rod consists of two parts 35 and 36 connected to each other by means of an articulated joint 34. One end of the rod 35 is attached pivotably to the crankshaft 24 and the other end of the rod 36 is attached permanently to the Nitinol*
strip 21. Above and underneath the rod 36, there are stops 37 whose distance from each other is shorter 3S than the diameter of the path of movement of the crank-~ shaft 24.
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Fig. 11 shows the heat exchangers 22 and 27 used in the embodiment of Fig. 10. Each heat exchanger consists of two parts, ~hich are attached to the frame of the heat exchanger by means of hinges 38. In the closed position of the heat exchanger, a slot remains between the opposite heat exchanger faces of the parts ; the width of which slot corresponds to the thickness of the Nitinol*strip 21. The heat exchangers 22 and 27 extend over the entire length of the Nitinol* strip. The pipe systems of the heat pump run inside the jaws of the heat exchangers. The jaws of the heat exchangers are normally kept in the opened position, e.g., by means of springs (not shown in the drawing).
When the Nitinol*strip 21 comes from the top downwards a]ong with the crankshaft 24, the rods 36 at its ends contact the lower stop members 37. ~his has the effect that the relay (not shown in the drawing) connected to the stop member makes the jaws of the heat exchanger 22 pull themselves against the spring force towards each other, into tight contact against the Nitinol*strip 21 at both sides of the strip. Thereby the strip is rapidly heated to its transi~ion temper-ature and is shortened intensively. The cranks of the crankshafts 2~ revolve in opposite directions beyond their lowermost points until the rod 36 starts rising apart from the stop member 37. The articulated joint 34 makes it possible that, during this period of time, the position of the Nitino~ strip has not been changed in the vertical direction. At the same time as the rod 36 moves apart from the stop member 37, the relay releases the jaws of the heat exchanger apart from each other, and -the strip 21 can rise.
When the rod 36 rises further, it reaches contact with the upper stop 37, which correspondingly 3~ makes the jaws of the upper heat exchanger 27 close themselves around the strip 21. Thereby the cooling faces 26 reach tight contact with the strip 21 and cool * (Trade mark) ., .

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it efficiently and rapidly. After that, the strip is again extended as pulled by the crankshaft 24. There-inafter the sequence of movements is repeated again.
Like in the embodiment of F~iyures 6 to 8, in the embodiment of Figures 10 and 11 several parallel strips 21 are also used. In such a case, there are heat exchangers 22 and 27 of its own for each strip.
The stop members 37 may be, e.g., fork-shaped, whereby the rod 36 ends up between the two vertical pins of the fork and remains reliably in its position.
Alternatively, the stop members 37 and the articulated joints 34 may also be omitted. In such a case, in stead of stop members 37, limit switches are used which activate the relays closing the jaws of the heat exchangers. In such a case, the heat exchangers are attached resiliently, e.g., by means of compression springs fltted at the hinge side, so that the heat ex-changers move along with the strips 21 in their closed position.
In stead of hinged jaws of heat exchangers, it is also possible to use parts that move towards each other and away from each other so that their heat ex-changer faces remain constantly parallel to each other.
Either one of the jaws or both of the jaws may be mobile.
The length of the movement may be very short; it is enough that the strip 21 can be detached from between the jaws.
In stead of a flat Nitino~ strip, a wire of circular section may also be used, whereat the jaws of the heat exchangers have recesses corresponding to the section of the wire. However, in view of efficient transfer of heat, a flat band is preferable. In view of efficient operation of the apparatus, it is also important that the contact faces of the jaws are as ~` 35 smooth as possible and uniformly heated.

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Claims (10)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A thermal power machine for converting ther-mal energy provided from a heat source to mechanical energy comprising at least one oblong metal alloy member being provided in a predetermined length which expands below a predetermined temperature and contracts to the prede-termined length at a certain transition temperature set by a composition of said alloy member, said member being stretchable below the predetermined temperature, wherein the machine is provided with a heat exchange cooling face, the metal alloy member being alternately brought into and out of contact with the cool-ing face while the metal alloy member moves.

2. A thermal power machine as claimed in claim 1, wherein the thermal power machine is also provided with a heat exchange heating face, the metal alloy member being alternatively brought into alternating contact with the heating face and the cooling face.

3. A thermal power machine as claimed in claim 1, wherein said metal alloy member is pivotally and ec-centrically connected to a rotary member revolving around a shaft perpendicular to said metal alloy member, contrac-tion of the metal alloy member causing a rotating move-ment of the rotary member which subsequently stretches the metal alloy member.

4. A thermal power machine as claimed in claim 2, wherein the heating face and the cooling face are sep-arate elements and contact the metal alloy member from two sides, a part of the heating face and of the cool-ing face being movable toward each other into tight contact against the metal alloy member and away from each other.

5. A thermal power machine as in claim 3, where-in an end of the metal alloy member is attached to the rotary member by means of an articulated rod, stop members being provided on either side of the articulated rod, the stop members being a predetermined distance from the ar-ticulated rod, the predetermined distance being shorter than a diameter defined by a path of movement of the rotary member, additional members being connected to the stop members and providing impulses for movements of parts of the heating face and of the cooling face.

6. A thermal power machine as claimed in claim 1, wherein the metal alloy member is a band shaped strip.

7. A thermal power machine as claimed in claim 1, wherein the cooling face is a metallic heat exchange face.

8. A thermal power machine as claimed in claim 2, wherein the heating face is a metallic heat exchange face.

9. A thermal power machine as claimed in claim 3, wherein an opposite end of the metal alloy member is pivotally and eccentrically connected to a second rotary member rotatable around a shaft perpendicular to said metal alloy member.

10. A power machine as claimed in claim 1, wherein the metal alloy member is connected between opposed crank portions of two crankshafts with the crankshafts being placed side by side and in a symmetrical position relative to each other.