Description

Technical Field

The present invention relates to the systems for energy generation and in particular has as object a liquid metal thermoelectric generator.

State of the art

As known, the common thermoelectric generators based on the coupling of a primary engine operating by the expansion of a working fluid, gas or liquid, and an electric generator, while having on the one hand several advantages in terms of cost and easiness of realization, on the other hand have some drawbacks.

In particular, the thermal fluids used in these known systems, while having high compressibility, requires high expansions to generate relatively low displacements. In this sense further systems are also known which use as working fluid metals or metal alloys which are liquefied or are liquid at room temperature since they, despite having low compressibility with increments of volume up to 20 times lower than those of the most commonly used fluids, allow to have very much higher pressure differentials per degree, even of a several thousand times greater, for an equal increasing of the temperature.

This feature allows to obtain high advantages in those cases wherein it is desired to obtain the transmission of high power to a load by means of small displacement of actuator means operating with a liquefied metal.

However, the known systems operating through the expansion of liquefied metals have proven to be low effective and operationally limited as they are generally designed to transmit simply a movement from an expansion element housing an amount of liquefied metal to an actuator element.

For example, GB2027814 discloses a working machine which comprises a container housing liquefied metal, placed in contact at a side with a heat source and at the other side with a piston operating in turn on an electric generator by means of a gear.

The oscillating movement produced by the expansion and contraction of the liquefied metal is directly transmitted to the piston which drives accordingly the generator or a possible load associated with it.

It appears obvious that such a solution is low efficient due to the reduced displacements that could be transferred to the piston and consequently to the load.

Furthermore, the need of cooling the metal to promote the contraction makes the apparatus even more disadvantageous from a point of view of the energy efficiency.

Scope of the invention

The object of the present invention is to overcome the above drawbacks providing a liquid metal thermoelectric generator which is particularly economical and effective. A particular object is to provide a liquid metal thermoelectric generator which can be used for different applications in several sectors, for example as the primary generator of electricity, in systems for the recovery of energy from degraded sources, as a portable generator or to provide power to electric vehicles.

Still another object is to provide a liquid metal thermoelectric generator which does not require the constant and cyclic cooling of the liquid metal, being able to reach higher efficiency.

Still another object is to provide a liquid metal thermoelectric generator that allows to obtain high forces upon relatively small expansion of the liquid metal.

These objects, as well as others which will appear more clearly hereinafter, are obtained by a liquid metal thermoelectric generator that, according to claim 1, comprises a containment chamber for at least one liquid or liquefied metal material, heating means for heating said containment chamber adapted to promote the expansion of said metal material, a transmission element operatively in contact with said metallic material to move upon the expansion thereof, means for generating an electromotive force operatively associated with said transmission element.

The means for generating the electromotive force comprise a magnetic or electromagnetic circuit powered by an electric current for generating a magnetic or electromagnetic field, said magnetic or electromagnetic circuit having at least one movable junction element operatively coupled to said transmission element to move between a first closing position of said circuit and a second opening position of said circuit upon the transmission by said transmission element of a force greater than the electromagnetic attraction acting on said at least one movable junction element to produce a variation of the field flow adapted to generate the electromotive force.

Thanks to this combination of features it will be possible to obtain an electromagnetic force of considerable value even after a small temperature increases transmitted to the liquid metal material, exploiting the high incompressibility thereof associated with high pressure gradients.

As matter of fact, it will be sufficient that the pressure transmitted by the liquid metal material exceeds even slightly the attractive magnetic force acting on the movable junction element to produce a large air gap.

Advantageously, the containment chamber may comprise one or more containment elements of said metallic material having elastically yielding walls adapted to transmit an elastic oscillation to the metallic material upon its return in non-expanded condition. In this way, the rapid expansion of the metallic material and the elastic return of the walls of the containment elements will produce oscillations that will promote the continuation of the cycle as long as heat is furnished to the metallic material.

Advantageously, the magnetic circuit may comprise an armature with two yokes and three columns with each of the yokes having a seat adapted to house in a precise manner a corresponding movable junction element in said first closed position.

Suitably, the movable junction element will have a wedge-shaped cross section to snugly fit in a seat of the respective yoke of complementary shape.

In this way also a translation of a few millimeters of the wedge-shaped element will be sufficient to create a relatively large air gap.

Advantageous embodiments of the invention are obtained according to the dependent claims.

Brief description of the drawings

Further features and advantages of the invention will become more apparent in light of the detailed description of a preferred but not exclusive embodiment of a liquid metal thermoelectric generator according to the invention, shown by way of non-limiting example with the aid of the accompanying drawing tables in which:

FIG. 1 is a side view of the generator partially broken to allow the view thereinside;

FIG. 2 is a front view of the generator of Fig. 1.

Best mode of carrying out the invention

With reference to the figures there is shown a liquid metal thermoelectric generator used to produce an electromotive force and having several applications depending on the materials used and on the systems to which it is applied, without particular limitations at least from a theoretical point of view.

As shown in Fig. 1, the generator, generally indicated by 1, essentially comprises a containment chamber 2 for at least one metallic material in liquid or liquefied state, heating means 3 for heating the containment chamber 2 adapted to transmit to the metal material at the liquid state a temperature gradient sufficient to promote the expansion thereof and the consequent increase of pressure inside the chamber 2. A transmission element 4 is also provided operatively in contact on one side with the liquid or liquefied metallic material to translate upon the expansion thereof and on the other side with means 5 for generating an electromotive force.

These latter comprise a magnetic or electromagnetic circuit 6 powered by an electric current for generating an electromagnetic field and having at least one movable junction element 7 operatively coupled to the transmission element 4 to move between a first closing position of the circuit, shown in the figures, and a second opening position of the circuit upon the transmission by the transmission element 4 of a force greater than the electromagnetic attraction acting thereon.

Following the opening of the circuit 6 produced by the movement of the movable junction element 7 a consequent reduction in the flow of the electromagnetic field will be produced which is adapted to generate the electromotive force.

In the shown embodiment, purely exemplary and not limiting the scope of protection of the present invention, the containment chamber 2 has an outer wall 8 suitably thermally insulated or made of thermally insulating material, for example plastic material, and internally houses one or more containment elements 9 of the liquid metallic material.

In particular, there is a plurality of containment elements 9 each having a tubular output portion 10 placed in fluid communication with an expansion chamber 11 in which the liquid metal flows to act on the transmission element 4.

Suitably, the output portions 10 of the tubular elements 9 will be firmly connected to the expansion chamber 11 in order to prevent disconnection during operation.

For example, the output portions 10 may present a thickening on which a flange welded on the inside of the cylinder 11 is made by plastic deformation.

The outer part of the expansion chamber 11 is welded by means of silver brazing on a bearing frame 12 that also connects the containment chamber 8 to the generation means 5 of the electromotive force.

In particular, the containment chamber 2 may be fixed to the bottom plate 13 of the frame 12 by means of a flange 14.

The tubular elements 9 will preferably have a diameter sufficiently small to withstand high pressures and ensure a more effective heat transmission.

The material used for the tubular elements 9 will be selected according to the specific liquid metallic material thereinside and to the regimes of temperature and pressure to obtain.

For example, if mercury or an amalgam thereof is used, one or more tubular elements 9 of a smaller diameter made of iron alloy, such as a carbon steel or alloy steel, may be used in view of the greater aggressiveness of mercury and of the lower conductivity and thermal expansion coefficient lower than the alkali metals, or even more expensive materials such as molybdenum.

In case alkaline metals or their alloys are used, for the tubular elements 9 materials with high thermal conductivity may be used, such as copper and copper alloys with high resistance, special beryllium-cobalt bronzes.

Preferably, the walls of the tubular elements 9 will be elastically yieldable to transmit an elastic oscillation to the liquid metal material upon its return in the not expanded condition due to the displacement of the transmission element 4 inside the expansion chamber 11.

The tubular elements 9 will act in practice as springs and their elastic oscillation, together with the magnetic attraction force that tends to bring the junction elements 7 of the circuit 6 in the first closed position, will have the aim of promoting the expansion and contraction cycle of the liquid metallic material necessary for the operation of the generator 1.

The transmission element 4 comprises a movable stem 15 having one end sealingly slidable in the expansion chamber 11 and the opposite end operatively coupled to the junction element 7 of the magnetic circuit 6.

In the shown embodiment, the stem 15 and the corresponding cylindrical sliding portion of the expansion chamber 11 will be suitably cylindrical mirror polished and made of a hard material, such as hardened special steel or carburized or nitrided steel, to ensure the coupling.

The stem 15 is connected to the movable junction element 7 through an interface and control element 16 adapted to selectively allow/exclude the contact between the two elements 15, 7.

For example, the control element 16 will be a screw and nut member operable manually or automatically to be brought into contact with the stem 15 before the operation and with the generator not working, only when the temperature in the containment chamber 2 is greater than a predetermined minimum value selected as a function of the used materials.

According to alternative embodiments, not shown, the shown transmission element 4 may be replaced by structurally different but functionally similar elements, such as springs or elastic tubular elements, closed bottom corrugated tubes in elastic metal, cup springs, ring springs, elastic membranes or similar elements which may also act directly on the movable junction elements 7 of the circuit 6.

As more clearly visible from Fig. 2, the magnetic circuit 6 has a structure of the type with three columns and two yokes connected to the frame 12, with a pair of side cores 17 formed by bundles of magnetic sheets that support respective electrical windings and a the central magnetic core 18 adapted to generate the electromagnetic field.

The magnetic field can be generated either by means of permanent magnets with high characteristics, in particular with high coercive force and high induction, through the use of neodymium magnets or other compositions based on rare earths, or alternatively by means of a winding crossed by continuous current.

According to an alternativ variant, it is also possible to use two magnets on the side cores and a winding on the central core.

The magnetic induction on the cores 17 of the windings may be maintained at lower values, for example lWB/sqm, while it will be necessary that in the yokes 19 it rises to higher values, for example 2WB/sqm or otherwise in function of the maximum levels allowed by the magnetic material used, keeping in mind that the magnetic attraction increases proportionally to the square of the induction. To this end, it is preferable to decrease the thickness of the yokes 19 instead that of the columns.

For generators with permanent magnetic core and for not high powers with intermittent operation it is not necessary to provide a cooling system of the electrical part, because the cooling takes place in a natural way, contrary to the cases in which there is provided a winding core and for high powers where it will be necessary to provide forced cooling.

Each yoke 19 comprises a pair of shaped seats 20 suitable to snulgy fit a corresponding movable junction element 7 in its first closing position of the circuit 6.

The junction elements 7 of each pairs are mutually joined to translate in a unitary way in response to a force imparted by the transmission element 4 greater than the magnetic attraction.

In particular, the junction elements 7 are rigidly connected with each other by means of an armature formed by two plates 21 and four guide rods 22 which slide with precision and reduced friction in bushings inserted in the second and third plates 23, 24 of the frame 12 for precisely guiding the upwards and downwards movement of the assembly. Conveniently, each movable junction element 7 has a wedge-shaped cross section to snugly fit in a corresponding seat 20 of complementary shape of the respective yoke 19. The wedge-shaped junction elements 7 will have flattened tip and the thickness equal to the upward shift imparted by the transmission element 4. Moreover, they may be formed by magnetic sheets joined by means of passing-through locking pins with smoothed heads slightly projecting from the side adapted to guide them in the slots formed in the inner surface of the assembly side plates of the yokes 19 having the function of limiting the stroke.

Preferably, both the inclined surfaces of the movable junction elements 7 and those of the seats 20 of the yokes 19 will be properly ground and reciprocally adapted to ensure the precise coupling between the parts.

The use of yokes 19 with low thickness will have the additional advantage of allowing the use of the wedge-shaped junction elements 7 with lower mass to have, thanks also to the use of lightweight materials for the frame 12, such as ultralight alloys, a lower inertia for the whole assembly.

In the shown embodiment, the yokes 19 are formed by three pieces joined together on the outer sides by two side bars in non-magnetic steel and through -bolts. Each of the two side pieces of the yokes formed from magnetic sheets has one end connected to the column fitted with the winding and the other end ground and inclined with the same angle of the junction elements 7 while the central piece connected to the magnetic core has both ends sloping and ground.

As for the heating means 3, a possible configuration is the one that provides for a supply conduit 25 of a hot fluid inside the containment chamber 2 so as to lick outside the containment elements 9 and to heat the liquid metallic material.

The supply conduit 25 may also comprise means for controlling the flow of hot fluid which may either be designed to control and regulate the flow of the incoming flow, for example through a solenoid valve 26, or to perform a thermal regulation through the detection of temperature of the fluid and/or inside of the containment chamber 2.

For example, means for thermal regulation wil be provided, which comprise a thermal sensor, not shown, adapted to detect the temperature of the hot fluid and which may be directly associated to the solenoid valve 26.

The thermal sensor may also be connected to the transmission element 4 to allow the contact between the stem 15 and the movable junction element 7 only with a temperature of the fluid and/or of the containment chamber 2 higher than a predetermined minimum value.

The liquid or liquefied metallic material must have a high coefficient of expansion, low specific heat at constant volume, low melting temperature, preferably below room temperature, low compressibility, high thermal conductivity, high ratio of specific heat at constant volume and pressure.

Of course, since it is not possible to find the optimal values for these parameters in a single material the choice will fall on the material having the best combination of features depending on uses.

In particular, it will be preferred metals or metal alloys which are liquid at room temperature, such as mercury and mercury amalgams, eutectic alloys of alkali metals, such as sodium and potassium as the alloy to 22% of Na and 78% of K which melts at - 11°C.

The containment elements 9 will be sized also in function of the features of the selected liquid metallic material and their material may have good properties of resistance to the aggression of these metals and high mechanical properties to withstand the severe stresses transmitted by the liquid metal.

In particular, it should have good elastic behavior and good fatigue resistance, low thermal expansion and high thermal conductivity.

From the above it appears evident that the invention achieves the intended purposes. The generator according to the invention is susceptible to numerous modifications and variations all falling within the inventive concept expressed in the accompanying claims. All the details may be replaced with other technically equivalent elements, and the materials may be different according to requirements, without departing from the scope of the present invention.

Even if the generator has been disclosed with particular reference to the accompanying figures, reference numbers used in the description and in the claims are used to improve the intelligence of the invention and do not constitute any limitation of the claimed scope.