IMPROVED THERMAL TO ELECTRICALENERGY CONVERTER

Field of the Invention

The present invention relates to the field of energy production. More particularly, the present invention relates to an energy converter unit (hereinafter sometimes simply 'converter') for converting thermal energy into electrical energy.

Background of the Invention

Currently, the most commonly used electrical energy production technologies still make massive use of fossil fuels, which are used for generating steam. The generated steam imparts rotation of movement to a turbine, the shaft of which is mechanically coupled to a rotor of an electrical generator. Upon rotation of the rotor, electrical energy is produced, the magnitude of which is a function, among other things, of the rotation of speed of the rotor and the size of the generator. Using coal, petroleum or gas for producing electricity has several drawbacks. For example, transportation of coal and fuel is expensive and raises the final cost of the electrical energy that is produced using them. In addition, using coal and fossil fuel greatly pollutes the environment. These, and other, drawbacks encourage the development and use of other alternative technologies, and in particular technologies that are based on the exploitation of energy of wind, sea waves and solar energy.

Presently existing technologies exploit solar energy in two ways. The first way involves directly heating a liquid, usually water, for, e.g., heating the interior of an apartment. According to this method, a conduit, through which the liquid (normally water) passes, is laid in a 'heat absorbing environment' where it is exposed to the solar energy. The 'heat absorbing environment' is normally a

fLat black metal platform, on which the conduit is coiled to absorb as much of the solar energy as possible. The conversion efficiency of this technology is known to be very low (usually not more than 10%).

The second way to exploit solar energy is to convert it directly into electricity. Direct Thermal to Electric Conversion (DTEG) technologies are known. Recent advances in thermal-to-electric conversion technologies such as thermoelectrics and thermophotovoltaics have demonstrated the potential for achieving high-efficiency, solid-state electric generators that could convert thermal energy into electricity. However, these technologies are very expensive, and they produce direct current, which is problematic because many electrical appliances use alternating current.

The efficiency, by which heat can be converted into electricity, is limited by the theoretical maximum efficiency of the Carnot cycle, which is known to be a cycle (of expansion and compression) of an idealized reversible heat engine that does work without loss of heat. Although the Carnot efficiencies drop as the temperature differences between hot and cold side decreases, the theoretical maximum conversion efficiencies can range from a low of about 40% to a high of about 77%, depending on the used thermal sources. However, current Direct Thermal to Electric Conversion (DTEC) technologies fall far short of Carnot conversion efficiencies and, in many cases, fail to exhibit sufficient power densities to meet requirements for many commercial applications.

It is a known phenomenon that a movement of an electrically conducting wire across a magnetic field induces an alternating electric current in the wire, which depends, among other things, on the flux of the magnetic field and on the velocity of the wire. Likewise, a flow of particles that either have a permanent magnetic moment or in which a magnetic moment can be induced

by an external magnetic field through a conduit, around which a conducting wire is coiled, can induce an alternating electric current in the wire.

In Published Co-pending International Patent Application WO2005/018626 by the inventor of the present invention, the description of which, including publications referenced therein, is incorporated herein by reference, the inventor describes a thermal to electrical energy converter based on the use of ferrofluids. Ferrofluids, which have the fluid properties of a liquid and the magnetic properties of a solid, contain tiny particles of a magnetic solid suspended in a liquid medium. A ferrofluid is a stable colloidal suspension of sub-domain magnetic particles in a liquid carrier. The particles, which have an average size of about IOOA (10 nm), are coated with a stabilizing dispersing agent (surfactant) which prevents particle agglomeration even when a strong magnetic field gradient is applied to the ferrofluid. A typical ferrofluid may contain (by volume) 5% magnetic solid, 10% surfactant and 85% carrier (liquid). Ferrofluids are commercially available. Pulses of ferrofluid are continually pushed around a closed circuit energy converter by pulses of gas. At selected locations there is a uniform magnetic field to align the permanent magnetic moments of the magnetic particles, at the same location where the magnetic field is located, the conduit through which the ferrofluid pulses moves is surrounded by a coil of wire in which an AC electric current is induced.

Theoretical calculations based on the use of ferrofluids, which are reproduced hereinbelow, demonstrate that, although the converter described in WO2005/018626 can produce electricity, the efficiency of the converter would be very low.

It is therefore an object of the invention to provide an apparatus for converting thermal energy into electricity with a higher efficiency then the conversion efficiency in conventional technologies.

It is a particular object to provide an apparatus for converting thermal energy into electricity with a higher efficiency then the conversion efficiency in previous non-conventional converters invented by the inventor of the present invention.

Other objects and advantages of the invention will become apparent as the description proceeds.

Summary of the Invention

The following meanings are given to the following terms herein: ♦ "Converter" is the term used for the magnetic fluid based closed-loop energy converter for converting thermal energy into electrical energy of the present invention.

♦ "First temperature /pressure" (Tl /Pl) is the instantaneous temperature /pressure of a Heat Absorbing Container (HAC) of the converter.

♦ "Second temperature /pressure" (T2/P2) is the instantaneous temperature /pressure of a Heat Dissipating Container (HDC), which is sometimes referred to as "condenser" of the converter.

♦ The "outlet conduit' is a conduit that conveys ferromixture from the outlet of the HAC to the inlet of the HDC.

♦ The "inlet conduit" is meant a conduit that conveys magnetic fluid and carrier gas from the outlet of the HDC (i.e. the condenser) to the inlet of the HAC.

♦ An 'activated valve' is a valve that is opened and closed by use of an actuator that can be, e.g., electro-mechanical, a mechanical, or magnetic.

The actuator can be operated by a mechanical controller (i.e., a mechanical synchronizer) or by an electronic controller (hereinafter referred to collectively as "control means"), to control the activation of the valve.

^♦ A "passive valve" is opened or closed as a result of the pressure differential on the two sides of the valve. The pressure differential required to open or close a passive valve can be predetermined by, for example, the use of a spring.

♦ A "magnetic fluid" is a liquid suspension of particles made of a material that either has an intrinsic magnetic moment or in which a magnetic moment can be induced.

♦ "Magnetic particles" are the solid component, i.e. the particles, in a magnetic fluid.

♦ "Vapor" is the gas phase of the liquid component of a magnetic fluid.

♦ A "ferrofluid" is a magnetic fluid in which the particles have an intrinsic magnetic moment.

♦ A "magnetorheological suspension" (MRS) or a "magnetorheological fluids" (MRF) is a magnetic fluid in which the particles do not posses their own magnetic moment but are easily magnetized in an external magnetic field.

♦ A "ferromixture" is the working substance of the energy converter of the invention. It is a mixture which comprises some or all of the following: magnetic fluid, a carrier gas, vapors, and magnetic particles. The exact instantaneous composition of the ferromixture at any location in the converter depends on the instantaneous temperature and pressure at that location. ♦ A "cloud" is a short burst of ferromixture that is created by the opening of a valve between a high pressure region in the converter and a lower pressure region. The cloud is propelled around the converter by the controlled differences in pressure created at predetermined times and predetermined locations in the closed loop of the converter. In the hot-to-cold part of the converter the cloud is primarily comprised of magnetic particles dispersed

in carrier gas and vapor, all of which are ejected from the HAC. In the cold- to-hot part of the converter the cloud is primarily comprised of magnetic fluid pushed out of the HDC by carrier gas.

♦ A "bullet" is one or more spatially discrete groups of magnetic particles that are formed when moving through a uniform magnetic field. The magnetic field induces the magnetic moment in a MRS, aligns the magnetic moments of the particles, and causes them to bunch together.

When moving from the HAC to the HDC ₃ the bullets are collections of magnetic particles carried along by the carrier gas and vapor. When moving from the HDC to the HAC, the bullets are comprised of magnetic fluid.

In a first aspect the invention is a magnetic fluid based closed-loop energy converter for converting thermal energy into alternating current electrical energy. The converter of the invention comprises:

(a) one or more heat absorbing containers (HAC), which absorb heat from an external heat source thereby raising the temperature and pressure of the ferromixture within the HAC;

(b) one or more heat dissipating containers (HDC), which dissipate heat to a surrounding heat sink thereby lowering the temperature and pressure of the ferromixture within the HDC;

(c) an inlet conduit and an outlet conduit connecting the HAC to the HDC to form the closed-loop;

(d) one or more reservoir containers in thermal contact with the heat sink are connected by conduits to the exit of the HDC and to the inlet conduit close to the HDC;

(e) valves for controlling the flow of ferromixture around the closed-loop;

(f) control means for activating the valves;

(g) magnetic field generation elements, which generate magnetic fields around selected sections of the inlet conduit and the outlet conduit;

wherein, when the ferromixture is transported through the selected sections of the conduits, the magnetic fields have direction and sufficient strength to induce magnetic dipoles in the magnetic particles of the magnetic fluid if necessary, to form bullets comprised of spatially discrete groups of the magnetic particles of the magnetic fluid in the ferromixture, and to align essentially all of the magnetic moments of the magnetic particles with respect to the field direction; and

(h) electricity conducting wires, coiled around the selected sections of the inlet conduit and the outlet conduit, wherein alternating electric current is induced in the coils of the wires when the bullets move through the coils of the wires.

In preferred embodiments of the converter of the invention the magnetic fluid is a magnetorheological suspension (MRS). The magnetic field generating elements are preferably permanent magnets.

Embodiments of the converter of the invention can comprise one or more bypass conduits; wherein the first end of each of the by-pass conduits is connected to a HAC through a valve and the second end is connected directly to a HDC. The converter can comprise one or more optical arrangements located at or near one or more of the valves and/or in one or more of the conduits.

In one embodiment the HAC is positioned on the top side of the wind wing of a sea wave energy converter and the HDC is installed on the bottom side of the wind wing. In another embodiment the converter of the invention is used to provide electric power to a vehicle. In the latter embodiment the heat from the vehicle's engine is the external heat source used to heat the ferromixture in the HAC and the wind is used to cool the HDC.

In another aspect the invention is a method for using the magnetic fluid based closed-loop energy converter of the first aspect of the invention to convert thermal energy into alternating current electrical energy. The method comprises synchronizing the opening and closing of the valves in the converter such as to maintain an essentially constant flow of bullets of the magnetic particles that are components of the magnetic fluid around the closed loop. In preferred embodiments of the method of the invention the magnetic fluid is a magnetorheological suspension (MRS).

In the converter the magnetic field generating elements generate magnetic fields which create the bullets, the thermal energy provides the force that moves the bullets around the closed loop, and alternating electric current will be induced in coils of electricity conducting wire wrapped around the conduits when the bullets pass through the coils.

All the above and other characteristics and advantages of the invention will be further understood through the following illustrative and non-limitative description of preferred embodiments thereof, with reference to the appended drawings.

Brief Description of the Drawings In the drawings:

Fig. 1 schematically illustrates the general layout and functionality of the converter, according to one embodiment of the present invention; - Fig. 2 schematically illustrates a layout and functionality of the converter, according to a preferred embodiment of the present invention;

- Fig. 3 (prior art) schematically illustrates a sea-wave energy converter based on a wave wing; and

- Fig. 4 schematically illustrates the sea-wave energy converter with additional wind wing.

Detailed Description of Preferred Embodiments

The energy converter of the invention is basically a closed loop device containing a medium that is capable of absorbing heat from an external heat source in a high temperature reservoir and producing AC electricity while delivering a portion of the heat to a cold temperature reservoir and then returning the medium to the high temperature reservoir. The converter comprises two half cycles - the first from a hot location to a colder one and the second from cold to hot - that are connected to form a complete cycle. This arrangement is a Carnot cycle having a very high efficiency of energy conversion. The external heat source, which provides the required heat to the converter, can be essentially any heat source. For example, the heat can be provided by a nuclear power station, from an air condition system, from a compressor, from any operating engine, or from a motor. In one preferred embodiment the heat source is solar radiation and in another preferred embodiment the heat source is a vehicle engine. In contrast to conventional industrial power plants, the present system does not use energy consuming machinery such as compressors or pumps. The working substance of the energy converter of the invention is a ferromixture, which replaces superheated steam that is usually utilized in conventional power plants to drive a turbine.

The energy converter of the invention, which will be described in detail hereinbelow, consists in its most basic embodiment of two chambers connected in series by conduits. The magnetic fluid coexists together with its vapor in a large chamber, called herein the Heat Absorbing Container (HAC), in which heat is absorbed from the external source. In order to control the boiling temperature of the magnetic fluid, a non-reacting carrier gas may be inserted into the chamber. The carrier gas must have a very low boiling temperature so that it will always remain in gas phase. Air, for example, is an appropriate

choice. When the temperature and pressure inside the HAC reach predetermined values a valve is momentarily opened to release a cloud of hot ferromixture from the HAG into the outlet conduit. By proper synchronization of the valves in the converter, as will be described hereinbelow, a valve ahead of the cloud will be kept closed, thereby causing the pressure on the leading edge of the cloud to increase causing the cloud to have a smaller volume and more sharply defined shape as it travels through the conduit. As the cloud of ferromixture is propelled around the closed-loop converter, it encounters a section of the conduit that is surrounded by a uniform magnetic field and a coil of electric wire. If the magnetic fluid is a MRS, the uniform magnetic field induces a magnetic moment in the particles and aligns them with respect to the direction of the field. In the case of ferrofluid, the magnetic field aligns the permanent magnetic moments of the particles. In both cases the magnetic field forms the magnetic particles in the cloud into closely spaced groups of particles called bullets. The aligned magnetic moments of the particles in the bullets produce an alternating electric current in the coil of electrical wire as they are propelled through this section of conduit. After passing through the region surrounded by the magnetic field, the alignment of the magnetic moments becomes random in a ferrofluid and disappears for the particles of an MRS and the ferromixture is pushed and sucked into a Heat Dissipating Chamber (HDC) in which the vapor condenses until the ferromixture comprises magnetic particles in the liquid suspension, i.e. reconstituted magnetic fluid, and carrier gas at low pressure and temperature. A quantity of magnetic fluid is then pushed by the carrier gas out of the HDC into the inlet conduit by the hotter ferromixture entering the HDC and returns to the main heating chamber, passing through a conduit that has another coil of electric wire and uniform magnetic field surrounding it, thereby producing more electricity.

The present invention utilizes the temperature differences between the HAC and the HDC and careful design of the dimensions of the outlet and inlet conduits to exploit known phenomena connected with the pressure and temperature changes that take place in fluids flowing through conduits having variable inner diameters to cause changes in the pressure and temperature of the ferromixture, as described in detail hereinbelow.

Fig. 1 schematically illustrates a simplified embodiment of the converter of the present invention, in order to describe the general layout and principle of operation of the converter. In all of the figures, the small arrows placed next to the conduits indicate the direction of flow of the magnetic particles through the conduits. Initially, i.e. at the assembly/installation stage, the HAC 101, HDC 102, and the conduits that connect them to form the closed-loop system, are partially filled with magnetic fluid and carrier gas in a ratio that is appropriate to prevent the pressure in the HAC from rising above dangerous levels. The exact ratio depends, among other factures, on the maximum temperature of the external heat source, the material of which the converter is built, and of the type of magnetic fluid. An appropriate ratio of magnetic fluid to carrier gas for most situations is thought to be about 1:4, but this ratio can be changed if necessary.

At the "start" of a cycle, HAC 101 inlet and outlet valves 107 and 104, respectively, HDC 102 inlet and outlet valves 105 and 106, respectively, and valve 117 are all in the "closed" state. Initially, if the temperature of the external heat source is not high enough, the pressure of the carrier gas in the HDC is lower than atmospheric pressure, to allow boiling of the liquid component of the magnetic fluid at lower temperatures than would have been possible at atmospheric pressure. In other cases, if the temperature of the heat source is very high, it may be necessary to make the pressure of the carrier greater than atmospheric pressure to maintain proper operating conditions in

the converter. HAC 101 and the magnetic fluid and carrier gas in it absorb heat from an external source, such as the sun, to heat the magnetic fluid and gas to a first temperature (Tl), and, at the same time, HDC 102 dissipates heat to an external heat sink, cooling the ferromixture contained therein to a second temperature (T2), lower than Tl in order to cause the vapor to return to its liquid state.

As HAC 101 absorbs heat from the external heat source, the temperature Tl of the magnetic fluid contained therein starts to increase causing the liquid portion of the magnetic fluid to vaporize and the total pressure inside HAC 101 (Pl) to increase. At the same time, the ferromixture is cooled in HDC 102 to T2 causing the vapor present in the ferromixture to condense and the pressure inside HDC 102 (P2) to decrease. In other words, the difference between the first and the second temperatures is translated into a corresponding difference in the pressure inside HAC 101 and HDC 102. The difference between these pressures is the force that will cause the magnetic particles to circulate in the closed-loop converter as described hereinbelow. The actual maximum and minimum values of Pl, P2, Tl, and T2 that will result in safe operation and maximum efficiency of the converter of the invention have to be determined for each specific embodiment of the converter. These values depend, upon many other factors on the materials of which the various parts of the reactor are built, wall thickness, etc. For example, if the HAC is made of non-reinforced glass, it is recommended to not allow Pl to exceed approximately three atmospheres.

When the pressure difference (P1-P2) reaches some predetermined value, valves 104 is opened to initiate the first half of the cycle by releasing a cloud of ferromixture comprising carrier gas, vapor, magnetic particles, and possible a small proportion of droplets of magnetic fluid into outlet conduit 118. Valve 105 can be opened essentially simultaneously with valve 104, but it is

normally preferred to open valve 105 after a short delay in order to allow the pressure inside conduit 118 to build up in front of the cloud, thereby confining the cloud to a relatively small volume within the conduit. As soon as valve 105 is opened the pressure in conduit 118 is lower than the pressure in HAC 101 and the cloud is "pushed" by the higher pressure on one side and "pulled" by the lower pressure on the other side. i.e. is propelled along conduit 118 from HAC 101 in the direction of HDC 102. As the cloud is ejected from the HAC, the pressure Pl and the temperature (Tl) inside HAC 101 decrease. When valve 105 is opened, the cloud pushes the (colder) magnetic fluid and carrier gas that were originally present in conduit 118 and in HDC 102 in the direction of closed valves 106 and 117. The cloud of ferromixture pushing against the ferromixture near the entrance to the HDC 102 compresses it causing the pressure (P2) in HDC 102 to rise. As the ferromixture is compressed and as the temperature of the part of the cloud that has reached the HDC 102 is lowered, the vapor condenses until the ferromixture near the outlet side of the HDC 102 comprises only magnetic fluid and carrier gas.

When P2 reaches its maximum value, valves 104 and 105 are closed, to complete the first half of the cycle. Then, valves 106 and 107 are opened, and the over-pressure of the carrier gas in HDC 102 relative to the pressure in conduit 120 and HAC 101, pushes the magnetic fluid through valve 106, through conduit 120, into HAC 101. When the pressure in HAC 101 equals that in HDC 102 valves 106 and 107 are closed, thereby completing the second half of the cycle.

Now, the next cycle begins, wherein: (1) HAC 101 absorbs external heat to raise the temperature of the (now) cold magnetic fluid contained therein to the first temperature Tl and pressure Pl at which part of the liquid component of the magnetic fluid is in its vapor state, and (2) HDC 102 dissipates heat to the heat sink, lowering the temperature of the (now) hot carrier gas, vapor, and

rαagnetic fluid contained therein to the second temperature T2 and pressure P2 at which most of vapor condenses, and (3) operating valves 104 to 107 as described in connection with the first cycle described hereinabove. One cycle will follow another cycle with a portion of the magnetic fluid being exchanged between HAC 101 and HDC 102 at each cycle, unless converter 100 malfunctions or it is necessary for some reason to halt the operation of the converter. In this manner, a substantially continuous train of bullets is propelled around the closed-loop converter. This flow is utilized to induce an alternating electric current in an electric wire, as will be described hereinbelow.

Electricity conducting wires 110 and 111 are coiled around conduits 120 and 118, respectively. Magnetic fluid or magnetic particles flowing through these conduits should induce electric currents in wires 110 and 111, which are connected to loads 112 and 113. However, since the particles in the magnetic fluid and the magnetic particles either have no intrinsic magnetic moment or their magnetic moments are aligned randomly (with respect to one another) in their carrier (whether a liquid or a gas, depending on the location in the converter and on the stage of the cycle), the net magnetic field of the particles is zero. Under such circumstances no current will be induced in electric wires 110 and 111. In order to produce electric current, the magnetic dipoles must be induced, if necessary, and aligned in such a way as to produce a non-zero net magnetic field moving through the coiled electric wires (110 and 111). This alignment is implemented by the use of permanent magnets 108 and 109 which are located so as to generate a constant magnetic field at sections of the closed-loop converter surrounded by the coils of wire and through which the bullets of ferromixture pass. It is to be understood, that the coils of wire 110 and 111 are shown symbolically only and can represent, for example a plurality of coils connected in series or any other arrangement suitable to meet the requirements of the invention. Similarly the alignment magnets 108 and

109 are shown symbolically only and can represent, for example a plurality of ring-shaped magnets, bar magnets, or any other arrangement known in the art for creating a uniform magnetic field in a given region. Also, there can be more than one electricity producing region located along the length of each of the conduits 118 and 120.

Magnets 108 and 109 are shown encircling conduits 118 and 120 in order to generate magnetic fields that will induce magnetic moments in the magnetic particles of a MRS and will align the magnetic moments of the magnetic particles with, such that their longitudinal axis substantially coincides with the longitudinal axis of the conduits. In this way, the flow of the magnetic particles will produce a local non-zero magnetic field that induces an electric current in electric wires 110 and 111. If a continuous stream of aligned magnetic dipoles flows through the induction coil the net electrical output will be zero. Therefore the dipoles are arranged into discrete bullets that will generate pulses of alternating electric current. In order to insure that the magnetic moments have been induced in time and to form the bullets out of the particles that are randomly distributed through out the cloud of ferromixture, at least some of the magnets are located around the conduit upstream of the induction coil. If a number of spaced apart ring magnets are used, then a series of bullets can be created from a single ferromixture cloud. As previously noted, the formation of the bullets can also be at least partially accomplished by proper synchronization of the opening and closing of valves 104 and 105 to form clouds that have a very small volume.

In order to further control the operating conditions within the converter, a reservoir container 103 is provided. Reservoir container 103 is initially partially filled with magnetic fluid and carrier gas, and it is used according to one of the following two scenarios:

(1) The cold magnetic fluid contained in the reservoir container is utilized for further cooling, during each cycle of operation of the converter, the magnetic fluid at the outlet of HDC, by opening valve 117, immediately after completing the first step of the cycle, whereby releasing cold magnetic fluid from the reservoir container 103 towards the outlet of the

HDC 102. The reservoir container is refilled with warmer magnetic fluid at the end of each cycle of operation of converter. Since the reservoir container is in thermal contact with the heat sink, the magnetic fluid within it is cooled and released at the outlet of HDC 102 in the successive cycle.

(2) In order to cause the magnetic fluid in HAC 101 be disassociated into vapor and magnetic particles before it flows through the outlet valve 104, it is essential to maintain a certain relationship between the temperature and the pressure of the magnetic fluid on both sides of valve 104. Because of possible unstable ambient conditions, the relationship must be adjustable within some known operating range. The aforesaid relationship is maintained in the following way: if the temperature inside HAC 101 decreases, the pressure in HAC 101 must be reduced such that the boiling temperature of the magnetic fluid in HAC 101 will be decreased as well, to allow it to boil at the lower temperature. The pressure in HAC 101 is reduced by reducing the overall pressure in the converter 100, by reducing the amount of ferrorαixture in the conduits. This is done by opening valve 117 allowing some of the ferromixture to enter the reservoir container 103 when the pressure in HDC 102 is higher than the pressure in the reservoir container 103. Likewise, when the temperature in HAC 101 increases, the pressure in HAC 101 must be increased as well, to maintain the aforesaid relationship. The required increase in this pressure is obtained by increasing the overall pressure in the main circuit of converter 100, by addition of at least some of the magnetic fluid and carrier gas contained in the reservoir container 103.

This is done by opening valve 117 only when the pressure in the reservoir container 103 is higher than the pressure in HDC 102, a situation that might occur essentially at any stage of an individual cycle of operation.

Normally, valve 117 should open or close in order to cool the magnetic fluid at the exit of the HDC 102, as described hereinabove in connection with the first scenario. However, if there is a need to increase or to decrease the overall pressure in the converter 100, as described hereinabove in connection with the second scenario, then the second scenario will prevail; i.e., valve 117 will operate according to the second scenario, to assure that the converter 100 operates within the preferred operating range, and, therefore, that the converter maintains the highest efficiency possible for the given ambient conditions.

A more efficient method of working with reservoir container 103 is to provide a separate outlet from the reservoir container by means of an exit pipe and exit valve inserted in the converter in the manner shown in Fig. 2. As a result, the magnetic fluid is pushed by the carrier gas through the reservoir 103 (217) in a continuous direction with warmer magnetic fluid entering at valve 117 (105) and colder magnetic fluid exiting through the additional valve (602 in Fig. 2). This would result in colder magnetic fluid being added to the flow through conduit 120 (214 in Fig. 2) than in the embodiment as shown in Fig. 1, thereby increasing the efficiency of converter 100. If reservoir 103 were connected to the converter in the manner shown in Fig. 2, then opening and closing the appropriate combinations of valves 106 (203), 117 (205), and 602 could allow either no magnetic fluid to flow into conduit 120 or could allow magnetic fluid to flow into conduit 120 (214) through either HDC 102, reservoir 103 (217), or through both of them.

Fig. 2 schematically illustrates the converter 200 according to a preferred embodiment of the present invention. HAC 101 is shown divided into two sections, Al and A2. Likewise, HDC 102 is shown divided into sections Bl and B2. Al and A2 function to create conditions for an acceleration phase (of ferromixture) inside 101. Likewise, Bl and B2 function to obtain an acceleration (of magnetic fluid) inside 102. In the following discussion of this embodiment of the converter the working fluid will be identified simply as ferromixture, where it is to be understood that the ferromixture primarily comprises magnetic fluid and carrier gas in Al, B2, reservoir container 217, and conduit 214 and the ferromixture primarily comprises magnetic particles, vapor, and carrier gas in A2, Bl, and conduits 220. In the embodiment shown in Fig. 2 the converter comprises two identical HACs 101 and 101' connected in parallel. As will be explained below, the two are utilized alternately to give a more constant output of alternating current. Alternative embodiments of the convertor envisaged by the inventor will have more than two chambers connected in series in the HAC and HDC and two or more HACs and HDCs connected in parallel.

Referring to Fig. 2, valves 202, 206, 213, and 213' are mechanical one way valves, which open and close according to the difference in the pressure on both sides of the valve. Each one of these valves can be provided with a spring, or other mechanism, to close the valve when the pressure difference on it is essentially zero, or, alternatively, the spring can be chosen to have a stiffness such that the valve will remain in the "closed" state as long as the counter (i.e., "opening") force exerted thereon is smaller than a predetermined value.

Valves 213 and 213' located in HAC 101 and HAC 101' can be one-way filters, that allow the passage of magnetic fluid but will confine and prevent the magnetic particles released by the vaporization of the magnetic fluid in section

A2/A2' of the HAC, from flowing back into section Al/Al' when valve 213/213' is open.

The activation of valves 201, 201', 205 203, 602, 204, 204', and 211 is controlled by a controller (mechanical or electronic, not shown), which is configured to respond to input signals indicative of pressures and temperatures at the relevant locations in the converter. By 'relevant location' is meant the locations at which the value of the temperature, pressure, or both pressure and temperature, is measured to activate the valves at the correct instants during each cycle of operation of the converter. There is a very large selection of commercially available pressure and temperature sensors (not shown in the figures), as well as valves and controllers, from which any person skilled in the art can choose for the purpose of the invention. The sensors and controller allow the operator to determine and change the synchronization of the opening and closing of the valves in order to achieve and maintain continuous and efficient motion of the ferromixture around the converter, even under changing conditions such as changing temperature of the external heat source or sink.

For the purpose of simplifying the description of the operation of the embodiment of the converter shown in Fig. 2, it is assumed that all the valves are initially in the "closed" state and the converter contains magnetic fluid and carrier gas at a predetermined ratio, for example the ratio of magnetic fluid to carrier gas can be about 1:4, and quantities that depend on the dimensions of the converter 200, the ambient conditions, operation frequency and desired electrical output of the converter 200. Reservoir container 217 is placed in a relatively cold place, for example, near the HDC, whereas the HAC is placed in a hotter location. Initially reservoir container 217 is also partially filled with magnetic fluid and carrier gas at ambient temperature in the same ratio.

At the beginning of the cycle, the ferromixture in A2 is at predetermined starting pressure. The starting pressure is such that for the effective

temperature, which is the sum of the ambient temperature and the temperature rise due to the accumulated heat from the external heat source, the liquid component of the magnetic fluid will vaporize. As heat starts to accumulate inside A2, the temperature of the magnetic fluid and the carrier gas inside A2 starts to increase, and therefore, the pressure inside A2 starts to increase. When the pressure in A2 reaches the predetermined starting pressure, valve 201 is opened. Simultaneously, valve 202 opens initiating a cycle of operation. As a result of the opening of these valves, a portion of the pressurized ferromixture in A2 escapes as a cloud of ferromixture through outlet conduit 220 into Bl. Valve 202 can be opened essentially simultaneously with valve 201, as described; but it is normally preferred to open valve 202 (in this case valve 202 must be a controlled valve) after a short delay in order to allow the pressure inside conduit 220 to build up in front of the cloud, thereby confining the cloud to a relatively small volume within the conduit. Because the ferromixture in the outlet conduit 220 is at relatively high pressure and is 'injected' into the elongate container Bl, a compression force is exerted on the ferromixture contained therein. Under these conditions, the temperature in Bl increases, which makes the heat dissipation phase from Bl to the heat sink more efficient.

When the ferromixture enters Bl, it contains a relatively high content of vapor. As the mixture is pushed in the direction of valve 206, the vapor of the magnetic fluid in the ferromixture gradually condenses, and, therefore, the ferromixture will contain a lower portion of gas at 206 than at 202.

When the pressure in Bl is higher than the pressure in B2, valve 206 opens to allow the transfer of ferromixture from Bl to B2, thus increasing the pressure in B2, compressing the relatively cold ferromixture in B2 until in B2 there is only magnetic fluid and carrier gas.. Valve 206 is one-way valve, which automatically closes when the pressure in B2 is essentially equal to, or greater

than, the pressure in Bl. The closure of valve 206 does not permit ferromixture to return from B2 to Bl. The closure of valve 206 sends a signal to the controller to close valve 201. Valve 202 will automatically close when the pressure in Bl exceeds that in conduit 220.

The closing of valve 206, at the instant mentioned before, sends a signal causing valves 203 and 204' to be opened. At this stage valves 203 and 204' are opened and the carrier gas pushes the magnetic liquid out of B2 and through inlet conduit 214 into Al'. In the area of the magnets 222 the magnetic fluid is formed into bullets that induce an electric current when passing through induction coil 215.

Because the ferromixture flows from relatively narrower inlet conduit 214 into a much wider container Al', its temperature further decreases (which makes the heat absorption phase in Al' more efficient). When ferromixture flows into Al', the pressure inside Al increases and additional increase in this pressure is obtained while Al' absorbs external heat. At some point, the pressure in Al' will be higher than the pressure in A2', in which case, valve 213' opens, to allow ferromixture to be transferred to A2'. At another time, the pressure in A2' will tend to be higher than the pressure in Al', which will cause one-way valve 213' to close. The closure of valve 213' indicates that one cycle of operation of the converter has been completed. The closure of valve 213' sends a signal causing valves 203 and 204' to be closed At the same time, the closure of valve 213' sends a signal that causes valve 201' to open, to start another cycle, essentially as described hereinabove.

The process now repeats itself cyclically, wherein: a portion of ferromixture is released from the first HAC and returns to the second one in the first cycle, a portion of ferromixture is released from the second HAC and returns to the

first HAC in the second cycle, a portion of ferromixture is released from the first HAC and returns to the second one in the third cycle, etc..

Reservoir container 217, permanent magnets 222, and induction wires 215 function in the same way as container 103, rings 108 and 109, and wires 110 and 111 (Fig. 1).

Reservoir container 217 is provided with a separate outlet through exit pipe 601 and exit valve 602. In this manner, the magnetic fluid is pushed through the reservoir 217 by the carrier gas in a continuous direction with warmer magnetic fluid entering at valve 205 and colder magnetic fluid exiting through valve 602. This prevents mixing of the relatively cold and warm magnetic fluid in reservoir 217 and results in colder magnetic fluid being added to the flow through conduit 214, thereby increasing the efficiency of converter 200. Opening and closing the appropriate combinations of valves 203, 205, and 602 allows either no magnetic fluid to flow into conduit 214 or magnetic fluid to flow into conduit 214 from either HDC 202, reservoir 217, or from both of them.

Safety means are provided to prevent the occurrence of the following events:

1) The pressure in A2 or A2' increases above the planned operating range. This is an indication that the ferromixture circulates with a velocity that tends to increase to progressively high levels. If the increase of velocity is not interrupted in time, then the overall pressure in the converter will increase to dangerous levels. In order to prevent this from happening, when a predetermined threshold pressure is exceeded, a controller sends a signal to open valve 211 momentarily permitting hot ferromixture to flow through by-pass conduit 221 directly from A2 into B2. Valve 211 can be used also for slowing down the operation of the converter, should the need arise for any reason, such as for routine

maintenance or to replace a malfunctioning part. For maximum effect, the end 225 of conduit 221 should be connected as closely as possible to the exit end of B2, where the magnetic fluid is at the lowest temperature. A bypass conduit from A2' can optionally also be added if necessary.

2) If valve 211 malfunctions or, if for any other reason, the pressure in the converter rises above predetermined dangerous levels then pressure safety valves 212 and 212' permit release of gas to the outside of the converter, to reduce the pressure in A2 and/or A2', respectively. Valves

212 and 212' can either be controlled by the controller or can be passively operated when the pressure exceeds the allowed value.

The high velocity of flow of the ferromixture in the converter may result in the creation of static electrical charges. In order to control the accumulation of such charges, it is essential that the relevant components of the converter be connected to the earth, to allow discharging charges to the earth. An exemplary connection is schematically shown in Fig. 2, by reference numeral 224.

In another embodiment of the invention, optical elements 604 are provided to focus solar radiation inside the outlet conduit 220. The light is focused through a window in the wall of the conduit. The window can be provided with an electrically or mechanically activated shutter. The shutter can be opened and closed either totally or partially and can be operated in several different modes, for example, opened completely when valves 201 or are 201' open, and closed completely when these valves close. Such an optical arrangement will add additional heat to the ferromixture in the outlet conduits, increasing the temperature, pressure, and velocity of the clouds and bullets moving in the conduits. Since the electric current generated in the coils 215 depends, upon

other factors on the velocity of the magnetic particles, the optical arrangements will increase the output of converter 200.

In another embodiment, the activated valve (201) connected to the first outlet of the HAC 101 and the valve (201') connected to the outlet of the HAC 101' are each provided with an optical arrangement, (201/1) and (20171), respectively, for collecting light rays and for focusing the collected light rays such as to raise the temperature of the ferromixture as it passes through the valve. The optical arrangement is arranged such that the focused light rays pass through the opening in the corresponding valve and the location of the corresponding focal point changes with the movement of the respective valve such that light rays are focused on the entrance to the valve whenever the valve is in the "open" state, and dispersed or blocked otherwise.

The design of an appropriate optical system, which preferably includes a heliostat, is within the ability of skilled persons and will not be further described herein. In addition reflectors can be used to concentrate the energy from the external heat source on critical elements of the converter such as the HAC 101 or HAC 101'.

The high velocity of the magnetic particles present in the ferromixture clouds and magnetic fluid that move through the conduits of the converter might cause mutual erosion of both the magnetic particles and the interior surfaces of the conduits and the valves through which the magnetic particles pass. One way of minimizing the erosion is to create external magnetic fields to guide the particles to assure that they are forced by the magnetic field to form a narrow beam that does not contact the sides. Such a solution could be employed for protecting particularly vulnerable regions of the converter such as the valves.

In the embodiment shown in Fig. 2, Bl and B2 (i.e., the HDC) can be effectively cooled by spraying thereon water, and by rapid evaporation thereof. The evaporation process is preferably made more efficient by utilizing wind. In International Patent Application WO 2005/065024, the inventor of the present invention describes an energy converter unit (a "sea wave converter") that converts the energy of sea waves and wind into electrical energy. The sea wave converter consists of a first wing ('wave wing'), to engage the sea waves, and a second wing ('wind wing') to engage the wind. The sea wave converter, the detail structure and functionality of which are described in the above referenced PCT application, is schematically illustrated in Figs. 3 and 4, which are described hereinafter.

Referring to Figs. 3 and 4, the sea wave energy converter includes a first (i.e., a wave) wing 301 and a second (i.e., a wind) wing 401 (Fig. 4). Only the wave wing 301 is shown in Fig. 3, for simplicity. The wave energy converter comprises, in addition to the aforesaid two wings, a wing trailing edge supporting means 402, pivotable flap 403, to which a flap weight is connected (404), and pivot supporting means 405, for pivotally supporting the leading edge (the edge facing the wave side) of wing 401. Pivotable flap 403 comprises an airfoil 403/A and a hydrofoil 403/H sections, which form a fixed angle η. Wing 401 is longitudinally located along the wing 301, and it is structured to resemble a typical wing of an airplane and is intended to function as such. Wing 401 is preferably structured to be as light as possible, such as by using light and resilient materials (metal and/or plastics) and, optionally, by leaving hollowed cavities therein, to obtain as much elevation force as possible. However, if desired, the mass of wing 401 can be made heavy enough to return wing 301 from any position to its rest (i.e., horizontal) position. The energy of the wind is translated, by use of wing 401, to an elevation force that is added to the force generated by the energy of the waves, which is obtained by use of wing 301. The combined force, i.e. the sum of the wind force and wave force,

displaces wing 301 more efficiently. The result of this is a larger electrical energy at the output of the converter.

In Fig. 3, reference numeral 300 denotes a buoy that floats on the surface of the sea to support sleeve 304 and wing 301. Wing 301 is shown comprising a plurality of wing cells, such as wing cells 312, which form a honeycomb -like structure. Reference numeral 314 denotes a pivotable sleeve, which is rigidly connected to (wave) wing 301 and contains electricity generation means that generate electricity as a function of the displacement of wing 301, relative to the horizon, which is caused by the motion of waves. Each wing cell 312 has a wide opening 305 that is directed to a direction substantially perpendicular to the plane of the wing, such that, whenever wing 301 is in its rest, i.e. normal or horizontal, position, the wide openings of the wing cells face the water side and are fully immersed in the body of water. Each wing cell includes also a narrower, elongate, passage (a 'vent' opening, 304), that connects the interior 310 of the wing cell to the atmosphere (306) in the opposite side of the wing. Therefore, whenever wing 301 is in horizontal position, the water 'pushes' the air locked in the interior 310 of the wing cells through the respective vent opening 304, whereby to allow to the interior 310 of each wing cell to be filled with water. Only four wing cells are shown in Fig. 3 (312), for simplicity. The honeycomb -like wing cells are arranged such that the closer the cells to the sleeve 314, the larger is their interior space, and therefore, the larger their water-holding capacity.

The energy converter of the present invention can be incorporated into the energy converter shown in Fig. 4 by installing the E-AC 101 on the upper side 401 of the "wind wing" (401), i.e., the side normally facing the sun; thereby using the energy of the sun to heat the interior of the HAC. The HDC 102 is installed on the lower side of the "wind wing" (401), thereby utilizing the spray of the water, which surges upwards, essentially vertically, through the Vent'

openings 304 in the honeycomb-like wave wing, to cool the HDC 102 and, the ferromixture contained within it.

In a preferred embodiment, the energy converter of the invention is used to provide electric power to a vehicle. In this embodiment, the heat from vehicle's engine is the external heat source used to heat the ferromixture in the HAC and the wind is used to cool the HDC.

Converters having much more complex designs than those shown in the figures are contemplated by the inventor. These embodiments would have multiple HACs, HDCs, reservoir containers, and especially more induction coils. All would be connected by conduits to contribute to the overall electrical output of the converter. Skilled persons would recognized that as in the simpler embodiments described herein, careful attention must be given to designing the dimensions of the components of the converter and planning and controlling the operating parameters in order to assure that the output of the induction coils is in phase to give a stable AC output.

Estimate of efficiency of energy conversion of the converter of the invention

The cycle efficiency of a heat engine is, following standard convention,

where Wcyc is the mechanical work done for a cycle and Qcyc is the heat added to the working substance during the cycle. It is well known that the simple cycle of any heat engine is less efficient than a Carnot cycle operated over the same temperature extremes. The efficiency of a Carnot cycle is

T - T Ic =\^ (D

where Ts is the highest absolute temperature of a heater and Ti is the lowest absolute temperature of a cooler.

Ferrofluids prepared on the base of organic carriers and stabilized (against aggregating) by hydrocarbon chains, e.g. by oleic acid, should not be heated to a temperature exceeding T2 = 130C, while for silicone-based ferrofluids it must be T2 < 200C. Then, taking the lowest temperature Ti - 25C, the Carnot efficiency for organic ferrofluids

and for silicone-based ferrofluids

_{7c =} 200 - 25 _{= 3?%} ^c 200 + 273

Equation (1) determines the efficiency of an ideal cycle. At perfect regeneration, an efficiency of conversion of heat into mechanical work may reach in principle the Carnot efficiency equation (1). Then the actual efficiency η of the cycle can be represented by a product where η _w→e is the efficiency of conversion of mechanical work into electricity.

We will now estimate 77 _w→e by considering two phase ferromixture, i.e. air- ferrofluid, flow through a conduit of diameter d = lcm. The fluid is magnetized in the field H created by the system of permanent magnets within an area of length I = 5cm, while the magnetic susceptibility of the gas phase is negligible. Then crossing the magnetic field, ferrofluid "bullets" generate in an induction coil an electromotive force S. The latter can be calculated from the expression

_{fi =} _I. *^ _J φ = BSN , (3) c dt

where c = 3 x 10 ¹⁰ cm/s is the speed of light, φ is the magnetic flux,

B(t) = H+ 4πM(t) (4) is the flux density (magnetic induction), S is the conduit cross-section, and JV is the number of turns in the induction coil.

The ferrofluid magnetization M is described well by the Langevin formula

M = nmL(ξ), L(ξ) = cothξ - l/ξ , (5) where n is the number density of magnetic grains, m = MbV is the magnetic moment of a single grain (Mb is the bulk magnetization of dispersed ferromagnetic particles and V is the particle volume), L(ξ) is the Langevin function, and ξ = mH/kbT is the Langevin parameter.

In the case under consideration, the number density of the grains may be described as a running wave propagating along the conduit axis: n(x,t) = ¹ An[I + sin(fex - at)] ; (6) here k and ω are expressed through the wavelength λ and the wave frequency / by the relations k = 2π/λ, ω = 2π/.

Substituting from Eqs. (4) - (6) into Eq. (3) yields

ε = ^J- φM _b L(ζ)SNf cos(fcc - ωt) . (7) c

Averaging this relationship over the length I of the induction coil gives

(s) (8) where φ — the volume fraction of magnetic grains in a ferrofluid.

First Estimate

In order to estimate the amplitude of ε ₀ of the electromotive force, we assume the following parameter values:

— temperature of ferrofluid in the coil T = 50 C,

- bulk magnetization at this temperature Mb = 460 G (magnetite Fe3O4),

- diameter of magnetic particles dp = 10 nm,

- concentration of these particles φ = 30 %,

- the conduit diameter d = 1 cm, - mean fluid velocity in the conduit u = 5 m/s,

- frequency f = ω/2π = 50 Hz ,

- length of the coil 1 = 5 cm ,

- winding number N = 1000 ,

- magnetic field strength into the coil H = 740 Oe. From here it follows that λ = u/f= 10 cm, so that jd/λ = π/2, hence one has in Eq. (8)

—sin— = 0.6366.

Ji λ

Substituting the above values in the definition of the Langevin parameter ξ = mH/kbT gives ξ =4, thus we find L(4) ~ 1- 1/4 = 0.75. Finally we find from (8) Sb = 1.02V. (9)

Let a winding of the coil be implemented out of six layers of copper wire of diameter δ = 0.3mm. Then the length of the wire is

/ι = π(d + 6<5)iV~ 37M so its resistance

The coil possesses an induction L leading to some inductive resistance ωL/c ² . However, the latter may be neutralized by means of inserting into the electric chain a capacitance C satisfying an equality

ω ¹ C ^ω c ^l2 ' Le, ' C = 4 ϋ, ² Lτ- (H) Then the electric current J(t) does not lag behind the electromotive force (8) and equals

J(t) = _£ ^o — _C osωt , (12)

where Rex is an external load. Thus the useful electric power P(t) = Averaging over the period of the current oscillations gives

This value reaches a maximum at R _&x = Ei _n ≡ R:

Substituting from (9) and (10) into (14) gives

P _maK = 0.025W , (15) while the total power Pel produced in the electric chain is twice P _max , i.e. Pel =

0.05W.

To obtain such an amount of electric power, one must expend a certain amount of mechanical work. First it is necessary to provide the ferrofiuid mass flux over the pipe through the inductive coil. Let us estimate the necessary power.

At the wavelength λ = 10cm, each ferrofiuid bullet represents a cylinder of diameter d = lcm and length λ/2 = 5cm, so the bullet volume Vb = πd ² λ/8 = 3.93cm ³ . The density of magnetite pm ⁼ 5.15gm/cm ³ , hence for φ = 30% the ferrofiuid density is about p = 2.2 gm/cm ³ . Thus, each ferrofiuid bullet has mass XW ₀ — 5m /s, this bullet possesses kinetic energy

_{£b =} ^L. = 1.08 χ l O ⁶ erg. (16)

Similar bullets follow one after the other with frequency / = 50Hz. Therefore, to provide these bullets with the kinetic energy (16), one must expend power p _khy = _Sh f = 5.4 χi07 _e rgs/s = 5.4W. (17) In addition, a certain amount of mechanical energy is consumed to overcome factional forces. The rate of energy dissipation is

where η is the ferrofluid viscosity. For the case under consideration, one can assume a Poiseuille pipe flow with the velocity v(r) = 2 _M (l - r ² /r ₀ ² ), (19) where u = <u(r)> is the mean fluid velocity and ro = d/2. Substituting v(r) from (19) into (18) and integrating over the conduit volume gives,

P _dis = - ^• ^Y- - 2π)r ³ dr = 4πηu ² L ; (20)

where here L is the conduit length. Note that, for a given mean velocity u, the power (20) does not depend on the comduit diameter. For u = 5m /s, L = 20cm and η = IPs, one gets from (20) Pdis = 6.3W. Adding this energy loss with Pkin from (17) and the total electric power P _e \ = 0.05W, we obtain the necessary mechanical power p _mech = 5.4W + 6.3W + 0.05W = 11.75W (21)

So, from (15) and (21) it follows that the efficiency of conversion of mechanical energy into useful electric energy is extremely low:

i7 _™ = γp| = 0.21% . (22)

Thus the total efficiency is negligible: η = η _c x η _w→e = 0.26 x 0.0021 = 0.055% (23) for organic ferrofluids and η = 0.37 x 0.0021 = 0.078% (24) for silicone-based ferrofluids.

Second Estimate

In this example we change some of the fluid and design parameters. Let the ferrofluid contain φ = 40% of magnetic grains and bullets of the fluid move through a conduit of diameter d = 0.6cm with velocity u — 4.8m/s and high frequency /= 400Hz. For this case the wavelength λ — u/f ^~ 1.2cm. We assume

the length of the induction coil is I = λ/2 and the number of windings is N = 500. Then we find from Eq. (8) £&=1.96V, which is about twice £& from (8).

In order to have N = 500 with coil length I = 0.6cm, the winding must have 25 layers. Hence with wire diameter δ = 0.3mm, the mean diameter of the coil winding is d = d + 2SS = 1.35 CXΆ, thus the length of the wire equals h = 7vdN = 21.2 m. The resistance of the wire JSi _n =SOQ and hence the maximum useful power is The mass of a bullet is now nib = pV\ _> = 0.42g (here p = 2.46g/cm ³ and Vb - 0.17cm ³ ) so the required kinetic energy [see Eq. (17)] is ^p _k i _n = -m _h u ² f = 1.92x lO ⁷ ergs /s = 1.92 W,

and, instead of (20) one finds Summarizing, the mechanical power required is + 7.2W + 0.32W = 9.44W. (26)

From (24) and (25) it follows

'~ -ISγ- ^1λ9 *- ⁽²⁷⁾

This is eight times larger than the efficiency (22), but the resulting efficiency is still negligible: η = η _c x η _w→e = 0.26 x 0.0169 = 0.44% for organic ferrofluids and

7 = 7 _C ^x 7 _w→e = °- ^{37 x} °- ⁰¹⁶⁹ = °- ^63% for silicone-based ferrofluids.

Substitution of a MRS for a Ferrofluid

The above results compelled the inventor to search for a replacement of the weakly magnetic ferrofluid by a more strongly magnetic fluid that could serve as the working substance for the converter. As general guidelines, the higher the temperature at which the magnetic fluid can be kept in its fluid state, the higher the maximum allowable temperature at which the system can operate, therefore, in the search for a material which will lead to an improvement in the efficiency of the converterTa material which can be heated to higher temperatures than ferrofluids should be chosen. Also the efficiency can be improved by using magnetic particles with a higher magnetic moment.

Such matter exists and is known as a Magneto-Rheological Fluid (MRF) or a Magneto-Rheological Suspension (MRS). MRSs are suspensions of magneto- soft particles (usually iron or nickel) grains whose diameter d~ 5 to lOμm which is about 500 to 1000 times the diameter of magnetic grains used in ferrofluids. These course magnetic grains are used in practice for polishing, visualization of domain boundaries, in magnetic clutches, braking mechanisms, etc. The technical applications of MRSs are based on their property of congealing under the influence of a magnetic field. In contrast to sub-domain magnetic grains of ferrofluids the large particles of a MRS do not possess their own magnetic moments, but they are easily magnetized in an external magnetic field. The magnetic permeability of multi-domain iron or nickel particles is μ ~ 10 ⁴ .

Magnetic permeability μ of a composite consisting of two components whose permeability are μi and μ% — where one of the components is a matrix and the other is presented in the form of spherical inclusions into the matrix — can be described in terms of the Effective Medium Theory (EMT). Proposed by Bruggeman in 1935, this theory is widely used for the calculation of the

dielectric constant ε for composite materials. Replacing in the EMT the dielectric permeability a by the magnetic one μι, we arrive at the expression

μ _x + 2μ(H- μ ₂ + 2μ-e-rt-o. (28) where φ is the volume fraction of the first component. Let this component be strongly magnetic, μ\ = μ»l, while the matrix is nonmagnetic, μ%= l. For this case φ = 50% and the last equation yields/} « μ/4 » 1. For iron (99.95% pure) 10,000 < μ < 200,000 and for Superpermalloy 100,000 < μ < 1,000,000.

The magnetization of a cylindrical magnetic bullet in an external magnetic field Hex directed along the axis of symmetry of the cylinder is M= χH, where χ — (μ ~ l)/4/r is the magnetic susceptibility of the MRS,

H= H _βx - 4πN _ά M (29) is an internal magnetic field, and Na is the demagnetization factor along the axis of the cylinder. Substituting M = χH into (29) determines the internal magnetic field

H = ^a

1 + 4πχN _d so the magnetic induction takes the form

B = H _ex + 4πM = H _ex + ^ ^πχE∞ . (30) ^a l + 4πχN _d

The magnitude of the demagnetization factor of a cylinder is well described by the formula

where d and I are the diameter and the length of the cylinder respectively. Assuming d = 0.6cm and I = 5cm, we find from (31) Na = 7.123xlO- ³ . Substituting from here and using 4πχ = {μ/4-l) in (30) and taking into account that μ~10 ⁴ reduces Eq. (30) to

B = H _{6x +} ^ = H _{3x +} IAOAH _n . (32)

Making allowance for alternation of magnetic bullets and portions of gas with the frequency ω = 2π/, one should rewrite (32) as

B = Hex +70.2[l+sin(/2x-fi#)] = 71.2H _ex sin(/ex-arf) (33) Thus instead of (8), we find now

140.4^ ^" ( λ . τdλ _{ττ Oλr /O} . _N ε ₀ = ^J - ■ — sin- IH _6x SN . (34)

C \M λ J

For I = λ/2 = 5cm, /= 50ηz, Hex = 1000Oe, and N = 1000, one obtains [using Eq. (9)] ε ₀ = 39.7W. (35)

With a wire diameter δ= 0.6cm, the winding should have 12 layers, therefore the length of the wire h = π(0.6+0.06xl2)1000cm = 41.5m. Hence the resistance of the coil is

λ _fc = 10-^ = 1.470.

TZO Thus if an external load i2 _e χt is equal to the internal one, the useful electric power [using (15) and (25)] will be

A magnetic bullet of density p = 4.3g/cm ³ and volume Vb = 1.41cm ³ has mass mb = 6.063g. Moving with velocity u = 5m/s, it has kinetic energy £b — 7.58xl0 ⁵ erg, thus the required power

Pkin = £b _/ = 3.8xlO ^? erg/s = 3.8W.

The energy dissipation rate due to the MRS viscosity is determined above by Eq. (20). For η = 2ps one gets Adding JW, Pdis, and two times P _max ; we find the total power which should be spent for the electricity production: Ptot = 284.4W. Hence we obtain

"- ⁸⁸ ^r ⁴⁷ - ¹ * ⁽³⁷⁾

In contrast to ferrofluids, there are no known limitations for heating MRS. Therefore, taking the temperature of the heat absorbing chamber at T2 = 250C or T2 = 400C and the temperature of the heat dissipating chamber at T ₁ = 25C, one gets respectively the Carnot efficiency

250-25 .... 400-25 _ „ . , _ocA η, = = 43% or η _r = = 56% . (38) ^c 250 + 273 ^c 400 + 273

Thus for a final efficiency η = η _c x η _w→e , we find from (37) and (38) η = 0.471 x 0.43 = 20.2% or η = 0.471 x 0.56 = 26.4%. (39)

Comparing the results obtained in Equations (23) and (24) with those in Equation (39) we see that the total efficiency obtainable by using an MRS as the working medium of the thermal to electrical energy converter is greater than that obtainable using a ferrofiuid by a factor of 300-400. For this reason an MRS is the preferred magnetic fluid that is used in the converter of the invention.