Centrifugal energy conversion device

Abstract

A thermodynamic energy conversion device based on different centrifugal forces acting on compressible fluid at different temperatures is provided for the use either as a heat engine or as a heat pump.

Description

Centrifugal Energy Conversion Device Technical Field The present invention relates generally to thermodynamic energy conversion devices and methods of their operation. In particular, this invention pertains to conversion devices, which make use of centrifugal force acting upon compressible working fluid. Background Thermodynamic energy conversion devices, which transform thermal energy into other forms of energy like mechanical or electrical and vice versa are well known from the prior art. A combustion engine working according to the Sterling cycle is an example of such a device transforming heat into mechanical energy. If the Sterling cycle is applied in reverse direction, the same engine can be used as a heat pump, which is a device converting lower-temperature heat into higher-temperature heat with an excess of applied work; the work being mechanical in this example. The fundamental principle of thermodynamics states that the coefficient of performance of any heat engine or heat pump can not be higher than that of a similar idealised device working according to the Carnot cycle. Therefore the thermodynamic energy conversion devices are usually rated as to their effectiveness, which is the ratio of the actual coefficient of performance to the coefficient of performance of the corresponding Carnot device. In theory a thermodynamic energy conversion device working according the Sterling cycle may have the highest possible effectiveness. The essential component of the Sterling engine, which allows to attain such effectiveness, is heat regenerator. It recycles heat, released when the engine working fluid is cooled down, for heating the working fluid up at the next stage of the cycle. As a result, the whole thermodynamic process of the heat engine involving working body and heat reservoirs remains isentropic or reversible, thus guaranteeing the maximal effectiveness. Despite being potentially good candidates for an efficient thermodynamic energy conversion device, the existing Sterling engine embodiments have several drawbacks, which limit their application. In particular, they are quite large for the amount of power that they produce, i.e. they have low specific power. In principle, the specific power of a Sterling engine could be increased by increasing pressure of the working fluid inside the engine, but such solution would create additional challenges because it is difficult to provide adequate seals around the engine pistons for keeping the working fluid inside the engine. Yet another drawback of a typical Sterling engine embodiment is relative complexity of its construction. Such drawback was partly eliminated in the United States Patent No. 9,086,013 B2, which proposes using rotors instead of pistons for reducing size and complexity of the engine. Another category of efficient thermodynamic energy conversion devices is represented by the centrifu- gal heat pumps. The early United States Patent No. 2,393,338 proposes theoretically highly efficient but impractical embodiment of such a device. In this device compressed gas like air is introduced into a U-shape tube which is rotated at high angular speed. While the gas moves radially outwardly from the axis of rotation it is compressed and heated by the centrifugal force created by the rotation. During this movement it is cooled by means of water flowing in cooling coils around the tube so that the temperature of gas remains substantially constant. While travelling along the axis of rotation the gas is unaffected by the rotational motion. However, while moving radially towards the axis of rotation the gas expands and becomes substantially cooler. The cold gas then flows out of the tube and can be used for refriger- ation. In theory, the thermodynamic cycle of such heat pump approaches a true Carnot cycle and thus is highly efficient. However, the heat pump operation requires separate mechanical gas compressor and troublesome gas seals around the tube inlet and outlet. To some extend this problem was resolved in the United States Patent No. 3,791,167, where movement of a working fluid along the U-shaped passages is provided by two coaxial rotors. When the working fluid moves radially outwardly in the first rotor it is compressed and heated by the centrifugal action of the rotor. Then the working fluid moves through a heat exchanger at a periphery of the first rotor and gives away some heat to a heat transfer medium. After this heat transfer the working fluid enters into passages of the second rotor, where it moves towards the rotor centre with decreasing temperature and density. The work required for rotating the first rotor can be partly recovered using the second rotor, providing it rotates at a lower speed than the first rotor. However, such work recovery is similar to work production by a radial turbine and is exposed to stage losses. Yet another disadvantage of this solution is the need for continuous flow of the working fluid through the heat pump. Making closed loop for the working fluid would require special seals around the first rotor inlet and the second rotor outlet. An energy conversion device with effectiveness approaching the effectiveness of the idealised Carnot device would be of high importance for the renewable energy applications. For example, photovoltaic cells can convert into electricity only visible and near-infrared parts of the sunlight spectrum, thus using about 30% of the available energy. An efficient thermodynamic energy conversion device can potentially deliver more electrical energy by utilising the whole sunlight spectrum including the ultraviolet and far-infrared radiation. Providing the sunlight is concentrated and transformed into heat energy at temperature about 1200K, said device can convert into electricity up to 75% of the sunlight energy. Another example of such device application would be conversion of geothermal energy into electricity. In turn, using the device as efficient heat pump can reduce energy consumption in general, thus making contribution to the green energy initiatives. Therefore an objective of the present invention is to provide simple, compact and efficient thermody- namic energy conversion device, e.g. for renewable energy applications. Statement of Invention It now has been found that different centrifugal forces acting upon hot and cold compressible working fluid in a rotating frame of reference can in appropriate device be used for efficient conversion between heat and mechanical or electrical energy. In particular, said device can operate as a heat pump by transferring heat from lower-temperature source to higher-temperature sink at a cost of added mechanical or electrical work, or it can operate as a heat engine by transferring heat from higher-temperature source to lower- temperature sink with a benefit of producing mechanical or electrical work. Thus, according to the present invention there is provided a centrifugal energy conversion device comprising: a main rotor supported for rotation within a housing; at least one secondary rotor disposed within said main rotor and supported for rotation relative to the main rotor around an axis, said secondary rotor axis being located at radial distance from the axis of the main rotor; means for rotating the main rotor; means for energy transfer between rotating frame of reference associated with the main rotor and stationary frame of reference associated with the device housing, said energy transfer means being in communication with rotational energy of the secondary rotor; a cold heat transfer medium disposed around the secondary rotor, said cold heat transfer medium being in thermal communication with a lower- temperature heat reservoir; a hot heat transfer medium disposed around the secondary rotor, said hot heat transfer medium being in thermal communication with a higher-temperature heat reservoir; means separating said cold and hot heat transfer media; at least one working body assembly disposed within the secondary rotor at radial distance from its axis of rotation, said working body assembly comprising: a cold heat conductive container being in thermal contact with the cold heat transfer medium; a hot heat conductive container placed at azimuthal distance from the cold container, said hot container being in thermal contact with the hot heat transfer medium; a compressible working fluid disposed within said cold and hot containers; a passageway connecting said cold and hot containers for moving working fluid between the containers. In a further aspect of the present invention there is provided a method of operating said energy conversion device as a heat engine, the method comprising: rotating main rotor for creating sufficient centrifugal force acting on the working body assembly, such that the maximal ratio between centrifugal and thermal energy related to one molecule of the working fluid is at least 0.1 and preferably is above 1; adapting the temperature differential between the higher-temperature and lower-temperature heat reservoirs above a critical value such that the secondary rotor rotates in the azimuthal direction from hot to cold container; transferring rotational energy of the secondary rotor from rotating to stationary frame of reference as the device output energy. In a further aspect of the present invention there is provided a method for operating said energy conversion device as a heat pump, the method comprising: rotating main rotor for creating sufficient centrifugal force acting on the working body assembly, such that the maximal ratio between centrifugal and thermal energy related to one molecule of the working fluid is at least 0.1 and preferably is above 1; transferring sufficient device input energy from stationary to rotating frame of reference for rotating the secondary rotor in the azimuthal direction from cold to hot container with angular speed above some critical value, such that the heat starts moving from the lower-temperature to higher-temperature heat reservoir. Optional Features In a further embodiment of the first aspect there is presented a centrifugal energy conversion device, in which axes of the secondary and main rotors are mainly parallel. In a further embodiment of the first aspect there is presented a centrifugal energy conversion device, in which the main rotor contains multiple secondary rotors positioned symmetrically relative to its axis of rotation. In a further embodiment of the first aspect there is presented a centrifugal energy conversion device, in which the secondary rotor has multiple working body assemblies positioned symmetrically relative to its axis of rotation. In a further embodiment of the first aspect there is presented a centrifugal energy conversion device, in which the compressible working fluid is xenon. In a further embodiment of the first aspect there is presented a centrifugal energy conversion device, in which the cold and hot heat transfer medium is air. In a further embodiment of the first aspect there is presented a centrifugal energy conversion device, in which the passageway connecting cold and hot containers in the working body assembly is thermally isolated from the containers and comprises a heat regenerator. In a further embodiment of the first aspect there is presented a centrifugal energy conversion device, in which the cold and hot containers in the working body assembly contain metal wire mesh or metal open cell foam for facilitating heat exchange between said containers and the working fluid. In a further embodiment of the first aspect there is presented a centrifugal energy conversion device, in which the energy transfer means between rotating and stationary frames of reference is realised as a gear transmission linking rotation of the secondary rotor with rotation of the main rotor. In a further embodiment of the first aspect there is presented a centrifugal energy conversion device, in which the energy transfer means between rotating and stationary frames of reference is realised as an electromagnetic transmission linking rotation of the secondary rotor with electric motor or generator attached to the main rotor and passing electrical current of said motor or generator to and from the stationary frame of reference. Brief Description of Drawings The invention will now be described solely by way of example and with reference to the accompanying drawings in which: Figure 1 shows density distribution of compressible fluid in potential field of centrifugal force (a) and ratio of total centrifugal forces acting on fixed amount of the compressible fluid (b) at different temperatures, Figure 2 shows schematic representation of an exemplary device with the sectioned housing, Figure 3 shows schematic block diagram illustrating thermodynamic cycle attributed to a single working body assembly, Figure 4 shows the centrifugal force torque (a), the work, that the torque creates (b), and the propor- tion of heat, which the working fluid receives from the higher-temperature heat reservoir (c) as functions of azimuthal angle between directions to the axis of the main rotor and to the working body assembly measured from the axis of the secondary rotor, Figure 5 shows variant of the working body assembly, where passageway is thermally isolated from the hot and cold containers and comprises a heat regenerator, Figure 6 shows alternative device embodiment, where the gear transmission is replaced by an electro- magnetic transmission. Detailed Description The working principle of presented centrifugal energy conversion device is based on difference in cen- trifugal forces acting on fixed amount of compressible fluid being at different temperatures. Indeed, the momentum equation of fluid dynamics stipulates that stationary density of compressible fluid in the potential field of centrifugal force at radial distance r is defined by the formula 1) _ muw?r? P= poexp %T )° ‘where pg is fluid density at the axis of rotation, w is angular speed, r is the radial distance, T is the fluid temperature, m is molecular mass, and k is the Boltzmann constant. For fixed amount of fluid contained within the radial interval [0, R] the density distribution normalised on axial density taken at temperature of the lower-temperature heat reservoir, po(T.), can be calculated as -1) XP / 7 (eo a € Prnorm = p / po(Tp) = ———, (2) 1) (ea / T — Ti where 7 = T / T, denotes ratio between temperatures of the higher-temperature T}, and lower-temperature T. heat reservoirs, a = (mw?r?) / (2kT.) is the ratio between centrifugal and thermal energy related to one molecule of fluid, and x = r / R is radial distance normalised on R. Figure 1(a) depicts density distributions calculated according to this formula for two values of 7, 1.0 and 4.0, and for a = 1, which is typical for this device. At small x the dashed line corresponding to 7 = 4.0 goes above the solid line corresponding to 7 = 1.0, thus demonstrating, that fluid moves closer to the axis of rotation as the temperature increases. Since centrifugal acceleration, w?r, decreases towards the axis of rotation, the total centrifugal force decreases with the fluid temperature. Figure 1(b) shows ratio of total centrifugal forces at temperatures 7. and 7}, which can be calculated as eal / m=D (ex _1)(ya — VTD(y / a / 7)) F(Ty) / F(T,) = ——————————— (3) (e2 / ™ — 1)(y / a — D(V / a)) where z D(z) = = [ er dy 0 is the Dawson function. The dotted, solid and dashed lines correspond to a = 0.5,1.0, 5.0 respectively. As it can be seen from the plot, the difference in forces acting on cold and hot fluid may reach 3% 15%, providing 7 = 4, or T, = 300K and T}, = 1200K. A schematic representation of an exemplary device with the sectioned housing is shown in Figure 2. In this embodiment, the device has main rotor 1 supported for rotation within housing 2. The main rotor 1 contains two secondary rotors 3 positioned symmetrically relative to its axis of rotation. The secondary rotors 3 are supported for rotation relative to the main rotor 1. In Figure 2, the axes of rotation of the secondary rotors 3 are located at radial distance and directed parallel to the axis of rotation of the main rotor 1, though in other examples the axes of the secondary rotors may not be parallel to the axis of rotation of the main rotor. The rotational support for the main 1 and secondary 3 rotors can be provided by appropriate bearings not shown in the plot. While only two secondary rotors are shown in Figure 2, the device may have any number of secondary rotors (one or more), and where those secondary rotors are not disposed in a balanced way around the main rotor, may comprise additional components to balance the main rotor. The main rotor 1 can be rotated relative to the housing 2 by means of an electric motor 4. The gear transmission comprising gears 5 and 5’ links rotation of the secondary rotors 3 with rotation of the main rotor 1, thus providing means for energy transfer between rotating frame of reference associated with the main rotor 1 and stationary frame of reference associated with the housing 2. Indeed, since the gears 5 are attached to the secondary rotors 3 and the gear 5’ is fixed to the housing 2, rotation of the secondary rotors 8 causes rotation of the main rotor 1, and vice versa rotation of the main rotor 1 causes rotation of the secondary rotors 3. The secondary rotors 3 are surrounded by a cold heat transfer medium 6, which is in thermal com- munication with some lower-temperature heat reservoir 7, and by a hot heat transfer medium 8, which is in thermal communication with some higher-temperature heat reservoir 8. Preferably the heat transfer medium is represented by a fluid with high thermal conductivity and low viscosity. In particular, it can be a gas such as air. The cold 6 and hot 8 heat transfer media are disposed within the housing 2 and can exchange heat with the lower-temperature 7 and higher-temperature 9 heat reservoirs respectively. Such heat exchange can be provided either directly through the walls of the housing 2, or using separate heat exchangers, not shown in the plot. In possible device embodiment the the lower-temperature heat reservoir 7 can be a coolant or the ambient air. In turn, the higher-temperature heat reservoir 9 can be represented by concentrated sunlight, by external combustion, by waste heat, or by any other heat source. It can also be represented by the ambient air if the device is operated as a heat pump. The rotating walls 10 and 10°, which form parts of the main 1 and the secondary 3 rotors respectively, serve as the means separating the cold 6 and hot 8 heat transfer media. Preferably they are made from a material with low thermal conductivity, because their main purpose is to reduce heat losses between the higher-temperature 9 and lower-temperature 7 heat reservoirs due to heat transfer and mixing of the heat transfer media. The secondary rotors 3 accommodate multiple working body assemblies 11, positioned at a radial distance, preferably symmetrically, relative to the axis of rotor rotation. The working body assembly 11 comprises a cold heat conductive container 12 thermally contacting the cold heat medium 6, a hot heat conductive container 13, placed at azimuthal distance relative to the cold container 12 and thermally contacting the hot heat medium 8, a compressible working fluid 14, preferably represented by a gas with high molecular mass such as xenon, disposed within the containers at elevated pressure 10° — 107 Pa, and a passageway 15 connecting the cold 12 and hot 13 containers for moving working fluid 14 between them. Each secondary rotor may accommodate any number of working body assemblies (at least one). A schematic block diagram illustrating thermodynamic cycle attributed to a single working body assembly 11 of the invented device is shown in Figure 3. The working body assembly 11 is subjected to centrifugal force due to rotation around the the main rotor axis 16. Since the working body assembly 11 also rotates around the secondary rotor axis 17, the centrifugal force changes with the azimuthal angle ¢ between directions to the axis 16 and to the working body assembly 11. Considering positive values of ¢ in the azimuthal direction from hot 13 to cold 12 heat conductive container, the thermodynamic cycle can be separated into 4 stages, which can approximately be identified by the ¢ intervals [0, 7 / 2), [r / 2,7), [=,37 / 2), and [37 / 2, 27). According to equation (2) at the first two stages, ¢ € [0,7), most of the working fluid is concentrated in the cold container 12, which is at longer radial distance from the axis 16 than the hot container 13. On contrary, at stages 3 and 4, ¢ € [r, 27), the cold 12 and hot 13 containers swap places, and most of the working fluid moves through passageway 15 to the hot container 13. Due to heat exchange between the working fluid 14 and the heat reservoirs 7 and 9 through the heat transfer media 6 and 8, the working fluid temperature in the cold 12 and hot 13 containers approaches temperature of the lower-temperature 7 and higher-temperature 9 heat reservoirs respectively. Since the temperature of the lower-temperature heat reservoir 7 is less then the temperature of the higher- temperature heat reservoir 9, in agreement with equation (3) the centrifugal force F(T) acting on the working fluid at stages 1 and 2 appears to be bigger than the centrifugal force F(T) acting on the working fluid at stages 3 and 4. As a result, the centrifugal force torque ¥ is positive on average over the cycle, despite the torque at stages 1 and 2 has opposite sign compared to stages 3 and 4. If the secondary rotor rotates in positive ¢ direction, namely from hot 13 to cold 12 container, the centrifugal force torque ¥ produces positive work A, thus turning the device into a heat engine. Due to the second law of thermodynamics such positive work A is a result of receiving heat Qx from the higher-temperature heat reservoir 9 and returning heat Q. = Qn — A to the lower-temperature heat reservoir 7. In more details the mechanism of heat transfer to and from heat reservoirs 7 and 9 can be explained taking into account change of the working fluid entropy within the cold 12 and hot 13 containers. In particular, the working fluid entropy per unit mass can be calculated using the Sackur-Tetrode formula for ideal gas as 2rkm T s=cy |im (Fr) + ” i 4) where h is the Planck's constant, ¥ = ¢, / cy, and ¢,, ¢, are heat capacities per unit mass at constant volume and pressure respectively. According to this equation, the entropy s decreases when the working fluid density p increases and vice versa, it increases when the working fluid density p decreases. During the first stage of the thermodynamic cycle, ¢ € [0, 7 / 2), density of the working fluid in the cold container 12 increases. As a result, the working fluid gives away heat to the lower-temperature heat reservoir 7, Q1 = — [ pT.ds, where integration is over volume of the cold container 12. During the second stage, ¢ € [r / 2,), the working fluid redistributes towards the hot container 13, and its density in the cold container 12 decreases. Therefore the working fluid receives some heat Q2 back from the lower-temperature heat reservoir 7. It appears that Q? <Q}, therefore total heat returned to the lower-temperature heat reservoir 7 is positive Q. = Q1 — Q2 > 0. During the third stage, ¢ € [r,37 / 2), the working fluid moves to the hot container 13, and its density in the hot container increases. As a result the working fluid gives away some heat Qj to the higher-temperature heat reservoir 9. During the fourth stage, ¢ € [37 / 2,2r), the working fluid expands in the hot container 13 towards the cold container 12. The working fluid density decreases and the working fluid receives heat from the higher-temperature heat reservoir 9, Q3 = [ pThds, where integration is over volume of the hot container 13. The heat received at this stage exceeds heat returned to the higher-temperature heat reservoir 9 at the third stage, Qf > Q3, so that total heat received from the higher-temperature heat reservoir 9 is also positive Qn = QF — Q3 > 0. Moreover, since the work A is positive, Q, appears to be bigger than Q.. Rotating the secondary rotor in negative ¢ direction, namely from cold 12 to hot 13 container reverses all described above processes. In particular, the centrifugal force torque ¥ creates negative work A, the lower-temperature heat reservoir 7 gives away heat Q. and the higher-temperature heat reservoir 9 receives heat QQ. Therefore in this case the device operates as a heat pump. Typical dependence of the centrifugal force torque T on the azimuthal angle ¢ is shown in Figure 4(a). The plot depicts torque T normalised on its maximal value %,,,.. Even though ¥ changes sign around ¢ =m, the work ® Half 40) = [ 36246, Alo) = J (edo, ©) 0 which the torque creates if the secondary rotor rotates in positive ¢ direction, remains positive during the whole thermodynamic cycle, as it can be seen from Figure 4(b) representing A(¢) normalised on its total value Ayo = A(2r). Figure 4(c) shows plot for the heat Qp, which the working fluid receives from the higher-temperature heat reservoir 9 during the thermodynamic cycle as proportion of the total work Apter. The plot is created for 7 = 3.333 assuming isentropic heat transfer between the working fluid and heat reservoirs and ignoring heat losses. According to the plot the ratio Qp / A¢ota becomes about 1.45 at the end of the thermodynamic cycle. This value corresponds to the heat engine coefficient of performance 7 = A¢otar / Qr = 0.69, which for assumed isentropic heat transfer and absent heat losses approaches maximal possible thermal efficiency of the Carnot cycle (r —1) / 7 = 0.7. A thermodynamic process with isentropic heat transfer between working fluid and heat reservoirs has maximal thermal efficiency because it is fully reversible. Such process can not be realised in practice, but it can be approximated by keeping temperature of the working fluid 14 entering cold 12 or hot 13 container close to the temperature of the container. This can be achieved by heating the working fluid 14 up, when it moves through the passageway 15 from cold 12 to hot 13 container, and cooling it down, when it moves in reverse direction. In order to reduce heat losses the heat that the working fluid gives away when it is cooled down should be reused for heating it up. The heat losses can further be reduced by minimising heat transfer from hot 13 to cold 12 container trough the passageway 15. Therefore for achieving maximal coefficient of performance a preferred device embodiment may have upgraded working body assembly 11 schematically depicted in Figure 5. In said working body assembly 11 the passageway 15 is thermally isolated from the containers 12 and 13 using low thermal conductivity spacers 18 and comprises a heat regenerator 19, which heats the working fluid 14 up, when it moves towards the hot container 13, and cools it down, when it moves towards the cold container 12. Keeping difference between temperatures of the working fluid 14 and a container, in which it is disposed at a minimum, also requires efficient heat exchange between the working fluid and said container. Therefore in a preferred device embodiment the cold 12 and hot 13 containers may contain metal wire mesh or metal open cell foam, facilitating such heat exchange. In case when the secondary rotor 3 contains multiple working body assemblies 11, the thermodynamic cycles related to each working body assembly 11 have to be integrated, so that the work A of centrifugal force can be attributed to the secondary rotor 3 as a whole. In particular device embodiment shown in Figure 2 the electric motor 4 has to constantly rotate the main rotor 1 compensating the negative work A produced by the centrifugal force in order to operate device in the heat pump regime. In contrast, operating the device as a heat engine requires using the electric motor 4 only as a starter for setting up initial rotation of the main rotor 1. When the main rotor rotation establishes it becomes self supported by the positive work A, which is transferred from the secondary 3 to the main 1 rotor by the gear transmission 5 and 5°. ‘While Figure 2 shows a gear transmission, the device may use any suitable means for transferring energy between the rotating frame of reference associated with the main rotor and the stationary frame of reference associated with the device housing, i.e. transferring energy from the rotation of the main rotor to the rotation of the secondary rotors or vice versa. Any suitable transmission may be used for this purpose, e.g. a mechanical transmission, such as gearing, a belt drive, a chain drive, or similar, or an electromagnetic transmission, e.g. as shown in Figure 6. In alternative device embodiment shown in Figure 6, the gear transmission 5 and 5’ can be replaced by an electromagnetic transmission, comprising electric motors or generators 20 attached to the main rotor 1 and linked to rotation of the secondary rotors 3, and electrical brushes 21 used for passing electrical current of said motors or generators to and from the stationary frame of reference associated with the device housing 2. The electric motors are required for operating the device as a heat pump, whereas the electric generators are needed for operating the device as a heat engine. In this embodiment in both modes of operation the device provides conversion between electrical and heat energy. The power of the electric motor 4 is required only for rotating the main rotor 1, whereas energy transfer to and from the secondary rotors 3 is provided by said electric motors or generators 20. Operating the energy conversion device either as a heat engine or as a heat pump, requires creating sufficient centrifugal force acting on the working body assembly 11, such that parameter a is preferably above 1. In practice it assumes rotating the main rotor 1 at high enough angular speed. For example, if the working fluid is xenon and the maximal radial distance between the main rotor axis 16 and the working body assembly 11 is about 0.125 m, the required angular speed is about 1560 rad / s or 14900 RPM. The minimum value, which parameter a can have in practice is about 0.1. Below this value, the difference between centrifugal forces acting on the working fluid in the cold and hot containers becomes too small to have noticeable effect. So for operating the energy conversion device as a heat engine, the main rotor 1 has to be rotated at high enough angular speed, such that parameter « is at least 0.1 and preferably is above 1. This can be done using the electric motor 4, or by other means, in particular by using the gear transmission 5 and 5’ after achieving required angular speed. The temperature differential between the higher-temperature 9 and lower-temperature 7 heat reservoirs has to be maintained above some critical value, such that the secondary rotor 3 starts rotating in the azimuthal direction from hot 13 to cold 12 container. The converted energy can be obtained as mechanical energy at the shaft of the main rotor 1 using the gear transmission 5 and 5°, or as electrical energy using the electromagnetic transmission 20 and 21. For operating the energy conversion device as a heat pump, the main rotor 1 should also be rotated at high enough angular speed, such that parameter o is at least 0.1 and preferably is above 1. This can be done using the electric motor 4. The secondary rotor 3 has to be rotated in the azimuthal direction from cold 12 to hot 13 container with angular speed above some critical value, such that the heat starts moving from the lower-temperature 7 to the higher-temperature 9 heat reservoir. The required rotation of the secondary rotor 3 can be achieved either by using energy of the electric motor 4 transferred through the gear transmission 5 and 5° or by using external electrical energy delivered directly by the electromagnetic transmission 20 and 21. In contrast to typical Sterling engine the provided centrifugal energy conversion device has more compact construction. The working fluid is disposed within sealed containers and can be kept at high pressure without need for any special seals. As a result, the device can deliver higher specific power. Also the device operation does not rely on any reciprocal movement of pistons and is more smooth compared to a Sterling engine. In contrast to typical centrifugal heat pump the provided device does not require additional means for circulating working fluid through the heat pump passages. The centrifugal force is used for both compression and circulation of the working fluid within the working body assembly. At the same time the provided device has effectiveness comparable to the effectiveness of the Sterling engine or the centrifugal heat pump.

Claims

Claims 1. A centrifugal energy conversion device comprising: a main rotor supported for rotation within a housing; at least one secondary rotor disposed within said main rotor and supported for rotation relative to the main rotor around an axis, said secondary rotor axis being located at radial distance from the axis of the main rotor; means for rotating the main rotor; means for energy transfer between rotating frame of reference associated with the main rotor and stationary frame of reference associated with the device housing, said energy transfer means being in communication with rotational energy of the secondary rotor; a cold heat transfer medium disposed around the secondary rotor, said cold heat transfer medium being in thermal communication with a lower-temperature heat reservoir; a hot heat transfer medium disposed around the secondary rotor, said hot heat transfer medium being in thermal communication with a higher-temperature heat reservoir; means separating said cold and hot heat transfer media; at least one working body assembly disposed within each secondary rotor at radial distance from the axis of rotation of the secondary rotor, said working body assembly comprising: a cold heat conductive container being in thermal contact with the cold heat transfer medium; a hot heat conductive container placed at azimuthal distance from the cold container, said hot container being in thermal contact with the hot heat transfer medium; a compressible working fluid disposed within said cold and hot containers; a passageway connecting said cold and hot containers for moving working fluid between the containers.

2. A centrifugal energy conversion device according to claim 1, in which axes of the secondary and main rotors are mainly parallel.

3. A centrifugal energy conversion device according to any one of claims 1 or 2, and comprising multiple secondary rotors positioned symmetrically relative to the axis of rotation of the main rotor.

4. A centrifugal energy conversion device according to according to any one of claims 1 to 3, in which the or each secondary rotor has multiple working body assemblies positioned symmetrically relative to the axis of rotation of the secondary rotor.

5. A centrifugal energy conversion device according to any one of claims 1 to 4, in which the com- pressible working fluid is xenon.

6. A centrifugal energy conversion device according to any one of claims 1 to 5, in which the cold and ‘hot heat transfer medium is air.

7. A centrifugal energy conversion device according to any one of claims 1 to 6, in which the passageway connecting cold and hot containers in the working body assembly is thermally isolated from the containers and comprises a heat regenerator.

8. A centrifugal energy conversion device according to any one of claims 1 to 7, in which the cold and hot containers in the working body assembly contain metal wire mesh or metal open cell foam for facilitating heat exchange between said containers and the working fluid.

9. A centrifugal energy conversion device according to any one of claims 1 to 8, in which the energy transfer means between rotating and stationary frames of reference is a gear transmission linking rotation of the secondary rotor with rotation of the main rotor.

10. A centrifugal energy conversion device according to any one of claims 1 to 8, in which the energy transfer means between rotating and stationary frames of reference is an electromagnetic transmis- sion linking rotation of the secondary rotor with electric motor or generator attached to the main rotor and passing electrical current of said motor or generator to and from the stationary frame of reference.

11. A method of operation of a centrifugal energy conversion device according to any one of claims 1 to 10 as a heat engine, the method comprising: rotating the main rotor to create sufficient centrifugal force acting on the working body as- sembly, such that the maximal ratio between centrifugal and thermal energy related to one molecule of the working fluid is at least 0.1 and preferably is above 1; adapting the temperature differential between the higher-temperature and lower-temperature heat reservoirs above a critical value such that the secondary rotor rotates in the azimuthal direction from hot to cold container; transferring rotational energy of the secondary rotor from rotating to stationary frame of reference as the device output energy.

12. A method of operation of a centrifugal energy conversion device according to any one of claims 1 to 10 as a heat pump, the method comprising: rotating the main rotor to create sufficient centrifugal force acting on the working body as- sembly, such that the maximal ratio between centrifugal and thermal energy related to one molecule of the working fluid is at least 0.1 and preferably is above 1; transferring sufficient device input energy from stationary to rotating frame of reference for rotating the secondary rotor in the azimuthal direction from cold to hot container of each working body assembly with angular speed above some critical value, such that the heat moves from the lower-temperature to higher-temperature heat reservoir. CLAIMS:

1. A centrifugal energy conversion device comprising: a main rotor supported for rotation within a housing; at least one secondary rotor disposed within said main rotor and supported for rotation relative to the main rotor around an axis, said secondary rotor axis being located at radial distance from the axis of the main rotor; means for rotating the main rotor; means for energy transfer between rotating frame of reference associated with the main rotor and stationary frame of reference associated with the device housing, said energy transfer means being in communication with rotational energy of the secondary rotor; a cold heat transfer medium disposed around the secondary rotor, said cold heat transfer medium being in thermal communication with a lower-temperature heat reservoir; a hot heat transfer medium disposed around the secondary rotor, said hot heat transfer medium being in thermal communication with a higher-temperature heat reservoir; means separating said cold and hot heat transfer media; at least one working body assembly disposed within each secondary rotor at radial distance from the axis of rotation of the secondary rotor, said working body assembly comprising: a cold heat conductive container being in thermal contact with the cold heat transfer medium: a hot heat conductive container placed at azimuthal distance from the cold container, said hot container being in thermal contact with the hot heat transfer medium: wherein the cold heat conductive container and the hot heat conductive container are each of fixed volume: a compressible working fluid disposed within said cold and hot containers; a passageway connecting said cold and hot containers for moving working fluid between the containers.

2. A centrifugal energy conversion device according to claim 1, in which axes of the secondary and main rotors are mainly parallel.

3. A centrifugal energy conversion device according to any one of claims 1 or 2, and comprising multiple secondary rotors positioned symmetrically relative to the axis of rotation of the main rotor.

4. A centrifugal energy conversion device according to according to any one of claims 1 to 3, in which the or each secondary rotor has multiple working body assemblies positioned symmetrically relative to the axis of rotation of the secondary rotor.

5. A centrifugal energy conversion device according to any one of claims 1 to 4, in which the compressible working fluid is xenon.

6. A centrifugal energy conversion device according to any one of claims 1 to 5, in which the cold and hot heat transfer medium is air. ?. A centrifugal energy conversion device according to any one of claims 1 to 6, in which the passageway connecting cold and hot containers in the working body assembly is thermally isolated from the containers and comprises a heat regenerator.

8. A centrifugal energy conversion device according to any one of claims 1to 7, in which the cold and hot containers in the working body assembly contain metal wire mesh or metal open cell foam for facilitating heat exchange between said containers and the working fluid.

9. A centrifugal energy conversion device according to any one of claims 1 to 8, in which the energy transfer means between rotating and stationary frames of reference is a gear transmission linking rotation of the secondary rotor with rotation of the main rotor.

10. A centrifugal energy conversion device according to any one of claims 1 to 8, in which the energy transfer means between rotating and stationary frames of reference is an electromagnetic transmission linking rotation of the secondary rotor with electric motor or generator attached to the main rotor and passing electrical current of said motor or generator to and from the stationary frame of reference.

11. A method of operation of a centrifugal energy conversion device according to any one of claims 1 to 10 as a heat engine, the method comprising: rotating the main rotor to create sufficient centrifugal force acting on the working body assembly, such that the maximal ratio between centrifugal and thermal energy related to one molecule of the working fluid is at least 0.1 and preferably is above 1; adapting the temperature differential between the higher-temperature and lower-temperature heat reservoirs above a critical value such that the secondary rotor rotates in the azimuthal direction from hot to cold container; transferring rotational energy of the secondary rotor from rotating to stationary frame of reference as the device output energy.

12. A method of operation of a centrifugal energy conversion device according to any one of claims 1 to 10 as a heat pump, the method comprising: rotating the main rotor to create sufficient centrifugal force acting on the working body assembly, such that the maximal ratio between centrifugal and thermal energy related to one molecule of the working fluid is at least 0.1 and preferably is above 1; transferring sufficient device input energy from stationary to rotating frame of reference for rotating the secondary rotor in the azimuthal direction from cold to hot container of each working body assembly with angular speed above some critical value, such that the heat moves from the lower-temperature to higher-temperature heat reservoir.

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