The technique of reducing the temperature of a paramagnetic substance by utilizing a magnetic field, known as the"magnetocaloric effect"or"adiabatic demagnetization"is also well known. The technique involves mounting a solid paramagnetic substance (usually a paramagnetic salt pellet) between the poles of a powerful electromagnet and turning on the magnetic field. The resulting heat of magnetization is transferred to a reservoir of liquid helium.

The magnetized substance is then thermally insulated from the liquid helium and the magnetic field is turned off. The effect of demagnetization (which occurs when the magnetic field is removed), lowers the temperature of the substance thereby creating an artificial low temperature heat sink below that of the liquid helium. Unfortunately, absorbing the heat of magnetization by an external reservoir of liquid helium is a very expensive process.

In 1989, the applicant discovered how to use the magnetocaloric effect to create and sustain an artificial low temperature heat sink at cryogenic temperatures without using any external liquid helium to enable a cryogenic engine to operate cyclically. The system involved using a cryogenic working fluid in the engine that is paramagnetic such as liquefied oxygen. By letting the expanded paramagnetic substance, that is gaseous instead of solid, move freely into and out of a magnetic field generated by a superconducting solenoid by means of a non-magnetic conduit, it is possible to remove the heat of magnetization mechanically by converting it into mechanical work using a non-magnetic turbine mounted inside the conduit. The invention was patented as U. S Patent 5,040, 373"Condensing System and Operating Method"issued August 20, 1991.

Unfortunately, the system required an extremely high magnetic field (on the order of 50 T) and the condensation ratio was very small (about 3 %). Although the engine was operable and could convert natural heat energy in the environment at ambient temperature into mechanical work, its power output was very small compared to its size and required a very expensive superconducting solenoid. Other systems such as solar cells and wind generators were more practical. However, a radically new design has been discovered which represents the basis of the present invention. This design involves using two separate cryogenic fluids instead of one, as in the original design. The first cryogenic fluid is paramagnetic, such as liquefied oxygen, and used in the cryogenic condensing system together with a plurality superconducting solenoids operating in tandem instead of one. The second cryogenic fluid is non-paramagnetic, such as liquefied nitrogen, which is used separately in the cryogenic engine. The resulting system is able to operate much more efficiently to obtain a significant increase in performance while using much weaker magnetic fields. Although the present invention is also based on utilizing the magnetocaloric effect to enable the engine to operate cyclically as in the previous invention, this effect does not operate on the working fluid used in the engine. In the present invention the paramagnetic substance is not the working fluid and it is not gaseous. It is liquid and remains liquid with no phase change. This enables 100 % of the expanded working fluid discharged from the cryogenic engine to be re-liquefied instead of only 3 %. And this is achieved by using a magnetic field of only 30 T which is well within engineering feasibility. Consequently, the present invention represents a vastly improved magnetic condensing system for cryogenic engines compared to my original invention.

Since it may appear that the present invention, and my prior 1989 invention, are fundamentally inoperable because they both violate the Second Law of Thermodynamics, this is not the case. The phenomenon known as the magnetocaloric effect or adiabatic demagnetization involves principles and processes in the field of electromagnetism that are outside the realm of classical thermodynamics. When electromagnetic processes, such as the magnetocaloric effect, are used in conjunction with thermodynamic processes, the results can no longer be predicted within the theoretical framework of classical thermodynamics. For example, when subjecting a paramagnetic substance to a magnetic field, the temperature of the substance increases but its entropy remains constant due to magnetic spin alignment. This is thermodynamically impossible. According to thermodynamics, any substance that is heated always results in an increase in entropy. This illustrates the fact that thermodvnamic laws cannot be applied to non-thermodvnamic processes. (See, "Classical Physics Gives Neither Diamagnetism nor Paramagnetism, "Section 34-6, page 34-8, in The Fevnman Lectures On Physics, by R. Feynman, Addison-Wesley Pub. Co. , 1964.)

Brief Description of the Invention A magnetic condensing system is provided for cryogenic engines by generating an artificial low temperature heat sink below ambient temperature by utilizing the magentocaloric effect. The system is designed by creating a plurality of magnetic fields and subjecting a liquefied paramagnetic fluid such as liquid oxygen to these fields at cryogenic temperature. The magnetic fields are generated by charging and discharging an even number of thermally insulated, spaced apart, superconducting solenoids having central bores. In the preferred embodiment, the solenoids are connected by a hexagonal non-magnetic metallic conduit passing through each bore that has high thermal conductivity such as copper or aluminum. The solenoids are mounted at each vertex and at the mid-section of each side giving a total of 12 solenoids.

Non-magnetic, one-way doors are mounted on each side of the bores designed to provide sealed chambers inside each solenoid. A plurality of elongated non-magnetic turbines are mounted at regular intervals inside the conduit between adjacent solenoids. The paramagnetic fluid, which represents the heat sink, is saturated liquefied oxygen which is highly paramagnetic at cryogenic temperatures. It is initially held inside the chambers of alternating solenoids by magnetic attractive forces with the doors closed while the adjacent solenoids are vacant without any current and therefore generate no magnetic fields. The liquid in each chamber is magnetized by the magnetic fields and have an initial temperature of 56° K, initial entropy of 2.148 J/gm K, and total initial enthalpy of 83.44 J/gm. The magnetic fields of the energized solenoids acting on the paramagnetic liquefied oxygen in their sealed chambers have a maximum field strength of 30 T.

The magnetic fields of the energized solenoids containing the liquefied oxygen are simultaneously turned off by transferring the current to the adjacent upstream solenoid that is vacant. By turning off the field in each solenoid containing the paramagnetic liquefied oxygen, the liquid inthe sealed chambers undergo demagnetization (producing the magnetocaloric effect) thereby creating a temperature drop of about two degrees to 54. 61° and a drop in enthalpy to 81.123 J/gm while the entropy remains constant. This temperature drop in the six solenoids creates a temperature drop throughout the entire length of the conduit surrounding the liquid thereby creating an artificial low temperature heat sink.

After the magnetic fields acting on the liquid are turned off by transferring the current to the adjacent vacant upstream solenoids, the doors between the adjacent solenoids are simultaneously opened. The paramagnetic liquefied gas is immediately pulled out of the solenoids by the magnetic attractive forces of the adjacent upstream energized solenoid in front thereby creating an accelerating flow of paramagnetic liquid through the conduit toward the vacant energized solenoids. The gradient of the magnetic fields of each solenoid is designed to pull the liquid around the central conduit in a clockwise direction. The increasing directed kinetic energy of the streams that are magnetically pulled towards the adjacent vacant solenoids

represent the heat of magnetization created by the magnetic fields of the adjacent vacant solenoids. This energy (heat of magnetization) is extracted from the fluid and converted into mechanical work by the non-magnetic turbines mounted in the flow paths of the streams between the adjacent solenoids. As a result, the liquid enters each adjacent solenoid and reaches maximum magnetization with very little directed kinetic energy and hence with a negligible increase in temperature. The process represents isothermal magnetization. Neglecting frictional losses which can be made very small by design, essentially all of the heat of magnetization of the paramagnetic liquid entering the magnetic fields of the vacant adjacent solenoids is converted into an equivalent amount of mechanical work by the rotating turbines. These turbines are connected to electric generators for generating electric current. This current is fed into each energized adjacent solenoid during the charging process to replenish the small current drop caused by the magnetized liquid entering each solenoid by the inductive coupling. The isothermally magnetized liquid undergoes a drop in entropy due to dipole spin alignment with the magnetic fields. After the magnetic fields pull the liquid into the chambers of the respective solenoids, all the doors are closed and a new demagnetization cycle is repeated creating a new temperature drop throughout the entire primary heat transfer conduit.

The decrease in temperature of the central primary heat transfer conduit caused by the demagnetization effect acting repetitively on the paramagnetic liquefied gas is transferred to a copper helical coil (secondary heat transfer conduit) that winds around the central primary conduit and in thermal contact with it. The design is such that the magnetic cooling effect generated in the primary conduit is transferred to the secondary conduit by virtue to its higher temperature. Thus, by feeding partially compressed low temperature noncondensed vapor discharged from the last expander of a cryogenic engine through the secondary conduit (condensing tube), the heat of vaporization is extracted by the temperature differential maintained by the circulating paramagnetic liquefied oxygen, and the vapor is liquefied. All the noncondensed vapor entering the secondary helical conduit leaves the conduit as condensed liquid at cryogenic temperature.

In the preferred embodiment, the cryogenic working fluid used in the cryogenic engine is nitrogen. Nitrogen is slightly diamagnetic and is not effected by the magnetic fields. Before feeding the liquefied nitrogen back into the cryogenic engine it is utilized as a cryogenic coolant forthe superconducting solenoids which are constructed with high-temperature superconducting wire.

Drawings These and other advantages and features of the present invention will be apparent from the disclosure, which includes the specification with the foregoing and ongoing description, the

claims and the accompanying drawings wherein: Fig. 1 is aTemperature-Entropydiagramofaparamagnetic substanceillustratingthebasic thermodynamic operating principles of adiabatic demagnetization known in the prior art; Fig. 2 is a perspective longitudinal cross-section of a non-magnetic conduit connected to the bore of a superconducting solenoid illustrating an accelerating flow stream of paramagnetic fluid accelerating through the conduit under magnetic attractive forces generated by the magnetic field of the superconducting solenoid; Fig. 3 is a perspective longitudinal cross-section of the non-magnetic conduit shown in Fig. 2 illustrating how the kinetic energy of the accelerating paramagnetic fluid is converted into mechanical work by mounting a non-magnetic rotating turbine in the flow stream inside the conduit; Fig. 4 is a block diagram of a cryogenic engine using the preferred embodiment of the magnetic condensing system; Fig. 5 is a schematic perspective plan view of the preferred embodiment of the magnetic condensing system illustrating its overall design and construction; Fig. 6 is an enlarged longitudinal perspective view of the primary heat transfer conduit between two adjacent solenoids further illustrating the design and construction of the magnetic energy turbines mounted inside; Fig. 7 is an enlarged transverse cross-sectional view illustrating the design and construction of the turbine supporting sleeves; and Fig. 8 is a schematic transverse cross-section through a cooling chamber of the magnetic condenser mounted inside the bore of a superconducting solenoid illustrating the design and construction of a plurality of heat transfer fins for increasing the thermal contact between the paramagnetic fluid that is magnetically cooled inside the chamber and the primary heat transfer tube.

Description of a Preferred Embodiment The basic underlying physical principles that are utilized in the design of the magnetic condensing system described herein are the principles of adiabatic demagnetization also known as"magnetic cooling"or the"magnetocaloric effect. "Therefore, before describing the detailed design and operating features of the magnetic condensing system, it will be useful to review the basic operating principles of adiabatic demagnetization, and how these principles are used in prior art magnetic refrigeration systems. This will provide a basic understanding of the unique operating features of the present invention that are easily distinguishable from the prior art.

In making this comparison it is important to point out and emphasize at the outset that all prior art"magnetic refrigeration systems"utilizing the magnetic cooling principles of adiabatic

demagnetization use a paramagnetic substance that is either solid, or in a powered form. In the present invention, the paramagnetic substance is a liquid at cryogenic temperature.

Consequently, the present invention is fundamentally different from all prior art magnetically cooled refrigeration systems and therefore is clearly distinguishable from all prior art refrigeration systems using adiabatic demagnetization. The second reason for this review is to develop the basic analytical equations which will provide a general mathematical framework to quantitatively investigate the design and performance of the present invention (i. e. , a mathematical framework for the underlying theory and operating principles).

Fig. 1 is a Temperature-Entropy diagram of a paramagnetic substance illustrating the basic thermodynamic operating principles of adiabatic demagnetization. Referring to this figure, the process begins at point A which denotes the initial temperature T,, and the initial entropy S,, of the paramagnetic substance. As is usually the case, the substance is solid and rigidly mounted on a support structure between the poles of an electromagnet and thermally insulated from the environment. The application of the magnetic field results in two physical effects: (1) The substance becomes magnetized due to partial alignment of the magnetic dipoles with the applied magnetic field, and (2) it heats up. The heating is caused by motion in the underlying crystal structure due to magnetic forces acting on the molecules. A solid paramagnetic substance carries thermal energy by atomic vibrations that vibrate along random directions when there is no external magnetic field. However, when it is subjected to an external magnetic field it has less heat capacity because it has fewer vibrational modes to store thermal energy due to magnetic dipole alignment with the external magnetic field. Consequently, in order to carry the same amount of thermal energy as it had before being magnetized its temperature must increase.

Since the substance is paramagnetic, dipole alignment with the external magnetic field B will prevent the entropy from increasing during this heating (i. e. , during the magnetization). The system is designed such that the heat of magnetization AH is absorbed by a liquid helium reservoir at some very low temperature which surrounds the substance and also positioned between the poles. Since the heat of magnetization is extracted during the magnetization process, the entropy is reduced by an amount AS.,,. Referring to Fig. 1, this isothermal magnetization process is represented thermodynamically on the Temperature-Entropy diagram by the movement vertically downward from point A to point B illustrating a drop in entropy = S1-S2 atconstanttemperatureT, givenby Ao AS. = 2T where M denotes the magnetization expressed in units of J/(gm T) and B denotes the magnetic field strength expressed in units of Tesla (T). (One Tesla = 10, 000 Gauss. MKS system of units

is used in all equations. ) The heat of magnetization DII, n is given by #Hm = T1#Sm (2) In view of equations (1) and (2), the heat of magnetization #Hm can also be expressed as MB #Hm = (3)<BR> <BR> 2<BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> After the heat of magnetization #Hm has been extracted from the substance by the liquid helium, and the substance is at point B on the Temperature-Entropy diagram, it is thermally insulated from the surrounding liquid helium and the magnetic field is turned off. By turning off the field, the substance undergoes adiabatic demagnetization and the temperature drops to the final temperature T2 represented by the horizontal line segment BC on the Temperature-Entropy diagram of Fig. 1.

The temperature drop can be determined as follows: Let C denote the heat capacity of the substance at temperature T"and let ATm denote the temperature drop due to the adiabatic demagnetization effect. Consequently, the heat loss in the substance due to the adiabatic demagnetization effect can be expressed approximately as CAT,,,. Since the heat of magnetization AH is equal to the heat loss, it follows that CATm = SHm. Hence, the temperature drop #Tm due to the adiabatic demagnetization effect can be calculated to a good approximation by the equation <BR> <BR> <BR> <BR> <BR> <BR> #Hm<BR> <BR> <BR> <BR> #Tm = (4)<BR> <BR> C A more detailed analytical exposition of adiabatic demagnetization (the magnetocaloric effect) can be found in the books: Principles and Application of Magnetic Cooling, North- Holland Publishing Co. , 1972 by R. P. Hudson; Magnetic Cooling. Harvard Monographs In Applied Science, No. 4,1954 by C. Garrett ; and Experimental Techniques In Low-Temperature Physics, Oxford Press, 1968 by G. White. By using these methods, temperatures T2 = T1 - #Tm as low as 001° I can be reaclled. In the present invention, however, the magnetocaloric effect will be used to obtain a heat sink at cryogenic temperature by using the paramagnetic substance to absorb thermal energy Q at temperature T, where the amount of heat energy absorbed AH. = CAT,.

In order to calculate the entropy drop #Sm, the heat of magnetization AH,, and the temperature drop #Tm, of a paramagnetic substance undergoing the process of adiabatic demagnetization described in equations (1) - (4), it is necessary to calculate the magnetization

M of the substance at a certain temperature T when subjected to a magnetic field of a given intensity B. Although magnetization calculations of paramagnetic substances are usually obtained by an approximation using Curie's Law, it will be accurately obtained herein using exact equations from quantum mechanics.

Let, u denote the magnetic dipole moment of a single molecule of the paramagnetic substance. (A magnetic dipoles a very small circular loop having current i and radius R defined as iA where A is a vector having magnitude equal to the area of the loop A = 7rR2 with direction normal to the loop determined by the direction of the current using the standard right-hand rule.) In quantum mechanics the scalar magnetic dipole moment of a substance can be expressed as where g is a constant called the g-factor, J is the total angular momentum quantum number, and tub is a constant called the Bohr magnetron. One Bohr magnetron, is equal to 9. 273x10-24 Joules/Tesla. (Joules/Tesla = amp m) If the substance is in a region of space where there is no magnetic field, then the directions of the magnetic dipole moments, of all the individual molecules have a random distribution because of thermal motion, and hence the substance as a whole, exhibits no net magnetism.

However, if there is an external magnetic field, then a certain fractionfof the individual dipoles will become aligned with the external field. The stronger the field, the greater the alignment; and the lower the temperature, the greater the alignment. The substance is said to have paramagnetic saturation when all of the dipoles are aligned with the magnetic field. In classical electromagnetic theory, the resulting magnetizationMo corresponding to paramagnetic saturation is given by Mo = Ny where N denotes the number of molecules per unit mass. In quantum mechanics however, it is impossible for all the dipoles to be aligned with the external field because of spatial quantization. Hence, in quantum mechanics, the maximum possible magnetization Mo will be somewhat less than that predicted from classical electromagnetic theory. In quantum mechanics Mo = NgJIl B. By setting N equal to Avogadro's number 6. 022169x1023 molecules/mole, and dividing by the molecular weight M of the substance, the magnetization M0 is obtained in units of Joules?(gm Tesla). Hence, NgJµ B M0 =<BR> <BR> <BR> M In practice, it is impossible to achieve complete paramagnetic saturation. Hence, the actual magnetization M that results from partial alignment is given by M= fMo (6) Omitting the mathematical details, it can be shown that the equation giving the magnetization

fractionfof a paramagnetic substance at temperature Tsubjected to a magnetic field of intensity Bis where the parameter gJll BB kT and k= Boltzmann's constant equal to 1. 38062x10-23 Joules/K°. The function on the right hand side of equation (7) is called the"Brillouin function." (See, Modern Magnetism, Cambridge University Press, 1963, pp. 43-44 by L. F. Bates; and"Tables oftheBrillouinFunction and of the Related Function for the Spontaneous Magnetization, "British Journal of Applied Physics, Vol.

18,1967, pp. 1415-1417 by M. Darby. ) To understand the basic operating principles of the present invention it is important to point out and emphasize that the phenomenon of adiabatic demagnetization described above, and illustrated thermodynamically in Fig. 1, applies to all paramagnetic substances whether they are solid, gaseous, or liquid. In the preferred embodiment of the invention the paramagnetic substance will be liquified oxygen at an initial temperature T, = 56° K which is just above the triple point (54. 359° K). (Liquefied oxygen is the most paramagnetic liquid at cryogenic temperatures. ) For oxygen, with molecular weighty= 32, g = 2 and J = 1. Hence, = 2.828 HB. The magnetic field will be generated by a superconducting solenoid having a maximum field strength B = 30 T. The heat capacity C of saturated liquid oxygen at 56° K is 1.6616 J/ (gin K).

(This value is obtained from The National Bureau of Standards Report, The Thermodynamic Properties Of Oxygen From 20° K to 100° K, Technical Report No. 2, Project No. A-593, National Bureau of Standards Contract No. CST-7339, March 1,1962 by J. C. Mullins, et al., page 40.) Upon substituting these quantities into the above equations, the operating parameters (8) of the adiabatic demagnetization process and the heat absorbing capacity Qm = AHm at temperature T, of the preferred embodiment of the magnetic condensing system are:

The fact that the phenomenon of adiabatic demagnetization described above and illustrated in Fig. 1, along with equations (1)- (7) holds for all paramagnetic substances whether they are solid, liquid, or gaseous is important in the present invention because by choosing a paramagnetic substance that is liquid or gaseous, it will be possible to extract the heat of magnetization Aha without using any external low temperature heat sink such as liquefied helium (which is very expensive). Contrary to the prior art, this can be achieved by initially placing liquefied oxygen in a sealed chamber positioned some distance away from a charged superconducting solenoid that is connected to the chamber by a straight, thermally insulated, non- magnetic conduit that is coaxial with the solenoid's bore. If there is nothing in the conduit to obstruct the flow when the fluid is released from the chamber, the magnetic attractive forces F ; n will continuously accelerate the fluid through the conduit into the bore of the solenoid. And, while moving through the conduit, it becomes magnetized by virtue of moving into a region having higher magnetic intensity. In this process, the heat of magnetization Ohm will be represented by the increasing directed kinetic energy of the substance as it is accelerated through the conduit into the bore. It follows from the principle of conservation of energy that the heat of magnetization OHm (given by equation 3) is represented by the increase in kinetic energy of the paramagnetic fluid as it enters the bore of the superconducting solenoid. For liquids and gases, most of the thermal energy, (heat content of a substance), is represented by the kinetic energy of the molecules. For solid substances, most of the thermal energy is in the form of vibrational energy. Since the total energy of the system must remain constant, the increase in the directed kinetic energy of the fluid moving through the conduit corresponds to an equivalent decrease in the energy of the solenoid's magnetic field. This decrease in the energy of the magnetic field of the solenoid, which is manifested by a small current drop, results from the inductive coupling between the dipoles entering the field and the field of the solenoid. This energy drop is equal to the heat of magnetization AHm. This equivalence principle between the directed kinetic energy of the fluid accelerating through the conduit toward the magnetic field

by magnetic attractive forces and heat of magnetization given by equation (3) can be proved analytically by calculating the acceleration of the fluid (comprising magnetic dipoles) as it passes through the conduit using the equation of force from electromagnetic theory and calculating the specific kinetic energy (KE/gm) as it enters the bore of the solenoid where it reaches maximum velocity.

Fig. 2 describes a paramagnetic fluid 10 (assumed to be liquefied oxygen with an initial temperature of 56° K) accelerating from a sealed chamber 12 through a 0.50 m (19.7 in) long non-magnetic conduit 14 leading into the central bore 16 of a charged superconducting solenoid 18 by magnetic attractive forces Fnl. The process of moving through the conduit 14 toward the charged superconducting solenoid 18, i. e. , moving into the magnetic field 20 of the superconducting solenoid 18 by virtue of moving through the conduit 14, represents the magnetization process of the paramagnetic fluid in the present invention. By mounting a non- magnetic rotating turbine 24 in this flow stream 26 inside the conduit 14 as shown in Fig. 3, it will be possible to convert this directed kinetic energy of the paramagnetic fluid flowing through the conduit into mechanical work without having to use any external heat sink as in prior art adiabatic demagnetization processes that use traditional paramagnetic salts that are solid. Thus, after passing through the turbine 24, the magnetized flow stream enters the bore of the solenoid with very little velocity. There is essentially no increase in temperature. The result is isothermal magnetization that is achieved without transferring the heat of magnetization A to any cryogenic heat sink because it is converted into mechanical work by the turbine. This fact, together with the fact that adiabatic demagnetization giving the temperature drop described by equation (4) applies to all paramagnetic substances undergoing demagnetization whether they are solid or not demonstrates the basic operating feasibility of the present invention.

The motion through the conduit is designed to achieve isothermal magnetization. This will result in the reduction of the entropy of the fluid inside the solenoid 18 but not the temperature. The temperature reduction occurs when the magnetic field of the solenoid is turned off. This will produce the magnetocaloric effect that reduces the temperature of the fluid below the initial temperature T, (56° K) to T2 = T,-ATm = 54. 61° K. By constructing the central conduit 14 with a metallic material having high thermal conductivity that is non-magnetic such as copper or aluminum, the heat loss of the liquefied oxygen 28 inside the bore of the solenoid 18 is transferred to the conduit 14 which becomes the primary stationary cooling surface. As shown in Fig. 3, a secondary heat transfer tube 30 is wound around the cooling conduit 14 and in thermal contact with it. The entire assembly is thermally insulated from the environment. By feeding vapor discharged from a cryogenic engine into the secondary coil 30, the cooling effect of the demagnetized liquid oxygen cools and liquefies the vapor. The cooling potential can be increased to extract any amount of heat from the vapor desired (within the operating limits) by

simply repeating the above steps. If the oxygen makes R passes through the conduit per minute (repetition rate), the system will be able to absorb heat (coolingpower) QC J/(gmminute), given by QC= RQnz= 231679R J/(gmminute) (9) In order to achieve this continuous magnetic cooling effect at cryogenic temperatures, the central conduit 14 (which will be referred to as the primary heat transfer conduit) will be designed as a closed loop. In particular, it will be designed as a polygon with superconducting solenoids mounted at the vertices. And, in order to increase the cooling potential of the system, an additional superconducting solenoid will be mounted at the mid points of each side and operated simultaneously. These are the basic operating principles and operating parameters of the preferred embodiment of the magnetic condensing system. The detailed design of the preferred embodiment will now be presented.

In the preferred embodiment the central conduit forms a closed hexagonal loop with 12 superconducting solenoids with six separate portions of liquified oxygen that move intermittently around the loop simultaneously in the same direction. This will enable the magnetic condenser to continuously condense much more vapor. It will be specifically designed for cryogenic engines capable of generating a continuous power output of several kilowatts.

In order to design the magnetic condenser that will be capable of condensing expanded vapor discharged from a cryogenic engine at the required mass flow rate, it will be necessary to determine the power output of a cryogenic engine corresponding to various mass flow rates. The cryogenic working fluid used in the engine will be assumed to be nitrogen.

Fig. 4 is a schematic block diagram of the cryogenic engine used in the preferred embodiment of the magnetic condensing system. The determination of the thermodynamic parameters of the engine at various flow points will be based on accurate thermodynamic data published in the paper,"Thermodynamic Properties Of Nitrogen", Journal of Physical Chemistry Ref. Data, Vol. 2, No. 4,1973, by Richard G. Jacobson and Richard B. Stewart. Referring to Fig.

4, saturated liquified nitrogen leaving the condensing tubes of the magnetic condenser 32 will have the following values for the thermodynamic state parameters: TNO = 76° K, Entropy SNO = 2.803 J/gm K, Enthalpy HNO =-124.221 J/gm, Pressure PNO = 1.0 Bar (The values of these parameters are taken directly from the cited reference and based on the zero points used in that reference. ) This liquified nitrogen is then fed into a small isentropic compressor 34 and pressurized to 2.0 Bar. (The thermodynamic state parameters are essentially unchanged. ) It is then circulated as cryogenic coolant for the superconducting solenoids, current switching system, and other components inside the magnetic condensing system 32. Since the passive multilayer

cryogenic thermal insulation around the magnetic condenser 32 is designed to keep the heat leaks from the environment to a minimum, the heat absorbed by the circulating liquefied nitrogen will not be very great. Thus, it can be assumed that after circulating as coolant for the various components inside the magnetic condenser 32, the liquid emerges with a temperature increase of 6°. The thermodynamic state parameters of the liquefied nitrogen after circulating around the various components of the magnetic condenser as coolant are: TNI = 82° K, SNI = 2.959 J/gm K, HNI =-111.736 J/gm, PNI = 2.0 Bar. The cryogenic fluid is then fed into a thermally insulated 10 gallon (37.85 liter) cryogenic storage vessel 36. The liquid nitrogen is then withdrawn from the storage vessel 36 and fed into a cryogenic hydraulic compressor 38 and isentropically compressed to a pressure of 600 Bar (8,702 lbs/in2). After this isentropic compression, the thermodynamic state parameters are : TN2=96. 186°K, SN2=2. 959 J/gmK, HN2 =-38. 975 J/gm, PN2 = 600 Bar. Consequently, the amount of specific mechanical work Wc consumed in this compression is HN2-HN, = 72.761 J/gm. (Specific mechanical work refers to a mass flow of 1.0 gm and will be denoted by the symbol W.) After leaving the compressor 38 at 96. 186° K the liquefied nitrogen is fed into a low temperature, thermally insulated heat exchanger 40 where it serves as a coolant for cooling the vapor discharged from the last expander 42 of the cryogenic engine 44 before this vapor is fed into the magnetic condenser 32. The compressed liquefied nitrogen leaves the low temperature heat exchanger 40 with thermodynamic state parameters equal to : TN3 = 125. 756° K, SN3 = 3. 412 J/gmK, HN3 = 11. 019 J/gm, PN3 = 600.0 Bar. (The calculation of these parameters was based on the assumption that the mass flow rate of the liquid coolant entering the low temperature heat exchanger 40 at a temperature TN2 = 96. 186° K and enthalpy HN2=-38. 975 J/gm is the same as the mass flow rate of the vapor entering the heat exchanger 40 at a temperature TNII = 173. 47° K and enthalpyHNll = 179. 336 J/gm with its thermodynamic parameters equal to the parameters of the expanded vapor discharged from the last expander 42, and the assumption that the temperature of these two components leaving the heat exchanger 40 are the same. Since the amount of heat absorbed by the liquid nitrogen is equal to the heat loss by the vapor, the outlet temperature is calculated as being 125. 756° K.) The amount of heat energy AQ absorbed in the low temperature heat exchanger 40 from the vapor is HN3 ~ HN2 = 49. 994 J/gm. After circulating through the low temperature heat exchanger 40, the compressed liquefied nitrogen is fed into the first ambient heat exchanger 46 where it is isobarically heated to ambient temperature which will be assumed to be 290° K (62. 3° F). This heat exchanger 46 is maintained in thermal contact with ordinary atmospheric air at ambient temperature that is continuously flowing over the heating surfaces of the heat exchanger 46 with a mass flow rate many times greater than that of the compressed nitrogen circulating through it due to the wind velocity and the size of the heat exchanger 46. (The heat exchanger 46 could also be mounted in thermal contact with water in

a lake at ambient temperature depending on the application of the invention. ) Thus, the outlet temperature of all ambient heat exchangers can be assumed to be equal to ambient temperature.

Since the temperature of the compressed liquefied nitrogen entering the first ambient heat exchanger 46 is significantly below that of the flowing air stream, the thermal gradient across its thermal surfaces is very large and thus the cryogenic nitrogen extracts the natural thermal energy from the air stream at a rapid rate. Therefore, the compressed nitrogen is rapidly heated above its critical temperature (126. 200° K) and vaporized to become a pressurized gas at a pressure of 600 Bar (8,702 lbs/in2) which is superheated to 290° K. The pressurized superheated nitrogen leaves the first heat exchanger 46 with its thermodynamic state parameters equal to: Ton4= 290. 0° K, Son4= 4.711 J/gm K, Han4= 262.742 J/gm, PN4 = 600.0 Bar.

The amount of natural thermal energy absorbed from the atmosphere while circulating through the first ambient heat exchanger 46 is HN4-HN3= 251.723 J/gm.

Upon leaving the first heat exchanger 46 (Fig. 4) the superheated pressurized nitrogen is fed into a load-leveling high-pressure storage vessel 48 (energy storage system). This vessel 48 is also designed to be in thermal contact with atmospheric air at ambient temperature. The compressed gas is withdrawn from this storage vessel 48 and fed into the first cascading isentropic expander 50 where it is isentropically expanded down to a pressure of 120 Bar (1,740 lbs/in2). The resulting thermodynamic state parameters are : TN5 = 191. 917° K, SN5 = 4. 711 J/gm K, Huns = 136. 106 J/gm, PN5 = 120 Bar. The mechanical work WNI generated from this first expansion is equal tow., = HN4 ~ HN5 = 126. 636 J/gm. The load-leveling storage vessels will enable the mass flow rates into the down stream expanders to vary over a wide range to generate power levels over a wide range. However, it will be assumed that the mass flow rates into each expander will be equal.

The expanded nitrogen leaving the first nitrogen expander 50 at 191. 917° K is fed into the second ambient heat exchanger 52 that is also maintained in thermal contact with a stream of atmospheric air at ambient temperature. The compressed nitrogen at 120 Bar is circulated through this second ambient heat exchanger 52 where it extracts and absorbs a considerable amount of additional natural thermal energy from the atmosphere. Thus, the nitrogen is isobarically reheated back to 290° K and emerges from the second ambient heat exchanger 52 as a superheated compressed gas. The thermodynamic state parameters of the compressed superheated nitrogen are: TN6 = 290° K, SN6 = 5. 310 J/gm K, HN6 = 276. 378 J/gm, PN6 = 120 Bar.

The amount of natural thermal energy jazz absorbed from the atmosphere while circulating through the second ambient heat exchanger 52 is HN6 ~ HN5 = 140. 272 J/gm.

After leaving the second ambient heat exchanger 52, the superheated pressurized nitrogen is fed into a second load-leveling energy storage vessel 54 that is also maintained in thermal contact with flowing atmospheric air. The high pressure nitrogen gas is withdrawn from this

storage vessel 54 and fed into the second isentropic expander 56 where it is expanded down to a pressure of 25 Bar (362.60 lb/in2). The resulting thermodynamic state parameters are: TN7 = 181. 630° K, SN7= 5.310 J/gm K, HN7 = 173. 397 J/gm, PN7 = 25 Bar. The specific mechanical work WN2 generated from this second isentropic expansion is FkN 2 = HN6-HN7 =102. 981 J/gm.

The expanded nitrogen leaving the second isentropic expander 56 at 181. 630° Kis fed into the third ambient heat exchanger 58 that is also maintained in thermal contact with atmospheric air at ambient temperature. The compressed nitrogen at 25 Bar is circulated through this third nitrogen heat exchanger 58 where it extracts and absorbs a considerable amount of additional natural thermal energy from the atmosphere. Thus, the nitrogen is isobarically reheated back to 290° K and emerges from the third heat exchanger 58 as a superheated compressed gas at a pressure of 25 Bar (362.594 lbs/in2). The thermodynamic state parameters of the compressed superheated nitrogen are: TNS = 290° K, SN8 = 5.838 J/gm K, Han8= 295.141 J/gm, PN8= 25 Bar.

The amount of natural thermal energy QN3 absorbed from the atmosphere while circulating through the third ambient heat exchanger 58 is HN8 - HN7 = 121. 744 J/gm.

After leaving the third ambient heat exchanger 58, the superheated pressurized nitrogen is fed into the third load-leveling energy storage vessel 60 that is also maintained in thermal contact with the atmosphere at ambient temperature. The compressed nitrogen gas is withdrawn from this vessel 60 and fed into the third isentropic expander 62 where it is expanded down to a pressure of 6 Bar (87.02 lb/in2). The resulting thermodynamic state parameters are: TN9 = 191. 731° K, SN9 = 5. 838 J/gm K, HN9 = 195.749 J/gm, PN9 = 6 Bar. The specific mechanical work WN3 generated from thisthird isenkopic expansion is WN3 = HN8 - HN9 = 99. 392 J/gm.

The expanded nitrogen leaving the third expander 62 at 191. 731° K is fed into the fourth ambient heat exchanger 64 that is also maintained in thermal contact with another stream of air at ambient temperature. The compressed nitrogen at 6 Bar is circulated through this fourth heat exchanger 64 where it extracts and absorbs still more natural thermal energy from the atmosphere. Thus, the nitrogen is isobarically reheated back to 290° K and emerges from the fourth heat exchanger 64 as a superheated compressed gas. The thermodynamic state parameters of the compressed superheated nitrogen are: TNIO = 290° K, SN, p = 6.275 J/gm K, HNIO = 299. 560 J/gm, PNIO = 6 Bar.

The amount of natural thermal energy QN4 absorbed from the atmosphere while circulating through the fourth ambient heat exchanger 64 is HNIO-HN9 =103. 811 J/gm.

After leaving the fourth ambient heat exchanger 64, the superheated pressurized nitrogen is deposited into the fourth load leveling compressed gas energy storage vessel 66 that is also maintained in thermal contact with the atmosphere at ambient temperature. The gas in the fourth energy storage vessel 66 is fed into the fourth isentropic expander 42 where it is expanded down to a pressure of 1.000 Bar. The resulting thermodynamic state parameters are: TN11 = 173. 47°

K, SNl 1 = 6. 275 J/gm K, HNII=179. 336J/gmP = 1. 000 Bar. The specific mechanical work generated from this fourth isentropic expansion is #N4 = HN, O-HNI, = 120.224 J/gm.

Upon leaving the fourth expander 42 at a temperature of 173. 47° K, the nitrogen vapor is fed into the thermally insulated low temperature heat exchanger 40 where it is isobarically cooled down to 125. 756° K by the liquefied nitrogen leaving the hydraulic compressor 38. The thermodynamic state parameters leaving the low temperature heat exchanger 40 are: TNl2 = 125. 756° K, SN = 5. 938 J/gm K, Han12 = 129. 302, PN12 = 1. 0 Bar. The vapor is then fed into the magnetic condenser 32 where it is cooled down to 76° K and liquefied. The amount of thermal energy QE that must be extracted in the magnetic condenser 32 to achieve this liquefaction is QE HNn2-HNo = 253.523 J/gm. (10) The operating principles of the magnetic condenser are such that this heat QE is absorbed in the condenser by using the demagnetization process to create the resulting heat of magnetization that is equal to QE which is converted into mechanical work by the rotating turbines and used to cancel out the current losses in the condenser's superconducting solenoids due to the inductive coupling of the magnetic dipoles in the paramagnetic oxygen. Thus, in order for the condenser to absorb this heat energy QE, it must be capable of generating a continuous heat sink where the total heat of magnetization is equal to QE. The design and dimensions of the preferred embodiment of the magnetic condenser are based upon this requirement which has been quantitatively determined in the above thermodynamic analysis of the cryogenic engine and expressed by equation (10).

The total amount of specific mechanical work WN generated by the cryogenic engine is #N = #N1 + #N2 + #N3 + #N4 = 449.233 J/gm.

Therefore, the net specific output work generated by the cryogenic engine is #NET = #N - #C = 376.472 J/gm. (11) If m denotes the rate of mass flow (gm/sec) through the cryogenic engine, the output power P (Watts) is P = 7SWNET (12) The total amount of natural thermal energy that the nitrogen working fluid absorbed from

the atmosphere while circulating through the four ambient heat exchangers is <BR> <BR> <BR> <BR> <BR> A/ A nA n/<BR> QN QN1 + QN2 + QN3 + QN4 617. 550 J/gm Hence, the thermal efficiency T) of the cryogenic engine is Since the thermal efficiency of large multi-megawatt prior art conventional condensing heat engines with maximum temperatures of about 1, 100° F is only about 0.40, the efficiency of the condensing cryogenic engine is significantly higher. And, most importantly, the cryogenic engine burns no fuel, generates no exhaust products (no pollution), and generates no sound.

The above quantitative analysis enables the total power output P of the cryogenic engine to be calculated corresponding to a given mass flow rate of working fluid m. For example, a mass flow rate of only 20 gm/sec will generate 7.5 KW. A flow rate of 50 gm/sec will generate an output of 18. 8 KW. This represents a significant improvement over my prior invention U. S.

Patent No. 5,040, 373.

Fig. 5 is a schematic perspective plan view of the preferred embodiment of the magnetic condensing system 32 designed for condensing the vapor discharged from the cryogenic engine 44 described above illustrating its design and construction. As is illustrated in this figure, the central primary heat transfer conduit 70 is designed as a closed hexagonal loop with superconducting solenoids 72 mounted at each vertex 74 and at the mid-sections of each side.

Thus, there are 12 superconducting solenoids 72 mounted around the primary heat transfer conduit 70. The system is designed such that the liquefied oxygen moves through this conduit 70 in a clockwise direction. The hexagonal primary conduit 70 is made of copper to give it high thermal conductivity. (Copper is non-magnetic and is not effected by magnetic fields. ) Each solenoid 72 is fitted with two, one-way doors 76 (Fig. 6) mounted on each end of the bores 78 thereby providing sealed chambers 80 inside each solenoid. The doors 76 are opened and closed by electrically energized, fast-acting, computer controlled actuators 82.

Referring to Fig. 5, since the cooling generated by the magnetic condenser occurs within the liquefied oxygen 84 inside the chambers 80 when the liquefied oxygen 84 undergoes demagnetization which occurs when the charged solenoids are discharged, the condensing tubes are designed as comprising twelve individual tubes 86 wound around the primary conduit 70 between each solenoid 72. The incoming vapor 88 discharged from the low-temperature heat exchanger 40 is fed into the magnetic condenser 32 via an inlet conduit 90 and divided into 12 equal streams with equal mass flows by a central distributer 92. Thermally insulated feeding

conduits 94 carry the vapor 88 from the distributing system 92 to each of the twelve condensing tubes 86. These condensing tubes 86 are also made of copper and are tightly wound around the primary heat transfer conduit 70 as helical coils 86 in thermal contact with the central heat transfer conduit 70. The vapor 88 is cooled by passing through the condensing coils 86 and emerges as liquefied nitrogen at 76° K. After circulating through the condensing coils 86, the liquefied nitrogen is fed into thermally insulated return conduits 96 which are connected to the liquefied nitrogen outlet conduit 98. The liquefied nitrogen is then fed into the low pressure isentropic compressor 34 (Fig. 4), compressed to 2.0 Bar, and circulated around the various components of the magnetic condenser as cryogenic coolant before leaving the condenser 32.

The superconducting solenoids 72 will have maximum magnetic fields of 30 T. The physical dimensions are: outside diameter = 30 cm (11.8 in), inside bore diameter = 10.4 cm (4.09 in), and the length (thickness) of the solenoids 100 mounted at the mid-points of the straight sections of the hexagonal primary conduit 70, will be taken to be 15 cm (4.7 in). (The detailed design and construction of high-field superconducting solenoids is described in the article, "Advanced High-Field Coil Designs: 20 Tesla,"Advances in Cryogenic Engineering, Vol. 29, pp. 57-66, by R. Hoard et al. ) The solenoids 72 in the preferred embodiment are designed such that the magnetic field gradient on one side is slightly different from the field gradient on the other side. This is obtained by concentrating more superconductor on one side of the solenoid. This will result in generating more magnetic attractive force on one side than on the other so that the liquefied oxygen will be forced to move around the hexagonal central conduit 70 in a clockwise direction. The solenoids 72 are also fitted with cylindrical tube sections 102 on each side made of soft iron which confine the magnetic fields generated by the solenoids to relatively small regions 104 that envelop the central conduit 70. A plurality of thermally insulated support struts 106 connect all the solenoids together in a rigid mounting structure which also supports the hexagonal heat transfer conduit 70 that passes through each solenoid 72.

The inside diameter of the primary heat transfer conduit 70 that passes through the solenoids 100 mounted at the mid-points of each side of the primary conduit sections is 10 cm. (3. 94 in). Thus, the chambers 80 inside these bores will have a volume V=1, 178.097 cm3.

The other solenoids 108 mounted around the vertices of the primary conduit 70 are curved but designed to have the same inside chamber volume V. The superconductor 110 of the solenoids 72 is constructed with high-temperature superconducting wires such that the cryogenic coolant 112 circulating in double-walled cryogenic thermal shields 114 around each solenoid 72 is liquefied nitrogen at a temperature of 77° K which is obtained from the condensing coils 86. (See "Critical Current Properties Under High Magnetic Fields Up To 30 T For Y-Ba-Cu-O Films By MOCVD", IEEE Transactions On Magnetic, Vol. 27, No. 2, March 1991, by S. Matsuno et al.)

Each side of the hexagonal primary heat transfer conduit 70 has a length of 100 cm (39.37 in). Hence, the length (see Fig. 5) of the hexagonal primary heat transfer conduit 70 (measured from the center of the conduit) is 200 cm (78.74 in or 6.56 ft) and the width is 173.21 cm (68. 16 in or 5. 69 ft). Since the outside diameter of the solenoids 72 is 30 cm, the outside length between opposite solenoids is 230 cm (90.55 in or 7.54 ft) and the width is 203.21 cm (80. 00 in or 6.67 ft). When the multilayer cryogenic thermal insulation 116 and the double wall thermal shield 114 is added, the total outside length of the magnetic condenser 32 will be approximately 232 cm (91.34 in or 7.61 ft) and the total outside width will be about 205.21 cm (80.79 in or 6.73 ft).

The overall outside thickness including the thermal insulation 116 will be about 35 cm (13. 78 in or 1.15 ft).

Fig. 6 is an enlarged longitudinal perspective view of the primary heat transfer conduit 70 between two adjacent solenoids 72 illustrating the design and construction of the magnetic energy turbines 120 mounted inside. There are a total of 12 such turbines 120 mounted inside the primary heat transfer conduit 70 as shown in Fig. 5. They are constructed with a non-magnet material such as plastic or fiberglass composite material. They are supported inside the conduit 70 by a system of rotating circular sleeve rings 122 with flanges 124 that fit into slots 126 mounted inside the wall of the stationary primary conduit 70. Fig. 7 is an enlarged transverse cross-sectional view further illustrating the design and construction of the supporting sleeves 122.

As shown in Fig. 6, the twisting (spiraling) shape of the turbine blades 128 have an increasing pitch so that the liquid oxygen 130 flowing inside the conduit 70 from the discharged solenoid 132 to the charged solenoid 134 through the turbine20 under the strong magnetic attractive forces of the charged solenoid 134 will decelerate the liquefied oxygen 130 as the liquefied oxygen 130 approaches the charged solenoid 134 such that the liquefied oxygen has very little translational velocity as it enters the bore 136 of the charged solenoid 134. Since the viscosity of liquefied oxygen at cryogenic temperature is among the lowest of all fluids, and therefore is an excellent cryogenic lubricant, it is possible to design the magnetic energy turbines 120 with very high efficiency. Essentially all of the directed kinetic energy of the liquefied oxygen pulled into the chamber 80 of the charged solenoid 134 by the magnetic attractive forces will be converted into mechanical work by the magnetic energy turbine 120. An electrical generator 138 converts the mechanical work generated by the turbine 120 into electric energy. The coupling system between the turbine 120 and generator 138 is illustrated in Figs. 6 and 7. A system of groves 140, mounted on the external side of the rotating sleeves 122, that are rigidly connected to the rotating turbine 120, turn the driving wheel 142 with sprockets 144 that fit into the grooves 140. The driving wheel 142 is connected to the drive shaft 146 of the electric generator 138. The design thereby provides a means for transferring the mechanical work AH. generated by the turbine 120 rotating inside the sealed primary conduit 70 to the electric generator 138 that is

mounted outside the conduit 70.

The current is switched from the charged solenoids to the discharged solenoids via superconducting switching circuits 148 controlled by a central operating computer 150 (Fig. 5).

The current is transferred from the solenoids and switching circuits 148 via superconducting conduits 152. Likewise, the current generated by the generators 138 is also fed into the current switching circuits 148 via electrical conduits 154 which is also fed into the solenoids during the charging process. As described above, when the paramagnetic liquefied oxygen is pulled into a charged superconducting solenoid by the magnetic attractive forces, the energy comes from the inductive energy of the solenoid. This results in a slight decrease in the inductive energy of the solenoid that is manifested by a slight decrease in its current. The mechanism that causes this current loss is due to the inductive coupling between the magnetic dipoles in the liquid oxygen and the magnetic field of the charged solenoids. By feeding all of the current generated by the electric generator 138 back into the solenoid when it is being charged, the original inductive energy of the solenoid will always be restored to its initial value. This is accomplished by the switching circuits 148. The control computer 150 operates from control commands sent by the human operator of the engine and by various transducers 156 that monitor the thermodynamic parameters at various flow points 158 in the magnetic condenser 32 and in the cryogenic engine 44. The current switching system 148 is similar to prior art current switching circuits designed for superconducting motors but operate at a much lower frequency. Detailed designs of superconducting current switching circuits can be found in the following references: "Superconducting Motors"pages 115-131 in the book, Superconductivity-The New Alchemy, 1989 by John Langone; Introduction To Superconducting Circuits, John Wiley & Sons, Inc., 1999 by Alan M. Kadin; and Superconducting Devices, Academic Press, Inc. , 1990, edited by Steven T. Ruggiero and David A. Rudman.

The detailed operating parameters of the magnetic condenser operating by the magentocaloric effect corresponding to the preferred embodiment of the condenser are given in equations (8). By converting the kinetic energy of the liquid oxygen moving through the primary heat transfer conduit 70 pulled by the magnetic attractive forces of the charged superconducting solenoids 134 (Fig. 6), the liquid will enter the chambers 80 inside the bores 136 of the charged solenoids 134 where it reaches maximum magnetization with very little velocity. Thus, the liquid inside the chambers 80 is isothermally magnetized. The temperature of the liquid as it enters the chambers 80 is equal to the initial temperature Tl = 56° K. However, the initial entropy S1 of the liquid oxygen inside the chambers 80 is reduced by an amount ASm given by equation (1) due to dipole alignment with the magnetic field B by an amount ASm given by equation (1). When the magnetic field B is turned off by transferring the current in the charged solenoids 134 to the upstream adjacent solenoids via the current switching circuit 148, the liquid

oxygen becomes demagnetized and its temperature drops by an amount AT, given by equation (4). Since this temperature drop is 1. 394° K, the temperature becomes T2 = Tl-AT) n = 54. 606° K. Thus, the liquefied oxygen inside the chambers 80 becomes a heat sink for absorbing an amount of thermal energy Qm = CAT.. = 2. 31679 J/gm = heat of magnetization MI »,. Since the density of liquefied oxygen at 56° K is 1. 299 gm/cm3, the total amount of heat that the liquid oxygen inside each chamber 80 can absorb at temperature T, = 56° K without its temperature rising above 56° K after the magnetic field is turned off is pVQM = 3,545. 495 J. This heat will be extracted from the vapor circulating around the primary heat transfer conduit 70 inside the condensing tube 86 at an initial temperature of 125. 756° K. Since the difference in temperature is so great the heat transfer between the nitrogen vapor moving through the condensing tube 86 and the liquefied oxygen inside the chambers 80 is fairly rapid. In order to achieve a high rate of heat transfer between the nitrogen and the oxygen, the chambers 80 are fitted with a plurality of thin thermal surfaces 160 made of copper that extend longitudinally through the chambers 80 in thermal contact with the liquefied oxygen and primary heat transfer tube 70 as shown in Fig.

8. The mass flow rate of the nitrogen vapor entering the condensing tubes 86 at a pressure of 1.0 Bar is such that the temperature is reduced down to 76° K where it becomes saturated, and is liquefied at this temperature by the extraction of additional thermal energy (heat of vaporization).

As described above, incoming vapor is fed into twelve heat transfer condensing tubes 86 via the distributer 92. The heat loss in the liquified oxygen due the demagnetization effect is transferred to the primary heat transfer conduit 70 which is, in turn, transferred to the twelve heat transfer tubes (condensing tubes) 86 via the distributer 92. The mass flow rate m of the vapor 88 entering the magnetic condenser 32 is designed such that this heat loss is exactly equal to the heat extracted from the vapor mQE given in equation (10). Since there are 6 portions of liquefied oxygen that undergo demagnetization simultaneously each time the current is switched from the charged solenoids to the discharged solenoids, and the current is switched R times per minute, the total amount of heat that is extracted from the incoming vapor per minute (cooling power) by the magentocaloric effect is given by the equation Qc = 6p VRQm = 21,272. 974R Joules/min (13) In the preferred embodiment, the magnetic condenser 32 is designed to enable the cryogenic engine to generate 10 KW of continuous output power. According to equations (11) and (12), the mass flow m of nitrogen that will generate 10 KW of continuous power is 26.562 gm/sec. Since the condenser has to extract QE = 253.523 J of thermal energy to liquefy each gram (see equation 10), the magnetic condenser would have to generate a cooling power of mQE = 26.562x253. 523 = 6734. 180 Joules/sec = 4. 041x105 Joules per min. Consequently,

the required repetition rate R can be calculated from the equation Hence, the time interval between the current switches is 3.16 sec. Since the time required for the liquefied oxygen to pass through the conduit sections from one solenoid to the adjacent solenoid will be less than 2 seconds, a repetition rate R = 19. 0 per minute will be well within the operating limits. (If the repetition rate R were less than 19.0, the temperature of the liquefied oxygen would begin rising above 56° K because the heat loss generated by the magnetocaloric effect would be less than that required to liquefy the nitrogen vapor. If it were greater than 19.0, the temperature of the liquid oxygen would begin to fall below 56° K.) Since the temperature drop AT in the liquefied oxygen occurs almost instantaneously when the current is switched from one solenoid to the adj acent solenoid, the magnetic condenser could be operated at a higher repetition rate R to generate a higher cooling power. This would enable the cryogenic engine to be operated at a higher mass flow rate th for generating a higher level of continuous power.

There are many other variations and modifications of the magnetic condensing system.

For example, smaller magnetic condensing systems could be used with small cryogenic engines for generating both electricity and refrigeration for private homes. The system could also be used for many different applications besides condensers of cryogenic engines. For example, the magnetic condensing system shown In Fig. 5 could also be used for manufacturing liquid air directly from the atmosphere. By feeding in atmospheric air at ambient temperature and pressure into the inlet duct 90, liquefied air would be discharged from the outlet duct 98. Another embodiment could be designed to provide air conditioning (refrigeration) for homes in hot environments. In this embodiment, hot air from the interior of a building would be fed into the inlet duct 90, cooled by transferring heat to the paramagnetic fluid to some comfortable temperature, and discharged back into the building through the outlet duct 98. Another embodiment could be designed to provide refrigeration for food storage (i. e. , refrigerators).

Still other embodiments and variations of the basic invention are possible. For example, since nitric oxide (NO) is another gas that is naturally paramagnetic, the magnetic condensing system could also be designed using liquefied nitric oxide as the paramagnetic working fluid instead of liquid oxygen. It may also be possible to artificially create another liquefied gas that is more paramagnetic than liquid oxygen which could be used in the practice of this invention.

The paramagnetic working fluid could also be a low temperature paramagnetic gas such as oxygen gas.

As various other changes and modifications can be made in the above method and apparatus for generating an artificial low temperature heat reservoir without departing from the

spirit or scope of the invention, it is intended that all subject matter contained in the above description or shown in the accompanying drawings should be interpreted as illustrative and not in a limiting sense.