For hundreds of years engineers and scientists have recognized that the ambient thermal energy of the natural environment that is heated by the sun contains essentially unlimited amounts of free thermal energy. Unfortunately, all prior attempts to harness this natural heat energy and convert it into mechanical work with high power densities by a closed cycle condensing heat engine utilizing the natural environment as its high temperature heat reservoir have failed. As a result of all of these unsuccessful attempts, thermodynamicists have concluded that such engines are impossible. In fact, thermodynamicists are so convinced that such engines are impossible, they have categorically labeled them as xe2x80x9cperpetual motion machines of the second kind.xe2x80x9d It is important to point out however, that this negative conclusion is not based on any fundamental physical law of nature but rather on the unsuccessful attempts to construct such engines. Although the xe2x80x9csecond law of thermodynamicsxe2x80x9d is usually cited as the basic reason why such engines are believed to be impossible, the second law itself is based on unprovable xe2x80x9cpostulatesxe2x80x9d laid down by Kelvin, Clausius and Planck over a century ago when the principle of conservation of mass and energy was accepted without question. (See Thermodynamics, Charles E. Merrill Publishing Co., Columbus, Ohio, pages 147-153 by Joachim E. Lay.) The Kelvin-Planck statement of the second law of thermodynamics is: xe2x80x9cIt is impossible to construct an engine which, operating in a cycle, will produce no other effect than the extraction of heat from a single heat reservoir and the performance of an equivalent amount of work.xe2x80x9d
By designing a cyclic heat engine that falls outside the operating conditions of the second law of thermodynamics (the premise) it is possible to harness the natural thermal energy of the environment at ambient temperature and convert a portion of it into useful mechanical work. One such heat engine is a simple toy called the xe2x80x9cdrinking birdxe2x80x9d that can be found in almost any novelty shop. Although this engine is a closed cycle condensing heat engine and uses the ambient environment as its high temperature heat reservoir, it operates by generating an artificial low temperature heat reservoir by evaporating water. Hence, it does not operate according to the prescribed conditions of the Kelvinxe2x80x94Planck statement of the second law of thermodynamics and therefore cannot violate this law.
The basic thermodynamic operating principles of the drinking bird engine were analyzed by Carl Bachhuber in his paper, Energy From the Evaporation Of Water, American Journal of Physics, Vol. 51, No. 3, March 1983, pp. 259-264. In particular, Bachhuber has shown that ordinary water can be used to extract an unlimited amount of natural thermal energy from the surrounding environment and convert it into mechanical work. Moreover, the specific energy of the water that can be converted into useful mechanical work by this engine is approximately twice the specific energy available in automotive storage batteries. In a technical report issued by the Rand Corporation in August 1966, entitled A Simple Heat Engine of Possible Utility in Primitive Environments, Rand Corporation Publication No. P-3367, Richard Murrow proposed constructing larger versions of this engine for pumping water from the Nile river. A scaled up model of the basic drinking bird engine was constructed to a height of seven feet and found to be able to extract a considerable amount of natural heat energy from the ambient environment and convert it directly into mechanical work. In particular, the engine would be capable of extracting an unlimited amount of natural heat energy and convert it into an unlimited amount of mechanical work. (See, xe2x80x9cThe Research Frontier-Where is Science Taking Us,xe2x80x9d Saturday Review, Vol. 50, Jun. 3, 1967, pp. 51-55, by Richard Murrow.) Obviously, engines such as these which operate by converting the natural heat energy of the environment at ambient temperature into an unlimited amount of mechanical work are not xe2x80x9cperpetual motion machines.xe2x80x9d In principle, larger engines of this type could be used to propel ocean going vessels indefinitely using ordinary sea water for generating an unlimited amount of mechanical work. Although this possibility is generally believed to be thermodynamically impossible, it is clearly not impossible. The existence of these engines proves that it is indeed possible to convert the natural heat energy of the environment at ambient temperature into an unlimited amount of mechanical work by creating an artificial low temperature heat reservoir below ambient. What has to be emphasized here regarding the possibility of violating the second law of thermodynamics is the creation of an artificial low temperature heat reservoir. If any cyclic heat engine produces such a low temperature heat reservoir while it operates it is, xe2x80x9cstrictly speaking,xe2x80x9d operating outside the domain of the second law and therefore, cannot logically be subject to this law. However, this is a moot point because the second law of thermodynamics is not really a fundamental law of physics as pointed out in the book cited above. However, it should also be emphasized that the present invention is not a heat engine, it is a condensing system.
In order to better understand the basic operating principles of the invention and its distinguishing operating characteristics that make it uniquely different from anything it the prior art, it will be useful to review the fundamental operating principles of prior art condensing heat engines, and, in particular, the operating principles of their condensing systems.
Prior art condensing heat engines such as the steam engine operate by compressing liquefied working fluid (such as water in the case of steam engines) to high pressure by a hydraulic compressor and feeding it into a boiler maintained at high temperature by burning fuel. Since a liquid is nearly incompressible and has very low specific volume, the amount of mechanical work consumed in compressing the liquefied working fluid is relatively low. When the compressed fluid is circulated through the boiler it is heated and vaporizes to high pressure gas (steam). This results in a several hundred fold increase in its specific volume. This high pressure gas is then fed into an expander which converts a portion of the heat absorbed in the boiler into mechanical work which is usually used for turning an electric generator. Since the specific volume of the high pressure gas expanding through the expander is many times greater than the specific volume of liquid, the mechanical work generated by the expander is many times greater than the mechanical work consumed by the compressor. After leaving the expander as low temperature vapor, this vapor is fed into a condenser where it is re-liquefied by utilizing the natural environment as a low temperature heat sink to extract the heat of vaporization. After the liquefied working fluid is discharged from the condenser it is recompressed and the cycle is repeated. The condenser is therefore just as important as the boiler because it reduces the specific volume of the working fluid so that the work consumed in recompressing it is a small fraction of the mechanical work generated by expanding it.
The most efficient cooling system (i.e., refrigerator) is known as a xe2x80x9cCarnot refrigerator.xe2x80x9d The amount of mechanical work W required to transfer a quantity of heat Q from a low temperature TL to a high temperature TH is given by   W  =      Q    ⁡          (                                    T            H                    -                      T            L                                    T          L                    )      
The natural environment at ambient temperature plays a key role in the design of condensing heat engines and refrigerators. It represents a temperature zone which divides the operating temperature regimes of cyclic heat engines and refrigerators. This is because the environment at ambient temperature represents the low temperature heat reservoir for condensing heat engines which operate by absorbing heat energy from a high temperature reservoir above ambient temperature and generating mechanical work, while in refrigerators the natural environment represents the high temperature heat reservoir which operate by absorbing heat energy from a low temperature reservoir below ambient temperature, transferring it to the high temperature heat reservoir, and consuming mechanical work.
The reason why prior art closed cycle condensing heat engines operate above ambient temperature (i.e., the boiler) is because there is no natural heat sink below ambient temperature that can be used in a condensing system to absorb the heat of vaporization to re-liquefy the vapor discharged from the work generating expansion system. Hence, closed-cycle condensing heat engines operating under the well known laws of thermodynamics must operate above ambient temperature (i.e., the high temperature heat reservoir must be above ambient temperature that is maintained by burning fuel). Unfortunately, burning fuel is expensive and harmful to the environment. However, the drinking bird engine is a cyclic heat engine that does not operate above ambient temperature because it generates an artificial low temperature heat reservoir by evaporating water. Unfortunately, the power densities of these engines are very low. But they are extremely important because they demonstrate the fact that it is possible to construct a cyclic heat engine that converts natural heat energy at ambient temperature in the environment into an unlimited amount of mechanical work. The key to designing this type of engine is finding a method for generating an artificial low temperature heat sink that does not consume more mechanical work than can be generated by the engine.
There is one type of heat engine that can be operated below ambient temperature and produces both mechanical work and refrigeration at very high power densities. As in the drinking bird engine, it operates by utilizing the natural and unlimited heat energy in the environment at ambient temperature as its high temperature heat reservoir by converting this heat energy directly into mechanical work. And it produces power densities far greater that any other heat engine. This engine is a xe2x80x9ccryogenic engine.xe2x80x9d In this engine liquefied working fluid at cryogenic temperature, such as liquefied nitrogen at 77xc2x0 K. (xe2x88x92196xc2x0 C. or xe2x88x92321xc2x0 F.) which is the usual working fluid in cryogenic engines) is compressed to very high pressure (e.g., 500 Bar or 7,252 lbs/in2) by a hydraulic compressor and fed through a plurality of serially connected heat exchangers maintained in thermal contact with the natural environment at ambient temperature, and a like plurality of expanders interposed between adjacent heat exchangers. The high pressure liquefied working fluid entering the first heat exchanger creates a significant temperature gradient across the thermal surfaces and a large amount of natural heat energy is extracted from the environment at ambient temperature and rapidly absorbed by the circulating working fluid at cryogenic temperature. The liquefied working fluid is isobarically heated above its critical temperature (126.3xc2x0 K. in the case of nitrogen working fluid) and completely vaporized into a super high pressure gas. The vaporization results in a several hundred fold increase in the specific volume of the condensed working fluid. The process is identical to that of feeding compressed water into a high temperature boiler. The water absorbs the heat and vaporizes into high pressure steam resulting in an increase of its specific volume. In the case of the cryogenic engine, the boiler is the natural environment at ambient temperature.
The cryogenic working fluid emerges from the first heat exchanger as a super high pressure, superheated gas at about ambient temperature. It is then fed into the first isentropic expander where a large portion of the heat energy absorbed from the natural environment in the first heat exchanger is converted into mechanical work. The pressure ratio of the first expander is such that the outlet pressure of the expanded gas leaving the expander is still fairly high. Thus, since the expansion process reduces the temperature of the exhaust gas significantly below ambient temperature, it is fed into another ambient heat exchanger that is also maintained in thermal contact with the natural environment in order to extract still more natural thermal energy. After this second isobaric heating process, the pressurized gas is withdrawn from the second ambient heat exchanger at about ambient temperature and fed into a second isentropic expander where a large portion of the natural thermal energy extracted from the environment while circulating through the second heat exchanger is converted into additional mechanical work. This process of absorbing natural thermal energy from the environment and converting it into mechanical work is continued until the exhaust pressure of the gas emerging from the last expander is equal to atmospheric pressure whereupon the gas is discharged into the open atmosphere. The operating details of this cryogenic engine can be found in U.S. Pat. No. 3,451,342 filed Oct. 24, 1965 by E. H. Schwartzman entitled xe2x80x9cCryogenic Engine Systems and Method.xe2x80x9d Since high-pressure cryogenic expanders are very small, have power densities far higher than any internal combustion engine, operate without generating any sound, and produce no polluting exhaust products, cryogenic engines may represent the ultimate power source for propelling road vehicles. (See the article, xe2x80x9cLiquid Nitrogen as an Energy Source for an Automotive Vehicle,xe2x80x9d Advances in Cryogenic Engineering, Vol. 25, 1980, pp. 831-837 by M. V. Sussman.)
Although cryogenic engines operate below the ambient temperature of the natural environment and generate both mechanical work and refrigeration, they are not cyclic heat engines. When the supply of liquefied working fluid at cryogenic temperature is consumed, the engine (and refrigerator) stops operating and must be re-filled with more liquefied gas. Since these engines operate by strictly thermodynamic processes according to the principles of thermodynamics, the expanded working fluid discharged from the last expander cannot be recondensed into a liquid at cryogenic temperature because there is no natural heat sink available at cryogenic temperature to absorb the heat of vaporization. Thus, there is no thermodynamic method that can be used to re-liquify the expanded working fluid in order to enable the engine to operate cyclically. Since the cost of liquefied gas at cryogenic temperature is very expensive, these prior art cryogenic engines are much more expensive to operate then internal combustion engines. However, there is a non-thermodynamic method that can be used to reduce the entropy of the working fluid of a cryogenic engine without having to transfer heat energy to a heat sink if the working fluid is paramagnetic. This method will enable cryogenic engines to be operated cyclically.
It follows from the Carnot equation for refrigators that when TLxe2x86x920, the required input work Wxe2x86x92∞. Thus, it is a physical impossibility to achieve temperatures below approximately 0.4xc2x0 K. by using strictly thermodynamic processes. For many years this temperature (0.4xc2x0 K.) was believed to represent an absolute xe2x80x9ctemperature barrierxe2x80x9d which could not be broken because of basic laws of thermodynamics. However, in 1926 Debye proposed using an electromagnetic process that is outside the theoretical framework of classical thermodynamics (i.e., that is not a thermodynamic process) to break this thermodynamic barrier and achieve temperatures that are several orders of magnitude below 0.4xc2x0 K. This process is called xe2x80x9cadiabatic demagnetizationxe2x80x9d or xe2x80x9cmagnetic cooling.xe2x80x9d Basically, this process involves subjecting a paramagnetic substance at low temperature (usually a solid paramagnetic salt) to an intense magnetic field. This external magnetic field will heat the substance. This heating effect is called the heat of magnetization. However, since the substance is paramagnetic, a large number of the magnetic dipoles within the substance will become aligned with the external magnetic field and because of this ordering, the entropy will remain unchanged during this heating. When the heat of magnetization is extracted by a cryogenic heat sink (e.g., liquid helium at 1xc2x0 K.) the entropy of the magnetized substance decreases by an amount xcex94Sm. By thermally isolating the substance and removing the magnetic field, the reduced entropy of the substance remains unchanged but the temperature will fall way below that of the heat sink. By using this non-thermodynamic electromagnetic process (also known as the xe2x80x9cmagnetocaloric effectxe2x80x9d), temperatures as low as 0.0001xc2x0 K. are possible.
It is important to point out and emphasize that 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 (i.e., the degree of random molecular motion) remains constant due to magnetic 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 thermodynamic laws cannot be applied to non-thermodynamic processes. (See, xe2x80x9cClassical Physics Gives Neither Diamagnetism nor Paramagnetism,xe2x80x9d Section 34-6, page 34-8, in The Feynman Lectures On Physics, by R. Feynman, Addison-Wesley Pub. Co., 1964.)
In 1989 the applicant discovered how to make a cryogenic engine operate cyclically (to provide a condensing cryogenic engine) by using a working fluid that is paramagnetic (such as oxygen) and achieving the required decrease in entropy by using the magnetocaloric effect (adiabatic demagnetization) generated by a superconducting solenoid. The technical details are described in my U.S. Pat. No. 5,040,373 entitled xe2x80x9cCondensing System And Operating Systemxe2x80x9d issued Aug. 20, 1991. This condensing cryogenic engine invention was important because theoretically it provided a cryogenic engine that operated cyclically capable of converting natural heat energy at ambient temperature into an unlimited amount of mechanical work at high power densities. Prior to this invention such an engine was taken for granted as being impossible because they were viewed as violating the second law of thermodynamics. What has to be pointed out and emphasized here is that the condensing cryogenic engine described in that invention, and in the present invention, do not violate the second law of thermodynamics because some of its operating principles and processes are outside the domain of classical thermodynamics. It is logically impossible for any engine to violate any of the laws of thermodynamics if some of the operating principles are outside the domain of classical thermodynamics. (In addition, as in the case of the drinking bird engine, the operating conditions of that invention do not satisfy the operating conditions of the second law and consequently cannot logically violate that law.)
Unfortunately, the condensing cryogenic engine disclosed in my original patent was not very practical because the condensation ratio (which is the fractional amount of vapor entering the condensing system that actually condenses) was only 6.53%. And this rather poor performance was based on using a superconducting solenoid generating a magnetic field of 100 T (1,000,000 Gauss) which is currently far beyond engineering feasibility. However, the invention was important because in theory, it provided a method for condensing a vapor at cryogenic temperature without transferring heat to a low temperature heat sink by using the magnetocaloric effect. Although the present invention is also based on utilizing the magnetocaloric effect, this effect does not operate on the working fluid. In the present invention the paramagnetic substance is not the working fluid. This will enable 100% of the expanded working fluid discharged from the last expander of a cryogenic engine to be re-liquefied. 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 compared to my original 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 gas 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 substance, 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 generate no magnetic fields. The liquid in each chamber is magnetized by the magnetic fields and have an initial temperature of 56xc2x0 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 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 in the sealed chambers undergo demagnetization thereby creating a nearly instantaneous temperature drop of about two degrees to 54.61xc2x0 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 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, 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 pulls the liquid into the chambers of the adjacent 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 extended into the secondary conduit. 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 for the superconducting solenoids which are constructed with high-temperature superconducting wire.