LOW TEMPERATURE MAGNETOHYDRODYNAMICS POWER SYSTEM

Abstract

The present invention discloses a magnetohydrodynamics power system which utilizes low temperature heat source. Variable control of the operation of the system, along with determining configurations for specific cases, are made possible by selecting the refrigerant, liquid metal circuit geometry, and by adjusting the system condensing pressure and/or temperature. Adjustable condensing pressure and/or temperature allows the system to react to changing ambient temperature and maximize power output. Adjusting condensing pressure and/or temperature of the system is made possible with a variable condenser pressure controller. The variable condenser pressure controller allows utilization of the physical properties of the refrigerant over a wide range of condensing temperatures/pressures, including pressures in the vacuum range. Meanwhile rare earth permanent magnets in paired Halbach arrays are used in the magnetohydrodynamics generator to augment the magnetic field, and a series electrode connection is made possible to achieve a high voltage output.

Claims

1. A system for converting a low-temperature heat source into power, comprising: a vertically positioned closed-looped liquid metal circuit for containing and circulating a liquid metal, a vertically positioned closed-looped refrigerant circuit for containing and circulating a refrigerant, the liquid metal circuit and the refrigerant circuit interacting with each other through a mixer, a riser and a separator shared by the liquid metal circuit and the refrigerant circuit, a closed-looped heat sink circuit interacting with the refrigerant circuit through a condenser shared by the heat sink circuit and the refrigerant circuit, a closed-looped heat source circuit interacting with the liquid metal circuit through a heat exchanger shared by the heat source circuit and the liquid metal circuit, and a pressure controller, wherein: the low-temperature heat source transfers heat to the liquid metal circulating the liquid metal circuit through the heat exchanger to provide a heated liquid metal, the heated liquid metal enters the mixer and heats the refrigerant circulating the refrigerant circuit into vapor form, the liquid metal and the refrigerant in vapor form producing a two-phase mixture, the two-phase mixture flows up the riser and into the separator to be separated, wherein: the refrigerant in vapor form, after being separated from the liquid metal in the separator, enters through: a recuperator, wherein the refrigerant in vapor form releases heat to liquid refrigerant, the condenser, wherein the refrigerant is further cooled down by passing through a coolant from a heat sink to release heat to the heat sink and the refrigerant in vapor form changes into liquid refrigerant, a liquid pump, the liquid pump drives flow of the liquid refrigerant, the recuperator, wherein the liquid refrigerant is preheated by the refrigerant in vapor form, and the mixer wherein the liquid refrigerant upon mixing with the heated liquid metal entering the mixer changes from liquid refrigerant into the refrigerant in vapor form, and wherein: the liquid metal, after being separated from the refrigerant in the separator, enters through: a magnetohydrodynamic generator through a downcomer, the magnetohydrodynamic generator converts kinetic energy of the liquid metal into electricity, the heat exchanger, wherein the low-temperature heat source transfers the heat to the liquid metal circulating the liquid metal circuit to provide the heated liquid metal, and wherein the pressure controller controls speed of the liquid pump and flowrate of the liquid refrigerant according to an adjustable pressure in the condenser following the changing temperature of the heat sink to vary condensing temperature in the condenser.

2. The system according to claim 1, wherein the low-temperature heat source is a heat source with a temperature below 150? C.

3. The system according to claim 1, wherein ambient air or ambient water is used as the heat sink.

4. The system according to claim 1, wherein the temperature of the heat sink is between ?50? C. and 50? C.

5. The system according to claim 4, wherein the temperature of the heat sink is between ?35? C. and 25? C.

6. The system according to claim 1, wherein the liquid metal is an alloy comprising gallium, indium, and tin.

7. The system according to of claim 6, wherein the liquid metal is Galinstan?.

8. The system according to claim 1, wherein the refrigerant is at least one of hydrocarbon refrigerants.

9. The system according to claim 1, further comprising a gas-lift pump to improve circulation of the liquid metal, wherein gas injection position is configured in the riser in central/axial, annular/axial, or annular/radial mode.

10. The system according to claim 1, wherein rare earth permanent magnets in paired Halbach arrays are used in the magnetohydrodynamics generator to augment the magnetic field, and a series electrode connection is made possible to achieve a high voltage output.

11. The system according to claim 1, wherein the condenser is installed at an elevation sufficient to compensate the inlet pressure of the pump thereby eliminating the use of the pump.

12. The system according to claim 1, wherein the recuperator and the separator are integrated.

13. The system according to claim 1, wherein the recuperator and the mixer are integrated.

14. The system according to claim 1, wherein an additional magnetohydrodynamics generator is installed on the riser.

15. The system according to claim 1, wherein a plurality of magnetohydrodynamics generators is installed in the liquid metal circuit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0083] By way of example only, preferred embodiments of the present invention are described hereinafter with reference to the accompanying drawings, wherein:

[0084] FIG. 1 is a diagram of a known typical configuration of an Organic Rankine Cycle system.

[0085] FIG. 2 is a graph of a typical Organic Rankine Cycle 1.sub.S-2.sub.S-3.sub.S-4.sub.S-5.sub.RS-6.sub.S-1.sub.S: based on heat sink at high end summer temperature; Organic Rankine Cycle 1.sub.W-2.sub.W-3.sub.S-4.sub.S-5.sub.RW-6.sub.W-1.sub.W: based on heat sink at low end winter temperature; Ericsson cycle 1.sub.S-2.sub.S-3.sub.S-4.sub.S-5.sub.ES-6.sub.S-1.sub.S: based on heat sink at high end summer temperature; Ericsson cycle 1.sub.W-2.sub.W-3.sub.S-4.sub.S-5.sub.EW-6.sub.W-1.sub.W: based on heat sink at low end winter temperature.

[0086] FIG. 3 is a diagram of the configuration of a known liquid metal magnetohydrodynamics system.

[0087] FIG. 4 is a graph showing theoretical cycle efficiencies based on Carnot's theorem.

[0088] FIG. 5 is a diagram of the configuration of an embodiment of a low temperature magnetohydrodynamics system according to the present invention.

[0089] FIG. 6 shows a configuration of permanent magnets in paired Halbach arrays and a series electrode connection for an embodiment of a low temperature magnetohydrodynamics system according to the present invention.

[0090] FIG. 7 is a diagram of the configuration of an embodiment of a low temperature magnetohydrodynamics system according to the present invention, without the use of a pump.

[0091] FIG. 8 is a diagram of the configuration of an embodiment of a low temperature magnetohydrodynamics system according to the present invention, with integrated recuperator and separator.

[0092] FIG. 9 is a diagram of the configuration of an embodiment of a low temperature magnetohydrodynamics system according to the present invention, with integrated recuperator and mixer.

[0093] FIG. 10 is a diagram of the configuration of the low temperature magnetohydrodynamics system according to the present invention, with the MHD generators having a dual location.

[0094] Other features and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings, which illustrate, by way of example, the principles of the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0095] It is to be understood that the disclosure is not limited in its application to the details of the embodiments as set forth in the following description. The invention is capable of other embodiments and of being practiced or of being carried out in various ways.

[0096] Furthermore, it is to be understood that the terminology used herein is for the purpose of description and should not be regarded as limiting. Contrary to the use of the term consisting, the use of the terms including, containing, comprising, or having and variations thereof is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The use of the term a or an is meant to encompass one or more. Any numerical range recited herein is intended to include all values from the lower value to the upper value of that range.

[0097] From a thermodynamics perspective, lowering the vapor condensing temperature (T.sub.C) can increase the overall power cycle efficiency.

[0098] For example, if the heat source temperature T.sub.H is 100? C. and the condensing temperature T.sub.C is ?30? C., the cycle temperature difference would be 130? C. Between 100? C. and ?30? C., with Genetron? 245fa (R-245fa) as the working fluid, the ideal Rankine cycle 1.sub.W-2.sub.W-3.sub.S-4.sub.S-5.sub.RW-6.sub.W-1.sub.W in FIG. 2 has an efficiency of 27.64% (vs. 15.87% between 100? C. and 30? C.) and the ideal Erisson cycle 1.sub.W-2.sub.W-3.sub.S-4.sub.S-5.sub.EW-6.sub.W-1.sub.W has an efficiency of 32.25% (vs. 17.65% between 100? C. and 30? C.), thus power generation from the same heat source becomes more favorable.

[0099] Comparison of cycle efficiencies is summarized below in Table 1.

TABLE-US-00001 TABLE 1 Comparison of cycle efficiencies Carnot Efficiency (maximum Rankine Cycle Ericsson Cycle theoretical) Efficiency Efficiency T.sub.H = 100? C. 18.75% 15.87% 17.65% T.sub.C = 30? C. dT = 100? C. T.sub.H = 100? C. 34.84% 27.64% 32.25% T.sub.C = ?30? C. dT = 130? C.

[0100] Further, based on Carnot's theorem, reducing the temperature T.sub.C in a heat engine has a higher cycle efficiency than the option to increase the hot temperature T.sub.H for the same temperature difference (T.sub.H?T.sub.C), as shown in FIG. 4.

[0101] FIG. 4 shows theoretical cycle efficiency based on Carnot's theorem. Reducing the cold sink temperature in a heat engine has higher cycle efficiency than the option to increase the hot temperature for the same temperature difference (T.sub.H?T.sub.C).

[0102] Therefore, a technology that can take advantage of a changing temperature T.sub.C will have the potential to produce more power than the Organic Rankine Cycles and the prior arts of liquid metal magnetohydrodynamics systems which are currently designed to a fixed cold sink temperature.

[0103] The prior arts of the Organic Rankine Cycle and the liquid metal magnetohydrodynamics technology did not provide such a feature in their design which would allow the lowering of the vapor condensing temperature following a change in the ambient temperature.

[0104] According to the present invention, the low temperature magnetohydrodynamics system as disclosed herein provides a means to take advantage of the full ambient temperature range and allows T.sub.C to change, for instance, in a range between 30? C. and ?30? C. as shown in FIG. 2. Therefore, such low temperature magnetohydrodynamics system is more effective in its conversion of heat to power.

[0105] The low temperature magnetohydrodynamics technology leverages the high efficiency of the Ericsson cycle of liquid metal magnetohydrodynamics systems in order to provide a means to produce electricity from low temperature sources.

[0106] The low temperature magnetohydrodynamics technology has specific advantages over competing technologies for applications in cold climate, such as in the Canadian climate.

[0107] The low temperature magnetohydrodynamics systems disclosed herein provide, inter alia, improved efficiency in the following aspects: [0108] 1) The system design and configuration enable better use of lower temperature sinks; [0109] 2) The use of new liquid metal such as Galinstan?; [0110] 3) The use of new refrigerant and/or working fluids; [0111] 4) The use of new lift pumps to improve circulation of metal through computational fluid dynamics and experiment; [0112] 5) The use of new rare earth permanent magnets in paired Halbach arrays and series connection of electrodes. [0113] 6) The use of new natural circulation to diminish or eliminate pump power consumption; [0114] 7) The integration of a separator and a recuperator; [0115] 8) The integration of a mixer and a recuperator; and [0116] 9) The use of a two-phase magnetohydrodynamics generator on a riser.
System Configuration with Better Use of Lower Temperature Sinks:

[0117] According to one aspect of the present invention, a two-pronged approach has been employed to maximize the energy recovery from the heat source: [0118] 1. A double loop system that includes both a refrigerant loop and a liquid metal loop; and [0119] 2. A configuration that takes advantage of cold heat sinks to optimize power output.

[0120] FIG. 5 illustrates the configuration of an embodiment of a low temperature magnetohydrodynamics power system according to the present invention.

[0121] This configuration can effectively transfer heat to a moving liquid metal that is also propelled with the assistance of a refrigerant. The metal passes through a magnetic field and produces its own electric potential that is drawn out to produce electricity.

[0122] FIG. 5 illustrates a configuration of the low temperature magnetohydrodynamics system that converts low temperature heat to power. The system comprises a closed-looped liquid metal circuit for containing and circulating a liquid metal (or liquid metal loop) 10, a closed-looped refrigerant circuit for containing and circulating a refrigerant (or refrigerant loop) 20, a closed-looped heat source circuit (or heat source loop) 30 and a closed-looped heat sink circuit (or heat sink loop) 40 with a pressure controller 50. Both the liquid metal loop 10 and the refrigerant loop 20 are vertically positioned.

[0123] Referring to FIG. 5, a liquid metal fills the liquid metal loop 10, and a refrigerant is used to fill the refrigerant loop 20. Fluids from both loops meet in a mixer 11 to form a two-phase mixture as the refrigerant is in vapor or gas state. This mixture flows up together, in a gas-liquid metal two-phase mode, along a riser 12 into a separator 13, where the refrigerant vapor and liquid metal are separated.

[0124] The refrigerant vapor, after being separated from the liquid metal, is cooled down first by a recuperator 22, then by a condenser 24 by passing through a coolant from heat sink 41 and giving off heat. The refrigerant changes from vapor to liquid in a condenser 24. The heat sink usually is the ambient surrounding. The condenser 24 may be connected to a natural coolant such as air or water. After the condenser 24, a liquid pump 26 drives the flow of the liquid refrigerant in the refrigerant loop 20. The liquid refrigerant first is preheated in recuperator 22, then meets again with hot liquid metal in the mixer 11 to change phase from liquid to vapor, and the cycle continues.

[0125] After separation, the single-phase liquid metal flows down a downcomer 14/16.

[0126] Since the two-phase mixture of liquid metal and refrigerant vapor in the riser 12 is lighter than that of the pure liquid metal in the downcomer 14/16, natural circulation in the liquid metal loop 10 is generated. A stationary magnetohydrodynamic generator (MHD generator) 15 is placed in the liquid metal loop 10 on the downcomer 14/16 to convert the kinetic energy of the moving liquid metal into electricity. Heat source 31 transfers heat to the liquid metal loop 10 via a heat exchanger 17 and helps driving the circulation of both the liquid metal loop 10 and the heat source loop 30. The heat source 31 may be a low-temperature heat source. Since liquid metal has a high thermal conductivity, the heat exchanger could effectively withdraw heat from the low-temperature heat source. Then the heated liquid metal enters the mixer 11 to heat the refrigerant.

[0127] The pressure controller 50 is used to control speed of the pump 26 for the refrigerant in order to adjust the pressure in the condenser 24 (P.sub.C) following the changing ambient temperature (T.sub.S) of the heat sink 41 to vary the condensing temperature (T.sub.C).

[0128] According to an embodiment of the present invention, ambient air or ambient water is used as the heat sink.

[0129] According to an embodiment of the present invention, temperature of the ambient air is between ?50? C. and 50? C.

[0130] For instance, when ambient air is used as heat sink with an ambient temperature (T.sub.S) at ?35? C. in the winter time, the condensing temperature (T.sub.C?30) could reach ?30? C. at a corresponding condensing pressure (P.sub.C?30). The condensing pressure (P.sub.C?30) plus the pressure drop through recuperator 22 and pipes 21 & 23 will be the pressure (P.sub.S?30) in the separator 13.

[0131] When the ambient temperature (T.sub.S) goes up, for instance, at 25? C. in the summer time, the cooling capacity of the heat sink will decrease, so does the rate of condensation, which will result in a higher condensing pressure (P.sub.C+30) at a corresponding condensing temperature reaching 30? C. (T.sub.C+30). Then the pressure in the separator 13 will go up to (P.sub.S+30).

[0132] At the same time, in order to keep the liquid level in the condenser 24, the pump 26 will decrease flow in the summer time following the rise of ambient temperature (T.sub.S) since the rate of condensation will decrease. In contrast, in order to keep the liquid level in the condenser 24, the pump 26 will increase flow in the winter time following the drop of ambient temperature (T.sub.S) since the rate of condensation will be increasing.

[0133] The pressure controller 50 allows the low temperature magnetohydrodynamics system described above to operate in a mode of adjustable condensing pressure (P.sub.C) and corresponding temperature (T.sub.C) following the change of ambient temperature (T.sub.S).

[0134] The benefits of employing an adjustable condensing temperature (T.sub.C) are, inter alia: [0135] The heat sink temperature T.sub.S is maintained by naturally existing coolants such as a body of water or surrounding air. In Canada, ambient air temperatures vary across both a daily and seasonal range. Daily temperature swings of more than 15? C. are common, and below-zero temperatures (sometimes as low as ?35? C.) are seasonally common from late fall through early spring. In order to take advantage of this below-zero ambient coolant, a refrigerant is deliberately used in the refrigerant loop 20 to allow condensing temperature (T.sub.C) to drop below zero so the system efficiency can be increased. [0136] According to thermodynamic principles, the efficiency of the Ericsson cycle power system increases when the temperature difference (T.sub.H?T.sub.C) increases (see FIG. 4) due to the drop of heat sink temperature T.sub.S. Uniquely, the low temperature magnetohydrodynamics system configuration disclosed herein, which is based on the Ericsson cycle, introduces a way to boost the cycle efficiency by allowing it to work in a greater range of temperature difference conditions when the heat sink temperature T.sub.S changes over a great range. [0137] Prior arts of low temperature magnetohydrodynamics systems employ a fixed condensing temperature (T.sub.C) usually based on heat sink or ambient temperature T.sub.S in the summer time. In contrast, the low temperature magnetohydrodynamics system disclosed herein greatly overcomes a below-zero heat sink limitation imposed on these existing systems.

Use of New Liquid Metal (Galinstan?)

[0138] According to one aspect of the present invention, use of an alloy comprising gallium, indium, and tin as the liquid metal is disclosed, and more particularly, Galinstan?, as this is commercially available.

[0139] Galinstan? (GaInSn) is a non-toxic liquid metal, a eutectic alloy of gallium (Ga), indium (In), and tin (Sn). The composition of GaInSn was patented in 2000 and its melting temperature was claimed to be about ?19.5? C. under normal pressure and atmospheric conditions, and its vaporization point was reported to be above 1800? C. With a reported melting temperature above 0? C., many GaInSn alloys retain their liquid state at room temperature. GaInSn has a very low vapor pressure and will not emit respirable metal vapor at room conditions, which generally makes GaInSn safe to use.

[0140] GaInSn is most used as a replacement for toxic mercury, which has been used in thermometers. Compared to mercury, Galinstan? exhibits a lower density (6360 kg/m.sup.3) that is about half of that of mercury which will result in reduced velocity of the buoyancy-driven flow in circulationa disadvantage given the magnetohydrodynamics power output is inversely proportional to the square of flow velocity.

[0141] However, Galinstan? exhibits a higher conductivity at ?=3.7?10.sup.6 S/m, an advantage given that the power output of an magnetohydrodynamics generator is directly proportional to its fluid's conductivity. Overall, Galinstan? would have a performance equivalent to mercury but with no similar safety concerns as that of mercury.

Use of New Refrigerant/Working Fluids

[0142] According to one aspect of the present invention, hydrocarbon refrigerants, which are low global warming alternatives that can replace the ozone-depleting refrigerants, are used. This is in contrast to the existing liquid metal magnetohydrodynamics systems, where the refrigerants used were Freon? based, for example, Genetron? 113, which causes ozone layer depletion.

Use of Gas-Lift Pumps to Improve Circulation of Metal Through Computational Fluid Dynamics and Experiments

[0143] According to further aspect of the present invention, there is provided the use of gas-lift pumps to improve circulation of metal through computational fluid dynamics and experiments.

[0144] Through computational fluid dynamics modeling study and experiments conducted on a two-phase flow of a gas-liquid metal mixture, a more efficient means for pumping gas-liquid metal two-phase flow has been identified.

[0145] The gas injection positions were configured in three modes in the riser: [0146] 1) central/axial, [0147] 2) annular/axial, and [0148] 3) annular/radial.

[0149] The annular/axial mode was found to be more efficient. The annular/axial mode can circulate the liquid metal at a higher velocity through the MHD generator, thereby increasing the power output and ultimately optimizing the performance of the low temperature magnetohydrodynamics system.

Use of New Rare Earth Permanent Magnets in Paired Halbach Arrays

[0150] According to a further aspect of the present invention, new rare earth permanent magnets in paired Halbach arrays are used in the magnetohydrodynamics generator.

[0151] A drawback of the low temperature magnetohydrodynamics systems is that they generally use electromagnets that consume electrical power in MHD generator. Some prior art systems have proposed using permanent magnets in the MHD generator to eliminate the power consumption but encountered the limitation of getting sufficiently high magnetic flux density in permanent magnets. New rare earth permanent magnets are the strongest type of permanent magnet available commercially. Using rare earth permanent magnets in paired Halbach arrays can augment the magnetic field.

[0152] FIG. 6 shows a novel configuration of permanent magnets in paired Halbach arrays and a series electrode connection for a low temperature magnetohydrodynamics system according to the present invention.

[0153] A Halbach array is a special arrangement of permanent magnets that augments the magnetic field on one side of the array while cancelling the field to near zero on the other side. A paired Halbach arrays will make magnet field polarity switch from section to section, confine and concentrate magnetic flux between the paired Halbach arrays, thus largely augment the magnetic field. The polarity switch of magnet field from section to section also allows a series connection of two adjacent electrodes to achieve an overall high voltage output of the MHD generator. Meanwhile, the Lorentz force exerted on electrons in conductive liquid metal will prevent current flow between two adjacent electrodes where exists electrical potential, thus preventing the shortage of adjacent electrodes.

[0154] A series connection of electrodes to achieve an overall high voltage output of MHD generator is also possible for using a normal single-polarity magnet field.

Configuration Using Natural Circulation without a Pump to Diminish or Eliminate Power Consumption

[0155] FIG. 7 is a diagram of the configuration of the low temperature magnetohydrodynamics system according to the present invention, without the use of a pump.

[0156] Because of the vertical position of the configuration, the condenser 24 may be installed at a high elevation and the head in lines 25, 27, and 28 in FIG. 5 could compensate the inlet pressure of the pump 26 thus reducing the pump power consumption, thereby reducing the energy loss of the entire system.

[0157] This configuration would improve the performance of the low temperature magnetohydrodynamics system. One option is to place the condenser at an elevation sufficiently high to eliminate the pump 26 and its power consumption, as shown in FIG. 7.

Configuration Using Integration of the Separator and the Recuperator

[0158] FIG. 8 is a diagram of the configuration of the low temperature magnetohydrodynamics system according to the present invention, with integrated recuperator and separator.

[0159] As shown in FIG. 8, integration of the separator and the recuperator makes the system design compact.

[0160] Also, the vapor out of the separator 13 is cooled down in the recuperator 22 to a temperature close to the ambient temperature so that the heat loss through pipe 21 in FIG. 5 is eliminated.

Configuration Using Integration of the Recuperator and the Mixer

[0161] FIG. 9 is a diagram of the configuration of the low temperature magnetohydrodynamics system according to the present invention, with integrated recuperator and mixer.

[0162] As shown in FIG. 9, integration of the recuperator 22 and the mixer 11 makes the system design compact.

Configuration Using Two-Phase Magnetohydrodynamics Generator on the Riser

[0163] FIG. 10 is a diagram of a configuration of the low temperature magnetohydrodynamics system according to the present invention, where MHD generators have a dual location (riser 12 and downcomer 14/16).

[0164] There is also the option to install the magnetohydrodynamics generator in the riser as opposed to the downcomer.

[0165] Although the present invention has been described in considerable detail with reference to certain preferred embodiments thereof, other embodiments and modifications are possible. Therefore, the scope of the appended claims should not be limited by the preferred embodiments set forth in the examples but should be given the broadest interpretation consistent with the description as a whole.