Abstract:
There is provided an AMTEC (alkali metal thermal-electric converter) with a heat pipe and more particularly, to an AMTEC with a heat pipe minimized a heating part and a condensation part of the AMTEC and improved in efficiency of thermal to electric conversion through installing the heating and cooling heat pipes in the AMTEC, in which a metal fluid is heated by latent heat of an operating fluid of the heat pipe, instead of the heat conduction from a heat source, thereby reducing a temperature difference needed for heat transfer to vaporize the metal fluid even by a heat source of a lower temperature than a conventional heat source; improving a cooling performance in a condensation part to result in the high efficiency of thermal to electric conversion; using no additional driving components for driving the heat pipe.

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATION 
     This application claims the benefit of Korean Patent Application No. 10-2008-0072854, filed on Jul. 25, 2008, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an AMTEC (alkali metal thermal-electric converter) with a heat pipe and more particularly, to an AMTEC with a heat pipe minimized a heating part and a condensation part of the AMTEC, and improved in efficiency of thermal to electric conversion through installing the heating and cooling heat pipes as a heating device and a condensing device in the AMTEC, in which a metal fluid is heated by a latent heat of an operating fluid of the heat pipe, instead of heat conduction from a heat source, thereby reducing a temperature difference needed for heat transfer to increase a vapor generation of the metal fluid by the heat source of a lower temperature than a conventional heat source; improving a cooling performance in a condensation part to result in a high efficiency of thermal to electric conversion; and using no additional driving components for driving the heat pipe. 
     2. Description of the Related Art 
     An AMTEC (alkali metal thermal-electric converter) is a device having a characteristic of directly converting thermal energy to electrical energy. In the AMTEC, when a temperature difference ΔT is applied to both ends of a BASE (beta-alumina solid electrolyte) having ion conductivity, a difference in vapor pressure of liquid Na filling the inside of a cell acts as a driving force to move Na +  ions through a space among loosely bonded lattice oxygen. The Na +  ions passing through the electrolyte are neutralized on the surface of an electrode during a condensing process, to generate electricity. Then, the electricity of a low voltage and a high current is output. High capacity generation is enabled by modulating and collecting the low voltage and high current electricity. 
     The principle of the AMTEC technology is that, when alkali metal sodium is vaporized in a vaporizer of a high pressure region by a heat source, sodium ions pass through the BASE and free electrons pass through electrical load from positive pole and return to negative pole to re-combine with the ions coming from the surface of the BASE of a low pressure region, thereby generating electricity. The neutral sodium vapor is condensed by cooling of a low temperature fluid in inner surface of a condenser of a low pressure region, and the condensed liquid returns to the vaporizer by a condenser wick to complete a cycle. The typical temperatures of the vaporizer and condenser of the metal fluid are respectively 900˜1100K and 500˜650K. The vaporization and condensation of sodium in these temperature conditions enables the efficiency of generating electricity by the thermal to electric conversion up to 40%. 
     A semiconductor thermoelectric generation system has been used as a power source for space application but there are drawbacks of low efficiency and heavy weight in such a generation system. The AMTEC technology is developed to substitute the thermoelectric generation system using a thermoelectric module. The characteristics of the AMTEC technology are to have high power density, high efficiency and low cost per unit area and to maintain stability during use. The AMTEC technology has the high a higher conversion efficiency compared to any other direct thermo-electric converters and directly converts heat energy to electric energy using various heat sources, such as fossil fuel, solar energy, radioactive isotopes, nuclear reactors or the like, as its fuel. 
     Unlike the conventional electricity generation technology, the AMTEC technology is the high efficiency technology relating to the thermal to electric converter, using the heat sources, such as not only the heat of combustion of gas but also waste heat, solar heat, heat of the earth, radioactive isotopes or the like, without a driving part, such as a turbine or boiler. Therefore, the AMTEC technology is considered as the new future-oriented technology of electricity generation, which is capable of producing high capacity electricity of several hundred MWs. Specifically, since the power density per mass is about 2˜3 times that of a solar power generator or Stirling engine, the AMTEC technology can be widely used for space application, military application, and power technology using high temperature waste heat. Further, since the AMTEC technology uses the condenser wick for circulation of a liquid metal, mechanical elements are not needed, to increase a stability of the converter. 
     Since the AMTEC technology has the high capacity of MWs in high efficiency, it may be used for the thermo-electric converter. Further, when the AMTEC technology is used for the cogeneration (combined heat and power), it is capable of improving the utilization of energy by 70% or more. Therefore, the research and development of the AMTEC technology are needed to generate power with no noise, to increase the effective utilization of energy, and to reduce the peak load. 
     The aforementioned AMTEC comprises: sodium as a metal fluid, a BASE (beta alumina solid electrolyte) for separating a system into a high pressure region and a low pressure region and allowing only sodium ions to pass to generate electricity, a condenser for condensing and absorbing sodium vapor, a condenser circulation wick for circulating liquid sodium, a vaporizer for converting sodium transferred from the condenser circulation wick in the liquid state into the vapor state, and a heater for heating sodium as a heat source. 
     The AMTEC receives heat from the heat source outside and transfers the heat to the vaporizer inside. In the conventional AMTEC, since heat is supplied to the inside of the vaporizer by conduction, a temperature difference needs to be high and thus, the temperature of the heat source needs to be high. Further, since the conventional condenser releases heat by conduction, there is a problem in that the AMTEC is large in size. Consequently, the efficiency of generating electricity by the thermal to electric conversion decreases. 
     Moreover, in the AMTEC, since heat supply to vaporize the metal fluid is performed by conduction, a temperature difference needs to be high and thus the temperature of the heat source needs to be high. Further, since the condenser for condensing the metal fluid vapor operates by conduction, there is a problem in that the heat conduction area increases. 
     SUMMARY OF THE INVENTION 
     The present invention provides an AMTEC which is installed with a heat pipe as an heater and/or a condenser, in which a vaporizing of a metal fluid is accomplished even though a difference between a temperature of heat source and a temperature needed for vaporizing the metal fluid is small, and a condensing of the metal fluid vapor is possible even though a difference between a temperature of the metal fluid vapor and a temperature needed for condensing the metal fluid vapor is small so that the AMTEC becomes small in size and the efficiency of thermal to electric conversion is improved through using the heat pipe for vaporization of the metal fluid and for condensing of the metal fluid vapor. 
     The present invention also provides an AMTEC which is installed with a heat pipe as a heater in which heat is directly transferred to a vaporizer of the AMTEC by using a latent heat of an operating fluid of the heat pipe, so that a metal fluid is vaporized at a heat source of a low temperature and therefore the thermal efficiency is improved through installing the heat pipe as a heater. 
     According to an aspect of the present invention, there is provided an AMTEC with a heat pipe, which converts heat energy to electric energy, comprising: a case which inside is closed and filled with a predetermined amount of a metal fluid; a heating heat pipe formed at a lower end of the case so as to be operatively connected with the case, for heating the metal fluid filling the inside of the case and vaporizing the metal fluid into vapor; a condenser circulation wick installed above the heating heat pipe protruded inside the case, for collecting the metal fluid vapor vaporized by the heating heat pipe and guiding the vapor of the metal fluid in one direction; a number of BASE (beta alumina solid electrolyte) tubes installed radially around the center of the case, for allowing the high-temperature the metal fluid vapor guided by the condenser circulation wick to pass and generate electricity; and a condenser formed at a top of the case inside, for collecting and condensing the metal fluid vapor which temperature becomes low to a predetermined temperature during passing through the BASE tubes. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings in which: 
         FIG. 1  is a sectional view of an AMTEC according to a first embodiment of the present invention; 
         FIG. 2  is a sectional view taken along line A-A of  FIG. 1 ; 
         FIG. 3  is a sectional view of a condenser circulation wick according to the first embodiment; 
         FIG. 4  is a sectional view taken along line B-B of  FIG. 3 ; 
         FIG. 5  is a sectional view of an AMTEC according to a second embodiment of the present invention; 
         FIG. 6  is a sectional view taken along line A-A of  FIG. 5 ; 
         FIG. 7  is a sectional view of a heating heat pipe according to the second embodiment; and 
         FIG. 8  is a sectional view taken along line C-C of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. 
     It will be understood that words or terms used in the specification and claims shall not be interpreted as the meaning defined in commonly used dictionaries. It will be further understood that the words or terms should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the technical idea of the invention, based on the principle that an inventor may properly define the meaning of the words or terms to best explain the invention. 
     As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     The present invention may be embodied in different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided as teaching examples of the invention. Therefore, it will be understood that the scope of the invention is intended to include various modifications and alternative arrangements within the capabilities of persons skilled in the art using presently known or future technologies and equivalents. 
       FIG. 1  is a sectional view of an AMTEC according to a first embodiment of the present invention,  FIG. 2  is a sectional view taken along line A-A of  FIG. 1 ,  FIG. 3  is a sectional view of a condenser circulation wick according to the first embodiment of the present invention, and  FIG. 4  is a sectional view taken along line B-B of  FIG. 3 . 
     As illustrated in  FIGS. 1 and 2 , the AMTEC with a heat pipe according to the first embodiment of the present invention comprises: a case  10 , a condenser circulation wick  20 , a heating heat pipe  30 , a condenser  50 , a BASE tube  40 , and a condensing heat pipe  60 . 
     The case  10  has a completely closed inside to be filled with a predetermined amount of a metal fluid. As the metal fluid, alkali metal sodium is used in the AMTEC. Sodium metal fluid is vaporized into sodium vapor by a heat source and the sodium vapor generates electricity while passing through the BASE tube  40 . The principle that the sodium vapor (hereinafter, referred to as the “metal fluid vapor”) generates electricity while passing through the BASE tube  40  will be described below: 
     After including the condenser circulation wick  20 , the condenser  50  and the BASE tube  40  inside the case  10 , the case  10  is sealed. Only parts of the heating heat pipe  30  and condensing heat pipe  60  are protruded outwardly. 
     The condenser circulation wick  20  is formed at a center part of the case  10  and is connected to the condenser  50 . One end of the heating heat pipe  30  is formed to protrude inside the condenser circulation wick  20 . When the metal fluid filling the inside of the case  10  is heated by the heat source of the heating heat pipe  30  and is vaporized, the condenser circulation wick  20  collects the vapor to be guided in one direction (toward the direction of the BASE tube). 
     An insertion opening  21  to position the heating heat pipe  30  is formed inside the condenser circulation wick  20 . The other space inside the condenser circulation wick  20  is filled with a condenser wick. Referring to  FIG. 3 , in the insertion opening  21  of the condenser circulation wick  20 , a number of groove wicks  22  are formed to guide the metal fluid vapor vaporized by the heating heat pipe  30  in one direction. Further, each groove wick  22  is formed to be extended long in a length direction of the insertion opening  21  and a number of groove wicks  22  are arranged along a circumferential direction of the insertion opening  21 . 
     Referring to  FIG. 4 , the groove wicks  22  may have a sectional view of the groove wicks  22  selected among various shapes, such as a square shape, a round shape and a triangle shape. 
     The heating heat pipe  30  comprises: a vaporization part  31  where an operating fluid filled inside is being vaporized by heat applied from outside, a transfer part  32  where the operating fluid vapor vaporized in the vaporization part is being transferred, and a condensation part  33  where the operating fluid vapor transferred through the transfer part  32  is being condensed by transferring heat to the outside. The inside of the heating heat pipe  30  is closed, the condensation part  33  of the heating heat pipe  30  is positioned inside the condenser circulation wick  20  installed inside the case  10 , and the vaporization part  31  is positioned outside the case  10 . 
     In the vaporization part  31 , the operating fluid filled inside the heating heat pipe  30  is vaporized by heat applied from outside. A number of pins  34  are formed passing through the vaporization part  31  so that heat from outside is rapidly and smoothly transferred to the inside of the heating heat pipe  30 . Each pin  34  is formed to be perpendicular to the heating heat pipe  30  so that the inside of the vaporization part  31  is connected to the outside. Here, the pins  34  are attached to the vaporization part  31  of the heating heat pipe  30  by welding or other methods. 
     In the vaporization part  31  of the heating heat pipe  30 , the operating fluid inside the heating heat pipe  30  is vaporized by the heat source, the operating fluid vapor rises to the condensation part  33  inserted into a lower part of the condenser circulation wick  20 , and heats the metal fluid in the lower part of the condenser circulation wick  20  to vaporize the metal fluid. 
     The transfer part  31  is integrally formed with the vaporization part  31  and guides the operating fluid vapor vaporized in the vaporization part  31  so as to be transferred to the condensation part  33 . 
     The condensation part  33  is integrally formed with the transfer part  32  and condenses the operating fluid vapor guided through the transfer part  32  back into the operating fluid by transferring heat to outside. 
     The BASE tube  40  means the beta alumina solid electrolyte tube and will be called “BASE” in the present invention. 
     A number of the BASE tubes  40  are formed radially around the condenser circulation wick  20 . While the metal fluid vapor guided by the condenser circulation wick  20  passes through the inside of each BASE tube  40 , electricity is generated from the BASE tubes  40  and heat energy is converted into electric energy in the BASE tubes  40  by the metal fluid vapor. 
     A transfer device, such as wire or the like, to transfer electricity is connected between the BASE tubes  40 . The transfer device is connected to an external electric load  70  so that the AMTEC  100  supplies power. 
     The principle of the BASE tube  40  is that only sodium ions vaporized by heating are allowed to pass through the BASE, and free electrons passes through the electric load  70  from the positive pole and return to the negative pole to re-combine with the ions coming from the surface of the BASE of a low pressure region. As the principle of the BASE tube  40  is applied as the core technology in the AMTEC, various programs have been rapidly disclosed to develop the operation principles, designs and technologies related to the AMTEC since the mid-1960s. In 1968, Kummer and Weber performed the thermal to electric conversion through sodium, using the beta alumina solid electrolyte patent assigned to Ford Motor. 
     Since the BASE tube  40  according to the present invention has the similar constitution, structure and principle to those described above, no detailed description of the BASE tube  40  will be presented herein. 
     The condenser  50  is positioned on the top inside the case  10 . The condenser  50  collects the metal fluid vapor, the temperature of which decreases to a predetermined temperature while passing through the BASE tubes  40 , and condenses the metal fluid vapor. 
     The condenser  50  comprises a condenser wick  51  in a net/mesh shape to collect and condense the metal fluid vapor. That is, the metal fluid vapor is collected by the condenser wick  51 , to be condensed into the metal fluid. Then, a number of condensing heat pipes  60  are inserted inside the condenser  50 , to improve the effect of condensation. 
     A number of pins  61  are installed around a part of the condensing heat pipe  60  which is protruded outside the case  10 . Each of the pins  61  is attached to be perpendicular to the condensing heat pipe  60 , by welding or other methods. 
     The condenser wick  51  is installed on the top inside the case  10  in the manner that the middle part of the condenser wick  51  is formed to be inclined downwardly. That is, the condenser wick  51  is formed in the shape of “V” from the sectional view, to collect the condensed fluid into one place. 
     The condenser wick  51  and the condenser circulation wick  20  are connected to each other, to transfer the metal fluid collected in the condenser wick  51  to the inside of the condenser circulation wick  20 . 
       FIG. 5  is a sectional view of an AMTEC according to a second embodiment of the present invention,  FIG. 6  is a sectional view taken along line A-A of  FIG. 5 ,  FIG. 7  is a sectional view of a heating heat pipe according to the second embodiment of the present invention, and  FIG. 8  is a sectional view taken along line C-C of  FIG. 7 . 
     As illustrated in  FIGS. 5 and 6 , the AMTEC with a heat pipe according to the present invention comprises: a case  10 , a condenser circulation wick  20 , a heating heat pipe  30 , a condenser  50 , a BASE tube  40 , a condensing heat pipe  60 , and an electric load  70 . Since the constitution, structure and reference number of each of the case  10 , condenser  50 , BASE tube  40  and condensing heat pipe  60  in the second embodiment are same as those in the first embodiment, no further description thereof will be presented. 
     In the second embodiment, there are no groove wicks  22  around the inner circumferential surface of the condenser circulation wick  20 . Groove wicks  35  for the heating heat pipe  30  are positioned around the outer circumference of the heating heat pipe  30 , to guide the metal fluid vapor in one direction. 
     The heating heat pipe  30  comprises: a vaporization part  31  where an operating fluid filled inside is being vaporized by heat applied from outside, a transfer part  32  where the vapor of the operating fluid vaporized in the vaporization part is being transferred, and a condensation part  33  where the operating fluid vapor transferred through the transfer part  32  is being condensed by transferring heat to the outside. The inside of the heating heat pipe  30  is closed, the condensation part  33  of the heating heat pipe  30  is positioned inside the condenser circulation wick  20  installed inside the case  10 , and the vaporization part  31  is positioned outside the case  10 . 
     A number of pins  34  are formed passing through the vaporization part  31  so that heat from outside is rapidly and smoothly transferred to the inside of the heating heat pipe  30 . Each pin  34  is formed to be perpendicular to the heating heat pipe  30  so that the inside of the vaporization part  31  is connected to the outside. Here, the pins  34  are attached to the vaporization part  31  of the heating heat pipe  30  by welding or other methods. 
     Referring to  FIG. 7 , a number of groove wicks  35  on heat pipe  30  are positioned at the outer circumference of the condensation part  33 , so that the inside heat of the heating heat pipe  30  is evenly and smoothly transferred to the inside of the case  10  and the metal fluid vapor is guided in one direction. 
     Each of the groove wicks  35  on heat pipe  30  is formed to be extended along in a length direction of the heating heat pipe  30  at a predetermined interval. The groove wicks  35  on heat pipe  30  are arranged along an outer circumferential direction of the heating heat pipe  30 , spaced apart by the predetermine interval. 
     Referring to  FIG. 8 , the groove wicks  35  for the heat pipe may have a sectional view of the groove wicks  35  selected among various shapes, such as a square shape, a round shape and a triangle shape. 
     As described with reference to the first and second embodiments of the present invention, in the AMTEC  100 , the metal fluid is heated by the heating heat pipe  30  and is vaporized in the case  10  which inside is closed. The vaporized metal fluid vapor generates electricity by converting heat energy into electric energy while passing through the BASE tubes  40 , and the metal fluid vapor is condensed by the condensing heat pipe  60  inside the condenser  50  and circulated back to the vaporizer  20  through the condenser circulation wick  20 . 
     As described above, in the AMTEC with the heat pipe according to the present invention, the metal fluid is heated and cooled by the latent heat of the heating heat pipe, instead of the heat conduction according to the conventional art. Therefore, the difference between the temperature of the heat source and the temperature needed for vaporizing the metal fluid becomes small and the size of the condenser becomes small, so that thermal energy is converted into electric energy even by the heat source of low temperature in high efficiency. 
     Furthermore, the heat pipe is installed in the AMTEC to heat and condense the metal fluid. Therefore, heat is directly transferred to the vaporizer for vaporizing the metal fluid inside the AMTEC, so that the speed of heat transfer is fast and the AMTEC has high performance and becomes small in size. 
     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.