METALLIC COMPOSITE PHASE-CHANGE MATERIALS AND METHODS OF USING THE SAME
Metallic composite phase-change materials and methods of using are disclosed. In some embodiments, a thermal energy storage module is provide that included one or more phase change alloys having a variable phase transition temperature between about 400° C. and about 1200° C. and having a latent heat of more than about 200 kJ/kg.
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This application claims the benefit of and priority to U.S. Provisional Application No. 61/717,068, filed on Oct. 22, 2012, which is incorporated herein by reference in its entirety.
STATEMENT OF GOVERNMENT SUPPORTThis invention was made with Government Support under Contract Number DE-AR0000181 awarded by the Advanced Research Projects Agency—Energy, Department of Energy. The Government has certain rights in the invention.
FIELDThe embodiments disclosed herein relate to composite phase-change alloys and methods of their synthesis and use.
BACKGROUNDConcentrated solar-thermal power (CSP) generation is a promising clean energy technology for the future. However, solar energy harvesting suffers from facts such as unpredictable interruptions due to weather fluctuations and lack of sun light in night time. To reduce weather dependence of CSP and provide uninterrupted electricity 24 hours a day, thermal energy storage (TES) can be employed. The use of TES for CSP can significantly increase the CSP capacity factor from about 30% to greater than about 60% which in turn can reduce the levelized cost of electricity produced. TES can also be used in addition to traditional nuclear power plants to provide peaking power by storing part of the thermal energy from the nuclear reactor to subsequently run a thermodynamic cycle, such as the Brayton cycle, for power generation. Such application will reduce the dependence on fossil fuel peaking power plants and consequently reduce the CO2 emission.
In order to achieve higher efficiency, both CSP and the fourth-generation nuclear power plants operate at high temperatures. For example, the dish-Stirling engine CSP system has a gas temperature of over 700° C., and the dish-Brayton application has a turbine inlet temperature of about 850° C. These dish-engine systems have demonstrated the highest solar-to-electricity efficiency of 29.4%. In another study, reported a nuclear power plant design based on supercritical CO2 with a predicted plant efficiency of 51%. In such a design, CO2 is heated from 488.9° C. to 879.4° C. through an intermediate heat exchanger between the nuclear reactor fluids and CO2. Existing research focus of TES has been on systems operating at below 500° C. Hence, there is an urgent demand on the development of TES materials operating in the high temperature range to enable continuous operation of CSP and peaking power capability of nuclear power plants which can result in a great increase in the share of these alternative energy systems.
SUMMARYMetallic composite phase-change materials (PCMs) and methods of their use and synthesis are disclosed.
In some aspects, there is provided a thermal energy storage module that includes one or more phase change alloys having a variable phase transition temperature between about 400° C. and about 1200° C. and having a latent heat of more than about 200 kJ/kg. In some embodiments, the one or more phase change alloys have a formula of Aluminum (Al)-Silicon (Si)—X, wherein X is one or more elements selected from the group consisting of boron (B), carbon (C), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), germanium (Ge), molybdenum (Mo), nobium (Nb), nickel (Ni), manganese (Mn), scandium (Sc), titanium (Ti), vanadium (V), and zirconium (Zr). In some embodiments, the one or more phase change alloys have a formula of Al—Si—Fe, where the concentration of Al is between about 40 atom percent and about 50 atom percent, the concentration of Si is between about 35 atom percent and about 45 atom percent and the concentration of Fe is between about 10 atom percent and about 20 atom percent. In some embodiments, a phase change alloy has a formula Al—Si—Fe, where the concentration of Al is about 45 atom percent, the concentration of Si is about 40 atom percent, and the concentration of Fe is about 15 atom percent. In some embodiments, a phase change alloy is Al—Si—B, where the concentration of B is between about 8 atom percent and about 28 atom percent.
In some aspects, there is provided a method of storing heat that includes providing one or more phase change alloys having a variable phase transition temperature between about 400° C. and about 1200° C. and having a latent heat of more than about 200 kJ/kg; charging the one or more phase change alloys by allowing heat transfer into the phase change alloy; and storing heat in the one or more phase change alloys.
The presently disclosed embodiments will be further explained with reference to the attached drawings, wherein like structures are referred to by like numerals throughout the several views. The drawings shown are not necessarily to scale, with emphasis instead generally being placed upon illustrating the principles of the presently disclosed embodiments.
While the above-identified drawings set forth presently disclosed embodiments, other embodiments are also contemplated, as noted in the discussion. This disclosure presents illustrative embodiments by way of representation and not limitation. Numerous other modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principles of the presently disclosed embodiments.
DETAILED DESCRIPTIONMetallic composite phase-change materials (PCMs) and methods of their synthesis and use are disclosed. In some embodiments, the PCMs disclosed herein can be used as part of a thermal energy storage module for high-temperature thermal storage and release. In some embodiments, PCMs of the present disclosure can have variable phase transition temperatures to achieve maximum energy efficiency for thermal energy storage. The PCMs of the present disclosure can have one or more of the following characteristics: phase change temperature variable between about 400° C. and about 1200° C. and, in some embodiments, between about 600° C. and about 900° C., large latent heat (more than about 200 kJ/kg and, in some embodiments, more than about 500 kJ/kg), high thermal conductivity values, high stability, long lifetime, low vapor pressure, and low-cost.
Latent heat storage is attractive because materials undergoing phase change have high energy storage density which can lead to more compact systems, such as, for example, solar home systems. Latent heat storage can be achieved with PCMs. Although liquid-gas phase transition can usually store the largest amount of energy, the significant change of volume may be problematic in practical engineering applications. Solid-liquid phase transition, however, does not involve large volume changes and it can still store a large amount of energy.
Solid-liquid PCMs divided into the categories of organic, inorganic (non-metal) and eutectic (metal/alloy) PCMs. The most widely used organic PCM is paraffin wax, which has relatively high latent heat (140-280 KJ/kg), good melting characteristics, and it is non-toxic, chemically stable, and relatively cheap. Although organic PCMs are popular, they generally have very low thermal conductivity (<0.6 W/mK) which may limit its output power density and the exergetic efficiency. On the other hand, organic PCMs also suffer from their relatively large volume change during phase transition, and they usually have low melting temperatures (<100° C.).
Inorganic (non-metal) PCMs like salt hydrates are also widely used for TES. Inorganic PCMs have similar latent heat per unit mass as that of the organic PCMs. Due to their higher density, the volumetric latent heat of inorganic PCMs is about twice as much as that of organic PCMs. However, these PCMs may fall short of the basic requirements of PCMs for TES application in concentrated solar power (CSP) systems.
Eutectics (metal/alloy) PCMs, generally referred to as mixtures of one or more metals plus inorganic compositions, melt and freeze without segregation since they freeze to an intimate mixture of crystals, leaving little opportunity for the components to separate. In some embodiments, the PCM of the present disclosure is a near-eutectic alloy, including a base alloy and one or more additional alloying elements added to arrive at desired thermal properties, that is, melting temperature and latent heat, among others.
In some embodiments, the base alloy is a silicon-based alloy, such as aluminum-silicon (Al—Si), germanium silicon (Ge—Si), ferum-silicon (Fe—Si), manganese-silicon (Mn—Si), berillium-silicon (Be—Si), and similar alloys, as shown, for example, in
In some embodiments, the base alloy may be a aluminum-silicon (Al—Si) alloy, where the concentration of Al may vary between about 0 atom percent (at. %) to about 100 at. % and the concentration of Si may thus also vary between about 0 at. % to about 100 at. %.
In some embodiments, adding one or more additional elements to the base alloy may result in improvement of one or more thermal properties of the resulting alloy. For example, the addition of one or more additional alloying elements to the base alloy may result in the resulting material having a variable melting temperature between about 400 and about 1200° C., latent heat of greater than 200 kJ/kg, or both.
The alloying elements may be selected based on their thermal properties, as well as the desired thermal properties of the final PCM alloy. By way of a non-limiting example,
In some embodiments, the PCM of the present disclosure is a Al—Si—B alloy. In some embodiments, the concentration of Boron may range between about 8 at. % and about 28 at. %. By way of non-limiting example,
In some embodiments, the PCMs of the present disclosure may be Al—Si—Fe alloys.
In reference to
To prepare the PCMs of the present disclosure, first powders of constituents of the base alloy and one or more additional elements in desired concentrations can be uniformly mixed together, and then the mixture can be consolidated under pressure and elevated temperature. In some embodiments, the mixture of powders may be consolidated by hot pressing. In some embodiments, direct current induced hot press can be used. Other consolidation techniques known in the art may also be used with the presently disclosed embodiments. By way of a non-limiting example,
The methods and materials of the present disclosure are described in the following Examples, which are set forth to aid in the understanding of the disclosure, and should not be construed to limit in any way the scope of the disclosure as defined in the claims which follow thereafter. The following examples are put forth so as to provide those of ordinary skill in the art with a complete disclosure and description of how to make and use the embodiments of the present disclosure, and are not intended to limit the scope of what the inventors regard as their invention nor are they intended to represent that the experiments below are all or the only experiments performed. Efforts have been made to ensure accuracy with respect to numbers used (e.g. amounts, temperature, etc.) but some experimental errors and deviations should be accounted for.
EXAMPLES Example 1 Synthesis of Ternary Near-Eutectic Al—Si—Fe AlloysFrom the ternary phase diagram of Al—Si—Fe system, the chemical composition of the near-eutectic point is around 45Al-40Si-15Fe (at %). In order to synthesize the bulk near-eutectic alloys for the measurement of latent heat and other characteristics, Al, Si, and Fe powders purchased from Alfa Aesar were uniformly mixed, followed by hot pressing at different temperatures (300, 500, 700, and 1000° C.), with a starting pressure at 94-110 MPa before heating (at room temperature).
Based on the melting point at around 875° C. for the near-eutectic Al—Si—Fe alloy, the hot-press temperature of 1000° C. was firstly tried (see
In order to decrease or prevent the loss of Al and Si during the hot-press, the eutectic alloy powder was pressed at 700° C. at lower static pressure (at 94 MPa, rather than 110 MPa at 1000° C.).
Considering the melting point of the near-eutectic Al—Si—Fe alloy is around 875° C. (by phase diagram), the highest temperature was set to 1000° C. for the DSC experiments.
On the other hand, based on the previous experimental DSC data, the latent heat of this near-eutectic Al—Si—Fe alloy could be estimated by a simple addition of the latent heat of each pure component/element multiplying the corresponding percentage. For the ternary near-eutectic Al—Si—Fe alloy, the estimated latent heat could be simply calculated as the following:
Al(38.24 wt %)—latent heat: 397×0.3824=151.81 kJ/kg
Si(35.38 wt %)—latent heat: 1800×0.3538=636.84 kJ/kg
Fe(26.38 wt %)—latent heat: 247×0.2638=65.16 kJ/kg
Therefore, the total latent heat might be close to 853.8 kJ/kg, which is reasonable and consistent with the experimental data, as shown in
At constant pressure, phase diagram of alloys can be determined by finding the minimum Gibbs free energy among all the phases at different temperature. When different species are mixed together, the change of Gibbs free energy (G) from mixing can be expressed as,
ΔG=ΔH−TΔS
where H is enthalpy, T is temperature and S is entropy.
The enthalpy change ΔH can be either negative or positive depending on the atomic bonding strength. When the bonding strength between atoms with different types is stronger than that between the same types of atoms, the mixing enthalpy is negative, and energy needs to be provided to form the mixture (or alloy). If the bonding strength in the mixture (or alloy) is week, the mixing enthalpy is positive.
When the mixing enthalpy is positive, the Gibbs free energy curve would show a convex shape in the middle composition as shown in
Experimental measurements show that the latent heat of fusion of Cu-16Si is less than 183.5 kJ/kg with eutectic temperature at 806.9° C. One reason for the low latent heat of fusion is because Si exists mainly in the form of SiCu3 compound after phase separation as shown in
From the above analysis, alloys with the following properties can be selected for high latent heat of fusion: (1) materials with high ratio of latent heat over melting temperature,
(such as Si, Al, B, etc.) can exist as much as possible in their pure element form after solidification; (2) the formed intermediate compound should have a high melting temperature; (3) the elements should have relatively even composition in order to increase the mixing entropy; (4) light elements should be used.
Based on the above rule, the Pd—Si eutectic alloy with 52% (at. %) Si could be a good choice as shown in
Another alloy that was analyzed is the ternary alloy Al—Fe—Si with phase diagram shown in
In some embodiments, a thermal energy storage module includes one or more phase change alloys having a variable phase transition temperature between about 400° C. and about 1200° C. and having a latent heat of more than about 200 kJ/kg. In some embodiments, the one or more phase change alloys have a formula of Aluminum (Al)-Silicon (Si)—X, wherein X is one or more elements selected from the group consisting of boron (B), carbon (C), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), germanium (Ge), molybdenum (Mo), nobium (Nb), nickel (Ni), manganese (Mn), scandium (Sc), titanium (Ti), vanadium (V), and zirconium (Zr). In some embodiments, the one or more phase change alloys have a formula of Al—Si—Fe, where the concentration of Al is between about 40 atom percent and about 50 atom percent, the concentration of Si is between about 35 atom percent and about 45 atom percent and the concentration of Fe is between about 10 atom percent and about 20 atom percent. In some embodiments, a phase change alloy has a formula Al—Si—Fe, where the concentration of Al is about 45 atom percent, the concentration of Si is about 40 atom percent, and the concentration of Fe is about 15 atom percent. In some embodiments, a phase change alloy is Al—Si—B, where the concentration of B is between about 8 atom percent and about 28 atom percent.
In some embodiments, a method of storing heat includes providing one or more phase change alloys having a variable phase transition temperature between about 400° C. and about 1200° C. and having a latent heat of more than about 200 kJ/kg; charging the one or more phase change alloys by allowing heat transfer into the phase change alloy; and storing heat in the one or more phase change alloys.
All patents, patent applications, and published references cited herein are hereby incorporated by reference in their entirety. While the methods of the present disclosure have been described in connection with the specific embodiments thereof, it will be understood that it is capable of further modification. Furthermore, this application is intended to cover any variations, uses, or adaptations of the methods of the present disclosure, including such departures from the present disclosure as come within known or customary practice in the art to which the methods of the present disclosure pertain.
Claims
1. A thermal energy storage module comprising one or more phase change alloys having a variable phase transition temperature between about 400° C. and about 1200° C. and having a latent heat of more than about 200 kJ/kg.
2. The thermal energy storage module of claim 1, wherein the one or more phase change alloys have a formula of Aluminum (Al)-Silicon (Si)—X, wherein X is one or more elements selected from the group consisting of boron (B), carbon (C), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), germanium (Ge), molybdenum (Mo), nobium (Nb), nickel (Ni), manganese (Mn), scandium (Sc), titanium (Ti), vanadium (V), and zirconium (Zr)
3. The thermal energy storage module of claim 2, wherein X is Fe.
4. The thermal energy storage module of claim 3, wherein the concentration of Al is between about 40 atom percent and about 50 atom percent.
5. The thermal energy storage module of claim 3, wherein the concentration of Si is between about 35 atom percent and about 45 atom percent.
6. The thermal energy storage module of claim 3, wherein the concentration of Fe is between about 10 atom percent and about 20 atom percent.
7. The thermal energy storage module of claim 3, wherein the concentration of Al is about 45 atom percent, the concentration of Si is about 40 atom percent, and the concentration of Fe is about 15 atom percent.
8. The thermal energy storage module of claim 2, wherein X is B in concentration of between about 8 atom percent and about 28 atom percent.
9. A thermal energy storage module comprising one or more phase change alloys having a general formula of Al—Si—Fe, wherein the concentration of Al is between about 40 atom percent and about 50 atom percent, the concentration of Si is between about 35 atom percent and about 45 atom percent, and the concentration of Fe is between about 10 atom percent and about 20 atom percent.
10. A method of storing heat comprising:
- providing one or more phase change alloys having a variable phase transition temperature between about 400° C. and about 1200° C. and having a latent heat of more than about 200 kJ/kg;
- charging the one or more phase change alloys by allowing heat transfer into the phase change alloy; and
- storing heat in the one or more phase change alloys.
11. The method of claim 10, wherein the one or more phase change alloys have a formula of Aluminum (Al)-Silicon (Si)—X, wherein X is one or more elements selected from the group consisting of boron (B), carbon (C), cobalt (Co), chromium (Cr), copper (Cu), iron (Fe), germanium (Ge), molybdenum (Mo), nobium (Nb), nickel (Ni), manganese (Mn), scandium (Sc), titanium (Ti), vanadium (V), and zirconium (Zr)
12. The method of claim 11, wherein X is Fe.
13. The method of claim 12, wherein the concentration of Al is between about 40 atom percent and about 50 atom percent.
14. The method of claim 12, wherein the concentration of Si is between about 35 atom percent and about 45 atom percent.
15. The method of claim 12, wherein the concentration of Fe is between about 10 atom percent and about 20 atom percent.
16. The method of claim 12, wherein the concentration of Al is about 45 atom percent, the concentration of Si is about 40 atom percent, and the concentration of Fe is about 15 atom percent.
17. The method of claim 11, wherein X is B having the concentration between about 8 atom percent and about 28 atom percent.
18. The method of claim 10, wherein, in the step of charging, heat is produced by a solar-thermal power system.
19. The method of claim 18 further comprising releasing heat stored in the one or more phase change alloys to generate electricity.
20. The method of claim 10, wherein, in the step of charging, heat is an exhaust heat from a nuclear power station.
Type: Application
Filed: Oct 22, 2013
Publication Date: Apr 24, 2014
Applicants: Massachusetts Institute of Technology (Cambridge, MA), The Trustees of Boston College (Chestnut Hill, MA)
Inventors: Zhifeng Ren (Newton, MA), Hengzhi Wang (West Roxbury, MA), Hui Wang (Brookline, MA), Gang Chen (Carlisle, MA), Xiaobo Li (Cambridge, MA), Keivan Esfarjani (New Brunswick, NJ)
Application Number: 14/060,024
International Classification: F28D 20/02 (20060101); F24J 2/34 (20060101);