Sub-zero phase change materials with multiple crystallization events

Abstract

To provide sub-zero phase change materials (sub-zero phase change substances) with multiple crystallization events.SOLUTION: There is disclosed herein compositions of sub-zero salt-water eutectic phase change materials which exhibit two crystallization processes on cooling. Furthermore, there is disclosed additives which can be used to alter the phase change transitions of one or more of these crystallization processes.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to thermal energy storage, particularly to thermal energy storage at temperatures below 0° C. More particularly, the present invention relates to the use and nucleation of inorganic phase change materials (PCMs) as cryogenic storage media. [Background technology]

[0002] The cooling system lacks thermal inertia and thermal mass. One solution is to add, for example, a glycol-water mixture to the buffer tank, which adds thermal mass and thermal inertia to the system. However, these systems are undesirable because they have high heat gain from the surroundings (low efficiency), high purchase and maintenance costs, and low energy density. Such systems require the use of chillers, which use a refrigerant to remove heat from the water-glycol circuit through a heat exchanger. This is a major source of low efficiency.

[0003] The use of phase change materials (PCMs) for thermal energy storage is a high-energy density alternative to water / glycol tanks. Such materials store energy using the latent heat of phase change (i.e., solid-liquid, solid-gas, liquid-gas). Phase change includes polymorphic change (i.e., solid-solid change).

[0004] Materials that exhibit a phase change below zero may be organic in nature (e.g., carbon-based) or inorganic salt-water eutectics. Compared to organics, inorganic PCMs are typically less expensive, have lower flammability / combustibility, and may have higher energy densities. However, they exhibit subcooling, a phenomenon in which a substance remains liquid below its thermodynamic phase change temperature and therefore requires nucleation aids or extremely low temperatures to initiate crystallization. Summary of the Invention [Problem to be solved by the invention]

[0005] It is an aim of at least one aspect of the present invention to obviate or at least mitigate one or more of the above problems.

[0006] It is an object of at least one embodiment of the present invention to provide a sub-zero phase change material (sub-zero phase change substance) that has multiple crystallization events.

[0007] It is an object of at least one embodiment of the present invention to provide a sub-zero phase change material having one or more nucleating agents that act to reduce supercooling in a specific one of multiple crystallization events.

[0008] It is a further object of at least one embodiment of the present invention to provide improved (enhanced) phase change materials for cryogenic storage media.

[0009] It is a further object of at least one embodiment of the present invention to provide a sub-zero phase change material having one or more nucleating agents selected to reduce supercooling in one crystallization event in combination with one or more other nucleating agents selected to reduce supercooling in other crystallization events.

[0010] One advantage of the present invention is that the PCM undergoes both crystallization processes with minimal cooling below the thermodynamic phase change temperature (i.e., the temperature at which the phase change can occur without supercooling).

[0011] One advantage of the present invention is that the PCM can be frozen with minimal cooling power, i.e., frozen at a high temperature.

[0012] One advantage of the present invention is that the PMC undergoes both crystallization phase transitions at temperatures close to the thermodynamic phase transition temperature (e.g., 0-20°C below the thermodynamic phase change temperature). [Means for solving the problem]

[0013] According to a first aspect of the present invention there is provided a phase change material (PCM) having a melting point below 0°C and exhibiting two crystallisation events on cooling, comprising: At least one salt; Water; and one or more nucleating agents that act to reduce supercooling in the first crystallization event, and / or one or more nucleating agents that act to reduce supercooling in the second crystallization event Includes. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 shows the temperature profile of a PCM that undergoes a double crystallization event upon cooling, according to an embodiment of the present invention. [Figure 2] FIG. 2 shows exemplary thermal data for a PCM (lithium nitrate-water eutectic) that undergoes a double crystallization event upon cooling, according to an embodiment of the present invention. [Figure 3] FIG. 3 shows exemplary thermal data for a disodium adipate-water eutectic in which only one crystallization event occurs and the subsequent effect of this on the melting transition, according to an embodiment of the present invention. [Figure 4] FIG. 4 shows exemplary thermal data for a disodium adipate-water eutectic in which both a first and second crystallization event occurs and the subsequent effect of this on the melting transition, according to an embodiment of the present invention. [Figure 5] FIG. 5 shows thermal data for a sodium acetate-water eutectic, where the PCM reaches a higher temperature after the first crystallization event than after the second crystallization event according to an embodiment of the present invention. [Figure 6] FIG. 6 shows thermal data for a sodium sulfate-water eutectic where the PCM reaches the same temperature after both the first and second crystallization events, and an example of the second crystallization event starting at a higher temperature than the first crystallization event, according to an embodiment of the invention. [Figure 7]FIG. 7 shows thermal data for a known hydrate-free material (KCl) in a water-containing eutectic composition, exhibiting two crystallization events, according to an embodiment of the present invention. [Figure 8] FIG. 8 shows thermal data for a material with multiple known hydrates in a water-containing eutectic composition (CaCl), exhibiting two crystallization events, according to an embodiment of the present invention. [Figure 9] FIG. 9 shows a comparison of magnesium nitrate-water eutectic with and without a SiC nucleating agent, according to an embodiment of the invention. [Figure 10] FIG. 10 shows thermal data for double nucleation of magnesium nitrate-water eutectic without any nucleating agent, according to an embodiment of the present invention. [Figure 11] FIG. 11 shows thermal data for the dual nucleation of magnesium nitrate-water eutectic with ceramic SiO / Al nucleating agents, according to an embodiment of the present invention. [Figure 12] FIG. 12 shows thermal data of two crystallization events in an ammonium chloride-water eutectic that coalesce upon addition of an ice-nucleating protein, according to an embodiment of the present invention. [Figure 13] FIG. 13 shows an image of a sub-zero PCM after its first crystallization event and in the process of its second crystallization event, with locations 1 and 2 representing regions of the PCM after the first and second crystallization events, respectively. [Figure 14] FIG. 14 shows the pattern of double crystallization events in a large (17 liter) sample of sub-zero salt-water eutectic PCM containing sodium acetate and water. [Figure 15] FIG. 15 shows the pattern of double crystallization events in a large (100 liter) sample of a sub-zero salt-water eutectic PCM containing magnesium sulfate and water. [Figure 16] FIG. 16 shows the supercooling length of both the first and second crystallization events in a eutectic of magnesium sulfate and water without one or more nucleating agents. [Figure 17]FIG. 17 shows the supercooling length of both the first and second crystallization events in a eutectic of magnesium sulfate and water with calcium carbonate acting as a nucleating agent for the first crystallization event and silver iodide acting as a nucleating agent for the second crystallization event. [Figure 18] FIG. 18 shows exemplary thermal cycles for samples of magnesium sulfate-water eutectic PCM with and without titanium dioxide nucleating agent. [Figure 19] FIG. 19 shows an example thermal cycle of a sample of magnesium sulfate-water eutectic PCM with aluminum oxide and without a nucleating agent. [Figure 20] FIG. 20 shows an example thermal cycle of a sample of magnesium sulfate-water eutectic PCM containing silicon carbide and without a nucleating agent. [Figure 21] FIG. 21 shows an example thermal cycle of a sample of sodium bromide-water eutectic PCM containing aluminum oxide and without a nucleating agent. [Figure 22] FIG. 22 shows an example thermal cycle of a sample of sodium bromide-water eutectic PCM containing silicon dioxide and without a nucleating agent. [Figure 23] FIG. 23 shows an example thermal cycle of a sample of sodium bromide-water eutectic PCM containing calcium carbonate and without a nucleating agent. [Figure 24] FIG. 24 shows an example thermal cycle of a sample of sodium bromide-water eutectic PCM containing silver iodide and without a nucleating agent. [Figure 25] FIG. 25 shows the cooling of a PCM with sodium acetate-water eutectic without a nucleating agent in a three-layer calorimeter. [Figure 26] FIG. 26 shows the cooling of a PCM with sodium acetate-water eutectic with silver iodide nucleating agent in a three-layer calorimeter. [Figure 27] FIG. 27 shows an example thermal cycle of a sample of strontium bromide-water eutectic PCM containing silver iodide and no nucleating agent. [Figure 28]FIG. 28 shows an example thermal cycle of a sample of potassium chloride-water eutectic PCM containing silver iodide and no nucleating agent. [Figure 29] FIG. 29 shows an example thermal cycle of a sample of ammonium chloride-water eutectic PCM containing silver iodide and no nucleating agent. [Figure 30] Figure 30 shows the effect of adding titanium dioxide to a KCl-hydrate-water eutectic PCM with an enhancement of the first crystallization event. [Figure 31] FIG. 31 shows, however, that changing the salt cation to sodium results in the opposite performance, with the addition of titanium dioxide improving the nucleation of the second crystallization event. [Figure 32] FIG. 32 shows the use of AgI to improve the first crystallization event of a PCM with magnesium sulfate-water eutectic. [Figure 33] FIG. 33 shows the use of AgI and SiC to improve the first and second crystallization events of a PCM with sodium sulfate-water eutectic. [Figure 34] FIG. 34 shows the two-stage crystallization of a PCM with lithium sulfate-water eutectic (i.e., about 25 wt. % lithium sulfate in water) without a nucleating agent. [Figure 35] FIG. 35 shows improved nucleation of the first crystallization event of potassium chloride-water eutectic when modified with calcium carbonate. [Figure 36] FIG. 36 shows vermiculite allowing a second crystallization event in the ammonium chloride-water eutectic compared to the blank. [Figure 37] FIG. 37 shows that the presence of calcium carbonate improves the crystallization of the first crystallization event of the eutectic of NH 4 Cl and water. [Figure 38] FIG. 38 shows the improvement of the first crystallization event of the sodium acetate and water eutectic due to the presence of iron oxide. [Figure 39] FIG. 39 shows the improvement of the first crystallization event of the eutectic of sodium acetate and water due to the presence of calcium carbonate. [Figure 40]FIG. 40 shows the improvement of the second crystallization event of the eutectic of sodium formate and water due to the presence of vermiculite. [Figure 41] FIG. 41 shows the improvement of the second crystallization event of the sodium formate and water eutectic due to the presence of silicon carbide. [Figure 42] FIG. 42 shows the crystallization of a eutectic of sodium formate and water without a nucleating agent. [Figure 43] FIG. 43 shows the crystallization of a eutectic of sodium formate and water with silver iodide nucleating agent. [Figure 44] FIG. 44 shows the improvement of the second crystallization event of a PCM with strontium chloride-water eutectic in the presence of silicon carbide and silver iodide. [Figure 45] FIG. 45 shows the improvement of the first crystallization event of a PCM with strontium chloride-water eutectic in the presence of aluminum oxide. [Figure 46] FIG. 46 shows the improvement of the first crystallization event of a PCM with sodium nitrate-water eutectic in the presence of calcium carbonate. [Figure 47] FIG. 47 shows the improvement of the first crystallization event of a PCM with sodium chloride-water eutectic in the presence of calcium carbonate. [Figure 48] FIG. 48 shows the improvement of the second crystallization event of a PCM with sodium chloride-water eutectic in the presence of vermiculite. [Figure 49] FIG. 49 shows the improvement of the first crystallization event of a PCM with lithium nitrate-water eutectic in the presence of iron oxide. [Figure 50] FIG. 50 shows the improvement of the second crystallization event of a PCM with lithium nitrate-water eutectic in the presence of silicon carbide. [Figure 51] FIG. 51 shows the improvement of the first crystallization event of a PCM with sodium bromide-water eutectic in the presence of alumina. [Figure 52] FIG. 52 shows the improvement of the first crystallization event of a PCM with strontium bromide-water eutectic in the presence of calcium carbonate. [Figure 53] FIG. 53 shows the freezing profile of a PCM containing Rochelle salt and water. [Figure 54] FIG. 54 shows the freezing profile of a PCM containing Rochelle salt, water, and calcium carbonate. [Figure 55] Figure 55 shows the improvement of the second crystallization event of a PCM with magnesium sulfate-water eutectic in the presence of calcium carbonate. [Figure 56] FIG. 56 shows the improvement of the first crystallization event of a PCM with potassium chloride-water eutectic in the presence of calcium carbonate. [Figure 57] FIG. 57 shows the improvement of the first crystallization event of a PCM with an ammonium chloride-water eutectic in the presence of aluminum oxide. [Figure 58] FIG. 58 shows the improvement of the second crystallization event of a PCM with ammonium chloride-water eutectic in the presence of silicon carbide. [Figure 59] Figure 59 shows the improvement of the second crystallization event of a PCM with strontium chloride-water eutectic in the presence of vermiculite. [Figure 60] Figure 60 shows the improvement of the second crystallization event of a PCM with sodium nitrate-water eutectic in the presence of vermiculite. [Figure 61] FIG. 61 shows the improvement of the second crystallization event of a PCM with sodium nitrate-water eutectic in the presence of aluminum oxide. [Figure 62] FIG. 62 shows the improvement of the first crystallization event of a PCM with sodium nitrate-water eutectic in the presence of iron oxide. [Figure 63] FIG. 63 shows the improvement of the first crystallization event of a PCM with sodium nitrate-water eutectic in the presence of silicon oxide. [Figure 64] Figure 64 shows the improvement of the first crystallization event of a PCM with sodium acetate-water eutectic in the presence of calcium carbonate. [Figure 65]Figure 65 shows the improvement of the first crystallization event of a PCM with sodium chloride-water eutectic in the presence of aluminum oxide. [Figure 66] Figure 66 shows the improvement of the second crystallization event of a PCM with sodium chloride-water eutectic in the presence of silicon carbide. [Figure 67] FIG. 67 shows TiO2 undergoing a second crystallization event in a PCM with lithium nitrate-water eutectic. [Figure 68] Figure 68 shows that SiO2 improves the second crystallization event of a PCM with lithium nitrate-water eutectic. Note - The anomalies labeled as artifacts are due to the temperature increase of nearby samples during crystallization and are not attributable to the sample depicted in the figure. [Figure 69] Figure 69 shows that vermiculite improves the second crystallization event of a PCM with potassium chloride-water eutectic. DETAILED DESCRIPTION OF THE INVENTION

[0015] Disclosed in this disclosure are PCM compositions that exhibit multiple crystallization events upon cooling.

[0016] Typically, the one or more salts may include: lithium; sodium; potassium; calcium; magnesium; strontium; ammonia; iron; copper; manganese; zinc; and / or aluminum; at least one or a combination of cations selected from and, Any halogen; Sulfuric acid; nitric acid; phosphoric acid; Carbonated; any carboxylic or dicarboxylic acid, and / or Any deprotonated amino acid At least one or a combination of anions selected from:

[0017] Typically, the PCM may contain one or more nucleating agents, including one or more of the following: 0-30 wt% MgSO4; 0-40 wt% Mg(NO3)2 0-30% by weight of MgCl2 0-35% by weight of CaCl2 0-50% by weight of Ca(NO3)2 0-50% by weight of SrBr2 0-50% by weight NaBr 0 to 25% by weight of NaCl 0-10% by weight of Na2SO4 0-25% by weight of NH4Cl 0 to 25% by weight of KCl 0-45% by weight of K2CO3 0-40% by weight of NaH2PO4 0-40 wt% NaOAc 0-35% by weight of NaOOCH 0-30% by weight of Na2CO3 0 to 35 wt% LiCl 0-60% by weight ZnCl2 0-40 wt% FeCl3 0-40% by weight CuCl2 0-40% by weight BaCl2 0-25% by weight KHCO3 0-40% by weight of Li-, Na-, and / or K-benzoates 0-50% by weight of Li-, Na-, and / or K-glycolates 0-50% by weight of Li-, Na-, and / or K-glycinate 0-50% by weight of Li-, Na-, and / or K-propionates 0-50% by weight of Li-, Na-, and / or K-β-alaninate 0-50% by weight of Li-, Na-, and / or K-aspartate 0-50% by weight of Li-, Na-, and / or K-lactate 0 to 50% by weight of Li-, Na-, and / or K-2,2'-bishydroxymethylpropionate 0 to 50% by weight of Li-, Li2-, Na-, Na2-, K- and / or K2-glutamate 0 to 40% by weight of Li-, Li2-, Na-, Na2-, K- and / or K2-adipates, and / or 0-50% by weight of Li-, Li2-, Na-, Na2-, K- and / or K2-tartrate The remainder of each composition is water.

[0018] Preferably, the PCM according to the present invention comprises one or more nucleating agents selected from one or more of the following: 3-6% by weight of sodium sulfate; 14-25% by weight of magnesium sulfate; 25-35% by weight of magnesium nitrate; 30-40% by weight of sodium nitrate; 20-30% by weight of lithium nitrate; 15-25% by weight of strontium chloride; 35-46% by weight of strontium bromide; 34-45% by weight of sodium bromide; 15-25% by weight of sodium chloride; 14-25% by weight of ammonium chloride; 15-25% by weight of potassium chloride; 5-15% by weight of sodium potassium tartrate; 18 to 30% by weight of sodium acetate; and / or 19-30% by weight of sodium formate; The remainder of each composition is water.

[0019] In a preferred embodiment of the invention, the PCM comprises one or more salts of Group 1 and / or Group 2 metals.

[0020] In a preferred embodiment of the invention, the PCM contains one or more of the following salts: lithium, sodium, potassium, magnesium, calcium, strontium, and / or ammonium.

[0021] In a preferred embodiment of the invention, the PCM contains one or more of a halide, sulfate, nitrate, carbonate, and / or carboxylate.

[0022] In this disclosure, the first and second crystallization events are defined by the order in which they occur chronologically as the PCM cools from its liquid state.

[0023] The nucleating agent may act to induce the nucleation of the first crystallization transition.

[0024] The nucleating agent may act to induce nucleation at the second crystallization transition.

[0025] Multiple nucleating agents may be used to nucleate both crystallization events.

[0026] In a preferred embodiment of the invention, two or more nucleating agents are used, at least one of which acts to reduce supercooling in the first crystallization event and at least one of which acts to reduce supercooling in the second crystallization event.

[0027] In certain embodiments of the present invention, upon cooling, nucleation at higher temperatures occurs prior to nucleation at lower temperatures.

[0028] One of the crystallization events may be a solid-solid phase transition.

[0029] The nucleating agent may be selected from at least one of the following oxides, carbonates, carbides, silicates, and / or halides: Silicon; calcium; aluminum; titanium; iron; silver; zirconium; zinc; and / or magnesium.

[0030] The nucleating agent may be at least one substance selected from the group comprising: silicon dioxide; Silicon carbide; Titanium dioxide; Iron oxide; Aluminum oxide; Silver iodide; Magnesium oxide; Zinc oxide; vermiculite; and / or combinations thereof.

[0031] The nucleating agent may be a ceramic composite composed of more than one oxide and / or carbide.

[0032] The nucleating agent may be present at a loading of at least 0.01 wt%, at least 0.1 wt%, at least 1 wt%, at least 5 wt%, at least 10 wt%, or at least 20 wt%.

[0033] The nucleating agent may be present at a loading of about 0.5% by weight.

[0034] The nucleating agent may be present at a loading greater than the solubility limit of the nucleating agent in the salt solution.

[0035] Other aspects of the invention are set out in the accompanying claims.

[0036] According to a further aspect of the present invention there is provided a use of a PCM according to the first aspect, wherein the PCM is retained in a solid state after its first crystallisation event and before a second crystallisation event occurs, which may be considered to be a solid-solid phase transition.

[0037] Further disclosed as part of this invention are nucleator materials that act to reduce supercooling in one of the crystallization events exhibited by salt-water eutectic PCMs.

[0038] As part of this invention, it is disclosed that beyond supercooling, salt-water eutectics often crystallize in two stages and at two different temperatures.

[0039] As further disclosed herein, the two or at least two crystallization events in a salt-water eutectic PCM may have distinctly different thermal energies. Control over these two or at least two crystallization events (including nucleation and crystal growth) is highly advantageous toward the production of sub-zero PCMs with reliable cyclability, advantageously utilizing the full heat capacity of the material.

[0040] In preferred embodiments of the present invention, silicon carbide, phyllosilicate materials (e.g., vermiculite, talc, or mica), and combinations thereof, are used as nucleating agents to nucleate the second crystallization event of the salt-water eutectic PCM.

[0041] Additionally, the application of this control of crystallization to the operation of heat storage devices is described.

[0042] Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0043] The present invention relates to the use of inorganic phase change materials (PCMs) as cryogenic storage media and the nucleation thereof.

[0044] In this disclosure, various salt-water eutectics are disclosed that have phase transition temperatures between about 0 and about −100° C. and exhibit a two-stage crystallization event.

[0045] The two-stage crystallization event is depicted schematically in FIG. 1. The PCM is shown being cooled by an external source of cooling, thereby decreasing the internal temperature of the PCM. Initially, the PCM temperature decreases according to the sensible heat of the PCM until a certain temperature is reached. At this point, a first crystallization event occurs, and heat is released as the PCM crystallizes. Once this first phase change is complete, the PCM temperature begins to drop again according to the sensible heat of the material. At a second, lower temperature, a further crystallization event is observed, and heat is again released. After this second nucleation / crystallization stage, the PCM continues to cool according to its sensible heat.

[0046] As defined in this disclosure, the first and second crystallization events are defined by the order in which crystallization occurs in time as the PCM cools from its liquid state.

[0047] However, experimentally, several different potential regimes can be observed depending on the composition of the PCM.

[0048] Figure 2 shows a typical double crystallization plot of a lithium nitrate-water sub-zero PCM, with supercooling evident at both transitions. The lithium nitrate-water eutectic is disclosed to have a thermodynamic phase transition at approximately -21°C, but upon cooling, two crystallization events are observed, beginning at approximately -28°C and approximately -32°C, indicating supercooling. Thus, although this PCM without additives is visibly solid after cooling to approximately -28°C, it would need to be cooled to approximately -32°C for it to fully crystallize.

[0049] The undercooling can be even more extreme than that seen in Figure 2, where the cold crystallization event undercools to such an extent that only a single crystallization event occurs within the temperature range used.

[0050] Figure 3 shows experimental data for a disodium adipate and water eutectic that undergoes its first crystallization event but not its second. This causes incomplete freezing of the PCM, resulting in only a very ill-defined melting plateau being observed as the PCM increases in temperature. In contrast, when this PCM undergoes both of its crystallization events (Figure 4), a clear flat melting transition is observed at approximately -14°C. Therefore, it is key that both the first and second crystallization events occur in the salt-water eutectic PCM disclosed in this disclosure, and thus, maximum energy storage is achieved at a single, well-defined temperature.

[0051] Furthermore, the maximum output temperature of a sub-zero PCM with multiple nucleation events may be biased more towards the crystallization process initiated by the first or second crystallization event.

[0052] For example, Figure 2 shows that a thermodynamic maximum freezing temperature of approximately -21°C is reached after the second crystallization event for lithium nitrate-water eutectic, while Figure 5 shows that sodium acetate-water eutectic, which has a thermodynamic phase transition temperature of approximately -20°C, reaches this temperature only after the first crystallization event, but not after the second crystallization event. Without intending to be limited by theory, it is suggested that this effect is due to a combination of supercooling and crystal growth rate.

[0053] Another situation is that both crystallization stages result in the same output temperature after each crystallization event.

[0054] Figure 6 shows the crystallization of sodium sulfate-water eutectic in two stages, with both crystallization stages reaching approximately -1°C after the onset of crystallization. The regime depicted in Figure 6 can result in slight supercooling and rapid crystallization.

[0055] A further important point made clear in Figure 6 is that the temperatures of the first and second crystallization events can be the highest or lowest first. For example, the first crystallization event can be relatively lower or higher in temperature than the second, over time, as the PCM cools.

[0056] As disclosed in the present disclosure, salts of halides, nitrates, sulfates, and carboxylic acids (e.g., acetic or formic acid salts), as well as mixtures thereof, exhibit the above multiple crystallization events.

[0057] The PCMs disclosed herein comprise at least one or more cations selected from the group including: lithium; sodium; potassium; calcium; magnesium; strontium; ammonium; iron; copper; Manganese; and / or zinc and At least one anion selected from the group including: Any halogen; Sulfuric acid; nitric acid; phosphoric acid; Carbonated; any carboxylic acid, dicarboxylic acid, or tricarboxylic acid; and / or Any deprotonated amino acid The compound may comprise at least one salt having the formula:

[0058] In a preferred embodiment of the invention, the PCM comprises one or more salts of Group 1 and / or Group 2 metals.

[0059] In a preferred embodiment of the invention, the PCM comprises one or more of the following: a salt of lithium, sodium, potassium, magnesium, calcium, strontium, and / or ammonium.

[0060] In preferred embodiments of the present invention, the PCM comprises one or more of the following: halides, sulfates, nitrates, carbonates, and / or salts of carboxylic acids.

[0061] It is noted in this disclosure that this double crystallization effect can be observed in salt-water eutectics where the salt of interest has one or more known hydrate forms, such as the sodium acetate-water eutectic depicted in Figure 5 or the lithium sulfate-water eutectic whose thermal cycle is shown in Figure 34. However, as disclosed in this disclosure, it can also be observed when the salt does not have a known hydrated form (e.g., the potassium chloride-water eutectic depicted in Figure 7). Thus, the technical advantages of controlling these nucleation events extend to salts that do not have hydrated forms, as well as salts that do.

[0062] Furthermore, as disclosed herein, even salts with multiple hydration forms tend to have only two distinct crystallization events. In Figure 8, a PCM with calcium chloride and water is shown to exhibit dual crystallization patterns in the same manner as other salt-water eutectics. It is noteworthy, however, that calcium chloride is known to exist in the forms of monohydrate, dihydrate, tetrahydrate, and hexahydrate, yet it exhibits only two crystallization stages when used as a salt-water eutectic. Therefore, as disclosed herein, the dual crystallization effect of a salt-water eutectic is independent of the number of available crystallization hydration forms. According to the inventors, a salt-water eutectic will exhibit two crystallization events.

[0063] The present invention discloses a material that can be used to assist in the nucleation of one of the crystallization events of a salt-water eutectic. Providing a material that assists in nucleation ensures that both crystallization stages are completed before the temperature of the material is increased, thus allowing for maximum utilization of the PCM as a thermal energy storage medium. The nucleating agent also reduces the temperature below which the PCM needs to be cooled to ensure nucleation for one or both of the phase transitions. The present invention further discloses that multiple nucleating agents, each acting individually to reduce supercooling at one of the crystallization transitions, can be combined to eliminate supercooling at both crystallization transitions.

[0064] As disclosed in the present disclosure, metal oxides, carbides, silicates, halides, and combinations thereof are effective nucleating agents for at least one of the phase transitions observed in sub-zero salt-water eutectic PCMs.

[0065] A nucleating agent may be effective in one of the two phase transitions, but not in the other. For example, as shown in Figure 9, silicon carbide (SiC) is an effective nucleating agent for the second crystallization event of the magnesium nitrate-water eutectic. In the absence of the SiC nucleating agent, the PCM does not undergo the second crystallization phase transition and therefore does not exhibit a detectable melting transition upon temperature increase. Conversely, SiC-containing PCMs exhibit both transitions and a melting transition at approximately -30°C. Meanwhile, the first crystallization event is largely unaffected by the addition of SiC.

[0066] Nucleating agents may affect only the first crystallization event. For example, a ceramic composite composed of alumina and silica has been disclosed as an effective nucleating agent for the first high-temperature nucleation event of the magnesium nitrate-water eutectic. Figure 10 shows this eutectic without the presence of a nucleating agent, in which case the first crystallization event occurs at approximately -38°C. In contrast, when the PCM contains a ceramic nucleating agent, the phase transition occurs at approximately -30°C, the thermodynamic phase transition temperature for this eutectic (Figure 11).

[0067] Ice nucleating proteins are disclosed in the present disclosure as effective nucleating agents for the first crystallization event. Figure 12 shows an ammonium chloride-water eutectic modified with ice nucleating proteins. While two crystallization events are observed in the plot, minimal supercooling is observed in the first compared to the sample without the nucleating agent (i.e., Figure 29). Therefore, it can be determined that the ice nucleating protein is a nucleating agent for the first crystallization event.

[0068] Nucleation is known to be a stochastic process; therefore, crystallization generally improves with increasing sample size, because the probability of stable nucleation points forming increases with increasing sample size. Given this, one might expect that the dual nucleation profile of a sub-zero salt-water eutectic PCM would be different at larger scales. However, as disclosed in the present disclosure, this is not the case; even at very large (i.e., >1 L) scales, such PCMs still exhibit two distinct crystallization events. Figure 14 shows that the crystallization of a 17 L sodium acetate-water eutectic proceeds in two stages, with the second crystallization event observed only below approximately -30°C, far from the thermodynamic phase change temperature of approximately -18°C. As with smaller samples, the inventors found that at this increased scale, both crystallization events must occur to fully access the energy storage capacity of the PCM. Thus, without a nucleating agent, crystallization of a salt-water eutectic PCM requires excessive cooling, even at large scales. However, with the nucleating agents defined in this disclosure, minimal supercooling can be achieved in both large and relatively small PCM samples. Figure 15 shows the dual crystallization of a large (approximately 100 L) sample of a magnesium sulfate and water eutectic combined with calcium carbonate and silver iodide nucleating agents, which, to the inventors' knowledge, improves nucleation in the first and second crystallization events, respectively (see Figures 16 and 17 for comparison). Minimal supercooling below the thermodynamic phase change temperature of approximately -5°C can be observed in both the first and second nucleation events, however, they are still distinct from each other. Thus, two crystallization events are predicted in a maximally frozen salt-water eutectic PCM, and a nucleating agent that drives one of the crystallization events is effective even at very large scales.

[0069] As a further non-limiting example, consider a PCM containing magnesium sulfate, water, and one or more nucleating agents. Figure 18 shows a comparison of typical thermal cycles for two samples of such a PCM, one containing a titanium dioxide nucleating agent and the other without. Improvements to the first crystallization event can be seen for the sample containing titanium dioxide, but no improvement in the second crystallization event can be observed. The blank sample eventually undergoes a second crystallization event, but only after exhibiting significant undercooling. The inventors have found that this second crystallization event in the blank is unreliable and does not occur on every thermal cycle. Thus, although the melting transitions for the blank and the titanium dioxide-containing sample are often broad, clear improvements to the first crystallization event can be obtained with the use of titanium dioxide. Similar tests using an aluminum oxide nucleating agent showed improvements to the first crystallization event and subsequent complete crystallization (Figure 19). Alumina has been shown to increase the temperature at which the first crystallization event occurs and is therefore a nucleation aid for the first crystallization event. This improved crystallization may also help induce a second crystallization event, due in part to the material being partially or completely solid before the second crystallization occurs. In contrast, as shown in Figure 20, the inventors have found that silicon carbide is a preferential nucleating agent for the second crystallization event. In Figure 20, a magnesium sulfate-water eutectic that also contains silicon carbide does not show an improvement in the crystallization temperature of the first crystallization event, but does show a significant increase in the temperature at which the second crystallization event occurs. Thus, silicon carbide is clearly a preferential nucleating agent for the second crystallization event.

[0070] As a further non-limiting example, consider a PCM containing sodium bromide, water, and one or more nucleating agents. We have found that aluminum oxide, silica, and calcium carbonate can be used as nucleating agents to initiate the first crystallization event (Figures 21, 22, and 23). When silver iodide was tested as a nucleating agent, we found that it served as a nucleating agent for the first crystallization event of the PCM containing sodium bromide and water (Figure 24). This differs from what we know about other PCMs, such as carboxylates (Figures 25 and 26) and 2+ metal halides (Figure 27). As shown in Figure 25, without the silver iodide nucleating agent, the sodium acetate-water eutectic PCM undergoes its first crystallization event but not the second. However, when silver iodide is added to the system, both crystallization events occur, as seen in Figure 26. Similarly, the 2+ halide salt strontium bromide-water eutectic exhibits increased supercooling in its second crystallization event when silver iodide is absent from the PCM compared to when silver iodide is present in the PCM, but the first crystallization event is unaffected by this change (Figure 27).

[0071] Further testing with other monovalent cation halides, such as KCl-water and NHCl-water eutectics, revealed that silver iodide would act as a nucleating agent for the first crystallization event. Figure 28 shows a comparison of a salt-water eutectic PCM where the salt is KCl, with and without an AgI nucleating agent. A detectable increase in the first crystallization event can be seen when AgI is present in the material, in a manner similar to that seen for other monovalent halide salt-water eutectics, but there is no indication of a second crystallization event. Presumably, the presence of AgI actually inhibits the second crystallization event in this example, which, like the blank that exhibits significant undercooling in the first crystallization event, goes through both transitions, thus having a relatively long melting transition, and no sign of any melting transition at about 0°C. Conversely, samples with AgI exhibit slight supercooling in the first crystallization event but no second crystallization event, and therefore have a short melting transition (and therefore less energy storage). Therefore, to use this type of PCM, a combination of nucleating agents that function in both the first and second crystallization events can be used (i.e., AgI, vermiculite, and / or silicon carbide). The NHCl-water eutectic responds to AgI in a similar manner, as seen in Figure 29; neither the blank nor the material prepared containing AgI exhibits a second crystallization event and therefore has a relatively short, broad melting transition.

[0072] In summary, Table 1 discloses nucleating agents that tend to act to reduce supercooling in their primary and secondary crystallization events, although not in all cases.

[0073] [Table 1]

[0074] More particularly, Table 2 shows salt types that, in accordance with the present invention, are used in sub-zero salt-water eutectic PCMs with nucleating agents that act in both primary and secondary crystallization events.

[0075] [Table 2]

[0076] The salt types defined in Tables 1 and 2 are representative of preferred nucleating agent(s). Further, more specific details are provided in Tables 3 and 4.

[0077] Table 3 discloses a preferred embodiment of the present invention.

[0078] [Table 3-1] [Table 3-2] [Table 3-3]

[0079] Table 4 shows further more specific preferred embodiments of the present invention.

[0080] [Table 4]

[0081] Table 5 details various nucleating agents and salts and the concentrations at which they may be used. [Table 5-1] [Table 5-2]

[0082] Additional specific embodiments of the present invention are further illustrated in Figures 32-69.

[0083] FIG. 32 shows the use of AgI to improve the first crystallization event of a PCM with magnesium sulfate-water eutectic (i.e., about 19 wt. % MgSO4 in water).

[0084] FIG. 33 shows a further sulfate-water eutectic, a sodium sulfate-water eutectic (i.e., about 3.5 wt. % Na2SO4 in water), where the addition of AgI and SiC, respectively, improves the nucleation of the first and second crystallization events relative to the blank.

[0085] FIG. 35 shows calcium carbonate at increasing temperatures for the first crystallization event of a PCM comprising a eutectic of KCl and water (i.e., about 19.5 wt % KCl in water).

[0086] FIG. 36 shows that the presence of vermiculite induces a second crystallization event in the eutectic of NH4Cl and water (i.e., about 18.6 wt% NH4Cl in water), while the blank containing no vermiculite goes through only one crystallization event and therefore exhibits a shorter melting transition over a wider temperature range compared to the sample containing vermiculite.

[0087] FIG. 37 shows that the presence of calcium carbonate improves the crystallization of the first crystallization event of the eutectic of NH 4 Cl and water (i.e., about 18.6 wt % NH 4 Cl in water).

[0088] Figure 38 shows that iron oxide improves the nucleation of the first nucleation event of the eutectic of sodium acetate and water (i.e., 22.7 wt% NaOAc in water). This effect is also confirmed in the case of calcium carbonate (Figure 39).

[0089] Figure 40 shows the improvement in the second crystallization event of a eutectic of sodium formate and water (i.e., about 24.0 wt. % sodium formate in water—abbreviated as NaFo) due to the presence of vermiculite. Figure 41 shows a similar improvement to the second crystallization event when silicon carbide is used as a nucleating agent.

[0090] Figure 42 shows the freezing process of a PCM with sodium formate-water eutectic (about 24.0 wt% sodium formate in water) without a nucleating agent. Two crystallization events can be observed, the second occurring at about -22°C. Figure 43 shows an improvement in this crystallization event for this PCM when silver iodide is present, with nucleation occurring at about -19°C in this case.

[0091] FIG. 44 shows the improvement to the second crystallization event of a PCM with strontium chloride-water (about 19.5 wt % SrCl in water) eutectic in the presence of silicon carbide and silver iodide.

[0092] FIG. 45 shows the improvement to the first crystallization event of a PCM with strontium chloride-water (about 19.5 wt % SrCl in water) eutectic in the presence of aluminum oxide.

[0093] FIG. 46 shows the improvement to the first crystallization event of a PCM with sodium nitrate-water (approximately 35.0 wt % NaNO in water) eutectic in the presence of calcium carbonate.

[0094] FIG. 47 shows the improvement to the first crystallization event of a PCM with sodium chloride-water eutectic (about 22.4 wt % NaCl in water) in the presence of calcium carbonate.

[0095] Figure 48 shows that the second crystallization event of a PCM with sodium chloride-water eutectic (approximately 22.4 wt% NaCl in water) may not occur upon cooling, resulting in a poor melting transition to its phase transition temperature (approximately -21°C) upon increasing temperature. However, a second crystallization event can be initiated in the presence of vermiculite.

[0096] FIG. 49 shows the improvement to the first crystallization event of a PCM with lithium nitrate-water eutectic (approximately 24.5 wt % LiNO3 in water) in the presence of iron oxide.

[0097] FIG. 50 shows the improvement to the second crystallization event of a PCM with lithium nitrate-water eutectic (about 24.5 wt % LiNO3 in water) in the presence of silicon carbide.

[0098] FIG. 51 shows the improvement to the first crystallization event of a PCM with sodium bromide-water eutectic (approximately 39 wt % NaBr in water) in the presence of alumina.

[0099] FIG. 52 shows the improvement to the first crystallization event of a PCM with strontium bromide-water eutectic (about 41 wt % SrBr2 in water) in the presence of calcium carbonate.

[0100] Figures 53 and 54 show the freezing profiles of eutectics containing Rochelle salt (potassium sodium tartrate) in water (approximately 5 wt% Rochelle salt in water). The blank (Figure 53) shows a first crystallization event, supercooling to approximately -11.5°C, while the sample with calcium carbonate (Figure 54) has a first crystallization event at approximately -7.8°C. In both cases, the second crystallization event occurs as a plateau at approximately -9.8°C and is therefore unaffected by the presence of calcium carbonate.

[0101] FIG. 55 shows the improvement to the second crystallization event of a PCM with magnesium sulfate-water eutectic (about 19 wt % MgSO4 in water) in the presence of calcium carbonate.

[0102] Figure 56 shows the improvement to the first crystallization event of a PCM with potassium chloride-water eutectic (approximately 19.5 wt% KCl in water) in the presence of calcium carbonate.

[0103] FIG. 57 shows the improvement to the first crystallization event of a PCM with ammonium chloride-water eutectic (approximately 18.6 wt % NH 4 Cl in water) in the presence of aluminum oxide.

[0104] FIG. 58 shows the improvement to the second crystallization event of a PCM with ammonium chloride-water eutectic (about 18.6 wt % NH 4 Cl in water) in the presence of silicon carbide.

[0105] Figure 59 shows the improvement to the second crystallization event of a PCM with strontium chloride-water eutectic (approximately 19.5 wt% SrCl in water) in the presence of vermiculite. The blank comparison sample exhibits a relatively short melting transition, indicating only partial crystallization (i.e., only the first crystallization event occurs). In comparison, the sample containing vermiculite exhibits a long, flat melting transition (i.e., has high energy) and therefore undergoes both crystallization events.

[0106] Figure 60 shows the improvement to the second crystallization event of a PCM with sodium nitrate-water eutectic (approximately 35 wt% NaNO3 in water) in the presence of vermiculite.

[0107] FIG. 61 shows the improvement to the second crystallization event of a PCM with sodium nitrate-water eutectic (approximately 35 wt % NaNO3 in water) in the presence of aluminum oxide.

[0108] FIG. 62 shows the improvement to the first crystallization event of a PCM with sodium nitrate-water eutectic (approximately 35 wt % NaNO3 in water) in the presence of iron oxide.

[0109] Figure 63 shows the improvement to the first crystallization event of a PCM with sodium nitrate-water eutectic (approximately 35 wt% NaNO3 in water) in the presence of silicon oxide.

[0110] Figure 64 shows the improvement to the first crystallization event of a PCM with sodium acetate-water eutectic (approximately 27.0 wt% NaOAc in water) in the presence of calcium carbonate.

[0111] Figure 65 shows the improvement to the first crystallization event of a PCM with sodium chloride-water eutectic (approximately 22.4 wt% NaCl in water) in the presence of aluminum oxide.

[0112] Figure 66 shows the improvement to the second crystallization event of a PCM containing sodium chloride-water eutectic (approximately 22.4 wt% NaCl in water) in the presence of silicon carbide. The relatively long melting transition upon melting indicates complete crystallization, which is absent in the blank but can be observed in the sample containing silicon carbide.

[0113] Figure 67 shows TiO2 initiating a second crystallization event in a PCM with lithium nitrate-water eutectic (approximately 24.5 wt% LiNO3 in water). A blank sample was found to exhibit supercooling of the second crystallization event below the minimum temperature used during thermal cycling.

[0114] Figure 68 shows that SiO2 improves the second crystallization event of a PCM with lithium nitrate-water eutectic (approximately 24.5 wt.% LiNO3 in water). The outliers, shown as artifacts, are due to the temperature increase of neighboring samples during crystallization and not the sample shown. It can be observed here that the improvement to the second crystallization event of the PCM caused by the introduction of SiO2 results in two indistinguishable crystallization events; no supercooling is observed in the second after the first or after the first. However, it is clear that complete crystallization (first and second crystallization events) has occurred because the melting transition is observable, flat, and long in duration. These features are only observed in samples that have undergone complete crystallization.

[0115] Figure 69 shows vermiculite improving the secondary crystallization of potassium chloride-water eutectic (approximately 19.5 wt% KCl in water). This improvement results in a higher temperature, flatter freezing plateau, while the blank has an approximately 1°C drop under the test conditions before flattening after the initial (first) crystallization event.

[0116] As disclosed herein, corrosion of metallic components in contact with a salt-water eutectic PCM can be reduced by reduced undercooling through the addition of a nucleating agent. Corrosion increases where the liquid PCM contacts the metallic component, while, in contrast, the solid phase of the same material has significantly reduced corrosion. By improving the nucleation properties of the salt-water eutectic PCM so that relatively little contact occurs between the liquid PCM and any metallic component, overall corrosion is limited.

[0117] Additionally, as disclosed herein, a sub-zero PCM featuring one or more nucleating agents that act to suppress supercooling during one of the PCM crystallization events can be part of a heated battery system. In this way, energy storage at sub-zero temperatures can be achieved with reliable nucleation and the potential for minimizing cooling below the thermodynamic phase transition of the PCM components. Cooling in such a system to induce both crystallization events can proceed via a heat exchanger or via the addition of a coolant such as dry ice or liquid nitrogen.

[0118] Determining the state of crystallization of sub-zero PCMs is also complicated by their dual crystallization characteristics. Because they appear solid after the first crystallization event, it may be concluded that the material is fully crystallized at this point and can be used for cooling applications. However, to the present inventors' knowledge, both crystallization events must occur in order to access the material's full latent heat. This poses a challenge when using such materials, for example, in heat battery devices; the crystallization state of the material must be known, thereby determining the available cooling potential (i.e., the state of charge of a heat battery containing such a PCM). In addition to the disclosure herein that one or more nucleating agents can be used to ensure both crystallization events occur, it is also disclosed that complete crystallization may be determined by various means, including, but not limited to, determining free water content (i.e., water not bound in solid form) and by optical means. It is also disclosed herein that a sub-zero PCM sample may be optically distinguishable after its first and second crystallization events. In Figure 13, the sub-zero PCM that solidified after the first crystallization event undergoes its second crystallization event. This is evident by the material changing from a translucent solid (1) to an opaque one (2). Thus, the progression of both crystallization events may be observed and quantified, for example, by optical refraction or transmittance. This is disclosed as being an advantage in heat batteries containing the necessary sub-zero PCM because it allows for the determination of both crystalline transitions.

[0119] As disclosed herein, a PCM having a phase change temperature of about −30° C. can be formed by adding magnesium nitrate to water to produce an approximately 29.9 wt. % solution. For this purpose, a hydrated form of magnesium nitrate (e.g., magnesium nitrate hexahydrate) can be used. This solution can then be combined with silica and / or alumina in an amount corresponding to greater than 0.1 wt. %, or preferably at least about 0.5 wt. %, to aid in the nucleation of a first crystallization event. This solution can also be combined with silicon carbide in an amount corresponding to greater than 0.1 wt. %, or preferably at least about 0.5 wt. %, to aid in the nucleation of a second crystallization event. This material can then be used by thermally cycling it through a phase change at about −30° C. Using this nucleating agent system, the first crystallization event can occur at about −30° C., while the second crystallization event can occur at about −30° C. to about −40° C.

[0120] As disclosed herein, a PCM having a phase change temperature of about −26° C. may be formed by adding strontium bromide to water to produce an approximately 41 wt. % solution. For this purpose, a hydrated form of strontium bromide (e.g., strontium bromide hexahydrate) may be used. This solution may then be combined with calcium carbonate in an amount corresponding to greater than 0.1 wt. %, or preferably at least about 0.5 wt. %, to assist in the nucleation of a first crystallization event. This solution may also be combined with silver iodide in an amount corresponding to greater than 0.1 wt. %, or preferably at least about 0.5 wt. %, to assist in the nucleation of a second crystallization event. This material may then be used by subjecting it to a thermal cycle that undergoes a phase change at about −26° C. Using this nucleating agent system, the first and second crystallization events can occur at temperatures from about −26° C. to about −32° C.

[0121] As disclosed herein, a PCM having a phase change temperature of about −25° C. may be formed by adding sodium bromide to water to produce an approximately 39 wt. % solution. This solution may then be combined with calcium carbonate in an amount corresponding to greater than 0.1 wt. %, or preferably at least about 0.5 wt. %, to support a first crystallization event. This solution may also be combined with silicon carbide in an amount corresponding to greater than 0.1 wt. %, or preferably at least about 0.5 wt. %, to support nucleation of a second crystallization event. This material may then be used by subjecting it to a thermal cycle that undergoes a phase change at about −25° C. Using this nucleating agent system, the first and second crystallization events can occur at temperatures from about −25° C. to about −33° C.

[0122] As disclosed herein, a PCM having a phase change temperature of about −22° C. may be formed by adding lithium nitrate to water to produce an approximately 25 wt. % solution. For this purpose, a hydrated form of lithium nitrate (e.g., lithium nitrate trihydrate) may be used. This solution may then be combined with iron oxide in an amount corresponding to greater than 0.1 wt. %, or preferably at least about 0.5 wt. %, to support the first crystallization event. This solution may also be combined with silicon carbide in an amount corresponding to greater than 0.1 wt. %, or preferably at least about 0.5 wt. %, to support the nucleation of the second crystallization event. This material may then be used by subjecting it to a thermal cycle that spans a phase change at about −22° C. Using this nucleating agent system, the first and second crystallization events can occur at temperatures from about −22° C. to about −27° C.

[0123] As disclosed in the present disclosure, a PCM having a phase change temperature of about −21° C. may be formed by adding sodium chloride to water to produce an approximately 22 wt. % solution. This solution may then be combined with calcium carbonate in an amount corresponding to greater than 0.1 wt. %, or preferably at least about 0.5 wt. %, to aid in the nucleation of a first crystallization event. This solution may also be combined with silicon carbide and / or vermiculite in an amount corresponding to greater than 0.1 wt. %, or preferably at least about 0.5 wt. %, to aid in the nucleation of a second crystallization event. This material may then be used by subjecting it to a thermal cycle that spans a phase change at about −21° C. Using this nucleating agent system, the first and second crystallization events can occur at temperatures from about −21° C. to about −28° C.

[0124] As disclosed herein, a PCM having a phase change temperature of about −18° C. may be formed by adding sodium acetate to water to produce an aqueous solution of about 20-30 wt %, preferably about 23 wt % or 27 wt %, sodium acetate. For this purpose, a hydrated form of sodium acetate (e.g., sodium acetate trihydrate) may be used. This solution may then be combined with calcium carbonate in an amount corresponding to greater than 0.1 wt %, or preferably at least about 0.5 wt %, to aid in the nucleation of a first crystallization event. This solution may also be combined with silver iodide in an amount corresponding to greater than 0.1 wt %, or preferably at least about 0.5 wt %, to aid in the nucleation of a second crystallization event. This material may then be used by subjecting it to a thermal cycle that crosses the phase change at about −18° C. Using this nucleating agent system, the first and second crystallization events can occur at temperatures from about −18° C. to about −30° C.

[0125] As disclosed herein, a PCM having a phase change temperature of about −17° C. may be formed by adding sodium nitrate to water to produce an approximately 35 wt. % solution. This solution may then be combined with iron oxide and / or silica in an amount corresponding to greater than 0.1 wt. %, or preferably at least about 0.5 wt. %, to aid in the nucleation of a first crystallization event. This solution may also be combined with aluminum oxide and / or vermiculite in an amount corresponding to greater than 0.1 wt. %, or preferably at least about 0.5 wt. %, to aid in the nucleation of a second crystallization event. This material may then be used by subjecting it to a thermal cycle that spans a phase change at about −17° C. Using this nucleating agent system, the first and second crystallization events can occur at temperatures from about −17° C. to about −25° C.

[0126] As disclosed herein, a PCM having a phase change temperature of about −16° C. may be formed by adding strontium chloride to water to produce an approximately 20 wt. % solution. For this purpose, a hydrate form of strontium chloride (e.g., strontium chloride hexahydrate) may be used. This solution may then be combined with aluminum oxide in an amount corresponding to greater than 0.1 wt. %, or preferably at least about 0.5 wt. %, to aid in the nucleation of a first crystallization event. This solution may also be combined with vermiculite and / or silver iodide in an amount corresponding to greater than 0.1 wt. %, or preferably at least about 0.5 wt. %, to aid in the nucleation of a second crystallization event. This material may then be used by subjecting it to a thermal cycle that crosses the phase change at about −16° C. Using this nucleating agent system, the first and second crystallization events can occur at temperatures from about −16° C. to about −25° C.

[0127] As disclosed herein, a PCM having a phase change temperature of about −15° C. may be formed by adding sodium formate to water to produce an approximately 24 wt. % solution. This solution may then be combined with calcium carbonate in an amount corresponding to greater than 0.1 wt. %, or preferably at least about 0.5 wt. %, to aid in the nucleation of a first crystallization event. This solution may also be combined with vermiculite in an amount corresponding to greater than 0.1 wt. %, or preferably at least about 0.5 wt. %, to aid in the nucleation of a second crystallization event. This material may then be used by subjecting it to a thermal cycle that spans a phase change at about −15° C. Using this nucleating agent system, the first and second crystallization events can occur at temperatures from about −15° C. to about 20° C.

[0128] As disclosed herein, a PCM having a phase change temperature of about −14° C. may be formed by adding ammonium chloride to water to produce an approximately 19 wt. % solution. This solution may then be combined with silver iodide in an amount greater than 0.1 wt. %, or preferably at least about 0.5 wt. %, to aid in the nucleation of a first crystallization event. This solution may also be combined with vermiculite and / or silicon carbide in an amount greater than 0.1 wt. %, or preferably at least about 0.5 wt. %, to aid in the nucleation of a second crystallization event. This material may then be used by subjecting it to a thermal cycle that crosses the phase change at about −14° C. Using this nucleating agent system, the first and second crystallization events can occur at temperatures from about −14° C. to about 20° C.

[0129] As disclosed herein, a PCM having a phase change temperature of about -10°C may be formed by adding potassium chloride to water to produce an approximately 20 wt% solution. This solution may then be combined with titanium dioxide and / or silver iodide in an amount corresponding to greater than 0.1 wt%, or preferably at least about 0.5 wt%, to aid in the nucleation of a first crystallization event. This solution may also be combined with vermiculite in an amount corresponding to greater than 0.1 wt%, or preferably at least about 0.5 wt%, to aid in the nucleation of a second crystallization event. This material may then be used by subjecting it to a thermal cycle that crosses a phase change at about -10°C. Using this nucleating agent system, the first and second crystallization events can occur at temperatures from about -10°C to about -20°C.

[0130] As disclosed herein, a PCM having a phase change temperature of about -5°C may be formed by adding magnesium sulfate to water to produce an approximately 19 wt% solution. For this purpose, a hydrated form of magnesium sulfate (e.g., magnesium sulfate heptahydrate) may be used. This solution may then be combined with aluminum oxide and / or silver iodide in an amount greater than 0.1 wt%, or preferably at least about 0.5 wt%, to aid in the nucleation of a first crystallization event. This solution may also be combined with silicon carbide and / or calcium carbonate in an amount corresponding to 0.1 wt%, or preferably at least about 0.5 wt%, to aid in the nucleation of a second crystallization event. This material may then be used by subjecting it to a thermal cycle that crosses a phase change at about -5°C. Using this nucleating agent system, the first and second crystallization events can occur at temperatures between about -5°C and about -10°C.

[0131] As disclosed herein, a PCM having a phase change temperature of about -1°C may be formed by adding sodium sulfate to water to produce an approximately 4 wt% solution. For this purpose, a hydrated form of sodium sulfate (e.g., sodium sulfate decahydrate) may be used. This solution may then be combined with silver iodide in an amount corresponding to greater than 0.1 wt%, or preferably at least about 0.5 wt%, to aid in the nucleation of a first crystallization event. This solution may also be combined with silicon carbide in an amount corresponding to greater than 0.1 wt%, or preferably at least about 0.5 wt%, to aid in the nucleation of a second crystallization event. This material may then be used by subjecting it to a thermal cycle that crosses a phase change at about -5°C. Using this nucleating agent system, the first and second crystallization events can occur at temperatures between about -5°C and about -10°C.

[0132] While various exemplary embodiments are disclosed, it is understood that variations, modifications, and combinations of the phase change materials disclosed in the present disclosure can be made without departing from the scope of the appended claims.

Claims

1. A phase change material (PCM) having a melting point below 0° C. and exhibiting at least two crystallization events upon cooling, comprising: at least one salt; Water; and one or more nucleating agents that act to reduce supercooling in the first crystallization event, and / or One or more nucleating agents that act to reduce supercooling in the second crystallization event.

2. 10. The PCM of claim 1, wherein the at least one salt is one or more salts of a Group I metal, a Group II metal, and / or an ammonium salt thereof.

3. 2. The PCM of claim 1, wherein the at least one salt is one or more selected from halides, sulfates, nitrates, phosphates, carbonates, and / or carboxylates of Group I and / or Group II metals.

4. 2. The PCM of claim 1 , wherein the one or more salts comprise: At least one cation or combination of cations selected from one of the following or any combination of the following: lithium; sodium; potassium; calcium; magnesium; Strontium; and / or Ammonium and, At least one anion or combination of anions selected from: Chloride; bromide; Sulfuric acid; nitric acid; Carbonated; formic acid; and / or Acetic acid.

5. 10. The PCM of claim 1, wherein the PCM comprises one or more nucleating agents selected from any one of the following or any combination of the following: 0-10% by weight of sodium sulfate; 0-30% by weight of magnesium sulfate; 0-40% by weight of magnesium nitrate; 0-50% by weight of sodium nitrate; 0 to 35 wt. % lithium nitrate; 0-30% by weight of strontium chloride; 0-50% by weight of strontium bromide; 0-50% by weight of sodium bromide; 0-25% by weight of sodium chloride; 0 to 25% by weight of ammonium chloride; 0-30% by weight of potassium chloride; 0-15% by weight of sodium potassium tartrate 0-40% by weight of sodium acetate, and / or 0-35 wt. % sodium formate; The remainder of each composition is water.

6. 10. The PCM of claim 1, wherein the PCM comprises one or more nucleating agents selected from any one of the following or any combination of the following: 3-6% by weight of sodium sulfate; 14 to 25% by weight of magnesium sulfate; 25-35% by weight of magnesium nitrate; 30-40% by weight of sodium nitrate; 20-30 wt. % lithium nitrate; 15 to 25% by weight of strontium chloride; 35-46% by weight of strontium bromide; 34-45% by weight of sodium bromide; 15 to 25% by weight of sodium chloride; 14 to 25% by weight of ammonium chloride; 15 to 25% by weight of potassium chloride; 5-15% by weight of sodium potassium tartrate; 18 to 30% by weight of sodium acetate; and / or 19-30% by weight of sodium formate; The remainder of each composition is water.

7. 10. The PCM of claim 1, wherein the PCM comprises one or more nucleating agents selected from one or more of the following: about 4% by weight of sodium sulfate; about 19% by weight magnesium sulfate; about 20% by weight of potassium chloride; about 19% by weight of ammonium chloride; about 24% by weight sodium formate; about 20% by weight of strontium chloride; about 35% by weight sodium nitrate; about 23% by weight sodium acetate; about 27% by weight sodium acetate; about 22% by weight sodium chloride; about 25% by weight of lithium nitrate; about 39% by weight sodium bromide; about 41% by weight of strontium bromide; or about 30% by weight magnesium nitrate; The remainder of each composition is water.

8. 10. The PCM of claim 1, wherein upon cooling, the first crystallization event nucleates at a temperature that is 0 to about 10°C, 0 to about 5°C, or 0 to about 3°C ​​below the melting temperature of the PCM.

9. 10. The PCM of claim 1, wherein upon cooling, the second crystallization event nucleates at a temperature between 0°C and about 20°C, between 0°C and about 10°C, or between 0°C and about 5°C below the melting temperature of the PCM.

10. 10. The PCM of claim 1, wherein upon cooling, the first crystallization event nucleates at a temperature between 0°C and about 10°C below the melting temperature of the PCM, followed by the nucleation of a second crystallization event at a temperature about 3°C ​​below the melting temperature of the PCM.

11. 10. The PCM of claim 1, wherein the nucleating agent acts to induce crystallization of only the second crystallization event.

12. 10. The PCM of claim 1, wherein the nucleating agent acts to induce crystallization in only the first crystallization event.

13. 10. The PCM of claim 1, wherein multiple nucleating agents are used to nucleate both crystallization events.

14. 2. The PCM of claim 1, wherein one of the crystallization events is a solid-solid phase transition or a polymorphic phase transition.

15. 2. The PCM of claim 1, wherein the nucleating agent is selected from at least one oxide, carbonate, carbide, silicate, and / or halide of any one of the following, or any combination of the following: calcium; Silicon; aluminum; titanium; iron; silver; and / or magnesium.

16. 2. The PCM of claim 1, wherein the nucleating agent is at least one substance selected from the group comprising any one of the following or any combination of the following: calcium carbonate; silicon dioxide; Silicon carbide; Titanium dioxide; Iron oxide; Aluminum oxide; Silver iodide; Vermiculite; and / or combinations thereof.

17. 10. The PCM of claim 1, wherein the nucleating agent that acts to reduce supercooling in the second crystallization event is silicon carbide, vermiculite, or a combination thereof.

18. 10. The PCM of claim 1, wherein the nucleating agent is present at a loading of at least 0.01 wt%, at least 0.1 wt%, at least 1 wt%, at least 5 wt%, or at least 10 wt%.

19. 10. The PCM of claim 1, wherein the volume of the PCM is greater than 1 L, greater than 10 L, greater than 20 L, greater than 100 L, greater than 200 L, or greater than 1000 L.

20. 2. The PCM of claim 1, wherein aluminum oxide is used as a nucleating agent for the first crystallization event and the salt is selected from the group comprising any one of the following or any combination of the following: Magnesium sulfate potassium chloride Ammonium chloride strontium chloride Sodium chloride sodium bromide, and Magnesium nitrate.

21. 2. The PCM of claim 1, wherein calcium carbonate is used as a nucleating agent for the first crystallization event and the salt is selected from the group comprising any one of the following or any combination of the following: Sodium potassium tartrate Ammonium chloride Sodium nitrate Sodium formate Sodium acetate Sodium chloride sodium bromide, and Strontium bromide.

22. 2. The PCM of claim 1, wherein silicon dioxide is used as a nucleating agent for the first crystallization event and the salt is selected from the group comprising any one of the following or any combination of the following: sodium acetate, and Magnesium nitrate.

23. 2. The PCM of claim 1, wherein silver iodide is used as a nucleating agent for the first crystallization event and the salt is selected from the group comprising any one of the following or any combination of the following: Sodium sulfate Magnesium sulfate ammonium chloride, and Sodium bromide.

24. 2. The PCM of claim 1, wherein titanium dioxide is used as a nucleating agent for the first crystallization event and the salt is selected from the group comprising any one of the following or any combination of the following: magnesium sulfate, and Potassium chloride.

25. 2. The PCM of claim 1, wherein iron oxide is used as a nucleating agent for the first crystallization event and the salt is selected from the group comprising any one of the following or any combination of the following: Sodium nitrate sodium acetate, and Lithium nitrate.

26. 2. The PCM of claim 1, wherein silicon carbide is used as a nucleating agent for the second crystallization event and the salt is selected from the group comprising any one of the following or any combination of the following: Sodium sulfate Sodium potassium tartrate Magnesium sulfate Ammonium chloride Sodium formate strontium chloride Sodium nitrate Sodium acetate Sodium chloride Lithium nitrate sodium bromide, and Magnesium nitrate.

27. 2. The PCM of claim 1 wherein silver iodide is used as a nucleating agent for the second crystallization event and the salt is selected from the group comprising any one of the following or any combination of the following: Sodium formate Sodium nitrate Strontium chloride, and Strontium bromide.

28. 2. The PCM of claim 1, wherein vermiculite is used as a nucleating agent for the second crystallization event and the salt is selected from the group comprising any one of the following or any combination of the following: potassium chloride Ammonium chloride Sodium formate strontium chloride Sodium nitrate Sodium acetate Sodium chloride Lithium nitrate sodium bromide, and Magnesium nitrate.

29. 2. The PCM of claim 1, wherein titanium dioxide is used as a nucleating agent for the second crystallization event and the salt is selected from the group comprising any one of the following or any combination of the following: sodium chloride, and Lithium nitrate.

30. 10. The PCM of claim 1, wherein calcium carbonate is used as a nucleating agent for the second crystallization event and the salt is magnesium sulfate.

31. 10. The PCM of claim 1, wherein the PCM comprises about 1-10 wt. % sodium sulfate in water, the nucleating agent for the first crystallization event comprises about 0.1-1.0 wt. % silver iodide, and the nucleating agent for the second crystallization event comprises about 0.1-1.0 wt. % silicon carbide.

32. 32. The PCM of claim 31 , wherein the PCM comprises about 3.5 wt. % sodium sulfate in water, the nucleating agent for the first crystallization event comprises about 0.5 wt. % silver iodide, and the nucleating agent for the second crystallization event comprises about 0.5 wt. % silicon carbide.

33. 33. The PCM of claim 32, wherein the PCM comprises about 15-25 wt. % magnesium sulfate in water, the nucleating agent for the first crystallization event comprises about 0.1-1.0 wt. % silver iodide and / or aluminum oxide, and / or the nucleating agent for the second crystallization event comprises about 0.1-1.0 wt. % silicon carbide and / or calcium carbonate.

34. 34. The PCM of claim 33, wherein the PCM comprises about 19 wt. % magnesium sulfate in water, the nucleating agent for the first crystallization event comprises about 0.5 wt. % silver iodide and / or aluminum oxide, and the nucleating agent for the second crystallization event comprises about 0.5 wt. % silicon carbide and / or calcium carbonate.

35. 35. The PCM of claim 34, wherein the PCM comprises about 15-25 wt. % potassium chloride in water, the nucleating agent for the first crystallization event comprises about 0.1-1.0 wt. % titanium dioxide and / or silver iodide, and the nucleating agent for the second crystallization event comprises about 0.1-1.0 wt. % vermiculite.

36. 36. The PCM of claim 35, wherein the PCM comprises about 19.5 wt. % potassium chloride in water, the nucleating agent for the first crystallization event comprises about 0.5 wt. % titanium dioxide and / or silver iodide, and the nucleating agent for the second crystallization event comprises about 0.5 wt. % vermiculite.

37. 10. The PCM of claim 1, wherein the PCM comprises about 15-25 wt. % ammonium chloride in water, the nucleating agent for the first crystallization event comprises about 0.1-1.0 wt. % silver iodide, and the nucleating agent for the second crystallization event comprises about 0.1-1.0 wt. % vermiculite and / or silicon carbide.

38. 38. The PCM of claim 37, wherein the PCM comprises about 18.6 wt% ammonium chloride in water, the nucleating agent for the first crystallization event comprises about 0.5 wt% silver iodide, and the nucleating agent for the second crystallization event comprises about 0.5 wt% vermiculite and / or silicon carbide.

39. 10. The PCM of claim 1, wherein the PCM comprises about 18-30 wt. % sodium formate in water, the nucleating agent for the first crystallization event comprises about 0.1-1.0 wt. % calcium carbonate, and the nucleating agent for the second crystallization event comprises about 0.1-1.0 wt. % vermiculite.

40. 40. The PCM of claim 39, wherein the PCM comprises about 24% by weight sodium formate in water, the nucleating agent for the first crystallization event comprises about 0.5% by weight calcium carbonate, and the nucleating agent for the second crystallization event comprises about 0.5% by weight vermiculite.

41. 10. The PCM of claim 1, wherein the PCM comprises about 15-25 wt. % strontium chloride in water, the nucleating agent for the first crystallization event comprises about 0.1-1.0 wt. % aluminum oxide, and the nucleating agent for the second crystallization event comprises about 0.1-1.0 wt. % vermiculite and / or silver iodide.

42. 42. The PCM of claim 41, wherein the PCM comprises about 19.5 wt% strontium chloride in water, the nucleating agent for the first crystallization event comprises about 0.5 wt% aluminum oxide, and the nucleating agent for the second crystallization event comprises about 0.5 wt% vermiculite and / or silver iodide.

43. 10. The PCM of claim 1, wherein the PCM comprises about 30-40 wt. % sodium nitrate in water, the nucleating agent for the first crystallization event comprises about 0.1-1.0 wt. % iron oxide and / or silica, and the nucleating agent for the second crystallization event comprises about 0.1-1.0 wt. % vermiculite and / or aluminum oxide.

44. 44. The PCM of claim 43, wherein the PCM comprises about 35 wt.% sodium nitrate in water, the nucleating agent for the first crystallization event comprises about 0.5 wt.% iron oxide and / or silica, and the nucleating agent for the second crystallization event comprises about 0.5 wt.% vermiculite and / or aluminum oxide.

45. 10. The PCM of claim 1, wherein the PCM comprises about 15-30 wt. % sodium acetate in water, the nucleating agent for the first crystallization event comprises about 0.1-1.0 wt. % calcium carbonate, and the nucleating agent for the second crystallization event comprises about 0.1-1.0 wt. % silver iodide.

46. 46. ​​The PCM of claim 45, wherein the PCM comprises about 22.7 wt% sodium acetate in water, the nucleating agent for the first crystallization event comprises about 0.5 wt% calcium carbonate, and the nucleating agent for the second crystallization event comprises about 0.5 wt% silver iodide.

47. 10. The PCM of claim 1, wherein the PCM comprises about 22-33.0 wt. % sodium acetate in water, the nucleating agent for the first crystallization event comprises about 0.1-1.0 wt. % calcium carbonate, and the nucleating agent for the second crystallization event comprises about 0.1-1.0 wt. % silver iodide.

48. 48. The PCM of claim 47, wherein the PCM comprises about 27.0 wt.% sodium acetate in water, the nucleating agent for the first crystallization event comprises about 0.5 wt.% calcium carbonate, and the nucleating agent for the second crystallization event comprises about 0.5 wt.% silver iodide.

49. 10. The PCM of claim 1, wherein the PCM comprises about 18-27 wt. % sodium chloride in water, the nucleating agent for the first crystallization event comprises about 0.1-1.0 wt. % calcium carbonate, and the nucleating agent for the second crystallization event comprises about 0.1-1.0 wt. % vermiculite and / or silicon carbide.

50. 50. The PCM of claim 49, wherein the PCM comprises about 22.4 wt.% sodium chloride in water, the nucleating agent for the first crystallization event comprises about 0.5 wt.% calcium carbonate, and the nucleating agent for the second crystallization event comprises about 0.5 wt.% vermiculite and / or silicon carbide.

51. 10. The PCM of claim 1, wherein the PCM comprises about 19-30 wt. % lithium nitrate in water, the nucleating agent for the first crystallization event comprises about 0.1-1.0 wt. % iron oxide, and the nucleating agent for the second crystallization event comprises about 0.1-1.0 wt. % silicon carbide.

52. 52. The PCM of claim 51 , wherein the PCM comprises about 24.5 wt. % lithium nitrate in water, the nucleating agent for the first crystallization event comprises about 0.5 wt. % iron oxide, and the nucleating agent for the second crystallization event comprises about 0.5 wt. % silicon carbide.

53. 10. The PCM of claim 1, wherein the PCM comprises about 34-45 wt. % sodium bromide in water, the nucleating agent for the first crystallization event comprises about 0.1-1.0 wt. % calcium carbonate, and the nucleating agent for the second crystallization event comprises about 0.1-1.0 wt. % silicon carbide.

54. 54. The PCM of claim 53, wherein the PCM comprises about 39 wt% sodium bromide in water, the nucleating agent for the first crystallization event comprises about 0.5 wt% calcium carbonate, and the nucleating agent for the second crystallization event comprises about 0.5 wt% silicon carbide.

55. 10. The PCM of claim 1, wherein the PCM comprises about 35-45 wt% strontium bromide in water, the nucleating agent for the first crystallization event comprises about 0.1-1.0 wt% calcium carbonate, and the nucleating agent for the second crystallization event comprises about 0.1-1.0 wt% silver iodide.

56. 56. The PCM of claim 55, wherein the PCM comprises about 41 wt% strontium bromide in water, the nucleating agent for the first crystallization event comprises about 0.5 wt% calcium carbonate, and the nucleating agent for the second crystallization event comprises about 0.5 wt% silver iodide.

57. 10. The PCM of claim 1, wherein the PCM comprises about 25-35 wt. % magnesium nitrate in water, the nucleating agent for the first crystallization event comprises about 0.1-1.0 wt. % silicon dioxide and / or aluminum oxide, and the nucleating agent for the second crystallization event comprises about 0.1-1.0 wt. % silicon carbide.

58. 58. The PCM of claim 57, wherein the PCM comprises about 30 wt. % magnesium nitrate in water, the nucleating agent for the first crystallization event comprises about 0.5 wt. % silicon dioxide and / or aluminum oxide, and the nucleating agent for the second crystallization event comprises about 0.5 wt. % silicon carbide.

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