Strontium bromide phase change material

Abstract

There is herein described a phase change material (PCM) for use in energy storage systems. More particularly, there is described a phase change material comprising Strontium Bromide and a Metal Halide that is optimal to storing heat in about the 76 C. to 88 C. temperature range.

Claims

1. A phase change material (PCM) comprising: about 65 wt. % to about 95 wt. % Strontium Bromide Hexahydrate; and at least one Metal Halide selected from the group consisting of Magnesium Bromide; Zinc Bromide; Cobalt Bromide; Lithium Bromide; Sodium Bromide; Potassium Bromide; Calcium Bromide; Iron Bromide; Copper Bromide; Aluminium Bromide; and any hydrate or combination thereof; wherein the PCM exhibits a phase change at a temperature range of about 76 C. to about 88 C.

2. A phase change material (PCM) according to claim 1, wherein the PCM is used in an energy storage system.

3. A phase change material (PCM) according to claim 1, wherein the Metal Halide is Magnesium Bromide or a hydrate thereof.

4. A phase change material (PCM) according to claim 1, wherein the PCM further comprises Strontium salts of Chloride.

5. A phase change material (PCM) according to claim 1, wherein the Strontium Bromide Hexahydrate is present in an amount of about 65 wt. %.

6. A phase change material (PCM) according to claim 1, wherein the Metal Halide is present in an amount from about 25 wt. % to about 35 wt. %.

7. A phase change material (PCM) according to claim 1, wherein the PCM is about 25 wt. % to about 35 wt. % MgBr.sub.2.6H.sub.2O, about 55 wt. % to about 75 wt. % SrBr.sub.2.6H.sub.2O and about 1 wt. % to about 5 wt. % water.

8. A phase change material (PCM) according to claim 1, wherein the PCM comprises 32 wt. % MgBr.sub.2.6H.sub.2O, 65 wt. % SrBr.sub.2.6H.sub.2O and 3 wt. % water and exhibits a phase change at a temperature of about 77 C.

9. A method for forming the phase change material (PCM) of claim 1 comprising: providing Strontium Bromide Hexahydrate; providing at least one Metal Halide; and mixing said Strontium Bromide Hexahydrate and at least one Metal Halide together; wherein the PCM exhibits a phase change at a temperature range of about 76 C. to about 88 C.

10. A method for forming a phase change material PCM according to claim 9, wherein when the PCM is formed directly in a final heat battery, the Strontium Bromide Hexahydrate and Metal Halide are mixed together to form a mixture in a mixing vessel or heat battery enclosure.

11. A method for forming a phase change material PCM according to claim 10, wherein during the mixing, the temperature of the mixing vessel or heat battery enclosure is increased and maintained at a temperature higher than the phase change temperature by about 2 C. to about 5 C.

12. A method for forming a phase change material PCM according to claim 11, wherein the resulting mixture is stirred or mixed until the mixture is liquid and homogenous.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:

(2) FIG. 1 is a representation of the relationship between the percentage of Strontium Bromide Hexahydrate against the phase change temperature.

BRIEF DESCRIPTION

(3) Generally speaking, the present invention resides in the provision of phase change material that is optimal to storing heat in about the 76 C. to 88 C. temperature range.

(4) The phase change material (PCM) of the present invention is based on a mixture of Strontium Bromide and a metal halide such as Magnesium Bromide. Alternatives to Magnesium Bromide may be any one of or combination of the following Bromides or their hydrates:

(5) Zinc Bromide;

(6) Cobalt Bromide;

(7) Uthium Bromide;

(8) Sodium Bromide;

(9) Potassium Bromide;

(10) Calcium Bromide;

(11) Iron Bromide;

(12) Copper Bromide; and

(13) Aluminium Bromide.

(14) In addition Strontium salts of Chloride may also be used.

Example 1

(15) Below is a non-limiting example of preparing a PCM according to the present invention.

(16) a) Starting from the Hexahydrate Forms: 1) Mix the correct ratio of the two components according to the required phase change temperature. 2) Increase the temperature of the mixing vessel or heat battery enclosure (if the PCM is made directly in the final heat battery) to a temperature higher than the phase change temperature by about 2 C.-5 C. (e.g. 3 C.) and keep it at this temperature to melt the materials. 3) Stir the mixture till it is liquid and homogenous.

(17) b) Starting from the Anhydrous Forms: 1) Mix the correct ratio of Strontium Bromide Anhydrous and Magnesium Bromide Anhydrous (or other phase change temperature depressing substance) according to the required phase change temperature. 2) Add hot water in the correct ratio to obtain the required phase change material at a temperature above the required final phase change temperature to melt the two components. Alternatively, add water in the right ratio to obtain the required phase change material at temperature below the required final phase change and increase the temperature of the mixing vessel or heat battery enclosure (if the PCM is made directly in the final heat battery) to a temperature higher than the phase change temperature by about 2 C.-5 C. (e.g. 3 C.) and keep it at this temperature to melt the materials. 3) Stir the mixture till it is liquid and homogenous.

(18) At compositions of about 30-35 wt. % Magnesium Bromide Hexahydrate and about 65-70 wt. % Strontium Bromide there exists a phase change at 75 C.-80 C. This temperature is important for phase change material applications.

(19) A minimum melting point at 32 wt. % MgBr.sub.2.H.sub.2O, 65 wt. % SrBr.sub.2.H.sub.2O and 3 wt. % water was found at about 77 C.

Further Examples

(20) The following non-limiting examples provided in the Experimental results are representative of the PCM composition MX.nH.sub.2O with varying amounts of miscible organic compound, as are the processes for their preparation.

(21) SrBr2.6H2O:

Example 2: Addition of Glycerol to Strontium Bromide Hexahydrate to Depress Melting Point

(22) Test samples of strontium bromide hexahydrate (Sunamp supplied) and glycerol (available from VWR CAS 56-81-5) were prepared, from 100% strontium bromide hexahydrate composition to 1:1 molar ratio using the masses listed below. The samples were then heated to 95 C. whilst stirring, to ensure a homogenous mixture. Upon cooling and solidifying, the samples remained as a single phase.

(23) TABLE-US-00001 Mass (g) Molar strontium bromide Ratio hexahydrate Glycerol 9:1 19.4405 0.5595 8:2 18.7837 1.2163 7:3 18.0018 1.9982 6:4 17.0551 2.9449 5:5 15.8855 4.1145

(24) Upon observing the melting and freezing of the materials (heating to 95 C. in a water bath, allowing the materials to fully melt, and then cooling to room temperature in air, recording temperature of material using thermocouple) it was seen that the melting point was progressively depressed, with increasing amounts of glycerol. Repeated cycling confirmed that the melting and freezing point of strontium bromide was decreased with the addition of glycerol. The extent of depression, with the corresponding molar and weight % of glycerol, is listed below.

(25) TABLE-US-00002 The effect of increasing the amount of glycerol on the freezing temperature of the samples Molar Temp/ C. Mass 0% 88 0% 10% 84 2.8% 20% 78 6.1% 30% 71 10% 40% 66 14.7% 50% 55 20.6%

Example 3: Addition of Trimethylolethane (TME) to Strontium Bromide Hexahydrate to Depress Melting Point

(26) Test samples of strontium bromide hexahydrate and TME (available from Fischer Scientific Ltd. CAS 77-85-0) were prepared using the ratios listed below and using the same method as in Example 1.

(27) TABLE-US-00003 Mass (g) Molar strontium bromide Ratio hexahydrate TME 9:1 19.2762 0.7238 8:2 18.4420 1.5580 7:3 17.4699 2.5301 6:4 16.3227 3.6773 5:5 14.9485 5.0515

(28) Temperatures during the melting and freezing of the materials were recorded using the same method as listed in Example 2. As seen in Example 2, increased melting and freezing point depression was observed with increasing amounts of TME.

(29) TABLE-US-00004 The effect of increasing the amount of TME on the freezing temperature of the samples Molar Temp/ C. Mass 0% 88 0% 10% 84 3.6% 20% 79 7.8% 30% 76 12.7% 40% 75 18.4% 50% 68 25.3%

Example 4: Addition of Acetamide to Strontium Bromide Hexahydrate to Depress Melting Point

(30) Test samples of strontium bromide and acetamide (available from Alfa Aesar CAS 77-85-0) were prepared using the ratios listed below and using the same method as in Example 2.

(31) TABLE-US-00005 Mass (g) Molar strontium bromide Ratio hexahydrate acetamide 9:1 19.6375 0.3625 8:2 19.2024 0.7976 7:3 18.6706 1.3294 6:4 18.0057 1.9943 5:5 17.1506 2.8494 The effect of increasing the amount of acetamide on the freezing temperature of the samples Molar Temp/ C. Mass 0% 88 0% 10% 86 1.8% 20% 84 4.0% 30% 73 6.6% 40% 68 10.0% 50% 64 14.2%

(32) Whilst specific embodiments of the present invention have been described above, it will be appreciated that departures from the described embodiments may still fall within the scope of the present invention. For example, any suitable type of mixture of Strontium Bromide and metal halide may be used along with additional components where necessary. The amount of each component may be varied to adjust for the required phase change temperature.