Patent Application
20160200956
The present invention relates to a phase change material (PCM) for use in energy storage systems. More particularly, the present invention relates to 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.
There exists a problem in the field of phase change materials of providing a phase change material that has a phase change in about the 75° C. to 80° C. temperature range. This is because there exists at this temperature range mild incongruent melting of compositions such as magnesium bromide hexahydrate.
Strontium bromide hexahydrate has a congruent melting point of 88° C. and has rarely, if ever, been used as a PCM before. The only previous mention in the literature is having been discounted by Lane who is a leading expert in the field [Lane G. A.: Solar Heat Storage: Latent Heat Material—Volume I: Background and Scientific Principles, CRC Press, Florida (1983)] for being too expensive. There is also reference to Strontium bromide hexahydrate in U.S. Pat. No. 4,003,426 which although mentioning the strontium bromide hexahydrate as being used as a phase change material it makes no disclosure of this being used in combination with a Metal Halide.
There has therefore been much effort in the field of phase change materials to find a phase change material that has a phase change in about the 76° C. to 88° C. temperature range and is capable of operating efficiently. Such a temperature change for a phase change is extremely useful for energy storage systems capable of being used in the domestic heating market.
It is an object of at least one aspect of the present invention to obviate or mitigate at least one or more of the aforementioned problems.
It is a further object of at least one aspect of the present invention to provide a phase change material with a phase change in about the 76° C. to 88° C. temperature range.
According to a first aspect of the present invention there is provided a phase change material (PCM) comprising:
Strontium Bromide; and
at least one Metal Halide;
wherein the PCM has a phase change in the region of about 76° C. to 88° C. temperature range.
Generally speaking, the present invention therefore resides in the provision of a PCM with a phase change in the region of about 76° C. to 88° C. This makes the PCM highly suitable for energy storage systems such as described in WO2009/138771 and WO2011/058383 which are incorporated herein by reference.
The PCM of the present invention is therefore based on a mixture of Strontium Bromide and a Metal Halide such as Magnesium Bromide or its hydrate. Alternatives to Magnesium Bromide may be any one of or combination of the following Bromides or their hydrates:
Zinc Bromide;
Cobalt Bromide;
Lithium Bromide;
Sodium Bromide;
Potassium Bromide;
Calcium Bromide;
Iron Bromide;
Copper Bromide; and
Aluminium Bromide.
Alternatives to Magnesium Bromide may be any miscible organic compound.
In addition Strontium salts of Chloride may also be used.
Typically, the Strontium Bromide and the at least one Metal Halide may be in the hydrated form.
Strontium Bromide Anhydrous (CAS: 100476-81-0) and Magnesium Bromide Anhydrous (CAS: 7789-48-2) may be used instead as initial components instead of the hexahydrate forms. In this case, water must be added to reach the final PCM.
The Strontium Bromide may be present in an amount from about 20-50 wt. % and preferably about 30-35 wt. %.
The Metal Halide may be present in an amount from about 50-85 wt. % and preferably about 65-70 wt. %.
For example, a preferred embodiment may be about 25-35 wt. % or preferably 32 wt. % MgBr2.H2O; about 55-75 wt. % or preferably about 65 wt. % SrBr2.H2O; and about 1-5 wt. % or preferably about 3 wt. % water. A PCM comprising 32 wt. % MgBr2.H2O, 65 wt. % SrBr2.H2O and 3 wt. % water was found to have a phase change of about 77° C.
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 such as found in energy storage systems.
A minimum melting point at 32 wt. % MgBr2.H2O, 65 wt. % SrBr2.H2O and 3 wt. % water was found at about 77° C.
According to a second aspect of the present invention there is provided a process for forming a PCM comprising:
providing Strontium Bromide; and
providing at least one Metal Halide;
mixing said Strontium Bromide and at least one Metal Halide together;
wherein the PCM has a phase change in the region of about 76° C. to 88° C. temperature range.
The Strontium Bromide and Metal Halide may be mixed together in a mixing vessel or heat battery enclosure if the PCM is made directly in a final heat battery.
During the mixing the temperature of the mixing vessel or heat battery enclosure may be increased to a temperature higher than the phase change temperature by about 2° C.-5° C. (e.g. 3° C.) and kept it at this temperature to melt the materials.
The resulting mixture may be stirred/mixed mixture until it is liquid and homogenous.
Alternatively, starting from the anhydrous forms the following process may be followed:
The PCM may be as defined in the first aspect.
Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which:
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.
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. Altematives to Magnesium Bromide may be any one of or combination of the following Bromides or their hydrates:
Zinc Bromide;
Cobalt Bromide;
Uthium Bromide;
Sodium Bromide;
Potassium Bromide;
Calcium Bromide;
Iron Bromide;
Copper Bromide; and
Aluminium Bromide.
In addition Strontium salts of Chloride may also be used.
Below is a non-limiting example of preparing a PCM according to the present invention.
a) Starting from the Hexahydrate Forms:
b) Starting from the Anhydrous Forms:
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.
A minimum melting point at 32 wt. % MgBr2.H2O, 65 wt. % SrBr2.H2O and 3 wt. % water was found at about 77° C.
The following non-limiting examples provided in the Experimental results are representative of the PCM composition MX.nH2O with varying amounts of miscible organic compound, as are the processes for their preparation.
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.
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.
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.
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.
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.
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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1315098.2 | Aug 2013 | GB | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/GB2014/052580 | 8/22/2014 | WO | 00 |
