STRONTIUM BROMIDE PHASE CHANGE MATERIAL
FIELD OF THE INVENTION
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.
BACKGROUND OF THE INVENTION
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 US4003426 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.
SUMMARY OF THE INVENTION
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 WO2009/1 38771 and
WO201 1/058383 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.H20 ; about 55 - 75 wt.% or preferably about 65 wt.% SrBr2.H20 ; and
about 1 - 5 wt.% or preferably about 3wt.% water. A PCM comprising 32 wt.%
MgBr2.H20 , 65 wt.% SrBr2.H20 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.H20 , 65 wt.% SrBr2.H20 and 3wt.%
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:
1) Mix the correct ratio of Strontium Bromide Anhydrous and Metal Halide
Anhydrous (e.g. Magnesium Bromide Anhydrous) with optionally another
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 a 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 until it is liquid and homogenous.
The PCM may be as defined in the first aspect.
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will now be described, by way of example
only, with reference to the accompanying drawings in which:
Figure 1 is a representation of the relationship between the percentage of
Strontium Bromide Hexahydrate against the phase change temperature.
BRIEF DESCRIPTION
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. 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.
In addition Strontium salts of Chloride may also be used.
EXAMPLE 1
Below is a non-limiting example of preparing a PCM according to the present
invention.
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
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.
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.H20 , 65 wt.% SrBr2.H20 and 3 wt.%
water was found at about 77°C.
FURTHER EXAMPLES
The following non-limiting examples provided in the Experimental results are
representative of the PCM composition MX.nH20 with varying amounts of miscible
organic compound, as are the processes for their preparation.
SrBr2.6H20:
Example 2 : Addition of glycerol to strontium bromide hexahydrate to depress
melting point
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.
Mass (g)
Molar
strontium bromide
Ratio Glycerol
hexahydrate
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 4.1 145
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.
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% 7 1 10%
40% 66 14.7%
50% 55 20.6%
Example 3 : Addition of trimethylolethane (TME) to strontium bromide hexahydrate
to depress melting point
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.
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
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 .
Mass (g)
Molar
strontium bromide
Ratio acetamide
hexahydrate
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%
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.

CLAIMS
1. 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.
2 . A phase change material (PCM) according to claim 1, wherein the PCM is
capable of being used in an energy storage system.
3 . A phase change material (PCM) according to any of claims 1 or 2 , wherein the
Metal Halide is Magnesium Bromide or its hydrate form.
4 . A phase change material (PCM) according to any of claims 1 or 2 , wherein the
Metal Halide is any one of or combination of the following Bromides or their hydrates:
Magnesium Bromide;
Zinc Bromide;
Cobalt Bromide;
Lithium Bromide;
Sodium Bromide;
Potassium Bromide;
Calcium Bromide;
Iron Bromide;
Copper Bromide; and
Aluminium Bromide.
5 . A phase change material (PCM) according to any preceding claim, wherein the
PCM also comprises Strontium salts of Chloride.
6 . A phase change material (PCM) according to any preceding claim, wherein the
Strontium Bromide is present in an amount from about 20 - 50 wt.% or about 30 - 35
wt.%.
7 . A phase change material (PCM) according to any preceding claim, wherein the
Metal Halide is present in an amount from about 50 - 85 wt.% or about 65 - 70 wt.%.
8 . A phase change material (PCM) according to any preceding claim, wherein the
PCM is about 25 - 35 wt.% or 32 wt.% MgBr2.H20 , about 55 - 75 wt.% or about 65 wt.%
SrBr2.H20 and about 1 - 5 wt.% or about 3 wt.% water.
9 . A phase change material (PCM) according to any preceding claim, wherein the
PCM comprises 32 wt.% MgBr2.H20 , 65 wt.% SrBr2.H20 and 3 wt.% water which has a
phase change of about 77°C.
10. A method 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.
11. A method for forming a PCM according to claim 10, wherein the Strontium
Bromide and Metal Halide are mixed together in a mixing vessel or heat battery
enclosure (if the PCM is made directly in the final heat battery).
12. A method for forming a PCM according to any of claim1 1, wherein during the
mixing the temperature of the mixing vessel or heat battery enclosure are 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.
13. A method for forming a PCM according to any of claim 12, wherein the resulting
mixture is stirred/mixed mixture until it is liquid and homogenous.
14. A method for forming a PCM according to any of claims 10 to 13, wherein starting
from the anhydrous forms the process comprises:
1) Mixing the correct ratio of Strontium Bromide Anhydrous and Metal Halide
Anhydrous (e.g. Magnesium Bromide Anhydrous) with optionally another
phase change temperature depressing substance according to the required
phase change temperature.
2) Adding 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 or alternatively, adding 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 -
(e.g. 3°C) and keep it at this temperature to melt the materials and
3) Stirring the mixture until it is liquid and homogenous.