CA2060215A1 - Calcium chloride hexahydrate formulations for low temperature heat storage application - Google Patents
Calcium chloride hexahydrate formulations for low temperature heat storage applicationInfo
- Publication number
- CA2060215A1 CA2060215A1 CA002060215A CA2060215A CA2060215A1 CA 2060215 A1 CA2060215 A1 CA 2060215A1 CA 002060215 A CA002060215 A CA 002060215A CA 2060215 A CA2060215 A CA 2060215A CA 2060215 A1 CA2060215 A1 CA 2060215A1
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- Canada
- Prior art keywords
- per cent
- chloride hexahydrate
- phase change
- calcium chloride
- weight
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
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Classifications
-
- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
- C09K5/00—Heat-transfer, heat-exchange or heat-storage materials, e.g. refrigerants; Materials for the production of heat or cold by chemical reactions other than by combustion
- C09K5/02—Materials undergoing a change of physical state when used
- C09K5/06—Materials undergoing a change of physical state when used the change of state being from liquid to solid or vice versa
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- Chemical & Material Sciences (AREA)
- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Combustion & Propulsion (AREA)
- Thermal Sciences (AREA)
- Materials Engineering (AREA)
- Organic Chemistry (AREA)
- Packages (AREA)
- Materials Applied To Surfaces To Minimize Adherence Of Mist Or Water (AREA)
Abstract
It is known to use phase change materials based on calcium chloride hexahydrate in low temperature heat storage systems. Additives to the calcium chloride hexahydrate affect its performance. To avoid problems experienced with prior art phase change materials, the present inventors add strontium chloride hexahydrate (in quantities upward from 0.1 per cent), fumed silica in the range from 0.02 to 1.0 per cent, and extra water above the stoichiometric quantity included in the calcium chloride hexahydrate in the range from 1.0 to 5.0 per cent. Other additives that may be included are sodium chlorite (in the range from 0.001 per cent to 1.0 per cent), ammonium chloride (up to 10 per cent), and potassium chloride (up to 10 per cent). (All percentages are by weight, with reference to the calcium chloride hexahydrate.) For improved efficiency of operation, a chemically inert colouring material, such as black drawing ink, may also be added to phase change materials enclosed in transparent containers.
Description
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' ~ TITLE: "CALCIUM CHLORIDE HEXAHYDRATE FORMULATIONS
-FOR LOW TEMPERATURE HEAT STORAGE APPLICATIONS"
: .
Technical Field This invention concerns heat storage systems. More 5 particularly, it concerns phase change materials ; based upon calcium chloride hexahydrate for use in thermal storage systems (such as low energy greenhouses).
Background 10 Low temperature heat storage systems have been the subject of considerable development over the years.
For some years, work was directed primarily to improvinq rock bed regenerative heating systems, such as the system described by C D Baird, W E Waters and 15 D R Mears in their paper entitled "Greenhouse solar heating system utilizing underbench storage", which was published ~in 1977 Annual Meeting of the American Society of Agricultural Engineers, North Carolina State University, June 1977, pages l to l;8. Rock bed 20 systems, however, are bulky and awkward to assemble, and most recent development of low temperature heat storage systems has been ~concentrated on those systems which incorporate phase change materials operating at temperatures around 30C. Such phase 2S change materials absorb heat from the environment when they change from their solid phase to their liquid phase and they release the latent heat~of t` fusion when they solidify again as their temperature ~ is lowered.
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:~ . , The phase change material first used in low energy heat storage systems was GIauber's salt, sodium sulphate decahydrate ~Na2SO4.10H2O), which has a phase change temperature of about 32C. However, as 5 noted by Charles Stein in the specification of his International patent application No PCT/US84/01005 (WIPO publication No WO 85/00212), sodium sulphate decahydrate changes its composition when cycled through a number of phase changes, and it exhibits a 10 strong "undercooling" (called "supercooling" by some workers in this field) before it solidifies spontaneously. Undercooling by as much as 11C is reported by Stein in his specification. This undercooling problem can be overcome by the addition 15 of a nucleating agent (borax) and a thickening agent ~fine silica) to the sodium sulphate decahydrate.
Stein also observes that phase change materials based on calcium chloride hexahydrate, CaC12.6H2O, are now preferred. However, his own invention, aimed at 20 avoiding ~he known problems of sodium sulphate decahydrate, involves the use of another phase change material - paraffin wax - in small structures with metal wool dividers.
The use of small cells filled with a phase change 25 material to avoid precipitation problems has also been proposed by Mario Stiffler for the latent heat accumulator described in the specification of his Australian p~tent No 559,354 Among Stiffler's ~` ~
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W O 91/00324 P ~ /A U90/00264 ,~ 2~3~D2~tS' preferred phase change materials are sodium sulphate decahydrate, bisodium phosphàte dodecahydrate and bisodium phosphate heptahydrate.
The storage of phase change materials in small 5 parcels - or microencapsulation of such materials -was a solution adopted by other workers and referred to by B Carlsson, H Stymne and G Wettermaxk in their paper entitled "An incongruent heat-of-fusion system - CaC12.6H20 - made congruent through modification of 10 the chemical composition of the system", which was published in Solar Energy, volume 23, 1979, pages 343 to 350. Carlsson et al, however, explained the physical chemistry involved when the phase change material calcium chloride hexahydrate is cycled 15 repeatedly through its melting/freezing point, and showed that the formation of the tetrahydrate CaC12.4H20 can be inhibited by the inclusion of up to 2 per cent of strontium chloride hexahydrate (SrC12.6H20), which acts as both a nucleating agent 20 (thus reducing the supercooling tendency) and as an additive that raises the solubility of the ; tetrahydrate while lowering the solubility of the hexahydrate, thereby preventing the tetrahydrate from solidifying as the ~temperature decreases towards the 25 freezing point of the calcium chloride hexahydrate.
Carlsson et al also observed that impurities in technical grade calcium chloride hexahydrate, such as sodium chloride and potassium chloride, :increase the ;;
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2~ 4 -incongruity of the CaC12.6H2O system, but their effect can be countered by the addition of calcium hydroxide (Ca(OH)2).
A more recent paper by H Feilchenfeld, J Fuchs and 5 S Sarig, entitled "A calorimetric investigation of the stability of stagnant calcium chloride hexahydrate melt", published in Solar Energy, volume 30, 1984, pages 779 to 784, has also emphasised the ; degradation of CaC12.6H2O without additives as a heat 10 storage phase change material due to its - "undercooling" tendency and its breakdown with the formatior,l of the tetrahydrate. This paper also draws attention to the use of additives to overcome these problems, notably strontium chloride hexahydrate 15 (SrC12.6H2O~ as a nucleating agent and furned silica as a thickening agent.
The use of such phase change materials in buildings has been suggested on a number of occasions. Some workers have recognised the problems inherent in the 20 use of phase change materials and have suggested techniques or special arrangements to overcome the ; problems. Others have tended to ignore the problems.
Examples of proposals involving the use of phase I change materials in buildings include (i) the 25 specification of Australian patent application No 47850/85 in the name of R K Prudhoe (a proposal for controlling the temperature fluctuations in ~; buildings which contain electronic equipment and the like); ~ii) the specification of Australian patent ~: .
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f application No 49046~85 in the name of Kubota Ltd, which describes a greenhouse in which a phase change material is stored in a tank structure; and (iii) the paper by A Brandstetter, entitled "Phase 5 change storage for greenhouses", published in Advances in Solar Energy Technology (Pergamon Press, 1988), pages 3353 to 3357, which describes a low energy greenhouse in which the heat storage medium is calcium chloride hexahydrate "appropriately lO formulated against supercooling and degradation".
In the above-mentioned specifications and papers, a number of different phase change materials have been proposed for use in a variety of situations. Thus it is clear that the concept of the use of phase change 15 materials as low temperature heat storage media, in greenhouses and other buildings, in heat pumps, in solar energy storage tanks and in industrial waste heat utilisation facilities, is now well accepted.
(This list is not exhaustive.) However, the 20 production of a satisfactory phase change material, which can be cycled numerous times through the melting and freezing point, has posed many problems to researchers in this field.
The specification of Australian patent application 25 No 55769/86 describes a number of phase change materials which have been investigated by N Yano, T Ueno and S Tsuboi. The preferred composition disclosed in that specification is a calcium chloride hexahydrate with additives including up to 5 per cent .
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W O 91/00324 PC~r/A U90/00264 .. . ,~. . ~
' ~ TITLE: "CALCIUM CHLORIDE HEXAHYDRATE FORMULATIONS
-FOR LOW TEMPERATURE HEAT STORAGE APPLICATIONS"
: .
Technical Field This invention concerns heat storage systems. More 5 particularly, it concerns phase change materials ; based upon calcium chloride hexahydrate for use in thermal storage systems (such as low energy greenhouses).
Background 10 Low temperature heat storage systems have been the subject of considerable development over the years.
For some years, work was directed primarily to improvinq rock bed regenerative heating systems, such as the system described by C D Baird, W E Waters and 15 D R Mears in their paper entitled "Greenhouse solar heating system utilizing underbench storage", which was published ~in 1977 Annual Meeting of the American Society of Agricultural Engineers, North Carolina State University, June 1977, pages l to l;8. Rock bed 20 systems, however, are bulky and awkward to assemble, and most recent development of low temperature heat storage systems has been ~concentrated on those systems which incorporate phase change materials operating at temperatures around 30C. Such phase 2S change materials absorb heat from the environment when they change from their solid phase to their liquid phase and they release the latent heat~of t` fusion when they solidify again as their temperature ~ is lowered.
,: ' ~:
~, , : .
. . . .
:::
:~ . , The phase change material first used in low energy heat storage systems was GIauber's salt, sodium sulphate decahydrate ~Na2SO4.10H2O), which has a phase change temperature of about 32C. However, as 5 noted by Charles Stein in the specification of his International patent application No PCT/US84/01005 (WIPO publication No WO 85/00212), sodium sulphate decahydrate changes its composition when cycled through a number of phase changes, and it exhibits a 10 strong "undercooling" (called "supercooling" by some workers in this field) before it solidifies spontaneously. Undercooling by as much as 11C is reported by Stein in his specification. This undercooling problem can be overcome by the addition 15 of a nucleating agent (borax) and a thickening agent ~fine silica) to the sodium sulphate decahydrate.
Stein also observes that phase change materials based on calcium chloride hexahydrate, CaC12.6H2O, are now preferred. However, his own invention, aimed at 20 avoiding ~he known problems of sodium sulphate decahydrate, involves the use of another phase change material - paraffin wax - in small structures with metal wool dividers.
The use of small cells filled with a phase change 25 material to avoid precipitation problems has also been proposed by Mario Stiffler for the latent heat accumulator described in the specification of his Australian p~tent No 559,354 Among Stiffler's ~` ~
~:
,. . . . . .
.. ~ , . . . :
W O 91/00324 P ~ /A U90/00264 ,~ 2~3~D2~tS' preferred phase change materials are sodium sulphate decahydrate, bisodium phosphàte dodecahydrate and bisodium phosphate heptahydrate.
The storage of phase change materials in small 5 parcels - or microencapsulation of such materials -was a solution adopted by other workers and referred to by B Carlsson, H Stymne and G Wettermaxk in their paper entitled "An incongruent heat-of-fusion system - CaC12.6H20 - made congruent through modification of 10 the chemical composition of the system", which was published in Solar Energy, volume 23, 1979, pages 343 to 350. Carlsson et al, however, explained the physical chemistry involved when the phase change material calcium chloride hexahydrate is cycled 15 repeatedly through its melting/freezing point, and showed that the formation of the tetrahydrate CaC12.4H20 can be inhibited by the inclusion of up to 2 per cent of strontium chloride hexahydrate (SrC12.6H20), which acts as both a nucleating agent 20 (thus reducing the supercooling tendency) and as an additive that raises the solubility of the ; tetrahydrate while lowering the solubility of the hexahydrate, thereby preventing the tetrahydrate from solidifying as the ~temperature decreases towards the 25 freezing point of the calcium chloride hexahydrate.
Carlsson et al also observed that impurities in technical grade calcium chloride hexahydrate, such as sodium chloride and potassium chloride, :increase the ;;
, , . .
!~ ; ' . ' ' ,, " . ' ' ' , ' ' " ' ~ ' .
2~ 4 -incongruity of the CaC12.6H2O system, but their effect can be countered by the addition of calcium hydroxide (Ca(OH)2).
A more recent paper by H Feilchenfeld, J Fuchs and 5 S Sarig, entitled "A calorimetric investigation of the stability of stagnant calcium chloride hexahydrate melt", published in Solar Energy, volume 30, 1984, pages 779 to 784, has also emphasised the ; degradation of CaC12.6H2O without additives as a heat 10 storage phase change material due to its - "undercooling" tendency and its breakdown with the formatior,l of the tetrahydrate. This paper also draws attention to the use of additives to overcome these problems, notably strontium chloride hexahydrate 15 (SrC12.6H2O~ as a nucleating agent and furned silica as a thickening agent.
The use of such phase change materials in buildings has been suggested on a number of occasions. Some workers have recognised the problems inherent in the 20 use of phase change materials and have suggested techniques or special arrangements to overcome the ; problems. Others have tended to ignore the problems.
Examples of proposals involving the use of phase I change materials in buildings include (i) the 25 specification of Australian patent application No 47850/85 in the name of R K Prudhoe (a proposal for controlling the temperature fluctuations in ~; buildings which contain electronic equipment and the like); ~ii) the specification of Australian patent ~: .
,. . .
,, .
'. : . - , .
: .
G ~:
.,: ' ~; ' ' ~
f application No 49046~85 in the name of Kubota Ltd, which describes a greenhouse in which a phase change material is stored in a tank structure; and (iii) the paper by A Brandstetter, entitled "Phase 5 change storage for greenhouses", published in Advances in Solar Energy Technology (Pergamon Press, 1988), pages 3353 to 3357, which describes a low energy greenhouse in which the heat storage medium is calcium chloride hexahydrate "appropriately lO formulated against supercooling and degradation".
In the above-mentioned specifications and papers, a number of different phase change materials have been proposed for use in a variety of situations. Thus it is clear that the concept of the use of phase change 15 materials as low temperature heat storage media, in greenhouses and other buildings, in heat pumps, in solar energy storage tanks and in industrial waste heat utilisation facilities, is now well accepted.
(This list is not exhaustive.) However, the 20 production of a satisfactory phase change material, which can be cycled numerous times through the melting and freezing point, has posed many problems to researchers in this field.
The specification of Australian patent application 25 No 55769/86 describes a number of phase change materials which have been investigated by N Yano, T Ueno and S Tsuboi. The preferred composition disclosed in that specification is a calcium chloride hexahydrate with additives including up to 5 per cent .
, . .
W O 91/00324 PC~r/A U90/00264 .. . ,~. . ~
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barium sulphide, from 0.001 to 5 per cent barium chlQride dihydrate and from 0.001 to 0.1 per cent strontium chloride hexahydrate, with a bromide ~potassium bromide, sodium bromide or ammonium 5 bromide~ added as a solidification point modifier and relatively large quantities of ultrafine silica powder and glycerine added as thickening agents.
With such additives, however, the~ phase change material becomes a costly material to produce.
10 Disclosure of the Present Invention It is an object of the present invention to provide a relatively low cost formulation of a phase change material which can be used successfully for numerous melting and freezing cycles without significant 15 departure from its performance as a heat storage medium.
This objective is achieved by the inclusion of selected quantities of specific additives to calcium chloride hexahydrate. The additives are 20 ~a) strontium chloride hexahydrate, as a nucleator, in quantities upward from 0.1 per cent (by weight) of the calcium chloride hexahydrate, (b) fumed silica in quantities ranging from 0.02 per cent to 1.0 per cent (by weight) of the calcium chloride hexahydrate, and 25 (c) extra water above the stoichiometric quantity included in the calcium chloride hexahydrate in the range of from 1.0 per cent to S.0 per cent (by weight) of the calcium chloride hexahydrate.
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In addition, from 0.001 per cent to 1.0 per cent (by weight) of sodium chloride may also be added.
Preferably, the strontium chloride hexahydrate is present in quantities ranging from 0.1 per cent to 5 4.0 per cent tby weight) of the calcium chloride hexahydrate. More preferably the upper concentration of the strontium chloride hexahydrate is about 2.0 per cent, and most preferably the strontium chloride hexahydrate comprises about 0.3 per cent ~by weight) 10 of the càlcium chloride hexahydrate.
The selection of these additives and the ranges of their concentrations to produce compositions which are stable phase change materials is the outcome of a long-term investigation of the performance parameters 15 of calcium chloride hexahydrate phase change materials in melt/freeze cycling experiments.
i Strontium chloride hexahydrate is known to be isomorphous with calcium chloride hexahydrate and to be capable of forming nearly ideal solid solutions 20 with CaC12.6H2O; and is also known to be a nucleator of the solidification of calcium chloride hexahydrate. The investigation showed that the minimum amount of strontium chloride hexahydrate that is required to sustain long-term nucleation stability 25 is 0.1 per cent. Any lower concentration of strontium chloride hexahydrate is close to the limit of dissolution of SrC12.6H2O in calcium chloride hexahydrate. An increase in the concentration of :: :
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W O 91/00324 PC~r/A V90/00264 ~-' ""
SrC12.6H20 to more than about 1.0 per cent (by weight) of the calcium chloride hexahydrate results in little significant improvement in the performance or in the long-term stability of the heat storage 5 phase change material formulation. Increasing the concentration of SrC12.6H20 to more than 2.0 per Gent of the CaC12.6H2O produces no improvement in performance of the phase change material but it adds significantly to the cost of the formulation. At the 10 time of writing this specification, in Australia, strontium chloride hexahydrate costs about $20.00 per kilogram whereas calcium chloride hexahydrate costs about $0.20 per kilogram. At concentrations of greater than about 4.0 per cent by weight of the 15 CaC12.6H20, the inert nature of the strontium chloride hexahydrate, with its lower thermal capacity than that oP the CaC12.6H2O, is expected to reduce the efficacy oP the phase change material formulation, and this factor, combined with the high ? cost of SrC12.6~2O, sets a practical upper limit to the concentration of strontium chloride hexahydrate.
.
It has also been found that, to produce a phase change material based on calcium chloride hexahydrate which possesses long term stability, only a small 25 quantity of fumed silica is required as a thickener.
Using fumed silica marketed under the trade mark CAB-O-SIL by Cabot Chemical Company, the above-mentioned investigation showed that a ~uantity of at least 0.02 per cent (by weight) was required to 30 ensure long-term, multi-cycle stability of the phase , ~.
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W09l/00324 PCT/AU90~00264 1-' '' ' . .
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g change material, but a concentration in excess of 1.0 per cent (by weight) added unnecessarily to the cost of the phase change material, with no improvement in stability or other performance 5 parameter.
The use of "extra water" (that is, water in excess of the quantity required stoichiometrically for the hexahydrate formulation) was not contemplated in the disclosures in the aforementioned specification of 10 Australian patent application No 55769/86. The use of "extra water" has been proposed in relation to sodium sulphate decahydrate and some other salt hydrates by S Furbo in the article entitled "Heat Storage Units Using Salt Hydrates", which was 15 published in Sunworld, volume 6, No 5, pages 134 to 139, 1982. In the context of calcium chloride hexahydrate, however, water in excess of the quantity required stoichiometrically was not proposed in this paper. The investigation by the present inventors 20 showed that the éxtra water is required to ensure the long-term stability of the phase change material.
The minimum quantity of extra water is 1.0 per cent (by weight), which corresponds to a degree of hydration of 6.123, and the maximum quantity of extra 1 25 water is about 5.0 per cent, which corresponds to a I degree of hydration of 6.61, which was determined on ` the basis of storage efficiency considerations.
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barium sulphide, from 0.001 to 5 per cent barium chlQride dihydrate and from 0.001 to 0.1 per cent strontium chloride hexahydrate, with a bromide ~potassium bromide, sodium bromide or ammonium 5 bromide~ added as a solidification point modifier and relatively large quantities of ultrafine silica powder and glycerine added as thickening agents.
With such additives, however, the~ phase change material becomes a costly material to produce.
10 Disclosure of the Present Invention It is an object of the present invention to provide a relatively low cost formulation of a phase change material which can be used successfully for numerous melting and freezing cycles without significant 15 departure from its performance as a heat storage medium.
This objective is achieved by the inclusion of selected quantities of specific additives to calcium chloride hexahydrate. The additives are 20 ~a) strontium chloride hexahydrate, as a nucleator, in quantities upward from 0.1 per cent (by weight) of the calcium chloride hexahydrate, (b) fumed silica in quantities ranging from 0.02 per cent to 1.0 per cent (by weight) of the calcium chloride hexahydrate, and 25 (c) extra water above the stoichiometric quantity included in the calcium chloride hexahydrate in the range of from 1.0 per cent to S.0 per cent (by weight) of the calcium chloride hexahydrate.
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In addition, from 0.001 per cent to 1.0 per cent (by weight) of sodium chloride may also be added.
Preferably, the strontium chloride hexahydrate is present in quantities ranging from 0.1 per cent to 5 4.0 per cent tby weight) of the calcium chloride hexahydrate. More preferably the upper concentration of the strontium chloride hexahydrate is about 2.0 per cent, and most preferably the strontium chloride hexahydrate comprises about 0.3 per cent ~by weight) 10 of the càlcium chloride hexahydrate.
The selection of these additives and the ranges of their concentrations to produce compositions which are stable phase change materials is the outcome of a long-term investigation of the performance parameters 15 of calcium chloride hexahydrate phase change materials in melt/freeze cycling experiments.
i Strontium chloride hexahydrate is known to be isomorphous with calcium chloride hexahydrate and to be capable of forming nearly ideal solid solutions 20 with CaC12.6H2O; and is also known to be a nucleator of the solidification of calcium chloride hexahydrate. The investigation showed that the minimum amount of strontium chloride hexahydrate that is required to sustain long-term nucleation stability 25 is 0.1 per cent. Any lower concentration of strontium chloride hexahydrate is close to the limit of dissolution of SrC12.6H2O in calcium chloride hexahydrate. An increase in the concentration of :: :
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W O 91/00324 PC~r/A V90/00264 ~-' ""
SrC12.6H20 to more than about 1.0 per cent (by weight) of the calcium chloride hexahydrate results in little significant improvement in the performance or in the long-term stability of the heat storage 5 phase change material formulation. Increasing the concentration of SrC12.6H20 to more than 2.0 per Gent of the CaC12.6H2O produces no improvement in performance of the phase change material but it adds significantly to the cost of the formulation. At the 10 time of writing this specification, in Australia, strontium chloride hexahydrate costs about $20.00 per kilogram whereas calcium chloride hexahydrate costs about $0.20 per kilogram. At concentrations of greater than about 4.0 per cent by weight of the 15 CaC12.6H20, the inert nature of the strontium chloride hexahydrate, with its lower thermal capacity than that oP the CaC12.6H2O, is expected to reduce the efficacy oP the phase change material formulation, and this factor, combined with the high ? cost of SrC12.6~2O, sets a practical upper limit to the concentration of strontium chloride hexahydrate.
.
It has also been found that, to produce a phase change material based on calcium chloride hexahydrate which possesses long term stability, only a small 25 quantity of fumed silica is required as a thickener.
Using fumed silica marketed under the trade mark CAB-O-SIL by Cabot Chemical Company, the above-mentioned investigation showed that a ~uantity of at least 0.02 per cent (by weight) was required to 30 ensure long-term, multi-cycle stability of the phase , ~.
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W09l/00324 PCT/AU90~00264 1-' '' ' . .
2 ~
g change material, but a concentration in excess of 1.0 per cent (by weight) added unnecessarily to the cost of the phase change material, with no improvement in stability or other performance 5 parameter.
The use of "extra water" (that is, water in excess of the quantity required stoichiometrically for the hexahydrate formulation) was not contemplated in the disclosures in the aforementioned specification of 10 Australian patent application No 55769/86. The use of "extra water" has been proposed in relation to sodium sulphate decahydrate and some other salt hydrates by S Furbo in the article entitled "Heat Storage Units Using Salt Hydrates", which was 15 published in Sunworld, volume 6, No 5, pages 134 to 139, 1982. In the context of calcium chloride hexahydrate, however, water in excess of the quantity required stoichiometrically was not proposed in this paper. The investigation by the present inventors 20 showed that the éxtra water is required to ensure the long-term stability of the phase change material.
The minimum quantity of extra water is 1.0 per cent (by weight), which corresponds to a degree of hydration of 6.123, and the maximum quantity of extra 1 25 water is about 5.0 per cent, which corresponds to a I degree of hydration of 6.61, which was determined on ` the basis of storage efficiency considerations.
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.
Variations to the basic formulation of the present invention are possible. For example, as already indicated, sodium chloride is preferably included in concentrations of from 0.001 per cent to 1.0 per cent 5 (by weight). Indeed, sodium chloride has been an implicit additive in most of the prior art formulations of phase change materials based on calcium chloride hexahydrate, for technical grade CaC12.6H2O has sodium chloride as one of its 10 impurities. Up to approximately 0.4 per cent (by weight) of sodium chloride can form a solid solution with calcium chloride hexahydrate in the temperature range in which phase change materials are normally used. The preferred addition of ~odium chloride is 15 in the range of from 0.2 per cent to 1.0 per cent (by weight) or the calcium chloride hexahydrate.
It is also advantageous, in some circumstances, to add up to 10 per cent (by weight) each of ammonium chloride and potassium chloride to the formulation of 20 the present invention, to reduce the melt/freeze transition temperature of the formulation.
The preferred formulation of the present invention comprises calcium chloride hexahydrate to which has been added 25 ~a) about 0.3 wt per cent strontium chloride hexahydrate;
(b) about 0.1 wt per cent fumed silica;
(c) about 1.5 wt per cent extra water; and (d) about 0.4 wt per cent sodium chloride;
.
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the percentages being relative to the calcium chloride hexahydrate.
Such a formulation has a solid/liquid transition temperature of 29.6 :L O.2 C. This transition 5 temperature can be reduced down to about 22C by the addition of up to 10 wt per cent each of ammonium chloride and potassium chloride.
Most inorganic phase change materials have a light colour. The formulations of the present invention 10 which have been discussed above have a light colour in the solid state and are colourless in the liquid state. Thus those formulations, like the other phase change materials, are not good absorbers of radiant energy. Indeed, most phase change materials used in 15 the past have been stored in opaque containers and the heat transfer to, and from, the phase change materials has occurred by conduction.
It has now been discovered that improved heat transfer to and from phase change materials generally 20 (including the formulations of the present invention) can be achieved by colouring the materials so that they have a dark colour, preferably black, and by holding the materials in transparent containers, such as containers made from glass or perspex.
25 Thus an optional, but preferred, variation of the phasè change material formulation of the present invention is the additlon of a chemically inert ~ ' `
, , ~ WO91/00324 PCT/AU90/00264 . ' ' ~
....
, colouring agent. The presence of a colouring agent (preferably a black, or at least a dark, colo~ring agent) has been found to improve the ability of the phase change material to absorb and release heat by 5 radiation.
.
A convenient technique for tinting the phase change material is to mix black drawing ink into the formulation, using ultrasonic activation to ensurè a substantially uniform distribution of colour within 10 the material.
To demonstrate the effectiveness of this modification of phase change materials, 60 grams of a calcium chloride hexahydrate formulation containing additives against incongruent melting and supercooling, in 15 accordance with the present invention as described , above, was placed in an 80 ml glass jar. 0.12 gram (0.2 wt per cent) of ROTRIN~ ttrade mark) black drawing ink was added to the sample of the formulation. The formulation and the glass jar were 20 held in warm water for S minutes in a 3-litres tank of an ultrasonic cleaner (model FX 10 having an output of 100 watts at 40 kHz). The resultant ultrasonic activation distributed the ink uniformly throughout the phase change material.
25 The phase change material containing the black drawing ink was then subjected to freezing ~at about 10C), then melting (at about 45C). The formulation .',,;
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was then held in its molten state or several days.
At the end of this period, no segregation of the ink from the other components was observed.
Samples of the tinted and untinted phase change 5 materials ~of otherwise identical formulations) were placed in identical transparent containers and the containers were exposed to full solar radiation. The tinted (black) formulation consistently melted in less than one third the time taken for the untinted 10 samples to melt. Measurements of the temperatures of the formulations during heating showed that the dark phase change material was up to 8C hotter than the untinted control formulation.
In over 20 melt/freeze cycles, the tinted formulation 15 has shown no indication of deterioration in its performance as a heat storage medium.
, It will be apparent that a tinted phase change material is particularly suitable for use within greenhouses, where it will be able to be exposed to 20 radiant energy when stored in a transparent container.
To test the formulations of the present invention, continuous calorimetric measurements o a range of formulations have been made over a period of several 25 years. Samples of formulations of the present invention, and some samples of phase change materials not in accordance with the present invention, .
.
:
W O 91/00324 PC~r/A U90/00264 2~ 14 -typically 0.4 kg in weight, have been subjected to daily (and sometimes more frequent) melting and freezing cycles. The behaviour of the materials has been monitored comprehensively and recorded. This 5 testing has shown that formulations in accordance with the present invention have not deteriorated during the test period, and their heat storage capacity has remained substantially constant within statistically reasonable limits. One sample of a 10 formulation in accordance with the present invention, for example, has retained its heat storage capacity at around 200 kJ/kg over 1000 melt/freeze cycles, with no indication of a deterioration in performance.
In another experiment, some 300 kg of calcium 15 chloride phase change material, held in 6 litre plastic containers, was used as the basis of an off peak heating system for a laboratory. In this experiment, the phase change material was heated with off-peak electricity and, with the aid of a water 20 circulation heat transport system, delivered its stored heat when required. At the time of writing this specification, the material is still in satisfactory working order in the fourth winter season of the use of the heating system.
25 Phase change materials having untinted formulations in accordance with the present invention have also been tested in a low energy greenhouse mounted on a roof of a building of The Australian National University, in C-nberra, Australia. In t~ct, one ~t .~
, .
:' f ~
the formulations of the present invention was the calcium chloride hexahydrate "appropriately formulated against supercooling and degradation" used to obtain the experimental data reported in the 5 aforementioned paper by A Brandstetter, entitled 'IPhase change storage for greenhouses".
': ' :. ' ' ~ . .
, . ' . ~
.
It is also advantageous, in some circumstances, to add up to 10 per cent (by weight) each of ammonium chloride and potassium chloride to the formulation of 20 the present invention, to reduce the melt/freeze transition temperature of the formulation.
The preferred formulation of the present invention comprises calcium chloride hexahydrate to which has been added 25 ~a) about 0.3 wt per cent strontium chloride hexahydrate;
(b) about 0.1 wt per cent fumed silica;
(c) about 1.5 wt per cent extra water; and (d) about 0.4 wt per cent sodium chloride;
.
..
~............... . .
the percentages being relative to the calcium chloride hexahydrate.
Such a formulation has a solid/liquid transition temperature of 29.6 :L O.2 C. This transition 5 temperature can be reduced down to about 22C by the addition of up to 10 wt per cent each of ammonium chloride and potassium chloride.
Most inorganic phase change materials have a light colour. The formulations of the present invention 10 which have been discussed above have a light colour in the solid state and are colourless in the liquid state. Thus those formulations, like the other phase change materials, are not good absorbers of radiant energy. Indeed, most phase change materials used in 15 the past have been stored in opaque containers and the heat transfer to, and from, the phase change materials has occurred by conduction.
It has now been discovered that improved heat transfer to and from phase change materials generally 20 (including the formulations of the present invention) can be achieved by colouring the materials so that they have a dark colour, preferably black, and by holding the materials in transparent containers, such as containers made from glass or perspex.
25 Thus an optional, but preferred, variation of the phasè change material formulation of the present invention is the additlon of a chemically inert ~ ' `
, , ~ WO91/00324 PCT/AU90/00264 . ' ' ~
....
, colouring agent. The presence of a colouring agent (preferably a black, or at least a dark, colo~ring agent) has been found to improve the ability of the phase change material to absorb and release heat by 5 radiation.
.
A convenient technique for tinting the phase change material is to mix black drawing ink into the formulation, using ultrasonic activation to ensurè a substantially uniform distribution of colour within 10 the material.
To demonstrate the effectiveness of this modification of phase change materials, 60 grams of a calcium chloride hexahydrate formulation containing additives against incongruent melting and supercooling, in 15 accordance with the present invention as described , above, was placed in an 80 ml glass jar. 0.12 gram (0.2 wt per cent) of ROTRIN~ ttrade mark) black drawing ink was added to the sample of the formulation. The formulation and the glass jar were 20 held in warm water for S minutes in a 3-litres tank of an ultrasonic cleaner (model FX 10 having an output of 100 watts at 40 kHz). The resultant ultrasonic activation distributed the ink uniformly throughout the phase change material.
25 The phase change material containing the black drawing ink was then subjected to freezing ~at about 10C), then melting (at about 45C). The formulation .',,;
.~ . ' .
.
, .
- 13 - 2~
was then held in its molten state or several days.
At the end of this period, no segregation of the ink from the other components was observed.
Samples of the tinted and untinted phase change 5 materials ~of otherwise identical formulations) were placed in identical transparent containers and the containers were exposed to full solar radiation. The tinted (black) formulation consistently melted in less than one third the time taken for the untinted 10 samples to melt. Measurements of the temperatures of the formulations during heating showed that the dark phase change material was up to 8C hotter than the untinted control formulation.
In over 20 melt/freeze cycles, the tinted formulation 15 has shown no indication of deterioration in its performance as a heat storage medium.
, It will be apparent that a tinted phase change material is particularly suitable for use within greenhouses, where it will be able to be exposed to 20 radiant energy when stored in a transparent container.
To test the formulations of the present invention, continuous calorimetric measurements o a range of formulations have been made over a period of several 25 years. Samples of formulations of the present invention, and some samples of phase change materials not in accordance with the present invention, .
.
:
W O 91/00324 PC~r/A U90/00264 2~ 14 -typically 0.4 kg in weight, have been subjected to daily (and sometimes more frequent) melting and freezing cycles. The behaviour of the materials has been monitored comprehensively and recorded. This 5 testing has shown that formulations in accordance with the present invention have not deteriorated during the test period, and their heat storage capacity has remained substantially constant within statistically reasonable limits. One sample of a 10 formulation in accordance with the present invention, for example, has retained its heat storage capacity at around 200 kJ/kg over 1000 melt/freeze cycles, with no indication of a deterioration in performance.
In another experiment, some 300 kg of calcium 15 chloride phase change material, held in 6 litre plastic containers, was used as the basis of an off peak heating system for a laboratory. In this experiment, the phase change material was heated with off-peak electricity and, with the aid of a water 20 circulation heat transport system, delivered its stored heat when required. At the time of writing this specification, the material is still in satisfactory working order in the fourth winter season of the use of the heating system.
25 Phase change materials having untinted formulations in accordance with the present invention have also been tested in a low energy greenhouse mounted on a roof of a building of The Australian National University, in C-nberra, Australia. In t~ct, one ~t .~
, .
:' f ~
the formulations of the present invention was the calcium chloride hexahydrate "appropriately formulated against supercooling and degradation" used to obtain the experimental data reported in the 5 aforementioned paper by A Brandstetter, entitled 'IPhase change storage for greenhouses".
': ' :. ' ' ~ . .
, . ' . ~
.
Claims (13)
1. A phase change material comprising calcium chloride hexahydrate containing the additives strontium chloride hexahydrate and fumed silica, characterised in that:
(a) the quantity of strontium chloride hexahydrate added is at least 0.1 per cent by weight of the calcium chloride hexahydrate;
(b) the fumed silica additive comprises from 0.02 per cent by weight to 1.0 per cent by weight of the calcium chloride hexahydrate;
and (c) water in excess of the stoichiometric quantity included in the hexahydrates is also added, the added water comprising from 1.0 per cent by weight to 5.0 per cent by weight of the calcium chloride hexahydrate.
(a) the quantity of strontium chloride hexahydrate added is at least 0.1 per cent by weight of the calcium chloride hexahydrate;
(b) the fumed silica additive comprises from 0.02 per cent by weight to 1.0 per cent by weight of the calcium chloride hexahydrate;
and (c) water in excess of the stoichiometric quantity included in the hexahydrates is also added, the added water comprising from 1.0 per cent by weight to 5.0 per cent by weight of the calcium chloride hexahydrate.
2. A phase change material as defined in claim 1, in which the strontium chloride hexahydrate additive is present in the range of from 0.1 to 4.0 per cent by weight of the calcium chloride hexahydrate.
3. A phase change material as defined in claim 2, in which the strontium chloride hexahydrate additive is present in the range of from 0.1 to 2.0 per cent by weight of the calcium chloride hexahydrate.
4. A phase change material as defined in claim 3, in which the strontium chloride hexahydrate additive comprises about 0.3 per cent by weight of the calcium chloride hexahydrate.
5. A phase change material as defined in any preceding claim, further characterised in that the phase change material includes added sodium chloride, the added sodium chloride comprising from 0.001 per cent by weight to 1.0 per cent by weight of the calcium chloride hexahydrate.
6. A phase change material as defined in claim 1, in which (i) the added strontium chloride comprises about 0.3 per cent by weight of the calcium chloride hexahydrate;
(ii) the added fumed silica comprises about 0.1 per cent by weight of the calcium chloride hexahydrate;
(iii) the excess water over the stoichiometric quantity included in the calcium chloride hexahydrate comprises about 1.5 per cent by weight of the calcium chloride hexahydrate;
and (iv) sodium chloride is also added, the added sodium chloride being about 0.4 per cent by weight, of the calcium chloride hexahydrate.
(ii) the added fumed silica comprises about 0.1 per cent by weight of the calcium chloride hexahydrate;
(iii) the excess water over the stoichiometric quantity included in the calcium chloride hexahydrate comprises about 1.5 per cent by weight of the calcium chloride hexahydrate;
and (iv) sodium chloride is also added, the added sodium chloride being about 0.4 per cent by weight, of the calcium chloride hexahydrate.
7. A phase change material as defined in any preceding claim, to which has been added up to 10 per cent by weight of ammonium chloride.
8. A phase change material as defined in any preceding claim, to which has been added up to 10 per cent by weight of potassium chloride.
9. A phase change material as defined in any preceding claim, further characterised in that a chemically inert colouring agent has also been added.
10. A phase change material as defined in claim 9, in which the colouring agent is a dark colouring agent.
11. A phase change material as defined in claim 9, in which the colouring agent is black drawing ink.
12. A phase change material as defined in claim 11, in which the colouring agent comprises about 0.2 per cent by weight of the phase change material prior to the addition of the colouring agent.
13. A phase change material as defined in any one of claims 9 to 12, in a transparent container.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AUPJ487889 | 1989-06-23 | ||
| AUPJ4878/89 | 1989-06-23 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2060215A1 true CA2060215A1 (en) | 1990-12-24 |
Family
ID=3774013
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002060215A Abandoned CA2060215A1 (en) | 1989-06-23 | 1990-06-22 | Calcium chloride hexahydrate formulations for low temperature heat storage application |
Country Status (2)
| Country | Link |
|---|---|
| KR (1) | KR920702712A (en) |
| CA (1) | CA2060215A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115298283A (en) * | 2020-03-16 | 2022-11-04 | 矢崎总业株式会社 | Heat storage material composition |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR100420008B1 (en) * | 2001-03-27 | 2004-03-02 | 최용학 | Energy storage type of heat accumultating material for a boiler |
-
1990
- 1990-06-22 CA CA002060215A patent/CA2060215A1/en not_active Abandoned
- 1990-06-24 KR KR1019910701939A patent/KR920702712A/en not_active Application Discontinuation
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN115298283A (en) * | 2020-03-16 | 2022-11-04 | 矢崎总业株式会社 | Heat storage material composition |
Also Published As
| Publication number | Publication date |
|---|---|
| KR920702712A (en) | 1992-10-06 |
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