WO2005017064A1

WO2005017064A1 - Reversible liquid/solid phase change composition

Info

Publication number: WO2005017064A1
Application number: PCT/AU2004/001098
Authority: WO
Inventors: Danh Thanh Trinh; Kester Howard Solomon
Original assignee: Thermal Energy Accumulator Products Ltd
Priority date: 2003-08-15
Filing date: 2004-08-13
Publication date: 2005-02-24
Also published as: AU2003904355A0

Abstract

The present invention relates broadly to a reversible liquid/solid phase change composition or phase change material (PCM). The PCM in each of the examples includes a hydrated mixture of calcium chloride and magnesium chloride at respective weight percentage amounts of between 35 to 60% and 15 to 30%, and an effective amount of a nucleating agent.

Description

Reversible Liquid/Solid Phase Change Composition

FIELD OF THE INVENTION

The present invention relates broadly to a reversible liquid /solid phase change composition and relates particularly, though not exclusively, to a phase change material (PCM) comprising calcium chloride and magnesium chloride. The invention further relates to an energy storage device adapted to contain a PCM.

BACKGROUND OF THE INVENTION

US patent nos.4,189,394 and 4,491,529 disclose the use of nucleating agents with the heat accumulating agent calcium chloride hexahydrate. The nucleating agents are used to reduce supercooling of the calcium chloride hexahydrate so that the stored latent heat of fusion can be extracted on cooling of the calcium chloride hexahydrate below the melting point of around 29°C. The nucleating agents described in these US patents include barium carbonate, strontium carbonate, barium fluoride, barium fluoride-hydrofluoride, strontium fluoride, caesium chlorate, caesium alumdodecahydrate, bismuth phosphate, bismuth tartrate hexahydrate, basic bismuth carbonate, bismuth hydroxide, lead carbonate, lead oxalate, and lead phosphate. These nucleating agents have very low solubility and are added to the calcium chloride hexahydrate in very small quantities of less than 1% by weight and typically between 0.1 to 0.5% by weight.

US patent nos.4,412,931 and 4,637,888 describe reversible phase change compositions for strong energy and include mixtures of calcium chloride /potassium salt and calcium chloride/ calcium bromide, respectively. Each of these phase change compositions also includes a nucleating agent which is effective in reducing supercooling. The selection of nucleating agents disclosed includes Ba(OH)₂, BaO, Bal^, BaS₂θ₃, BaC0₃, BaCL* BaF* BaF₂.HF, Sr(OH)₂, SrO,

Sri SrClj, and SrBr₂. The nucleating agents of US 4,412,931 were added in an amount from 0.005 to 2.0 weight % whereas the agents of US 4,637,888 were added at 0.5 weight %.

SUMMARY OF THE INVENTION

According to one aspect of the present invention there is provided a reversible liquid /solid phase change composition comprising a hydrated mixture of CaCl₂ and MgQ^ or derivatives thereof, at respective weight percent amounts of between 35 to 60% and 15 to 30%, and an effective amount of a nucleating agent.

According to another aspect of the invention there is provided a reversible liquid /solid phase change composition having a melting temperature of between 15 to 35°C, said composition comprising a mixture of CaCl₂ and MgCl* or derivatives thereof, and an effective amount of a nucleating agent.

Preferably the composition further comprises from between about 15 to 50 weight % water.

Preferably the nucleating agent is present in the effective amount wherein crystallisation of the composition for retrieval of stored energy is effected at 20°C or greater. More preferably the nucleating agent is present at less than about 7.0 weight %. Even more preferably the nucleating agent is at between 1.0 to 5.0 weight %.

Preferably the nucleating agent is one of a plurality of nucleating agents. More preferably the nucleating agent is selected from the group consisting of BaC0₃, Na₂ WO₄, KC1, SrCl₂ and derivatives or mixtures thereof. Even more preferably the nucleating agent is present in the effective amount wherein during crystallisation supercooling of the composition is reduced to less than about 5°C.

According to a further aspect of the invention there is provided an energy storage device comprising encapsulation means being adapted to contain a reversible liquid/ solid phase change composition comprising a hydrated mixture of CaCl₂ and MgCL or derivatives thereof, at respective weight percent amounts of between about 35 to 60% and 15 to 30%, and an effective amount of a nucleating agent.

Preferably the encapsulation means is in the form of macro and /or micro encapsulation means and includes sealing means to prevent evaporation of the composition. More preferably the encapsulation means includes a coating, powder or resin, a plastic or metal container, or hermetically sealed films, foils or plastic and/ or metal laminates.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a plan and part sectional view of an energy storage device of an embodiment of an aspect of the invention; and Figure 2 is a part sectional view of another storage device of an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In order to achieve a better understanding of the nature of the present invention, preferred examples of a reversible liquid/ solid phase change composition or phase change material (PCM) will now be described. The PCM in each of the following examples includes a hydrated mixture of calcium chloride and magnesium chloride at respective weight percentage (wt %) amounts of between 35 to 60% and 15 to 30%, and an effective amount of a nucleating agent.

Example 1:

CaQ-₂ From about 35 to about 60 wt % MgCl₂ From about 15 to about 30 wt % Na₂W0 In an amount greater than zero and less than 2 wt % KC1 In an amount greater than zero and less than 3 wt % H₂0 Balance of up to 100 wt %

Example 2:

CaCl₂ From about 35 to about 60 wt % MgCl₂ From about 15 to about 30 wt % BaC0₃ In an amount greater than zero and less than 2.5 wt % Na₂W0 In an amount greater than zero and less than 2 wt % H₂0 Balance of up to 100 wt %

Example 3:

CaCl₂ From about 35 to about 60 wt % MgCl₂ From about 15 to about 30 wt % KC1 In an amount greater than zero and less than 3 wt %

Na₂W0₄ In an amount greater than zero and less than 2 wt % SrCl₂ In an amount greater than zero and less than 2 wt % H₂O Balance of up to 100 wt % Example 4:

CaCl₂ From about 35 to about 60 wt % MgCl₂ From about 15 to about 30 wt % KC1 In an amount greater than zero and less than 3 wt % SrCl₂ In an amount greater than zero and less than 2 wt % H₂O Balance of up to 100 wt %

The PCM of these examples has a melting temperature of between 15 to 35°C but more particularly in the 20 to 30°C range. The PCM has application as a buffer or passive or non- passive heat sink in buildings to modulate swings in temperatures and to assist in stabilisation of temperatures to enhance the effect of insulation -and building materials.

The nucleating agents of the preceding examples are understood to be effective in ensuring the congruent melting behaviour of the CaCl₂ and MgCl₂ mixture. It is also recognized that the nucleating agents are effective in reducing supercooling of the PCM to less than about 5°C during crystallisation. The nucleating agents are understood to provide crystallisation or freezing temperatures of the PCM at greater than 20°C during retrieval of the stored PCM energy. The nucleating agent is preferably present at less than about 7 wt % and as reflected in the preceding examples and more preferably present at between 1.5 to 4.5 wt %. It is possible that the nucleating agent may exist in amounts greater than 7 weight percent without detriment to the function of the PCM, although at these high amounts the nucleating agent does not exhibit any further benefits in reducing supercooling.

The PCM may also include impurities which do not detrimentally affect the function of the hydrated CaCl₂ and MgCl₂ mixture. For example CaS0 and NaCl are impurities which at appropriate levels can be tolerated in the PCM. The enthalpy of the preferred PCM of the invention is from about 130 to 230 Joules per gram (J/g). It is to be understood that enthalpy is equivalent to the internal energy plus the product of the pressure and volume and is measured by the heat content per unit mass, for example in J/g. It has been found that the PCM mixture based on hydrated CaCl₂ and MgCl₂ are particularly well suited in that they display congruent melting. That is, at the melting point of the PCM, solid and liquid phases are in stable equilibrium. In the preferred example the solid phase contains no hydrated CaCl₂ and MgCl₂ other than the correct hydrate or solid solutions thereof whereas the liquid phase contains, for every mole of CaCl₂ and MgCl* correct moles of water plus sufficient water to form the stable hydrate of any additive materials in solution. In another aspect of the invention the PCM is contained in an energy storage device. The energy storage device may have application in buildings where for example it is used as a heat sink placed in ceilings or walls. The energy storage device includes a macro and /or micro encapsulation means. As shown in figure 1, the macro encapsulation means of the storage device 10 includes a plurality of interconnected and dome shaped capsules 12A to 12F sealed with a cover strip 14. Six (6) of the capsules 12A to 12F are shaped circular. In this embodiment the capsules 12A to 12F are thermo-formed from high density polyethylene PVC and the cover strip 14 is an aluminium faced polyethylene PVC/ polyester material. Each of the capsules 12A to 12FC is injected with a predetermined volume of the PCM 16 prior to hermetic sealing with the cover strip 14.

Figure 2 show a spherical or ball shaped energy storage device 100. The encapsulation means of this embodiment includes a spherical shell 102 formed of a polyethylene plastic material having a flanged opening 104. The device 100 also includes a polyethylene plug 106 designed to be inserted and ultrasonically welded to the flanged opening 104 for hermetically sealing the shell 102. The shell 102 or encapsulation means contains a select volume of the PCM 108 with an air pocket 110 disposed above the PCM 108.

Now that several preferred embodiments of the invention have been described in some detail it will be apparent to those skilled in the art that the reversible liquid /solid phase change composition and energy storage device have the following advantages:

1. The selection of CaCl₂ and MgCl₂ in conjunction with the nucleating agent provides freezing temperatures, preferably at greater than 20°C of the PCM during crystallisation;

2. The selection of CaCl₂ and MgCl₂ in conjunction with the nucleating agent reduces supercooling of the PCM during crystallisation;

3. The selection of CaCl₂ and MgCl₂ in conjunction with the nucleating agent provides congruent melting during phase changes; and

4. The PCM tolerates impurities without its function being detrimentally affected.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. For example, the particular compositions exemplified may be varied provided they remain within the broad scope of the invention. All such variations and modifications are to be considered within the scope of the present invention the nature of which is to be determined from the foregoing description.

All publications mentioned in this specification are herein incorporated by reference. Any discussion of documents, acts, materials, devices, articles or the like which has been included in the present specification is solely for the purpose of providing a context for the present invention. It is not to be taken as an admission that any or all of these matters form part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed anywhere before the priority date of each claim of this application.

Claims

1. A reversible liquid/ solid phase change composition comprising a hydrated mixture of CaCl₂ and MgCl₂, or derivatives thereof, at respective weight percent amounts of between 35 to 60% and 15 to 30%, and an effective amount of a nucleating agent.

2. A reversible liquid/ solid phase change composition having a melting temperature of between 15 to 35°C, said composition comprising a mixture of CaCl₂ and MgCl^ or derivatives thereof, and an effective amount of a nucleating agent.

3. A reversible composition as defined in either of claims 1 or 2 further comprising from between about 15 to 50 weight % water.

4. A composition as defined in any one of the preceding claims wherein the nucleating agent is present in the effective amount wherein crystallisation of the composition for retrieval of stored energy is effected at 20°C or greater.

5. A composition as defined in claim 4 wherein the nucleating agent is present at less than about 7.0 weight percent.

6. A composition as defined in any one of the preceding claims wherein the nucleating agent is selected from the group consisting of BaCO₃, Na₂ WO-j, KC1, SrCl₂ and derivatives or mixtures thereof.

7. A composition as defined in claim 6 wherein the nucleating agent is present in the effective amount wherein during crystallisation supercooling of the composition is reduced to less than about 5°C.

8. An energy storage device comprising encapsulation means being adapted to contain a reversible liquid /solid phase change composition comprising a hydrated mixture of CaCl₂ and MgCl^ or derivatives thereof, at respective weight percent amounts of between about 35 to 60% and 15 to 30%, and an effective amount of a nucleating agent.

9. A device as defined in claim 8 wherein the encapsulation means is in the form of macro and /or micro encapsulation means and includes sealing means to prevent evaporation of the composition. A device as defined in either of claims 8 or 9 wherein the encapsulation means includes a coating, powder or resin, a plastic or metal container, or hermetically sealed films, foils or plastic and /or metal laminates.