Heat accumulating material

This invention relates to a heat accumulating material, particularly to a latent heat accumulating material comprising three components of CaCl.sub.2, CO(NH.sub.2).sub.2 and H.sub.2 O as its principal ingredients.
Generally, two types of heat accumulating material are known, one type utilizing the sensible heat of material and the other type making use of the latent heat. The heat accumulating material of the type utilizing the latent heat, as compared with the type utilizing the sensible heat, has the advantage that its heat accumulating capacity per unit weight or unit volume is high, and hence a smaller amount of material is needed for accumulating a required quantity of heat, allowing a size reduction of the heat accumulator. Also, the heat accumulating material making use of the latent heat has an advantageous property that the temperature thereof does not decrease with heat dissipation unlike the heat accumulating material of the type utilizing the sensibile heat. Also, it releases heat of a fixed temperature at the transition point thereof. Especially, the heat accumulating material utilizing the latent heat of fusion of an inorganic hydrate is known for its high heat accumulating capacity per unit mass and per unit volume.
Now, CaCl.sub.2.6H.sub.2 O (melting point: 29.5.degree. C.) has a high heat accumulating capacity and much expectation has been placed on it for its utilization as a heat accumulating material, such as for air conditioning systems. However, the melting point of CaCl.sub.2.6H.sub.2 O is fixed at 29.5.degree. C., and hence the temperature of heat accumulation and heat releasing is necessarily restricted to that temperature, and this has been a problem for its broader application. Also, CaCl.sub.2.6H.sub.2 O has another problem in that, during the repeated fusion and solidification, CaCl.sub.2.4H.sub.2 O separates out, causing gradual decrease of latent heat of the system.
An object of this invention is to provide a heat accumulating material having a high heat accumulating capacity and a stable heat absorbing and releasing property at a low cost. The temperature for heat accumulation and heat releasing of which material can be controlled by, in a composition comprising three components of CaCl.sub.2, CO(NH.sub.2).sub.2 and H.sub.2 O or comprising these as its principal ingredients, varying the proportion of said composition.
The feature of the heat accumulating material according to the present invention consists in comprising three components system of CaCl.sub.2, CO(NH.sub.2).sub.2 and H.sub.2 O or comprising the system as its principal ingredient. Preferably the material comprises 40-57.5% by weight of CaCl.sub.2, 30% by weight or less (excluding 0%) of CO(NH.sub.2).sub.2 and 30-52.5% by weight of H.sub.2 O (providing that the total of said three components is 100% by weight). More preferably, the material is of a composition having CaCl.sub.2.6H.sub.2 O and CaCl.sub.2.4CO(NH.sub.2).sub.2.2H.sub.2 O as its two end components and containing CO(NH.sub.2).sub.2 in a range of amount of 25% by weight or less (excluding 0%) based on the total amount of CaCl.sub.2, CO(NH.sub.2).sub.2 and H.sub.2 O.
In order to prevent the supercooling of the composition comprising CaCl.sub.2, CO(NH.sub.2).sub.2 and H.sub.2 O, an appropriate nucleating agent such as BaFeO.sub.3-x (0.ltoreq.x.ltoreq.0.53) is preferably added. The amount of the nucleating agent to be added is preferably 40 parts by weight or less to 100 parts by weight of the composition comprising CaCl.sub.2, CO(NH.sub.2).sub.2 and H.sub.2 O.

BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a DSC (differential scanning calorimeter) diagram obtained during the fusion of Sample 7.
FIG. 2 is a graph showing the changes in the degree of supercooling (difference between the solidification temperature and the temperature at which supercooling is broken) of Sample 54 when it is subjected to 1000 consecutive repeated heating and cooling cycles.

The present invention is further described below by way of the embodiments thereof.
EXAMPLE
Commercially available reagent grade CaCl.sub.2, CaCl.sub.2.6H.sub.2 O and CO(NH.sub.2).sub.2 as well as water purified by distillation followed by ion exchange were used to be mixed in prescribed amounts as shown in Tables 1 and 2. The mixture was heated up to 45.degree. C. to dissolve as much solid as possible, and was used as a sample.
Each of these samples was measured for its transition temperature and latent heat by use of a differential scanning calorimeter (DSC). The transition temperature was determined from the temperature at the peak of DSC diagram, and the latent heat was determined from the peak area of DSC diagram. The DSC diagram of Sample 7 shown in Table 1 is illustrated in FIG. 1. The samples for which two transition temperatures are indicated in Tables 3 and 4 are those having two peaks in DSC diagram, as seen in the above DSC diagram. Actual transition is considered to occur continuously between these temperatures.
Each of the samples shown in Table 1 is of a composition having CaCl.sub.2.6H.sub.2 O and CaCl.sub.2.4CO(NH.sub.2).sub.2.2H.sub.2 O as its two end components, while each of the samples shown in Table 2 is of a composition lying in peripheral area of the composition having CaCl.sub.2.6H.sub.2 O and CaCl.sub.2.4CO(NH.sub.2).sub.2.2H.sub.2 O as its both end components.
Needless to say, transitions below 0.degree. C. were not determined since they were considered to be unnecessary in this case. Regarding the ratings shown in Tables 3 and 4, samples having a latent heat not less than 25 cal/g were marked with the symbol o, those having a latent heat not less than 15 and less than 25 cal/g were marked with the symbol .DELTA., and the others were marked with the symbol x. Samples marked with the symbol o have a high heat accumulating capacity and can be used practically. Samples marked with the symbol .DELTA. are considered to be fairly satisfactory for practical application since, though their heat accumulating capacity is not so high, they have transition temperatures in a temperature range not obtainable by prior heat accumulating materials.
TABLE 1______________________________________ Composition (% by weight)Sample No. CaCl.sub.2 CO(NH.sub.2).sub.2 H.sub.2 O______________________________________1 50.6 0.2 49.22 50.5 0.4 49.13 50.4 0.6 49.04 50.3 1.1 48.65 49.9 2.2 47.96 49.5 3.2 47.37 49.1 4.3 46.08 48.8 5.3 45.99 47.9 7.9 44.210 47.4 9.3 43.311 46.8 10.9 42.312 46.3 12.4 41.313 45.7 14.0 40.314 45.2 15.5 39.315 44.6 17.1 38.316 43.8 18.5 37.717 41.9 24.8 33.318 41.0 27.0 32.019 40.2 29.5 30.320 39.5 31.0 29.5______________________________________
TABLE 2______________________________________ Composition (% by weight)Sample No. CaCl.sub.2 CO(NH.sub.2).sub.2 H.sub.2 O______________________________________21 45.0 2.5 52.522 40.0 5.0 55.023 45.0 5.0 50.024 47.5 5.0 47.525 50.0 5.0 45.026 52.5 5.0 42.527 55.0 5.0 40.028 45.0 10.0 45.029 47.5 10.0 42.530 50.0 10.0 40.031 52.5 10.0 37.532 55.0 10.0 35.033 57.5 10.0 32.534 60.0 10.0 30.035 39.0 15.0 46.036 45.0 15.0 40.037 50.0 15.0 35.038 55.0 15.0 30.039 42.5 20.0 37.540 46.0 25.0 29.0______________________________________
TABLE 3______________________________________ TdransitionSample temperature Latnet heatNo. (.degree.C.) (cal/g) Rating______________________________________1 29.3 43 o2 29.1 43 o3 28.9 43 o4 28.2 42 o5 27.3 40 o6 26.0, 15.0 39 o7 25.0, 15.1 39 o8 25.0, 16.0 37 o9 24.0, 16.3 37 o10 22.3, 16.8 35 o11 20.8, 17.3 34 o12 18.1 33 o13 18.1 34 o14 15.8 32 o15 14.1, 0.8 28 o16 14.0, 1.0 26 o17 14.0, 1.6 25 o18 13.2, 1.6 23 .DELTA.19 13.0, 1.7 18 .DELTA.20 13.0, 1.8 12 x______________________________________
TABLE 4______________________________________ TransitionSample temperatureNo. (.degree.C.) Latent heat Rating______________________________________21 19.5 17 .DELTA.22 4.0 10 x23 19.6 20 .DELTA.24 23.0 25 o25 24.0 37 o26 27.0 36 o27 33.6, 20.0 35 o28 10.3 21 .DELTA.29 20.8, 17.0 38 o30 20.9, 18.3 37 o31 21.3 36 o32 32.6, 18.3 33 o33 32.6, 19.0 25 o34 33.3, 19.3 14 x35 4.3 7 x36 16.3 31 o37 19.6 33 o38 33.0, 20.3 24 o39 16.0, 2.5 21 .DELTA.40 13.0, 1.8 10 x______________________________________
When the data shown in Table 3 are examined, in Sample 1, which is of the composition having CaCl.sub.2.6H.sub.2 O and CaCl.sub.2.4CO(NH.sub.2).sub.2.2H.sub.2 O as the two end components and contains 0.2% by weight of CO(NH.sub.2).sub.2, the transition point lowers to 29.3.degree. C. and the latent heat is 43 cal/g, approximately equal to that of CaCl.sub.2.6H.sub.2 O. As the content of CO(NH.sub.2).sub.2 is increased, the transition point goes down gradually, accompanied by, though slight, a decrease of the latent heat. When the content of CO(NH.sub.2).sub.2 is 3.2% by weight or more, a transition point appears around 15.degree. C. aside from previous transition point of around 26.degree. C. As the content of CO(NH.sub.2).sub.2 increases further; the transition at around 26.degree. C. shifts to the lower temperature side.
In Sample 12, which contains 12.4% by weight of CO(NH.sub.2).sub.2, the transitions at higher and lower temperature sides are observed in an overlapped state. Accordingly, the composition which contains about 12.4-15.5% by weight of CO(NH.sub.2).sub.2 and has CaCl.sub.2.6H.sub.2 O and CaCl.sub.2.4CO(NH.sub.2).sub.2.2H.sub.2 O as its two end components, such as Samples 12, 13 and 14, is an excellent heat accumulating material having a transition point at 15.degree.-18.degree. C. and a large latent heat of 35 cal/g.
In samples containing 17.1% by weight or more of CO(NH.sub.2).sub.2, the transition appears around 1.degree. C. in the further lower temperature side. As the content of CO(NH.sub.2).sub.2 is increased, the latent heat decreases, while the transition around 15.degree. C. shifting toward the lower temperature side and the transition around 1.degree. C. shifting somewhat toward the higher temperature side.
In sum, the heat accumulating material of three components system of CaCl.sub.2, CO(NH.sub.2).sub.2 and H.sub.2 O, which has CaCl.sub.2.6H.sub.2 O and CaCl.sub.2.4CO(NH.sub.2).sub.2.2H.sub.2 O as its two end components and contains CO(NH.sub.2).sub.2 in a range of amount of 25% by weight or less (excluding 0%), is a very excellent heat accumulating material unobtainable hitherto, because the heat accumulating and heat releasing temperature can be controlled by varying the percentage composition thereof and yet the material has a latent heat of not less than 25 cal/g.
In the next place, samples shown in Table 4, whose composition lies in the peripherial area of the composition having CaCl.sub.2.6H.sub.2 O and CaCl.sub.2.4CO(NH.sub.2).sub.2.2H.sub.2 O as its two end components, are examined for their characteristic properties. Samples 22-27, as apparent from Table 2, are obtained by varying the proportion of CaCl.sub.2 and H.sub.2 O contained while keeping the content of CO(NH.sub.2).sub.2 at a constant value of 5% by weight. Samples 22, 23 and 24 are those which have their composition in the H.sub.2 O excess side, that is, the CaCl.sub.2 deficiency side, of the composition having CaCl.sub.2.6H.sub.2 O and CaCl.sub.2.4CO(NH.sub.2).sub.2.2H.sub.2 O as its two end components, while Samples 25, 26 and 27 are inversely those which have their composition in the H.sub.2 O deficiency side, that is, the CaCl.sub.2 excess side, of the composition having CaCl.sub.2.6H.sub.2 O and CaCl.sub.2.4CO(NH.sub.2).sub.2.2H.sub.2 O as its both end components. Accordingly, as the content of CaCl.sub.2 is increased starting from the composition of Sample 22 lying in the H.sub.2 O excess side without varying the content of CO(NH.sub.2).sub.2, namely, as the composition is varied into that of Sample 23 and further into that of Sample 24, the latent heat increases and the transition temperature rises.
In Sample 25, which has the composition nearest to the one having CaCl.sub.2.6H.sub.2 O and CaCl.sub.2.4CO(NH.sub.2).sub.2.2H.sub.2 O as its two end components, the latent heat assumes a maximum value. On increasing the CaCl.sub.2 content further, there is observed not an increase but a decrease of the latent heat. The transition temperature rises with increasing CaCl.sub.2 content without showing any maximum value in the course. Such a relationship can also be observed among the samples containing 10% by weight of CO(NH.sub.2).sub.2, such as Samples 28-34. It is observed that Sample 29, which has the composition nearest to the composition having CaCl.sub.2.6H.sub.2 O and CaCl.sub.2.4CO(NH.sub.2).sub.2.2H.sub.2 O as its both end components, has the largest latent heat and that the transition point rises with the increase of the content of CaCl.sub.2.
In other words, when compared with the composition having CaCl.sub.2.6H.sub.2 O and CaCl.sub.2.4CO(NH.sub.2).sub.2.2H.sub.2 O as its two end components, if the proportion of the CO(NH.sub.2).sub.2 contained is the same, the transition temperature lowers on the H.sub.2 O excess side, namely the CaCl.sub.2 deficiency side, and inversely, the transition temperature rises somewhat on the H.sub.2 O deficiency side, namely the CaCl.sub.2 excess side. The latent heat decreases in both cases when the composition shifts toward the H.sub.2 O excess side, namely CaCl.sub.2 deficiency side, and toward the H.sub.2 O deficiency side, namely CaCl.sub.2 excess side, from the composition having CaCl.sub.2.6H.sub.2 O and CaCl.sub.2.4CO(NH.sub.2).sub.2.2H.sub.2 O as its two end components.
To sum up the results mentioned above, the composition of a heat accumulating material is preferably in the composition area of Samples marked with the symbols of .DELTA. and o shown under the ratings in Tables 3 and 4. In other words, in the three components system comprising CaCl.sub.2, CO(NH.sub.2).sub.2 and H.sub.2 O, it is preferably in the range of 40-57.5% by weight of CaCl.sub.2, 30% by weight or less (excluding 0%) of CO(NH.sub.2).sub.2 and 30-52.5% by weight of H.sub.2 O. More preferably, the material is of the composition having CaCl.sub.2.6H.sub.2 O and CaCl.sub.2.4CO(NH.sub.2).sub.2.2H.sub.2 O as its two end components and contains 25% by weight or less (excluding 0%) of CO(NH.sub.2).sub.2 based on the total amount of CaCl.sub.2, CO(NH.sub.2).sub.2 and H.sub.2 O.
When a composition comprising CaCl.sub.2, CO(NH.sub.2).sub.2 and H.sub.2 O is employed as a heat accumulating material, an appropriate nucleating agent is preferably used for the purpose of decreasing supercooling. It was found that BaFeO.sub.3-x (0.ltoreq.x.ltoreq.0.53) acts as said nucleating agent for said composition. Since BaFeO.sub.3-x (0.ltoreq.x.ltoreq.0.53) is a substance of limited solubility in water, it exhibits a nucleating effect in an amount of about 0.01 parts by weight based on 100 parts by weight of said composition. Of course it may also be used in larger amounts.
In use of the heat accumulating material of this invention as a heat accumulator for air conditioners and the like, said material is usually used in an amount of about 100 to 1000 kg. In this case, even if the composition comprising CaCl.sub.2, CO(NH.sub.2).sub.2 and H.sub.2 O is fused down, the whole system would not become a uniform composition, and a solution with a low CaCl.sub.2 concentration would exist in the upper portion while the precipitate of the nucleating agent and a high concentration solution of CaCl.sub.2 and the nucleating agent would stay in the lower portion. Therefore, even if the amount of the nucleating agent added in the composition is far less than the minimum amount which would be required when the whole system forms a uniform solution, said nucleating agent would not dissolve completely, and would retain and perform its due action. The minimum amount of the nucleating agent necessary for forming the crystal nuclei, that is, the lower limit of the amount to be mixed, depends, accordingly, on the amount and constitution of the composition employed as well as the size and form of the container which holds the accumulating material. Thus, the amount of the nucleating agent to be actually used needs to be chosen according to the conditions of use.
However, addition of the nucleating agent in a too great amount leads to a substantial reduction of heat accumulating capacity of the heat accumulating material as a whole. For practical use, therefore, it is desirable that the nucleating agent is blended in an amount not exceeding 40 parts by weight to 100 parts by weight of the composition comprising CaCl.sub.2, CO(NH.sub.2).sub.2 and H.sub.2 O.
The BeFeO.sub.3-x used as the nucleating agent was obtained by mixing BaCO.sub.3 or Ba(NO.sub.3).sub.2 with Fe.sub.2 O.sub.3 in a molar ratio of 1:1 and then burning the mixture in an oxygen gas atmosphere. The value of x was determined by chemical analysis.
This invention is further illustrated with reference to Example. The compositions of samples used in Example are shown in Table 5.
TABLE 5______________________________________ Nucleating agentSample Composition (% by weight) AmountNo. CaCl.sub.2 CO(NH).sub.2).sub.2 H.sub.2 O BaFeO.sub.3-x added (g)______________________________________51 50.3 1.1 48.6 BaFeO.sub.2.47 0.0152 50.3 1.1 48.6 BaFeO.sub.2.74 0.0153 50.3 1.1 48.6 BaFeO.sub.3.00 0.0154 50.3 1.1 48.6 BaFeO.sub.2.74 1.055 50.3 1.1 48.6 BaFeO.sub.2.74 40.056 50.5 0.4 49.1 BaFeO.sub.2.74 1.057 49.9 2.2 47.9 BaFeO.sub.2.74 1.058 48.8 5.3 45.9 BaFeO.sub.2.74 1.059 46.3 12.4 41.3 BaFeO.sub.2.74 1.060 45.2 15.5 39.3 BaFeO.sub.2.74 1.0______________________________________
The amount added of the nucleating agent indicated in Table 5 is based on 100 g of the composition comprising CaCl.sub.2, CO(NH.sub.2).sub.2 and H.sub.2 O.
Eight hundred grams of each of Samples 41 to 50 was placed respectively in a cylindrical vessel measuring 100 mm in inner diameter and 100 mm in height, and the vessel was tightly closed by a plug having a thermocouple insert tube. The vessel was then subjected to repeated heating and cooling between 0.degree. C. and 35.degree. C. In every case, the supercooling broke in a temperature range 2.degree. C. to 4.degree. C. below the solidification temperature, no deposition of CaCl.sub.2.4H.sub.2 O was observed, and fusion and solidification could be repeated in a stable state. When a sample of CaCl.sub.2.6H.sub.2 O to which a small amount of BaFeO.sub.2.74 had been added was subjected to repeated heating and cooling under the same conditions, though the supercooling was broken satisfactorily, CaCl.sub.2.4H.sub.2 O separated out and the latent heat of the sample decreased gradually.
FIG. 2 shows the changes of the degree of supercooling (difference between the solidification temperature and the temperature at which supercooling is broken) observed when Sample 54 was subjected to 1000 consecutive repeated heating and cooling cycles.
All of these samples had a latent heat of 25 cal/g or more and had a sufficient heat accumulating capacity for use as a heat accumulating material.
From the foregoing, it was confirmed that the heat accumulating material of this Example has a stable heat absorbing and heat releasing property and no problem is encountered even in continuous use.
As described above, the heat accumulating material of this invention comprises three components of CaCl.sub.2, CO(NH.sub.2).sub.2 and H.sub.2 O or comprises these as its principal ingredients, the heat accumulating and heat releasing temperature of said material can be controlled by varying the proportion of these three components, and moreover, supercooling of said material can be decreased by employing a nucleating agent such as BaFeO.sub.3-x (0.ltoreq.x.ltoreq.0.53), and the material has a very stable heat absorbing and heat releasing property as well as a high heat accumulating capacity.
It is needless to say that, in the present invention, other fusing point depresser may be jointly used, other nucleating agent may be used, a thickening agent for preventing sedimentation or aggregation of the nucleating agent may be used, and other additives may be optionally incorporated. The heat accumulating material of this invention can be used not only for a heat accumulator of an air conditioner for room cooling and heating purpose, but for all fields of applications utilizing heat accumulation.

Number	Date	Country
55-149373	Nov 1980	JPX
7801037	Sep 1979	SEX

Heat accumulating material

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Malec et al., "Heat of Solution of Urea in Water and Aqueous Solutions of Calcium Chloride . . . ", Rocz. Chem., 1971, 45 (9), 1369-1375.
Kuemmel et al., "Osmotic and Activity Coefficients in . . . Water-Calcium Chloride-Urea at 298.15K," Fluid Phase Equilib., 1978, 2(3), 215-223.