A MOLTEN SALT COMPOSITION FOR HIGH TEMPERATURE THERMAL ENERGY STORAGE FIELD OF INVENTION

The present invention relates to a novel thermal storage material for use in thermal energy storage systems and process of preparation thereof. More particularly, the present invention provides a ternary salt composite for storage/transfer of thermal energy particularly as a sensible heat energy having a melting point in the range of 130 °C - 147 °C and thermal stability upto 700 °C. The present invention provides a composite for thermal energy storage which works on wider temperature range.

BACKGROUND OF THE INVENTION

Concentrating solar power (CSP) systems integrated with a thermal energy storage (TES) is capable of reducing the demand of conventional energy sources by turning the sun into a 24X7 energy source. It offers a realistic solution that can meet the global need for reliable, emissions-free electric power that is available around the clock and is a viable alternative to base load coal, nuclear or natural gas-based electricity generation facilities. Thermal energy storage (TES) works on utilization of storage and release of thermal energy using specific heat storage materials to drive a power cycle for the generation of electricity. One of the advantages of concentrating solar power (CSP) with a thermal energy storage is that, it made possible to buffer the power generating cycle of sunny, clear days and so that a solar power plant is enabled to supply electrical energy at night time and during bad weather as well.

Hence, the thermal energy storage (TES) can be defined as the temporary storage of thermal energy at high or low temperatures. Thermal storage enables solar thermal power plants to operate just like a conventional fossil fuel or nuclear power plant, reliably generating electricity when it is needed the most - but without the associated harmful emissions and without any fuel cost. Three modes of thermal energy storage include, sensible heat storage (SHS), latent heat storage (LHS), and bond energy storage (BES). The specific application for which a thermal storage system (TES) is to be used determines the storage method to be adopted. The sensible heat storage (SHS) refers to the energy systems that store thermal energy without phase change. The SHS occurs by adding heat to the storage medium and increasing its temperature. Heat is continuously added from a heat source to the liquid or solid storage medium. On the other hand, latent heat storage works on absorption or release of heat when phase changes from solid to liquid by storing the heat as latent heat of fusion or from liquid to vapor as latent heat of vaporization. Whereas, bond energy storage (BES) works on absorption or release of energy through chemical bond reactions. For storage of thermal energy in bond energy, one prefers reversible chemical reactions.

Sensible heat storage systems are simpler in design than latent heat or bond storage systems. The thermal stratification is important for the SHS. In the case of sensible heat storage systems, energy is stored or extracted by heating or cooling a liquid or a solid, which does not change its phase during this process. A variety of substances have been used in such systems. These include liquids like water, heat transfer oils, sugar alcohols and certain inorganic molten salts, and solid like rocks, pebbles and refractory. In the case of solids, the material is invariably in porous form and heat is stored or extracted by the flow of a gas or a liquid through the pores or voids .

The problems with water and oils is the fact that the maximum operating temperature for these systems are between 100 to 300 °C. This seriously limits the maximum receiver temperature and curbs the maximum efficiency of the power plant.

Molten salt thermal energy storage technology working as sensible heat storage material is the most efficient, reliable and cost-effective way to store solar power at large scale. In prior arts, a series of salts are investigated as candidate for potential application in solar plants for storage as well as transfer of heat absorbed such as alkali nitrates, carbonates, sulphates or phosphates in large range of temperature (200 to 1000°C).

A few molten inorganic salts have been considered for high temperatures (300 °C and above). One is an eutectic mixture of 40 percent NaN02, 7 percent NaNOs and 53 percent KNO2 (by weight) and is available under the trade name of 'Hitec'. Hitec has a low melting point of 145°C and can be used up to a temperature of 425 °C. Above this temperature; decomposition and oxidation begin to take place.

Another molten salt being considered for high temperature storage is sodium hydroxide, which has a melting point of 320 °C and could be used for temperatures up to 800 °C. However, it is highly corrosive and there is difficulty in containing it at higher temperatures.

US 2004/0118229 Al discloses a solar power system capable of storing heat energy and converting sun light to electrical power; the solar power includes a solar collection system which gathers and transmits concentrated solar energy on to a concentrator. A fluid extracts the heat and is transported to a heat conversion system consisting of plurality of heat exchanger tubes. The absorptive material may include, for example, castable refractory brick, graphitic absorbers or heat pipe absorbers. The heat exchanger tubes are of radiant absorber to liquid type and in this embodiment, are preferably constructed of Inconel alloy, and may be configured as straight or coiled tubes. Heat exchanger tubes receive thermal energy from the absorption of concentrated sunlight and transfer the energy into a fluid. The fluid is retained and flows within the heat exchanger tubes. in this embodiment, the fluid is a mixture of sodium and potassium nitrate.

U. S. Patent no. 4, 119, 556 describes a thermal energy-storage material comprising of a ternary salt mixture of sodium chloride, potassium chloride, and magnesium chloride in a NaCl:KCl:MgCh in a weight ratio range of 22.5 to 26.5 :18:5 to 22.5:53.0 to 57.0 having melting point in the range of 385 to 393 °C. But the melting point of said eutectic mixture is above 380 °C and hence operating temperature is limited from 380 °C and above. As regards, in the field of high-temperature solar thermal power, generally the material for heat storage as well as heat transfer should have following properties;

• It must be inexpensive and easy to handle, non-toxic, non-combustible, and widely available. · It must have high thermal conductivity, high specific heat, and high thermal stability.

• It must have low viscosity, low melting point and moderate density for maximum heat transfer when used in CSP.

Hence, the inventors of present invention have worked to provide a novel eutectic inorganic salt composite in order to be able to optimize sensible heat storage by improving the physical properties of molten salts for the respective utility. It is necessary to have available storage materials which not only have the correct melting temperature but also meet numerous other criteria as mentioned above. These criteria include maximum heat capacity, thermal stability, chemical and physical stability, moderate viscosity and high fluidity for pumping, high heat conductivity, recyclability, and a low price.

Accordingly, the present invention provides a novel molten inorganic salt composite directed at improving the melting temperature range, cost and higher thermal stability upto 700 °C, in order to compete more effectively with available molten salts for use in concentrated solar power plants.

OBJECTIVES OF THE INVENTION:

• It is an objective of the present invention to provide a novel molten inorganic salt composition for use in thermal energy storage system. · One more objective of the present invention to provide a process of preparation of a novel molten inorganic salt composition for use in thermal energy storage system. • Yet one more objective of the present invention to provide a novel molten inorganic salt composition for use in thermal energy storage system which has a low melting point and high thermal stability.

• Another more objective of the present invention to provide a cost effective and efficient molten inorganic salt composition for use in thermal energy storage system.

SUMMARY OF THE INVENTION:

The present invention relates to a novel thermal storage material for use in thermal energy storage systems and process of preparation thereof. More particularly, the present invention provides a ternary salt composite for storage and transfer of thermal energy particularly as sensible heat energy having a melting point in the range of 130 °C - 147 °C and thermal stability upto 700 °C. The present invention provides a composite for thermal energy storage which works on wider temperature range.

Accordingly, the said thermal energy storage composition comprising a ternary eutectic mixture of salts selected from copper chloride (CuCl), potassium chloride (KC1), sodium chloride (NaCl), characterized in that, the said composite has a melting point between 130 °C - 147 °C and Thermal stability is upto 650 °C to 700 °C.

Further, the present invention provides a novel eutectic-based composition for storage and transfer of sensible thermal energy comprising: copper chloride, sodium chloride, potassium chloride, wherein the molar ratio of copper chloride: sodium chloride: potassium chloride is between 40:40:20 to 65 :25: 10. More preferably the molar ratio of copper chloride: sodium Chloride: potassium chloride is selected from 56.8:31.4: 11.8. Further wherein the present invention provides a novel eutectic-based composition for storage and transfer of sensible thermal energy comprising: copper chloride, sodium chloride, potassium chloride and additionally comprises of 0.1 % to 15 % weight percent of additives of total weight of composition. The novel eutectic-based composition for storage and transfer of sensible thermal energy is inexpensive and easy to handle, non-toxic, non-combustible, widely available and has good thermophysical properties. Wherein, the therm ophysical properties for effective thermal energy storage and transfer includes high thermal conductivity, specific heat and thermal stability, whereas low viscosity, melting point and density.

Accordingly, the present invention provides an efficient thermal storage/transfer composition which is having high thermal conductivity, high specific heat, and high thermal stability within the operating temperature range i.e. between 138 °C to 700 °C. Whereas, the said composition is having low viscosity, low melting point and moderate density within said temperature range. Hence, the ternary composition provided by present invention is suitable for maximum heat transfer in Concentrating solar power (CSP) systems for storage and transfer of solar energy.

BRIEF DESCRIPTION OF DRAWINGS

It is to be noted, however, that the drawing illustrates only typical embodiment of the present invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

Figure No. 1 : Illustrate the DSC graph for ternary salt composition prepared as per example 1.

Figure No. 2: Illustrate the TGA graph for ternary salt composition prepared as per example 1.

Figure No. 3: Illustrate the DSC graph for Ternary eutectic salt mixtures with 7 % of CaCh additive prepared as per example 4. Figure No. 4: Illustrate the TGA graph for Ternary eutectic salt mixtures with 7 % of CaCl2 additive prepared as per example 4.

Figure No. 5: Illustrate the DSC graph for Ternary eutectic salt mixtures with 5 % of ZnCb additive prepared as per example 5.

Figure No. 6: Illustrate the TGA graph for Ternary eutectic salt mixtures with 5 % of Ζη(¾ additive prepared as per example 5.

Figure No. 7: Illustrate the Viscosity Profile of ternary salt composition of a) copper chloride, potassium chloride and sodium chloride alone and b) ternary salt composition with 7% CaCh and c) ternary salt composition with 5% ZnCl 2 prepared as per example 6.

Figure No. 8: Illustrate the Thermal conductivity Profile of ternary salt composition of a) copper chloride, potassium chloride and sodium chloride alone and b) ternary salt composition with 7% CaCh and c) ternary salt composition with 5% ZnCh prepared as per example 7.

Figure No. 9: Illustrate the Specific heat capacity of ternary salt composition of b) copper chloride, potassium chloride and sodium chloride alone and a) ternary salt composition with 5%ZnChc) ternary salt composition with 7% CaCh and prepared as per example 8.

Figure No. 10: Illustrate the Density Profile of ternary salt composition of a) copper chloride, potassium chloride and sodium chloride alone and b) ternary salt composition with 7% CaCh and c) ternary salt composition with 5% ZnCl ₂ prepared as per example 9.

DETAILED DESCRIPTION OF THE INVENTION:

While the making and using of various embodiments of the present invention are discussed in detail below, it should be appreciated that the present invention provides many applicable inventive concepts that can be embodied in a wide variety of specific contexts. The specific embodiments discussed herein are merely illustrative of specific ways to make and use the invention and do not delimit the scope of the invention.

The terms mixture and composition are used as equivalents in this description.

The terms fluid, material and medium are used as equivalents in this description. The terms heat transfer fluid and heat storage material are used as equivalents in this description.

As used herein, the term "eutectic" is meant to refer to any material or composition which may be provided in a solid form and controllably heated to effectively liquefy. The present invention relates to a molten salt composition comprising of a ternary salt mixture and process of preparation thereof. More specifically, the present invention relates to a molten salt composition comprising of a ternary salt mixture and at least one additive salt.

Thus, according to one of its aspects, the subject matter of the present invention is a thermal energy storage composition comprising a ternary eutectic mixture of salts selected from copper chloride (CuCl), potassium chloride (KC1), sodium chloride (NaCl), characterized in that the said composite has a melting point between 130 °C -147 °C and Thermal stability is upto 700 °C, more preferably at least upto 650 °C. Thus, according to second of its aspects, a subject matter of the present invention is a thermal energy storage composition comprising a ternary eutectic mixture of salts selected from copper chloride (CuCl), potassium chloride (KC1), sodium chloride (NaCl) and at least one additive salt, characterized in that the said composite has a melting point between 130 °C - 147 °C and Thermal stability is upto 700 °C. According to a specific embodiment of the invention, the present invention provides a molten salt composition for storage of thermal heat consisting of ternary salt mixture, wherein 40 to 60 mol% of copper chloride, 25 to 40 mol% of potassium chloride and 10 to 20 mol% of sodium chloride. In addition to ternary salt eutectic mixture, the present invention comprising of additive salt in weight ratio from 0.1 to 15% to that of total weight of ternary salt mixture. A low melting point and thermal stability at high temperatures are desirable properties in a Thermal Energy Storage (TES) medium. Traditionally used nitrate salts have relatively low boiling points as compared to chlorides and hence limit the efficiency of the Rankine cycle used to produce steam to generate electricity. The current invention which is a eutectic mixture of CuCl, KCl and NaCl and at least one additive salts can be used over a wider operating temperature range thereby increasing the efficiency of steam generation. The thermal behaviour of the salt was studied using simultaneous differential scanning calorimetery and thermogravimetric analysis under a nitrogen atmosphere. The melting point was found to be 144 °C and the mixture was found to be stable upto 650 °C -700 °C at which the mass loss is 1-2%. The enthalpy of fusion is about 57.52 kJ/kg.

In accordance to one more embodiment, the present invention relates to a eutectic mixture of CuCl, KCl and NaCl as a thermal storage material, that optionally comprising of one or more additional salts as an additive.

The additives are selected from the calcium chloride (CaCl), zinc chloride (ZnCl). Wherein the concentration of additive salt is more preferably from the 2 % to 15% of total weight of a ternary salt mixture.

In accordance to second embodiment, the present invention provides a process for preparation of a ternary eutectic mixture of salts selected from copper chloride (CuCl), potassium chloride (KCl), sodium chloride (NaCl), characterized in that the said composite has a melting point below 140 °C and thermal stability is upto 650 °C. The process comprising of following steps:

Step a) Weighing and mixing of salts composition Step b) Melting of composition in furnace at 250 °C.

Step c) Meting of mixture under nitrogen atmosphere

Step d) Cooling at room temperature.

Step e) Crushing to form uniform particle size powder The present invention provides a novel molten salt for the thermal storage material in TES system. During daytime, salt is heated to elevated temperatures with the solar energy. The molten salt at elevated temperatures is stored in large insulated containers. At night time, the energy from the molten salt is used to directly or indirectly heat high pressure water to steam. The high-pressure steam drives a steam turbine generator unit producing electricity.

The following example is not intended to limit embodiments herein in any way and is merely presented to illustrate the formation of a composite phase change material described above. The composition provided in examples are illustrated in weight percent by considering respective mole percent of an individual compound.

EXAMPLES:

Example 1: Process of preparation of Ternary eutectic composition:

6.5 g copper chloride, 2.7 g potassium chloride and 0.8 g sodium chloride were carefully weighed and added into a quartz crucible to obtain 10 g of the ternary base mixture. Crucible was then placed in a circular coil furnace with a glass window at the top which allows for observation. The temperature of the furnace was ramped up and the mixture was observed through the window. Once the mixture was observed to melt (at temperature 200-220 °C) and become liquid, the temperature was further allowed to increase about 60 to 70 ^C C to ensure a homogenous mixture. The furnace was then turned off and the liquid mixture was allowed to cool to a solid. This heating, melting and recrystallization cycle was repeated once more. The crucible was removed from the furnace and the solid mass was scraped out of the crucible and was ground to a fine powder using a mortar and pestle. The resulting ternary salt composition then subjected to thermal analysis by using the instrument NETZSCH STA 449 F3 (Germany) to determine the melting point and the thermal stability of the mixture in presence of inert (nitrogen) atmosphere. (Mole percent of final product (CuCl:KCl:NaCl is: 56.8:31.4: 11.8)

Figure 1 shows the DSC analysis of CuCl:KCl:NaCl mixture. From DSC curve it was observed that melting point of mixture was 144°C and heat of fusion was 62.81 kJ/kg.

Figure 2 shows the TGA analysis of CuCl:KCl:NaCl mixture. It shows that the composition is stable around 658°C and 3-4 % weight loss was observed when temperature raised upto 700°C.

Example 2: Different Ternary eutectic composition: copper chloride, potassium chloride and sodium chloride were carefully weighed and added into a quartz crucible to obtain 10 g of the ternary base mixture. Further procedure for preparation of ternary eutectic mixture was same as described in Example 1. The resulting ternary salt compositions then subjected to thermal analysis by using the instrument NETZSCH STA 449 F3 (Germany) to measure the DSC and TGA graphs for determination of the melting point and the thermal stability of the mixture in presence of inert (nitrogen) atmosphere. Results are depicted in Table no. 1. Table No. 1: Comparative study of different Composition of ternary eutectic mixtures

From the Table 1, it was concluded that the composition 1 having CuCl (56.8%), KCl (31.4%) and NaCl (11.8%) has lower melting point ( 144 °C) and higher thermal stability (6 8°C).

Example 3: Effects of different additives on ternary eutectic mixtures: The ternary eutectic mixture from the above examples, with composition CuCl (56.8 mole %), KCl (31.4 mole %) and NaCl (11.8 mole %) was selected for the further study. The effect of additives on the eutectic mixture was studied using calcium chloride (CaCh) and zinc chloride (ZnCb). The concentration of additive salts was varied from 2 % to 15% of total weight of a ternary salt mixture. Example 4: Preparation and study of ternary eutectic mixture with different concentrations of additive Calcium chloride (CaCh): The ternary eutectic mixture was prepared as described in Example 1. The different concentrations of CaCh i e. 2, 5, 7, 10 and 15% were added to ternary salt mixture. A. Ternary eutectic salt mixtures with 7 % of CaCh additive: 10 g of ternary eutectic mixture [CuCl:KCl:NaCl: 56.8:31.4: 11.8] and 0.7 g of CaCl ₂ i.e 7 % of total weight of ternary eutectic mixture were added into a quartz crucible. Crucible was then placed in a furnace and heated up to 250-280 ^c C. When the mixture became liquid, the temperature was further allowed to increase about 60 to 70°C to ensure a homogenous mixture. The furnace was then turned off and the liquid mixture was allowed to cool to a solid. This heating, melting and recrystallization cycle was repeated once more. The crucible was removed from the furnace and the solid mass was scraped out of the crucible and was ground to a fine powder using a mortar and pestle. The resulting ternary salt composition then subjected to thermal analysis by using the instrument NETZSCH STA 449 F3 (Germany) to determine the melting point and the thermal stability of the mixture in presence of inert (nitrogen) atmosphere.

Figure No. 3 shows the DSC analysis of mixture with 7 % of CaCh additive. It was observed that from the DSC curve that melting point of mixture was 138.3 °C and heat of fusion was 58.94 kJ kg.

Figure No. 4 shows the TGA analysis of mixture with 7 % of CaCh additive. It shows that the composition was stable around 691 °C and 2-3 % weight loss was observed up to 700 °C.

Table No. 2: Comparative study at different concentrations of additive CaCh in ternary eutectic mixture (CuCl- Cl-NaCl)

Table no. 2 provides the melting point, decomposition temperature, heat of fusion and weight % loss at different concentrations of additive CaCh in ternary eutectic mixture. As the concentration of additive CaCh increases in the mixture, the moisture content also increases and thermal stability decreases. It can be concluded that additive concentration range 5-7 % have the lowest melting point and higher thermal stability.

Example: 5-Preparation and study of additive Zinc chloride (Z11CI2) at different concentrations on ternary eutectic mixture

The ternary eutectic mixture was prepared as described in Example 1. The different concentrations of ZnCh i.e. 2, 5, 7, 10 and 15 % (% of total wt. of Mixture) were added to ternary salt mixture [CuCl:KCl:NaCl: 56.8:31.4: 11.8]. Further procedure for preparation of ternary eutectic mixture with different concentration of additive (ZnCh) is same as described in Example 4.

Figure No. 5 shows the DSC analysis of mixture with 5 % of ZnCh additive. It was observed that from the DSC curve that melting point of mixture was 139.2 °C and heat of fusion was 44.45 kJ/kg.

Figure No. 6 shows the TGA analysis of mixture with 5 % of ZnCh additive. It shows that the composition was stable around 686 °C and 2-3 % weight loss was observed up to 700 °C.

Table No. 3: Comparative study at different concentrations of additive ZnCh in ternary eutectic mixture (CuCl-KCl -NaCl)

Wherein, *a Melting point of curve 1 *b Melting point of curve 2 Table 3 provides the melting point, decomposition temperature, heat of fusion and % weight loss at different concentrations of additive ZnCb in ternary eutectic mixture. As the concentration of Additive ZnCb was increased, at 10% and 15% no proper eutectic mixture was formed. Thus, two DSC curves was observed. Curve 1 was of ternary salt mixture and curve 2 may be ZnCb alone. It can be concluded that additive concentration range 2-5 % have the lowest melting point and higher thermal stability.

Example 6: Study of viscosity of ternary eutectic salt mixture with and without additives

A. Viscosity of ternary eutectic salt mixture without additive: 6.5 g copper chloride, 2.7 g potassium chloride and 0.8 g sodium chloride were carefully weighed and added into a quartz crucible to obtain 10 g of the ternary base mixture. Further procedure for preparation of ternary eutectic mixture was same as described in Example 1.

Figure No. 7 a) shows the viscosity analysis of CuCl (56.8%)-NaCl (31.4%)-KC1 (11.8%) without additive. The viscosity of the eutectic mixture without additive decreased from 16.5 to 3.99 Cp as temperature was increased from 200 to 700 °C.

B. Viscosity of ternary eutectic salt mixture with additive: The ternary eutectic mixtures with additives (CaCh and ZnCb) were prepared according to Example 3,

4 and 5 respectively. These resulting ternary salt composition were then subjected to viscosity analysis by using the instrument Anton Paar Rheometer MCR102 to determine the viscosity of sample at temperature from 200-700 °C under nitrogen atmosphere. Figure No. 7 b) shows the viscosity analysis of CuCl (56.8%)-NaCl (31.4%)-KC1 (11.8%) mixture with 7% CaCb. The viscosity of the eutectic mixture decreased from 17.5 to 3.3 Cp as temperature was increased from 200 to 700 °C.

Figure No. 7 c) shows the viscosity analysis of CuCl (56.8%)-NaCl (31.4%)-KC1 (11.8%) mixture with 5% ZnCb. The viscosity of the eutectic mixture with 5% ZnC . decreased from 15 to 2.88 Cp as temperature was increased from 200 to 700 °C.

Example 7. Study of thermal conductivity of eutectic ternary mixture without and with Additives:

The ternary eutectic composition comprising copper chloride, potassium chloride and sodium chloride with and without additives (7% CaCh and 5% ZnCh) were prepared according to Example 3, 4 and 5 respectively. These resulting ternary salt composition were then subjected to thermal conductivity analysis by using the instrument Laser Flash Analyser NETZSCH LFA 457 to determine the thermal conductivity of sample at temperature from 200-660 °C under nitrogen atmosphere. Figure No. 8 a) shows the thermal conductivity analysis of CuCl (65%)-NaCl (27%)-KCl (8%) without additive. The thermal conductivity of the eutectic mixture without additive increases from 0.513 to 0.881 W/m°C as temperature increases from 150 to 660 °C. Figure No. 8 b) shows the thermal conductivity analysis of CuCl (56.8%)-NaCl (31.4%)-KC1 ( 11.8%) mixture with 7% CaCh. The thermal conductivity of the eutectic mixture with 7% CaCh increases from 0.456 to 0.855 W/m°C as temperature was increased from 150 to 660 °C.

Figure No. 8 c) shows the thermal conductivity analysis of CuCl (56.8%)-NaCl (31.4%)-KC1 ( 11.8%) mixture with 5% ZnCl ₂ . The thermal conductivity of the eutectic mixture with 5% ZnCh increases from 0.554 to 0.944 W/m°C as temperature was increased from 150 to 660 °C. Table No. 4: Viscosity and Thermal conductivity of ternary salt mixture with and without additives

Table no. 4 provides the viscosity and thermal conductivity data of ternary eutectic mixture with and without additives. From table 4 it was concluded that ternary eutectic mixture with 5 % ZnCl ₂ showed lowest viscosity was 2.88 Cp and higher thermal conductivity was 0.944 W/m*°C.

Example 8: Study of specific heat capacity of ternary eutectic salt mixture with and without additives: The eutectic ternary mixture of CuCl (65%)-KCl (27%)- NaCl (8%) with the additives of 7% CaCl ₂ and 5% ZnCl ₂ was prepared and considered for the analysis of viscosity measurement. Specific heat capacity of the sample was measured by STA 449 F3 differential scanning calorimeter (DSC-TGA, NETZSCH, Germany) both in solid state and liquid state with sapphire as reference standard material. The empty crucible, the same crucible with sapphire and the same crucible with sample (5-15 mg) were successively heated from RT to 700°C with a heating rate of 20°C/min. Initially temperature was allow to increase from RT to 40°C with minimum heating rate (5°C/min.). After this temperature was increased to 700°C (20°C/min) followed by 10 min. hold on. The measurements were all under the protection of nitrogen atmosphere and the flow rate of the gas was maintained at 50 ml/min. Figure 9 a) shows the specific capacity analysis of CuCl (65%)-NaCl (27%)-KCl (8%) ternary eutectic mixture without any additives, b) with 5% ZnCb additive and c) with 7% CaCb additive. It was observed that the specific heat capacity of mixture with additives was found similar to specific heat capacity for said ternary eutectic mixture without additives within temperature range 200-700 °C and its average value of specific heat capacity was 0.8 J/(g°C). (Refer: Table no.5)

Example 9: Study of Density of ternary salt eutectic mixture with and without additives: The eutectic ternary mixture of CuCl-KCl-NaCl with the additives of 7% CaCh and 5% ZnCb was prepared and considered for the analysis of density measurement. Density of the sample was measured by optical dilatometer (Lenseis, Germany) by varying the temperature from 200-650°C.

Figure 10 a) shows the density analysis of CuCl (56.8%)-NaCl (31.4%)-KC1 (11.8%) without additive. It was observed that the density of the eutectic mixture decreases from 2.942 to 2.5 g/cm ³ as the temperature increases from 200 to 650 °C. The density of the eutectic mixture decreases from 3.11 to 2.623 g/cm ³ with 7% CaCb (Figure 10 b) and 3.234 to 2.699 g/cm ³ with 5% ZnCh (Figure 10 c) as the temperature was increases from 200 to 650 °C.

Table No. 5: Heat capacity and density of ternary salt mixture with and without additives

Above Table provides the heat capacity and density data of ternary eutectic mixture with and without additives. From Table No. 5, it was concluded that the heat capacity and density of ternary eutectic mixture with and without additives was found almost similar. (7 % CaCh showed highest heat capacity was 0.85 J/ (g°C) and the density was found similar for ternary salt mixture with and without additives.)