Calcium Potassium Nitrate Double Salt for Low-Melting Heat Transfer Fluid
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Solution Overview
Problem
Current nitrate-based heat transfer fluids for solar energy applications have high melting temperatures and decomposition temperatures, making them costly and difficult to handle, and existing solutions require high energy consumption for water evaporation or contain undesirable components like lithium nitrate.
Innovation Solution
A double salt composition of calcium potassium nitrate (Ca(NO3)2 and KNO3) is used to create a nitrate-based heat transfer fluid with a low melting point and high decomposition temperature, manufactured as a particulate product with controlled heating, avoiding water evaporation and using a specific weight ratio of Ca(NO3)2, NaNO3, and KNO3 to achieve a eutectic melt with improved thermal properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a binary salt mixture (60% NaNO3 and 40% KNO3) is used as heat transfer fluid, then thermal stability is improved, but melting temperature remains high (222°C)
Solution Approach 1:
The invention changes the compositional parameters of the salt mixture by adding calcium nitrate to create a ternary system (NaNO3-KNO3-Ca(NO3)2). This parameter change in composition transforms the phase diagram, creating a new eutectic point with lower melting temperature (131°C) while preserving thermal stability through the nitrate-based chemistry of all components.
Solution Approach 2:
The invention uses a composite salt mixture combining three different nitrate salts (NaNO3, KNO3, and Ca(NO3)2) in specific proportions (40-60 wt% NaNO3, 20-40 wt% KNO3, and 10-30 wt% Ca(NO3)2). This composite material leverages the eutectic formation between multiple components to achieve both low melting point and high thermal stability simultaneously.
2Temperature
If calcium nitrate is added to lower melting temperature, then melting point is reduced, but decomposition temperature decreases
Solution Approach 1:
The invention optimizes the concentration parameter of calcium nitrate within a specific range (10-30 wt%). This parameter optimization balances two competing effects: sufficient Ca(NO3)2 to lower the eutectic melting point to 131°C, but not so much that it significantly reduces the decomposition temperature. The balanced composition achieves both low melting point and adequate thermal stability.
Solution Approach 2:
The invention creates local compositional optimization by positioning the mixture at a specific point in the ternary phase diagram where the eutectic melting point is minimized while maintaining acceptable decomposition characteristics. This local compositional quality ensures that the beneficial low-temperature property is achieved without excessively compromising high-temperature stability.
3Temperature
If aqueous solution of ternary nitrate salt is used, then low melting temperature is achieved, but high energy consumption is required for water evaporation
Solution Approach 1:
The invention extracts and eliminates water from the salt mixture, transitioning from an aqueous solution to a dry particulate composite material. This extraction removes the need for energy-intensive water evaporation steps while preserving the low melting temperature property achieved through the ternary eutectic composition of the anhydrous salts.
Solution Approach 2:
The invention performs preliminary mixing of the three nitrate salts in their dry particulate forms before any thermal processing. This preliminary action establishes the correct eutectic composition in advance, ensuring that when the mixture is heated, it melts at the low eutectic temperature (131°C) without requiring prior water removal, thereby eliminating energy-wasting evaporation steps.
4Reliability
If lithium nitrate is used to adjust composition, then thermal properties are improved, but cost increases and handling difficulty increases
Solution Approach 1:
The invention replaces expensive lithium nitrate with cheaper, readily available common nitrate salts (NaNO3, KNO3, and Ca(NO3)2). These conventional salts are inexpensive, easily handled in particulate form, and widely available from commercial suppliers, thereby improving both cost-effectiveness and ease of manufacture while maintaining desirable thermal properties through eutectic composition design.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves a melting temperature of about 131°C and a decomposition temperature of up to 569°C, reducing energy costs and extending system component lifetime, while being easy to produce and handle, with a wide operating temperature range and reduced corrosiveness.
Implementation Method 1
A double salt composition of calcium potassium nitrate (Ca(NO3)2 and KNO3) is used to create a nitrate-based heat transfer fluid with a low melting point and high decomposition temperature, manufactured as a particulate product with controlled heating, avoiding water evaporation and using a specific weight ratio of Ca(NO3)2, NaNO3, and KNO3 to achieve a eutectic melt with improved thermal properties.
Data Source
AI summary
The present invention relates to the use of a double salt of Ca(NO3)2 and KNO3 for the manufacture of a melt, in particular a nitrate-based heat transfer fluid (HTF) and/or thermal energy storage fluid, for example in solar energy applications, such as in solar electrical power plant systems using a parabolic through, a central receiver or a linear Fresnel, which have both a low melting temperature and a high decomposition temperature, as well as to methods for the manufacture thereof. Using said double salt, a melt could be manufactured comprising at least NaNO3, KNO3 and Ca(NO3)2, preferably, an eutectic ternary melt comprising Ca(NO3)2, NaNO3 and KNO3 in a weight ratio of about 42:15:43 with an operating temperature of about 131° C. to about 560° C.