Form-Stabilized Eutectoid Salt Hydrate PCMs for 8–16°C Storage
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Solution Overview
Problem
Existing salt hydrate phase change materials (PCMs) suffer from incongruent melting, phase separation, and reduced thermal storage capacity due to the use of thickeners like attapulgite clay and sodium polyacrylate, which fail to maintain stability and homogeneity over multiple cycles, especially when used in cooling systems requiring higher chilled water temperatures.
Innovation Solution
A combination of attapulgite clay and sodium polyacrylate is used as a dispersant and stabilizing agent in a specific ratio to create a form-stabilized, homogeneous salt hydrate PCM, preventing incongruent melting and maintaining thermal storage capacity over thousands of cycles, with eutectoid compositions melting and freezing between 8°C and 16°C.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If attapulgite clay is used as a thickener for salt hydrate PCM, then the PCM can be stabilized to some extent, but the vertical depth cannot exceed 6.35 cm without phase separation caused by incongruent melting
Solution Approach 1:
The patent combines attapulgite clay with sodium polyacrylate to create a composite thickening system. This composite approach leverages the dispersing and thickening capabilities of attapulgite clay while adding the form-stabilizing and suspending properties of sodium polyacrylate, enabling the PCM to maintain stability at greater vertical depths without phase separation
2Stability of the object's composition
If attapulgite clay is used as a thickener, then dispersion is improved, but undesirable lesser hydrates still form reducing thermal energy storage capacity
Solution Approach 1:
Sodium polyacrylate acts as an intermediary agent that works in conjunction with attapulgite clay to prevent the formation of undesirable lesser hydrates. The sodium polyacrylate provides additional stabilization that suppresses the formation of these unwanted hydrate phases, thereby preserving the thermal energy storage capacity while maintaining good dispersion
3Stability of the object's composition
If sodium polyacrylate is used alone as a thickener, then a form-stabilized lattice matrix is provided, but anhydrous salts clump together at the bottom of mixing vat
Solution Approach 1:
The patent merges attapulgite clay with sodium polyacrylate in a specific combination. The attapulgite clay provides excellent dispersing properties that prevent salt clumping during mixing, while sodium polyacrylate provides the form-stabilized lattice matrix. Together, they achieve both homogeneity and form stability that neither agent can achieve alone
4Stability of the object's composition
If existing thickeners are used, then some stabilization is achieved, but they fail to maintain stability and homogeneity over multiple cycles
Solution Approach 1:
The patent applies preliminary action by using the combined attapulgite clay and sodium polyacrylate system to establish a robust, stable structure before the PCM undergoes multiple heating and cooling cycles. This pre-established composite stabilization mechanism prevents phase separation and maintains homogeneity throughout the cycle life, addressing the long-term durability issue that single thickeners fail to resolve
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 combined use of attapulgite clay and sodium polyacrylate ensures a stable, homogeneous PCM that maintains thermal storage capacity and prevents undesirable hydrate crystal growth, suitable for cooling systems with higher chilled water temperatures, reducing energy consumption and system inefficiencies.
Implementation Method 1
the attapulgite clay functions as both a thixotropic dispersant in the mixing process and in concert with SPA in forming a stabilizing lattice matrix
Implementation Method 2
salt hydrate phase change materials (PCMs) have been used in cool storage systems because of their high latent heat of fusion
Implementation Method 3
high latent heat of fusion
Implementation Method 4
Dr. Telkes disclosed attapulgite clay as an effective thickener for use with salt hydrate PCMs
Data Source
AI summary
Eutectoid salt hydrate phase change material compositions for thermal energy storage are disclosed. A congruently melting, form-stabilized, homogenous salt hydrate phase change material includes both attapulgite clay and sodium polyacrylate, where the attapulgite clay functions as both a thixotropic dispersant during the mixing of the salt hydrate, and thereafter in concert with sodium polyacrylate in forming a permanent stabilizing matrix. In addition, in one preferred embodiment, a eutectoid salt hydrate is disclosed which changes phase between 11 degrees C. and 16 degrees C. and whose composition is one mol sodium sulfate decahydrate to 0.5 mols ammonium chloride to 0.22 moles potassium chloride. In a second preferred embodiment, a eutectoid salt hydrate is disclosed that changes phase between 8 degrees C. and 13 degrees C. and whose composition is one mol sodium sulfate decahydrate to 0.65 mols ammonium chloride to 0.22 mols potassium chloride.