Core-Shell Phase Change Material Fiber Encapsulation
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Solution Overview
Problem
Current methods for encapsulating salt hydrate phase change materials face challenges such as leakage and low volumetric energy density, with no reliable solution existing for salt hydrates, particularly due to the high surface area and porosity of materials like expanded graphite.
Innovation Solution
A method involving a co-axial ejector to form core-shell phase change material fibers by simultaneously ejecting a core composition containing salt hydrates and a polymer coating composition onto a collector, without applying voltage, resulting in encapsulated fibers with improved stability and energy density.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If salt hydrates are impregnated in high-surface-area porous materials such as expanded graphite to minimize leakage, then leakage is reduced, but volumetric energy density decreases
Solution Approach 1:
The patent applies microencapsulation by nesting the salt hydrate phase change material inside polymer microcapsules. This nested structure prevents leakage of the salt hydrate while minimizing the volume occupied by encapsulation materials, thereby maintaining high volumetric energy density. The core-shell structure with salt hydrate core and polymer shell directly addresses both requirements.
Solution Approach 2:
The patent uses thin polymer shell films to encapsulate the salt hydrate material. These flexible thin films provide effective leakage prevention while occupying minimal volume, thus preserving the volumetric energy density of the phase change material system.
2Speed
If expanded graphite is used to increase thermal conductivity, then charge/discharge rates improve, but volumetric energy density decreases
Solution Approach 1:
The patent applies local quality by adding thermal conductivity enhancers (such as graphite flakes or carbon nanotubes) only in specific locations or at specific concentrations within the polymer shell or at the core-shell interface, rather than using bulk expanded graphite. This localized approach improves thermal conductivity for faster charge/discharge rates while minimizing the volume occupied by conductivity-enhancing materials, thus preserving volumetric energy density.
3Adaptability or versatility
If conventional solution-based encapsulation methods are used, then organic and inorganic PCMs can be encapsulated, but salt hydrates cannot be encapsulated reliably
Solution Approach 1:
The patent applies parameter changes by modifying the chemical composition and formulation parameters of the polymer shell material to be compatible with salt hydrate chemistry. This includes selecting polymers with appropriate functional groups and adjusting formulation parameters such as crosslinking density and surface chemistry to enable reliable encapsulation of salt hydrates, which have different properties compared to organic PCMs.
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 method effectively encapsulates salt hydrates, reducing leakage and enhancing volumetric energy density, as demonstrated by thermogravimetric analysis showing increased water retention and energy storage capacity compared to unencapsulated controls.
Implementation Method 1
simultaneously ejecting a core composition containing salt hydrates and a polymer coating composition onto a collector
Implementation Method 2
phase change materials (PCMs)... The thermal energy is stored during daytime when temperatures are high and subsequently released during night when temperatures are low
Implementation Method 3
The core composition is surrounded by the coating composition and together ejected onto the collector to form a core-shell phase change material fiber
Data Source
AI summary
A method of encapsulating a phase change material includes providing a co-axial ejector including first and second coaxially-disposed outlets, with the first outlet being inside of and surrounded by the second outlet. A core composition including a phase change material is fed to the first outlet. A coating composition is fed to the second outlet. The core composition and the coating composition are simultaneously ejected from the ejector onto a collector. The core composition is surrounded by the coating composition and together ejected onto the collector to form an encapsulated core-shell phase change material fiber. No voltage is applied to the ejector during ejection, and the method does not include electrospinning. The core-shell fiber has a phase change material core surrounded by a polymer shell and a diameter in the range of 10-10,000 μm. The core constitutes from 30% to 97% by volume of the core-shell fiber.