Graphite Matrix PCM Composite with Surfactant Bridge
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Solution Overview
Problem
Current thermal energy storage systems, particularly phase change materials (PCMs), face challenges such as high cost, low volumetric energy capacity, flammability, excessive supercooling, incongruent melting/phase separation, and low thermal conductivity, limiting their adoption in building and HVAC applications.
Innovation Solution
A composition and method involving a graphite matrix with expanded pores, coated with a surfactant, filled with a mixture of phase change material and nucleating agent, where the surfactant acts as a bridge between the hydrophobic graphite and hydrophilic PCM, enhancing infiltration and preventing supercooling, and a hydrogel may be used to encapsulate the PCM for improved thermal energy storage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If hydrophobic graphite is used as matrix material, then thermal conductivity is improved, but PCM infiltration is reduced
Solution Approach 1:
A surfactant is introduced as an intermediary substance between the hydrophobic graphite matrix and the hydrophilic PCM. The surfactant molecules have hydrophobic tails that interact with the graphite surface and hydrophilic heads that interact with the PCM, creating a compatible interface that enables effective PCM infiltration while maintaining the graphite's thermal conductivity properties
Solution Approach 2:
The invention creates a composite structure consisting of graphite matrix, surfactant coating, and PCM filling. This multi-component composite system combines the thermal conductivity of graphite with the infiltrability provided by surfactant and the energy storage capacity of PCM, resolving the contradiction between these properties
2Use of energy by moving object
If pure PCM is used, then energy storage capacity is improved, but supercooling occurs
Solution Approach 1:
A nucleating agent is introduced as a mediator substance within the PCM mixture. The nucleating agent provides nucleation sites that facilitate crystal formation during phase change, preventing supercooling while maintaining the high energy storage capacity of the pure PCM
Solution Approach 2:
The invention changes the compositional parameters of the PCM by adding a nucleating agent at controlled concentrations (greater than zero wt % and less than about 6.0 wt %). This parameter modification enables the PCM to achieve both high energy storage capacity and reliable phase change behavior without excessive supercooling
3Quantity of substance
If pore volume is increased to maximize PCM storage, then volumetric energy capacity is improved, but structural integrity is reduced
Solution Approach 1:
The invention utilizes expanded graphite as a porous matrix material that naturally provides high porosity (between about 60% and about 95% of total volume) for PCM storage. The porous structure of expanded graphite maintains structural integrity while providing abundant space for PCM infiltration, achieving high volumetric energy capacity without compromising strength
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 higher PCM infiltration, reduced supercooling, and enhanced thermal energy storage capabilities, addressing the limitations of traditional PCM systems by maximizing pore filling and utilizing a nucleating agent to prevent supercooling and phase separation.
Implementation Method 1
a surfactant having a first end and a second end, in which the first end of the surfactant is bonded to the expanded graphite, the second end of the surfactant is bonded to the phase change material
Implementation Method 2
a phase change material comprises a salt hydrate
Implementation Method 3
the nucleating agent is present in the mixture at a concentration between greater than zero weight percent (wt %) and less than about 6.0 wt %
Implementation Method 4
a graphite matrix comprising an expanded graphite having a plurality of pores defining a pore volume
Data Source
AI summary
Among other things, the present disclosure relates to phase change material (PCM) composites composed of an PCM mixed with a nucleating agent contained within the pores of a graphite matrix and/or a hydrogel. The process to create these PCM composites includes coating the surface of graphite with a surfactant, compressing the graphite to form a matrix, then filling the graphite matrix with the PCM.