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US-20260125590-A1 - ENCAPSULATED INORGANIC SALT HYDRATE PHASE CHANGING MATERIAL COMPOSITES FOR THERMAL ENERGY STORAGE USING DOUBLE EMULSION TECHNIQUES

US20260125590A1US 20260125590 A1US20260125590 A1US 20260125590A1US-20260125590-A1

Abstract

The present invention provides micro- to milli-meter sized polymer encapsulated inorganic salt PCM and PCM gel composite spheres for high thermal energy storage, minimal subcooling, high thermal stability, no phase segregation, and high thermal conductivity using double emulsion synthesis techniques. The encapsulated PCM invention addressed the common issues encountered such as subcooling, leakage, instability, and poor thermal energy density. An innovation of the present art is in the constituents which make up the invention being low cost, safe and environmentally friendly. Inclusion of graphene oxide in the encapsulated PCM invention results in enhanced thermal conductivity and up to 33% subcooling reduction. Applications of the invention are in the building envelope, integrating with cooling/heating equipment (HVAC, refrigeration, water cooling) and building materials (insulation, ceiling, roof, flooring, drywall, paint), the aerospace and textile industry, and the transport and storage of biological materials, organs, medicines, chemicals, food and drink, and other temperature-sensitive materials.

Inventors

  • MANOJ KUMAR RAM
  • Brandon Xavier Lorentz
  • Arthur Henriques Pons
  • Henrique Costa Lima D'Avila Trindade

Assignees

  • MANOJ KUMAR RAM
  • Brandon Xavier Lorentz
  • Arthur Henriques Pons
  • Henrique Costa Lima D'Avila Trindade

Dates

Publication Date
20260507
Application Date
20241129

Claims (17)

  1. 1 . The invention described here-in comprises of micrometer to millimeter in diameter encapsulated phase change material (PCM) and PCM gel composite spheres for high thermal energy storage, minimal subcooling, high thermal stability, no phase segregation, and high thermal conductivity using double emulsion synthesis techniques.
  2. 2 . The encapsulated PCM invention in claim 1 is composed of a core material of pure or a mix of inorganic salt and/or inorganic salt hydrate (50-70 wt. %), natural or modified starch and/or cellulose (1-10 wt. %), polyvinyl alcohol (PVA) (1-10 wt. %) and water (15-30 wt. %) with or without added <5.0 wt. % graphene oxide.
  3. 3 . The encapsulated PCM invention in claim 1 is encapsulated with a polymer such as but not limited to polystyrene (PS), polymethylmethacrylate (PMMA), polyethylene, silicon rubber, polypropylene or any combination thereof.
  4. 4 . A surfactant can be used for enhanced dispersion preparation of the core gel composite in claim 2 .
  5. 5 . The core PVA gel composite in claim 2 is synthesized in a container with constant stirring at 80-110° C. for 1-2 hours and subsequent cooling to room temperature.
  6. 6 . Resources of cellulose and/or starch in the gel composite of claim 2 include but are not limited to plant derived cellulose and/or bacterial cellulose, other biologically derived or modified cellulose (methyl cellulose, carboxymethyl cellulose, sodium carboxymethyl cellulose, hydroxypropyl methyl cellulose, ethyl cellulose, ethyl hydroxyethyl cellulose, ethyl methyl cellulose, cellulose acetate, cellulose triacetate, nitrocellulose, cellulose sulfate, etc.), corn starch, starch acetate, oxidized starch, hydroxypropyl starch, etc. may be added prior to gelling or during the cooling stage.
  7. 7 . An embodiment of claim 2 may prepare the PCM gel composite with up to 5 wt. % graphene oxide (GO) for enhanced thermal conductivity, providing a thermal energy storage capsule with up to 33% reduction of subcooling.
  8. 8 . The formation and encapsulation of the PCM or PCM gel composite spheres in claim 2 performed by injecting aliquots of PCM or gel by pump or syringe into an immiscible solvent such as but not limited to dichloromethane, acetone, dimethyl sulfoxide, toluene, and chloroform with a dissolved polymer such as but not limited to PS, PMMA, polyethylene, silicon rubber, polypropylene, any combination thereof (single emulsion).
  9. 9 . In another embodiment of claim 8 , the PCM or PCM gel spheres may be formed and encapsulated via shearing in the immiscible solvent and dissolved polymer using shear forces such as but not limited to stirring or ultrasonication.
  10. 10 . In another embodiment of claim 8 , the PCM or PCM gel may be injected dropwise into a cold immiscible solvent and dissolved polymer bath (−15-0° C.) with or without stirring to form solid gel spheres and perform the encapsulation with sphere size formation relying solely on the droplet size.
  11. 11 . In an embodiment of claim 10 , the PCM or PCM gel may be injected dropwise into a cold immiscible solvent without dissolved polymer, stored in a freezer and later dipped or mixed in a solution of solvent and dissolved polymer to perform the encapsulation.
  12. 12 . In one embodiment of claim 11 , the PCM or PCM gel spheres formed in polymer and solvent may be mixed for 24 to 48 hours for adequate coating thickness and then separated out and dried using air or an inert gas to be made ready for storage or application.
  13. 13 . In another embodiment of claim 8 , the PCM or PCM gel spheres suspended in the polymer and solvent solution are then injected dropwise using a syringe or pump into a second emulsion step (double emulsion) with but not limited to mineral oil, water or ethanol as the continuous phase to leach out solvent, precipitate and harden the polymer over the PCM or PCM gel spheres.
  14. 14 . The encapsulation process claim 13 can be performed two or more times for developing a thick encapsulant shell.
  15. 15 . The encapsulated PCM spheres fabricated in claim 14 is rinsed with an immiscible solvent such as water, ethanol, or acetone and made dry for storage or application.
  16. 16 . The claim I comprises of microfluidic equipment and air drying is ideal for the double emulsion synthesis, encapsulation and final preparation of the PCM or PCM gel micrometer sized spheres.
  17. 17 . The invention of claim 1 presents a mechanical strong, high thermal energy density, thermal conductivity, and thermal cycling stability encapsulated PCM product with capabilities to be cycled >1000 up to 7000 melting/freezing cycles with irreversible loss in its structure, composition, and overall thermal performance.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority to U.S. Provisional Patent Application No. 63/717,486, filed on 7 Nov. 2024, the entire contents of which are fully incorporated herein by reference. STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH This invention was made with government support under the contract number: DE-SC0020834 awarded by Office of Science (SC-1) U.S. Department of Energy. The government has certain rights in the invention. REFERENCE TO A SEQUENCE LISTING Not Applicable FIELD OF THE INVENTION The invention described here-in presents encapsulated phase change material (PCM) composite capsules for providing thermal energy storage solutions to wide variety of applications. The encapsulated PCM spherical capsules range in size from 50 μm to up to 5 mm in diameter depending on the technique used for fabrication. The encapsulated PCMs address the issues of subcooling, incongruent melting, heat transfer, thermal cycling stability, leakage, and corrosivity using state of the art nanomaterials and fabrication techniques. BACKGROUND Thermal energy storage (TES) can have many uses in buildings and contribute to increased energy efficiency in the form of increased renewable energy fraction, reduced emissions, increased efficiency in HVAC equipment, reduced peak loads, utility cost savings, as well as increased indoor comfort with reduced temperature swings and excess temperatures[1-3]. Of the types of TES used, thermochemical materials (TCM) and phase change materials (PCM) are receiving much focus due to their associated advantages compared to sensible TES. TCM storage needs research regarding both materials as well as systems and costs in order to find reliable and useful system solutions for energy savings in building applications[3, 4]. PolyMaterials research on low cost encapsulated inorganic materials removes the obstacles currently encountered with PCMs including their corrosiveness, poor stability, and thermal regulation performance, while offering high thermal storage capabilities for buffering peak and regular utility costs and reducing energy consumption. In the art of encapsulated PCMs, many different organic and inorganic salt hydrate PCMs have been used for producing a variety of melting/freezing temperature thermal energy storage products in the size range of micro- to milli-meters[5]. These encapsulated PCMs consist of a solid/liquid core material of pure PCM encapsulated with a polymeric shell such as with acrylate coatings or with a plastic pouch. One major issue with the present technology available is the use of a pure PCM core material which results in undesirable degrees of PCM subcooling, phase segregation, melting/freezing hysteresis, incongruent melting, and eventually core leakage[6, 7]. The pure PCM pouch cell design restricts heat transfer compared to an individually coated PCM micro- or milli-sphere and poses serious issues with uniform melting/freezing, subcooling, and phase segregation. Additionally, organic PCMs have been employed for low temperature applications (0-30° C.) and not inorganic salt hydrates. Limitations exist with the effectiveness and feasibility of encapsulating PCMs using acrylic based coatings due to the need for excess heat, UV radiation or Pickering emulsions required for encapsulation, resulting in high manufacturing costs and setting discrepancies between research development and industrial realization[8]. The state of the art micro- to milli-meter sized PCM capsules composites described here-in offer maximum surface area for enhanced heat transfer properties, and innovative nanocomposites for addressing issues with the current encapsulated PCM technology such as subcooling, phase segregation, melting/freezing hysteresis, incongruent melting, and stability. The encapsulated PCM invention is comprised of an aqueous gel of inorganic salt hydrate, cellulose and/or starch and polyvinyl alcohol (PVA) with a polymer shell such as but not limited to polystyrene (PS), polymethyl methacrylate (PMMA), polyethylene, silicon rubber, polypropylene, or any combination thereof. An embodiment of the invention also includes ≤5 wt. % graphene oxide nanoparticles for amplifying thermal conductivity and minimizing PCM subcooling. The synthesis of the micro-milli-sphere products relies on simple double emulsion techniques using dichloromethane, acetone, ethanol, mineral oil, and/or water as continuous phases with no heat, UV radiation, or Pickering emulsion required for polymer precipitation and polymerization over the core material. The attributes of the double emulsion process present a low cost and fully scalable solution to the production of high performance encapsulated inorganic salt hydrate PCMs for thermal energy storage from subzero to >100° C. temperature range. There are many thermal storage applications where the proposed encapsulated PCMs will provide energy savings and reduced utility and equipment expenditures in the buildin