Thermal Energy Storage Systems Utilizing Phase Change Materials

Abstract

A thermal energy storage system utilizes a phase change material with an encapsulating material surrounding the phase change material. The encapsulating material fully contains the phase change material to prevent passage of the phase change material out of the encapsulating material and/or prevent direct contact of the phase change material with external objects. The encapsulating material is a high density polyethylene (HDPE), which may be a non-crosslinked or crosslinked HDPE. In a method of forming a thermal energy storage system a phase change material is surrounded with the encapsulating material.

We claim: 
     
         1 . A thermal energy storage system comprising:
 a phase change material; and   an encapsulating material surrounding the phase change material so that the phase change material is fully contained therein to prevent passage of the phase change material out of the encapsulating material and/or prevent direct contact of the phase change material with external objects, the encapsulating material being a high density polyethylene (HDPE).   
     
     
         2 . The thermal storage system of  claim 1 , wherein:
 the HDPE encapsulating material has an environmental stress crack resistance (ESCR) while in contact with phase change materials at 5° C. to 27° C. of from 100 hours or more.   
     
     
         3 . The thermal energy storage system of  claim 1 , wherein:
 the phase change material has a liquid-solid phase transition temperature of from 50° C. or less at standard pressure.   
     
     
         4 . The thermal energy storage system of  claim 1 , wherein:
 the phase change material has a liquid-solid phase transition temperature of from 10° C. or less at standard pressure.   
     
     
         5 . The thermal storage system of  claim 1 , wherein:
 the phase change material is a selected from at least one of an alkane, an alcohol, an organic acid, an ester, polyethylene glycol, an inorganic salt hydrate, a mixture of inorganic salts and/or inorganic hydrates, eutectic mixtures of organic-organic materials, eutectic mixtures of organic-inorganic materials, and eutectic mixtures of inorganic-inorganic materials.   
     
     
         6 . The thermal storage system of  claim 1 , wherein:
 the HDPE material is a cross-linked HDPE.   
     
     
         7 . The thermal storage system of  claim 6 , wherein:
 the HDPE material has from 90% or less crosslinking.   
     
     
         8 . The thermal storage system of  claim 1 , wherein:
 the encapsulating material has a wall thickness of from 3 mm or less.   
     
     
         9 . The thermal storage system of  claim 1 , wherein:
 encapsulating material contains a heat conducting additive.   
     
     
         10 . The thermal storage system of  claim 1 , wherein:
 the thermal storage system is formed in at least one of 1) a sphere having a diameter of from 10 mm to 40 mm, and 2) an elongated cylindrical body having a diameter of from 2 to 5 mm.   
     
     
         11 . A method of forming a thermal energy storage system comprising:
 surrounding a phase change material with an encapsulating material so that the phase change material is fully contained therein to prevent passage of the phase change material out of the encapsulating material and/or to prevent direct contact of the phase change material with external objects, the encapsulating material being a high density polyethylene (HDPE).   
     
     
         12 . The method of  claim 11 , wherein:
 the HDPE encapsulating material has an environmental stress crack resistance (ESCR) while in contact with phase change materials at from 5° C. to 27° C. of from 100 hours or more.   
     
     
         13 . The method of  claim 11 , wherein:
 the phase change material has a liquid-solid phase transition temperature of from 50° C. or less at standard pressure.   
     
     
         14 . The method of  claim 11 , wherein:
 the phase change material has a liquid-solid phase transition temperature of from 10° C. or less at standard pressure.   
     
     
         15 . The method of  claim 11 , wherein:
 the phase change material is a selected from at least one of an alkane, an alcohol, an organic acid, an ester, polyethylene glycol, an inorganic salt hydrate, a mixture of inorganic salts and/or inorganic hydrates, eutectic mixtures of organic-organic materials, eutectic mixtures of organic-inorganic materials, and eutectic mixtures of inorganic-inorganic materials.   
     
     
         16 . The method of  claim 11 , wherein:
 the HDPE material is a cross-linked HDPE.   
     
     
         17 . The method of  claim 16 , wherein:
 the HDPE material has from 90% or less crosslinking.   
     
     
         18 . The method of  claim 11 , wherein:
 the thermal storage system is formed in at least one of 1) a sphere having a diameter of from 10 mm to 40 mm, and 2) an elongated cylindrical body having a diameter of from 2 to 5 mm; and wherein   the encapsulating material has a wall thickness of from 3 mm or less;   
     
     
         19 . The method of  claim 11 , wherein:
 encapsulating material contains a heat conducting additive.   
     
     
         20 . The method of  claim 11 , wherein:
 the encapsulating material is formed into a selected shape by at least one of injection molding, gas-assisted injection molding, water-assisted injection molding, thermo-forming, blow molding, blown film extrusion, and 3D-printing.