Articles and devices for thermal energy storage and methods thereof

Abstract

The present invention relates to articles and heat storage devices for storage of thermal energy. The articles include a metal base sheet and a metal cover sheet, wherein the metal base sheet and the metal cover sheet are sealingly joined to form one or more sealed spaces. The articles include a thermal energy storage material that is contained within the sealed spaces. The sealed spaces preferably are substantially free of water or includes liquid water at a concentration of about 1 percent by volume or less at a temperature of about 25° C., based on the total volume of the sealed spaces. The articles include one or more of the following features: a) the pressure in a sealed space is about 700 Torr or less, when the temperature of the thermal energy storage material is about 25° C.; b) the metal cover sheet includes one or more stiffening features, wherein the stiffening features include indents into the sealed space, protrusions out of the sealed space, or both, that are sufficient in size and number to reduce the maximum von Mises stress in the cover sheet during thermal cycling; c) the metal cover sheet and/or the metal base sheet includes one or more volume expansion features; or d) the metal cover sheet has a thickness, t c , and the metal base sheet has a thickness, t b , wherein t c is greater than t b ; so that the article is durable. For example, the article does not leak after thermal cycling between about 25° C. and about 240° C., for 1,000 cycles.

What is claimed is: 
     
         1 . An article comprising:
 a metal base sheet;   a metal cover sheet, wherein the metal base sheet and the metal cover sheet are sealingly joined to form one or more sealed spaces;   a thermal energy storage material, wherein the thermal energy storage material is contained within the sealed spaces;   wherein the sealed spaces are substantially free of water or includes liquid water at a concentration of about 1 percent by volume or less at a temperature of about 25° C., based on the total volume of the sealed spaces; and   wherein the article includes one or more of the following features:
 a. the pressure in a sealed space is about 700 Torr or less, when the temperature of the thermal energy storage material is about 25° C.; 
 b. the metal cover sheet includes one or more stiffening features, wherein the stiffening features include indents into the sealed space, protrusions out of the sealed space, or both, that are sufficient in size and number to reduce the maximum von Mises stress in the cover sheet during thermal cycling; 
 c. the metal cover sheet and/or the metal base sheet includes one or more volume expansion features; or 
 d. the metal cover sheet has a thickness, t c , and the metal base sheet has a thickness, t b , wherein t c  is greater than t b ; 
   so that the article does not leak after thermal cycling between about 25° C. and about 240° C., for 1,000 cycles.   
     
     
         2 . The article of  claim 1 , wherein the pressure in a sealed space is a vacuum of about 600 Torr or less, at a temperature of about 25° C. 
     
     
         3 . The article of  claim 2 , wherein the article is prepared by a process including a step of joining the metal base sheet and the metal cover sheet when the thermal energy storage material is at a joining temperature (T j ) of at least the liquidus temperature of the thermal energy storage material (T L, TESM ). 
     
     
         4 . The article of  claim 1 , wherein
 i) the ratio of the thickness of the metal cover sheet to the thickness of the metal base sheet, t c /t b , is about 1.05 or more;   ii) the difference between the thickness of the metal cover sheet and the thickness of the metal base sheet, t c −t b , is about 0.02 mm or more; or   iii) both i) and ii).   
     
     
         5 . The article of  claim 1 , wherein the article includes one or more welds joining the metal cover sheet and the metal base sheet, wherein the one or more welds completely encloses the sealed spaces; the article has an opening near the center of the article so that a heat transfer fluid can flow through the opening; and the article is sealed around a periphery of the opening, so that the heat transfer fluid does not contact the thermal energy storage material in the sealed space. 
     
     
         6 . The article of  claim 1 , wherein the metal cover sheet includes one or more stiffening features. 
     
     
         7 . The article of  claim 1 , wherein the metal cover sheet, the metal base sheet, or both includes one or more volume expansion features. 
     
     
         8 . The article of  claim 7  wherein the one or more volume expansion features includes dimples, chevrons, wrinkles, folds, convolutions, or any combination thereof. 
     
     
         9 . The article of  claim 1 , wherein the metal cover sheet is embossed so that the Von Mises stress of the article at a temperature of about 250° C. is reduced by about 10% or more compared with an article in which the metal cover sheet is generally flat. 
     
     
         10 . The article of  claim 1 , wherein the Von Mises stress in both the metal base sheet and the metal cover sheet due to the thermal expansion of the thermal energy storage material during repeated thermal cycling between about 30° C. and about 250° C. is less than the yield stress of the metal of the cover sheet. 
     
     
         11 . The article of  claim 1 , wherein the sealed spaces of the article do not leak after being heated to about 400° C. for about 4 hours. 
     
     
         12 . The article of  claim 1 , wherein the thermal energy storage material has a liquidus temperature of about 25° C. or more. 
     
     
         13 . The article of  claim 12 , wherein the thermal energy storage material has a liquidus temperature of about 150° C. or more; and the thermal energy storage material is substantially anhydrous. 
     
     
         14 . A process for forming an article of  claim 1 , wherein the metal base sheet includes one or more troughs capable of containing a liquid, and the process comprises a step of at least partially filling one or more troughs with the thermal energy storage material. 
     
     
         15 . The process of  claim 14 , wherein the thermal energy storage material is at a predetermined temperature that is at least the liquidus temperature of the thermal energy storage material when the base sheet and the cover sheet are sealingly joined, so that upon cooling the article to about 25° C. a vacuum is formed in the sealed space. 
     
     
         16 . A process of  claim 14 , wherein the step of sealingly joining the base sheet and the cover sheet is started prior to the step of filling the trough with the thermal energy storage material and is finished after the step of filling the trough with the thermal energy storage material. 
     
     
         17 . The process of  claim 14 , wherein the article is prepared by a process including a step of joining the metal base sheet and the metal cover sheet to form the sealed space, wherein the step of joining includes a step of applying a vacuum to the region of the sealed space prior to joining the sheets. 
     
     
         18 . A device including a stack of two or more articles of  claim 1 . 
     
     
         19 . The device of  claim 18 , wherein each articles each include an opening and wherein the articles are arranged so that openings are generally aligned in an axial direction, and the stack of articles is contained in an insulated container. 
     
     
         20 . A process for storing heat comprising a step of:
 transferring a sufficient amount of thermal energy to the article of  claim 1 , so that the thermal energy storage material in the article is heated to a temperature of about 200° C. or more.