Space- and Structurally-Efficient Recta-Cylinder Molded Liquid Storage Tanks

Abstract

This invention is an improvement to the shape of liquid storage tanks, in particular to unpressurized molded polymer tanks used for thermal storage in solar systems. Although solar storage tanks represent the first commercial application, this invention is well suited to ambient-temperature water and chemical storage tanks as well. By using a tank with a square footprint instead of a cylindrical tank, storage capacity can be increased by more than 20%, while consuming the same floorspace. For large indoor applications, doorway access amplifies the advantages of a rectangular tank versus cylinders. This invention combines the higher volume of square and rectangular footprint tanks with the structural efficiency of cylinder tanks. The tank walls are formed by alternating vertically-stacked cylinders and rectangular prisms. The cylinders take advantage of hoop strength and also provide a place for external reinforcing bands. Edges and corners may be sharp, chamfered or filleted.

1 . A molded liquid storage tank whose vertical walls are formed by alternating, vertically-stacked and aligned cylinders and rectangular prisms with square footprints, with connecting horizontal planes enclosing the spaces between. 
     
     
         2 . Claim  1  with the cylinders spaced more closely near the tank bottom and more widely near the tank top to create approximately equal deflections of vertical wall sections under hydraulic tank loads. 
     
     
         3 . Claim  1  with the cylinders spaced more closely near the tank top and more widely near the tank bottom to create approximately equal deflections of vertical wall sections in stratified thermal storage applications where polymer materials are less stiff at the top of the tank than at the bottom due to higher temperature. 
     
     
         4 . Claim  1  with equally-spaced cylinders. 
     
     
         5 . Claim  1  with one or more cylinders reinforced with external straps. 
     
     
         6 . Claim  1  with the edges of each vertically-extended square chamfered. 
     
     
         7 . Claim  1  with the edges of each vertically-extended square formed to a radius. 
     
     
         8 . Claim  1  with connecting planes flared from horizontal to facilitate demolding. 
     
     
         9 . Claim  1  with smoothed corners to reduce stress concentrations and optimize material usage. 
     
     
         10 . A molded liquid storage tank whose vertical walls are formed by alternating, vertically-stacked and aligned cylinders and rectangular prisms with rectangular footprints, with at least two side-by-side vertical-axis cylinders, with the rectangle footprint aspect ratio having integer values (2:1, 3:1, etc.) corresponding to the number of cylinders, and with connecting horizontal planes enclosing the spaces between the cylinders and the rectangles. 
     
     
         11 . Claim  10  with cylinder diameter slightly smaller than the length of the shorter side of the rectangle, resulting in through-holes where the at least two adjacent cylinders meet. 
     
     
         12 . Claim  10  with the cylinders spaced more closely near the tank bottom and more widely near the tank top. 
     
     
         13 . Claim  10  with cylinders variably spaced to create approximately equal deflections of vertical wall sections under hydraulic tank loads. 
     
     
         14 . Claim  10  with equally-spaced cylinders. 
     
     
         15 . Claim  10  with one or more cylinders reinforced with external straps. 
     
     
         16 . Claim  10  with the edges of each rectangular prism chamfered. 
     
     
         17 . Claim  10  with the edges of each rectangular prism formed to a radius. 
     
     
         18 . Claim  10  with corners smoothed to reduce stress concentrations. 
     
     
         19 . Claim  10  with connecting planes flared from horizontal to facilitate demolding. 
     
     
         20 . Claim  10  with the rectangular tank footprint broken up by horizontal-axis cylinders spaced between the adjacent vertical-axis cylinders.