High temperature thermal energy storage system

[0018]Referring now to the drawings, in which like numerals indicate like elements throughout the several views, FIG. 1 depicts one embodiment of the helically grooved tube-capsules 104. The capsules may be formed from a thin wall metal tube by enrolling helical grooves along the length of the tubes or by extrusion or other metal forming procedure. The grooved tubes may resemble the rifled barrel of guns. The ratio of the length to the diameter of the tube is from 6 to 300. The angle 107 between the tangent of the helix of the grooves and the axis of the tube may be from 0 to 30 degrees. The shape of the profile of the groove 105 is curved that may be circular or oval. The number of the grooves on the tube may be from 2 to 12. The ratio of the depth of the groove to the diameter of the tube may be from 0.02 to 0.4. The purpose of the grooving is to provide radial and axial flexibility of the tube wall to accommodate the thermal expansion of the encapsulated phase change material. At th