Method of making a recuperator structure by crystallization

A method for making a recuperator heat exchange assembly having plural strata of parallel flow fluid passages therein, comprising

• a. forming a multiplicity of elongated tubes of a glass that is thermally crystallizable to a low expansion glass ceramic having a coefficient of lineal thermal expansion of about -18 to +50 .times. 10.sup.-7 /.degree. C over the range of 0.degree. - 300.degree. C;
• b. each of said tubes being sealed at each end and containing an expansible fluid medium, each of said tubes having a portion intermediate the ends thereof which is substantially straight;
• c. tightly packing pluralities of said tubes into a plurality of layers of tubes with the axes of the intermediate portion of the tubes in each layer essentially parallel to each other;
• d. arranging said pluralities of layers with the intermediate tube portions thereof in a stacked array with respect to each other and with the axes of the intermediate portions of the tubes in each layer being essentially parallel to the axes of corresponding intermediate tube portions in the other layers;
• e. spacing each layer of tubes from at least one of the adjacent layers in said array by interposing spacer means between each of the ends of the layers being spaced, each of said spacer means extending transversely across the tubes in the layers being spaced and adjacent the intermediate tube portions of the layers to define a passageway extending from a first spacer means at one end of the intermediate tube portions to a second spacer means at the other end of the intermediate tube portions of spaced tube layers, said spacer means being formed of a glass that is thermally crystallizable to a low expansion glass ceramic having a coefficient of lineal thermal expansion that is substantially the same as said elongated tubes;
• g. constraining the outer surface of said assembly of elongated tubes, said spacer means, and said fluid flow directing means to restrict outward movement of those portions of the assembly;
• h. subjecting said constrained assembly to an initial heat treatment which includes temperatures sufficient to soften said elongated tubes and thus to cause said fluid medium entrapped therein to expand and urge said tubes into contact with adjacent tubes and said spacer means and said flow directing means to fuse said assembly portions into an integral mass;
• i. opening the sealed ends of said elongated tubes to enable reception and discharge of a fluid to obtain a heat exchange between fluid flowing in said passageways, and
• j. further heat treating said assembly to elevated temperatures sufficient to effect crystallization of said tubes, said spacer means and said flow directing means into a low expansion glass-ceramic.