(US5103871-A)      The one-end closed ceramic double tube has an integral structure comprises: a one-end closed outer cylinder, an inner cylinder extending concentrically with the outer cylinder and one support portion extending laterally to bridge the outer and inner cylinders and longitudinally from near the closed end up to the open end of the outer cylinder. The ratio of a total thickness of the support portions in contact with the inner circumference of the outer cylinder to the inner circumference of the outer cylinder at cross section is most 25%, and preferably, the outside diameter ratio of the outer cylinder to the inner cylinder is at most 3.3.    An air passage formed on the inner cylinder near the closed end side of the tube communicates between the inner passageway inside the inner cylinder and the outer passageway defined by the inner and outer cyinders. This double tube has high reliability and sufficient mechanical strength and can be suitably used as filters, heat exchangers, concentrators and as supporting tubes for fuel cells. This double tube is manufactured by means of extrusion moulding.    ADVANTAGE -   Low cost.    (US5112544-A)      The mfg. method for one-end closed ceramic double tube involves extruding a ceramic material from a die having at least one inner and one outer circular slits arranged concentrically. At least one slit extends centripetally between the outer and inner slits. The extruded material forms a mould for a ceramic double tube (1) with inner (2) and outer (3) concentric tubes linked by one or more support portions (4.1-4.3), which extend along the tube longitudinal axis.    The double tube material is then dried, and at least one opening is formed at one end of inner tube to connect inside of the inner tube with the spacing between both tubes. The outer cylinder adjacent to the inner tube opening is sealed entirely while the inner tube at the same end remains open. The double tube is fired after grinding the outer cylinder and part of the support portion(s) at the open end of tube, so that part of the inner tube extends beyond the outer tube end.    USE/ADVANTAGE -   For filter, heat exchanger, condenser, solid oxide fuel cell, etc. Support link between tubes prevents movement of tubes w.r.t. each other ensuring no variation of gas flow rate.