Abstract: A compact multiple coil heat exchanger having a high heat transfer density is provided to include at least an inner coil formed from a continuous tube into a plurality of contiguous turns about a common axis in a spiral arrangement and having a pitch in one direction and an outer coil formed from the continuous tube into a plurality of overlapping turns concentrically about the inner coil in a spiral arrangement having an opposite pitch. Further, a coil-forming apparatus and continuous coil-forming method is directed to form a multiple coil heat exchanger from a continuous tube using a coil-forming die rotatably mounted on a support frame. The coil-forming die includes a continuous spiral thread constructed to receive and laterally support the continuous tube while fabricating the multiple coil heat exchanger according to the continuous coil-forming method of this invention.

Abstract: Helically corrugated tubing with corrugations of variable depth is manufactured in a twisting machine by rotating one end of a deformable tube relative to the opposite end and simultaneously applying axially directed forces to the tube to progressively develop the helical corrugations in the tube wall. The depth of the corrugations is varied by means of a tapered mandrel which is located within the tube while the corrugations are being formed. Tubing sections with variable depth corrugations define flow paths in which the effective cross sectional area varies correspondingly, and such sections are useful in various heat exchangers.

Abstract: Helically corrugated tubing with corrugations that have a gradually changing pitch from one end to the other is manufactured in a twisting machine by rotating one end of a deformable tube about the tube axis relative to the opposite end and simultaneously applying axially directed forces to the tube to progressively develop helical corrugations along the tube wall. The ratio of the torque and the axially directed forces applied to the tube is continuously varied to produce corresponding variations in the pitch of the corrugations. Tubing sections in which the pitch of the corrugations increases gradually from one end to the other are used in shell-and-tube or tube-in-tube heat exchangers and define flow paths having cross sectional areas which increase correspondingly.

Abstract: Helical corrugations are formed in a tube having a cylindrical wall by generating pressure radially of the unsupported tube wall at localized areas distributed around the tube circumference. While the radial pressure is being generated, twisting of the tube about its own axis is initiated and as a result, radial deformation of the unsupported tube wall takes place. By controlling the axial length of the tube while it is twisted, the radial deformations develop into flutes which grow axially along a selected helical path in the tube wall.