Patent ID: 8132326

Claim:
A method of making a needle-fin tube having an internal fin structure comprising the steps of: providing a needle-fin tube having needle-like fin parts wrapped around a tube for a heat carrier liquid, placing within the tube an internal fin structure in the form of a spiral wire which is elastically biased against an inner wall defined by the tube; wherein a wire is brought to releasably attach to a cylindrical bar, which bar is rotated to wind the wire about the bar and linearly transferred while rotating to form thereon the spiral wire as a spring wound along the bar and attached to the bar; wherein the spiral wire wound along the bar and attached to the bar is moved inside the tube so that the spiral wire wound along the bar extends from a first end to a second opposite end of the tube; and wherein the spiral wire wound along the bar is released from the bar to attach to the inside surface of the tube under a self-generated spring force.