Patent ID: 8724978

Claim:
A fluid heating device, comprising: an inner cylinder having a plurality of annular grooves provided around an outer side surface of the inner cylinder and a plurality of sets of connecting grooves provided on the outer side surface, each set of connecting grooves connecting two of the annular grooves, circumferential positions of connecting grooves in two of the sets of connecting grooves provided on respective sides of one of the annular grooves are displaced from each other; and a cylinder containing the inner cylinder in close contact with each other, wherein one of a gas and a liquid flows through a flow path defined by an inner wall of the cylinder and the outer side surface of the inner cylinder, and whereby heat is exchanged between the one of the gas and the liquid and the flow path; wherein the inner cylinder defines a central axis; and wherein the inner cylinder further has (i) an inlet side at one end of the central axis, (ii) an outlet side at another end of the central axis, and (iii) a heater cavity which extends along the central axis to a heater opening to receive a heater, the heater opening being disposed on the inlet side of the inner cylinder and being coaxial with the central axis.