Shell and coil heat exchanger

Claim 1

A heat exchanger comprising: a shell having: a tubular outer wall having a first and second end, a tubular inner wall having a first and second end coaxial with said outer wall, and first and second end plates attached to the outer and inner walls to form an enclosed tubular shell cavity therebetween having a first and second end; means for admitting a first fluid into the shell cavity; means for removing the first fluid from the shell cavity; and a pair of spiral coils of tubing each having a first and second end sealingly exiting through the shell cavity wall for carrying a second fluid therebetween, said spiral coils lying within the shell cavity and having a plurality of spiral windings formed about the axis thereof, each coil having a section of windings formed at a large diameter and a section of windings formed at a small diameter, said coils coaxially nested together with the small diameter section of each coil within the large diameter of the opposite coil to form a generally cylindrical unit within the shell cavity, said coils being substantially equal in size, length and shape so that the pressure drop, flow and heat transfer characteristics of each coil is substantially the same, said spiral coils sized to fit between the inner and outer shell walls with limited radial clearance therebetween to allow limited axial flow of the first fluid, said windings axially spaced from one another to define a spiral flow path therebetween for the first fluid, said radial clearance and axial spacing relatively sized to expose substantially all of the surface of the coils to moving first fluid and to induce the first fluid to travel in a generally spiral motion to maximize the heat transfer between the first and second fluids.