A
helical heat exchanger assembly comprises a plurality of
helical heat exchangers, each
helical heat exchanger comprising a tube having first and second ends, a length, an inner
diameter and a cross-section incorporating the inner
diameter, a thermally conductive tube insert having a length and an outer
diameter substantially equal to the inner diameter of the tube, the tube insert having first and second ends and comprising a single
helix extending along the length of the tube insert and twisted around a central axis. The tube insert is sealed within the tube by sealing an outer edge of the
helix to an inner surface of the tube to form fluid-tight first and second fluid flow paths defined between opposing sides of the
helix and the inner surface of the tube, respectively. A plurality of inlet and outlet fluid ports are positioned for passage of a first and second fluid into and out of each tube. A first manifold connects each of the first ends of the
heat exchanger tubes and a second manifold connects each of the second ends of the heat exchanger tubes, wherein at least one of the first or second manifolds includes baffles to direct fluid flow within the manifold such that at least some of the helical heat exchangers may be arranged in series, or in parallel, within the heat exchanger
assembly via the baffles. Each helix has a predetermined
pitch which may be less than or greater than the tube inner diameter and defines a length of the first and second fluid flow paths within each heat exchanger tube, wherein the
pitch of the helix may be constant or variable along the length of the tube insert.