  This paper first reviews non-traditional heat exchanger geometry, laser
welding, practical issues with microchannel heat exchangers, and high
effectiveness heat exchangers. Existing microchannel heat exchangers have low
material costs, but high manufacturing costs. This paper presents a new
expanded microchannel heat exchanger design and accompanying continuous
manufacturing technique for potential low-cost production. Polymer heat
exchangers have the potential for high effectiveness. The paper discusses one
possible joining method - a new type of laser welding named "forward conduction
welding," used to fabricate the prototype. The expanded heat exchanger has the
potential to have counter-flow, cross-flow, or parallel-flow configurations, be
used for all types of fluids, and be made of polymers, metals, or
polymer-ceramic precursors. The cost and ineffectiveness reduction may be an
order of magnitude or more, saving a large fraction of primary energy. The
measured effectiveness of the prototype with 28 micron thick black low density
polyethylene walls and counterflow, water-to-water heat transfer in 2 mm
channels was 72%, but multiple low-cost stages could realize the potential of
higher effectiveness.
