Fabrication, modeling, and testing of micro-cross-flow heat exchangers

Planar micro-cross-flow heat exchangers, similar in concept to most automobile radiators, have been fabricated using two different processes. A process that was previously reported (Harris et al., 2000) to fabricate a polymer heat exchanger involved embossing two identical polymer parts using the LIGA process. Then the two parts were aligned and bonded together. In this paper, a process is described to fabricate a nickel micro-cross-flow heat exchanger by embossing a sacrificial polymer mandrel using a LIGA-fabricated mold insert. The mandrel is coated with nickel (using either electroplating or electroless plating), then the sacrificial mandrel is dissolved. Experimental results are reported for both the polymer and nickel heat exchangers to determine the rates of heat transfer between the in-plane liquid (water) and the through-plane gas (air). Pressure drops of both fluid streams were also measured. The experimental results compare favorably with a modified version of the analytical model that was described previously. The fabricated heat exchangers have values of heat transfer/volume that are more than five times higher than conventional scale counterparts (with characteristic dimensions at least one order of magnitude larger than those reported here) and values of heat transfer/mass that are 50% greater than their conventional scale counterparts.