Fabrication of metallic heat exchangers using sacrificial polymer mandrils

This paper demonstrates the use of poly(dimethylsiloxane) (PDMS), polyurethane (PU), epoxy, and poly(methyl methacrylate) (PMMA) as mandrils to fabricate metallic heat exchangers having 300-700 μm internal channels. The mandrils were prepared using two soft lithographic techniques-replica molding and microembossing. To fabricate the heat exchangers, the polymeric mandrils were coated with a thin layer of metal by thermal evaporation or sputtering; this layer acted as the cathode for electrodeposition of a shell of nickel or copper that was 100 μm thick. The polymers were removed by burning them out at 400°C in air, or by dissolving them with a tetrahydrofuran solution of tetrabutylammonium fluoride. Studies of heat dissipation showed that the nickel heat exchangers with features that range in size from 150-750 μm have thermal resistances ranging from 0.07 to 0.12°^-2 C W^-1 cm at flow rates of water of ~20 L h^-1 and pressures of 8.6-83×10³ N m^-2