Simple and low cost method for metal-based micro-capillary channels for heat exchanger use

Abstract

In this work, we present an alternative, low cost method for the fabrication of a heat exchanger utilizing metal-based microchannels using the UV-LiGA technique. Lithography is used to pattern dry film negative photoresist (Ordyl P-50100) on the substrate. The resist is laminated over the substrate and exposed with a UV source. The use of dry film resist allows for simple and inexpensive microchannel patterns without requiring advanced cleanroom equipment. Following the lithography process, electrodeposition of metals is used to fill the recesses patterned in the resist. In this work, nickel has been electroplated into the bounding resist structure. After electroplating, the remaining resist is dissolved leaving free standing metal structures. The fabricated exchanger is then evaluated based on thermal absorption of simulated waste heat sources and capillary action of the metal channels themselves. Channels are fabricated to heights of 60, 70 and 90 μm respectively on copper substrate using these methods. Working fluid mass transfer rate from the heated microchannel heat exchanger (MHE) is utilized as a basic metric of operation. The mass transfer rate recorded from the nickel-based MHE is 2.19, 2.81 and 3.20 mg s−1 respectively for the different channel heights. This implies an effective thermal power consumption rate of 1.66, 2.13 and 2.42 kW m−2 respectively. By contrast, an MHE fabricated with 115 and 142 μm tall channels on silicon substrate is shown to evaporate up to 2.84 and 3.04 mg s−1 respectively, giving an effective thermal power consumption of 2.15 and 2.31 kW m−2 respectively. An investigation of working fluid contact angle with the electroplated nickel surface is also presented. The surface is found to be a porous structure stemming from the electroplating process.