Superinsulating heat transfer surfaces for microfluidic channels

In microreactors and lab-on-a-chip devices it is often important to heat a liquid above ambient temperature while it flows through thermally insulated microfluidic channels. In this paper we introduce, for the first time, the heat transfer analogue of pressure drop reduction associated with patterned superhydrophobic (SH) surfaces, by showing how there is an also significant reduction in the convective heat transfer coefficient between the liquid and the SH surface. We use experiments and computational fluid dynamics to simulate a variety of surface patterns and wall thermal conductivities to investigate the effect of SH surfaces on heat transfer rate. We demonstrate that without altering the bulk material properties the interfacial thermal resistance can be significantly increased. The effect is shown to be highly dependent on a variety of conditions including the Peclet number, the thermal conductivity of the wall and the shear free area. Under certain conditions we demonstrate heat transfer reductions of up to 67% using glass walls relative to a smooth surface Thus we call such surfaces superinsulating.