Counter-flow for stabilization of microfluidic thermal reactors: Experimental and numerical study

Abstract

This work presents a novel counter-flow design for stabilizing microfluidic thermal reactors. In such devices, the substrate material is held in an unchanging thermal state while any combination of isothermal and gradient regions may be enacted on the surface region, all of which are stable in time. When such a state is achieved, precise control of the temporal temperature of the moving liquid is possible. The aim of this work is to establish a linear thermal gradient within the microfluidic reactor under a no-flow condition and to maintain the temperature profile for a broad range of flow conditions. Experimental results show that counter-flow will have a powerful stabilizing effect: isothermal regions remain isothermal, and gradient regions linearize. Distortions due to both external and internal convection/advection are reduced by several orders of magnitude. Counter-flow and direct-flow glass composite devices with different interlayer materials (silicon, quartz, and glass) were fabricated to investigate the role of interlayer thermal conductivity. The best performance was achieved for a counter-flow case with silicon interlayer for which a wide and stable linear thermal gradient (1 K/mm) was established, enabling ramp rates of up to 143 K/s. 3-D numerical models are used to predict the in-channel fluid temperature, its relation with the device surface temperature, and to evaluate the performance of the devices under other heating configurations.