Microfluidic Systems for Studying Chemical Reactions, Mixing, and Heat Transfer

Abstract

Microsystems comprising microfluidic networks and miniaturized actuators, transducers, and sensors provide a convenient, revealing, and low-cost means for studying chemical reactions, separation processes such as filtration and extraction, phase changes, mixing, heat and mass transfer, and fluid flow phenomena. For instance, palm-sized plastic cartridges or cassettes (‘chips’) with channels, chambers, manifolds and other components for flow control and fluid actuation can be instrumented with embedded thermocouples and pressure sensors, and operated with small Peltier coolers/heaters and programmable syringe pumps or microrotary pumps. With proper design, the on-chip microfluidic processes can also be imaged with CCD cameras (especially using fluorescent dyes and particles), and infrared thermal cameras for temperature profiling. Such image (including video) capture and processing affords much more data compared to point sensors such as thermocouples and pressure transducers, and can be directly compared with finite element modeling. These systems are effective vehicles for project-based learning in fluid mechanics, heat transfer, chemical reaction engineering, separation processes and other unit operations, process control, and various biotechnical operations such as enzymatic digestion, nucleic acid amplification, and sample fractionation. The chips are made as bonded laminates from patterned acrylic, polycarbonate, thin metal sheet, and many other material types. Students can quickly design (using CAD software such as SolidWorks™), simulate (using FEM programs such as Comsol) microfluidic platforms, that can be rapid prototyped with laser machining, 3D printing, CNC machining, soft lithography, engraving and printed circuit board fabrication methods with a turn-around time of 1 day. The chip is instrumented using LabView™ or an Arduino™ microcontroller for data acquisition and process control. These benchtop or desktop systems make only modest demands on the resources of educational institutions, due to their low cost and safety, and minimal waste generation and reagent consumption. Also, their multidisciplinary nature affords an excellent opportunity for students to integrate their knowledge of CAD, simulation, prototyping, instrumentation and microcontrollers, statistical data analysis, and image processing and analysis. Further, these experiments give students a high level of hands on interaction and visualization of important unit operation processes. We discuss in detail some representative systems for heat exchangers, mixers, chemical reactors, and crystal growth, and their use as educational, project-based modules in the undergraduate engineering curriculum.