Digital Microfluidic Thermal Switch in Magnetocaloric Cooling

Among the related technologies, magnetocaloric energy conversion represents one of the most promising alternatives to vapour compression. Despite the fact that this technology has made substantial progress over the last two decades, there are unfortunately still unsolved and strongly relevant challenges regarding the use of rare-earth materials, energy efficiency, and the competitive cost of potential future devices.<br/><br/>Namely, today’s state-of-the-art devices are based on the so-called Active Magnetic Regeneration, which is moderately efficient at low operating frequencies (up to 5 Hz). To achieve considerable cooling power and magnetic fields at such low frequencies, a significant amount of magnetocaloric and permanent magnet material is required, which also affects the cost. Therefore, a new research direction has emerged in recent years in which researchers are trying to develop devices that operate efficiently at much higher frequencies (up to 20 Hz or more). This would increase the power density, which in turn would allow miniaturization of the devices and the use of drastically less magnetocaloric and magnetic material. There are two major challenges to be solved. One concerns the application of new magnetic field sources that can generate a fast and efficient alternating magnetic field at high frequencies. The other one deals with the application of new thermal management principles in a form of thermal control devices. One particular sub-domain of thermal control devices are thermal switches.<br/><br/>An interesting field, to look for thermal switch mechanisms, is microfluidics, which has enabled the development of integrated lab-on-chip devices. Although most microfluidic devices are based on a continuous flow of liquids in microchanells, there has been an increasing interest for the past couple of years in devices that rely on manipulation of discrete droplets using surface tension effects. One such technique is ElectroWetting On Dielectric (EWOD), which is based on wettability of liquids on a dielectric solid surface by varying the electrical potential. EWOD system’s similarity to the digital microelectronic systems has led to the term digital microfluidics.<br/><br/>In this contribution we will present a new concept of magnetocaloric device which couples magnetocaloric effect and EWOD droplet actuation as thermal switch mechanism. We will show different potential designs of such a devices and their operation. Furthermore, the materials and its properties, which constitute the whole device will be discussed.