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In this work, the influence of eddy effect of coils on magnetic, flow, and temperature fields in an electromagnetically levitated molten droplet was investigated by a serial of axisymmetric numerical simulations. In an electromagnetic levitation device, both metal droplet and coils are conductive materials, therefore the distributions of current density in them should be nonuniform as a result of the eddy effect. However, in previous works, the eddy effect was considered alone in metal droplet but ignored in coils usually. As the distance of coils and metal droplet is several millimetres in general, the non-uniform distribution of current density in coils actually gives important influences on calculations of magnetic, flow, and temperature fields. Here, we consider the eddy effect both in metal droplet as well as that in coils simultaneously. Lifting force, absorbed power, fluid flow, and temperature field inside a 4-mm radius molten copper droplet as a typical example are then calculated and analyzed carefully under such condition. The results show that eddy effect leads to higher magnetic force, velocity, and temperature in both levitating and melting processes than those when the eddy effect is ignored. What is more, such influence increases as the distance of droplet and coils becomes closer, which corresponds to experimental measurement. Therefore, we suggest that eddy effect of coils should be considered in numerical simulation on this topic to obtain more reliable result.

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The spontaneous movements of condensate droplets on either superhydrophobic surfaces or homogenous slippery surfaces are generally driven by capillary forces. It is difficult to shift a millidroplet without using, e.g., a wettability gradient or asymmetric bump. Its motion direction is not related to the surface temperature of the substrate, although the condensation strongly depends on the surface temperature. This Letter reports a self-excited thermocapillary motion during condensation on a heterogeneous slippery liquid-infused porous surface without an externally imposed tangential temperature gradient, where the droplet moves directionally toward cold areas on the surface. The spontaneous thermocapillary motion is driven by the thermocapillary force originating from the local nonuniform temperature distribution on the surface, which is several orders of magnitude larger than the capillary force for a millidroplet. Even a millidroplet could move on such a heterogeneous surface and move upward against the gravity on an inclined surface. In addition to the spontaneous motion directly related to the temperature of the cooling substrate, the dropwise condensation rate may be significantly increased up to two times compared to that of a homogenous slippery surface.