Controlling shedding characteristics of condensate drops using electrowetting
Abstract: We show here that ac electrowetting (ac-EW) with structured electrodes can be used to control the gravity-driven shedding of drops condensing onto flat hydrophobic surfaces. Under ac-EW with straight interdigitated electrodes, the condensate drops shed with relatively small radii due to the ac-EW-induced reduction of contact angle hysteresis. The smaller shedding radius, coupled with the enhanced growth due to coalescence under EW, results in an increased shedding rate. We also show that the condensate droplet pattern under EW can be controlled, and the coalescence can be further enhanced, using interdigitated electrodes with zigzag edges. Such enhanced coalescence in conjunction with the electrically induced trapping effect due to the electrode geometry results in a larger shedding radius, but a lower shedding rate. However, the shedding characteristics can be further optimized by applying the electrical voltage intermittently. We finally provide an estimate of the condensate volume removed per unit time in order to highlight how it is enhanced using ac-EW-controlled dropwise condensation.
Summary (1 min read)
- The condensate drops thus accumulate at the gap apices till the droplet weight overcomes the CAH force and the additional electrical trapping force.
- Finally, the increasing value of hR sh i due to the electrical trapping effect results in the lower shedding rate for the zigzag interdigitated electrodes, as compared to the straight interdigitated electrodes [Fig. 2(c)] .
- This faster growth does not translate into a higher shedding rate because of the electrostatic trapping effect, as described before.
- From an applied perspective, the most interesting performance indicator of a condensation process is the total condensate volume obtained per unit time (_ v).
- In fact, a more accurate estimate of h_ vi should also include the condensate drop volumes swept away by the shedding drop, which should lead to even higher net condensation rates.
- Yet, such an analysis is beyond their current scope.
- In summary, the authors have shown that the gravity-driven shedding of condensate drops can be enhanced using ac-EW with structured electrodes.
- The enhanced condensate shedding can be beneficial for applications like water-harvesting and heat transfer.
- Moreover, the electrical control over the characteristics of the condensate droplet pattern (e.g., periodicity) in itself can be useful for applications like breath figure templated self-assembly.
- See supplementary material for the movies (S1-S5) of breath figure evolution under different ac-EW conditions, schematic of the experimental setup (Fig. S1 ), image analysis procedure, discussion on CAH under ac-EW in air (Fig. S2 ), and discussion on the electrical trapping effect (Fig. S3 ).
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