Enhancement of the condensation process under low heat flux density conditions via electric fields

Low-heat-flux condensation is commonly encountered in compact water-recovery, humidity-control, and thermal-management systems. Under such conditions, enhancement strategies should not only improve heat-transfer performance, but also promote condensate removal, increase recoverable condensate yield, and control auxiliary power consumption. In this work, a tunable needle–plate non-uniform direct-current (DC) electric field is introduced into dropwise condensation on a vertical plate. A custom experimental platform integrating high-definition visualisation, multi-channel synchronous measurements, and split-drainage condensate weighing is developed, allowing electric-field parameters, droplet evolution, centreline local heat flux, net condensate yield, and electrical power consumption to be evaluated within a unified framework. The results show that the electric field markedly alters droplet nucleation, growth, coalescence, and departure, accelerates surface renewal, and produces a persistent droplet-sparse/cleared region near the needle-tip-affected area under strong-field conditions. Statistics of image-resolved medium-to-large droplets further indicate a voltage-stage-dependent response: the intermediate-voltage regime mainly promotes droplet coalescence and growth, whereas the higher-voltage regime is more favourable for droplet migration, rapid departure, and repeated surface renewal. The performance evaluation shows that the preferred operating condition depends on the optimisation target. For maximum local heat-transfer enhancement, the largest centreline local heat-flux enhancement reaches 66% under negative polarity at d=5mm and V=5kV. When heat-transfer enhancement, condensate yield, and electrical power consumption are considered together, the best overall condition among the tested cases based on the selected metrics is negative polarity at d=10mm and V=5kV, requiring only 29 mW while achieving simultaneous enhancements of 29% in net condensate yield and 63% in centreline local heat flux. When ultralow-power operation is prioritised, positive polarity at d=15mm and V=5kV still provides 20% net-condensate enhancement and 52% centreline local heat-flux enhancement with an electrical input of only 5.8 mW. These results demonstrate that needle–plate electric-field-assisted condensation can regulate droplet dynamics, promote surface renewal, and enhance low-heat-flux condensation performance with milliwatt-level electrical input. The established link among “electric-field parameters–droplet renewal–local heat transfer/net condensate yield–electrical power consumption” provides experimental guidance for selecting operating conditions in compact low-power condensation devices.