Increase in Leidenfrost point via plasma-activated water

We exploit plasma-activated water to increase the Leidenfrost point for application in spray cooling. Due to the presence of reactive oxygen and nitrogen species in the plasma-activated water, compared to deionized (DI) water, we observe up to an 18% increase in the solution density and up to 21% reduction in the surface tension. This gives rise to a significant increase in evaporation rate using the plasma-activated water compared to DI water and also leads to a shift in Leidenfrost point. Specifically, in the nucleate and transition boiling regimes, we observe a considerable reduction in the surface temperature when the plasma-activated water droplet is impinging on the heated plate as compared to the DI water droplet, i.e., up to 220%. We further demonstrate the practicality of plasma-activated water droplets as a viable alternative to replace DI water droplets in spray cooling through a commonly used graphene–epoxy surface coating enhancement technique. With the plasma-activated water droplet, we show a further reduction in the surface temperature of the heated plate by up to 11% as compared to the DI water droplet. Given that plasma-activated water can be easily produced and its bacterial inactivation characteristic can circumvent bacteria growth, these promising results highlight its potential applicability to replace DI water as a coolant in practical cooling systems.