Cooling enhancement for light-emitting diode using plasma-activated water

We exploit the two-phase heat transfer enhancement using plasma-activated water for application in LED cooling. Within the steady-state LED temperature 80 °C ≤T_LED≤ 110 °C, up to 73% increase in heat transfer coefficient can be achieved by replacing deionized water with plasma-activated water; concomitantly, we observe up to 14% increase in illuminance. This enhancement can be attributed to the presence of reactive oxygen and nitrogen species in the plasma-activated water that reduces surface tension, and, quite unexpectedly, minimizes the oxidation of the copper (heat source) surface. Specifically, the lower surface tension of plasma-activated water can lead to smaller vapor bubbles as well as reduction in their residence times on the heated surface. On the other hand, by increasing the electrical conductivity of plasma-activated water, i.e., higher concentrations of reactive oxygen and nitrogen species, we observe significant reductions in surface oxidation on the copper (heat source) surface. Peculiarly, unlike the copper surface oxidized by deionized water, for the plasma-activated water, we observe isolated oxidized islands that consist of nanosphere structures; these islands are hydrophobic and can lead to significantly shorter residence times of vapor bubbles. Since plasma-activated water can be produced easily via the corona discharge plasma, these promising results highlight its potential to be used in two-phase cooling systems.