Graphene-mediated electrospray cooling for discrete heat sources in microslits

Abstract

Efficient and targeted cooling of small discrete heat sources located in a confined gap, such as a microslit, is challenging. In this study, we demonstrate by using electrospray technique, the charged droplets can be effectively transported within a microslit – consisting of a top substrate and a bottom substrate – and subsequently deposited on the heated spots located within it; up to approximately 28% cooling enhancement can be obtained, and, increases to approximately 67% cooling enhancement when the surface of the heated electrode (representing a heated spot) is coated with graphene nanoplatelets (GNPs), which can be attributed to the fast water permeation. Specifically, two heated electrodes are located within the microslit – one on the top substrate (top electrode) and one on the bottom substrate (bottom electrode) – and induced convection within the microslit. We observe that majority of the charged droplets are dragged by the convection and deposited mostly on the top heated electrode, indicating that near the heated electrodes, drag force exerted on the charged droplets is significant. Interestingly, by applying the GNPs coating only on one heated electrode, for the positively charged droplets, we observe a reduction in the cooling enhancement when the top electrode is coated with GNPs. This can be attributed to the positively charged GNPs surface repels the positively charged droplets. On the other hand, for negatively charged droplets, we observe a reduction in cooling enhancement when the bottom electrode is coated with GNPs. This can be attributed to the positively charged GNPs surface attracts the negatively charged droplets. These findings are crucial for the design of an effective cooling system, particularly for the targeted cooling of small heat sources within microslit.