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.

高效，有针对性地冷却位于狭窄缝隙（例如微缝隙）中的离散热源是一项挑战。在这项研究中，我们通过使用电喷雾技术证明，带电液滴可以在微缝隙中有效传输，微缝隙由顶部基板和底部基板组成，然后沉积在其中的加热点上。可获得高达约28％的冷却增强，当加热电极（代表加热点）的表面涂有石墨烯纳米片（GNP）时，冷却增强可提高至约67％，这归因于快速水渗透。特别，两个加热的电极位于微缝隙内-一个在顶部基板（顶部电极）上，一个在底部基板（底部电极）上-并在微缝隙内引起对流。我们观察到，大多数带电液滴被对流拖拉，并大部分沉积在顶部加热电极上，这表明在加热电极附近，施加在带电液滴上的拖曳力非常大。有趣的是，通过仅在一个加热的电极上涂覆GNPs，对于带正电荷的液滴，当顶部电极上涂覆有GNPs时，我们观察到冷却效果有所降低。这可以归因于带正电的GNPs表面排斥带正电的液滴。另一方面，对于带负电荷的液滴，我们观察到，当底部电极涂有GNP时，冷却效果会降低。这可以归因于带正电的GNPs表面吸引了带负电的液滴。这些发现对于有效冷却系统的设计至关重要，特别是对于微缝隙内小型热源的目标冷却而言。