Ultrathin Lubricant-Infused Vertical Graphene Nanoscaffolds for High-Performance Dropwise Condensation

Abstract

Lubricant-infused surfaces (LIS) are highly efficient in repelling water and constitute a very promising family of materials for condensation processes occurring in a broad range of energy applications. However, the performance of LIS in such processes is limited by the inherent thermal resistance imposed by the thickness of the lubricant and supporting surface structure, as well as by the gradual depletion of the lubricant over time. Here, we present an ultrathin (∼70 nm) and conductive LIS architecture, obtained by infusing lubricant into a vertically grown graphene nanoscaffold on copper. The ultrathin nature of the scaffold, combined with the high in-plane thermal conductivity of graphene, drastically minimize earlier limitations, effectively doubling the heat transfer performance compared to a state-of-the-art CuO LIS surface. We show that the effect of the thermal resistance to the heat transfer performance of a LIS surface, although often overlooked, can be so detrimental that a simple nanostructured CuO surface can outperform a CuO LIS surface, despite filmwise condensation on the former. The present vertical graphene LIS is also found to be resistant to lubricant depletion, maintaining stable dropwise condensation for at least 24 h with no significant change of advancing contact angle and contact angle hysteresis. The lubricant consumed by the vertical graphene LIS is 52.6% less than that of the existing state-of-the-art CuO LIS, also making the fabrication process more economical.

Ultrathin Durable Organic Hydrophobic Coatings Enhancing Dropwise Condensation Heat Transfer

“…Due to its, up to by an order of magnitude, higher heat-transfer coefficient, DWC is highly desired in all heat-transfer applications. 5 − 9 Most of the condenser surfaces (copper, aluminum, steel, etc.) used in the industry are naturally hydrophilic.…”

“…Condensation of water vapor plays a vital role in multiple energy conversion applications such as thermal management, power generation, refrigeration, air conditioning, and water desalination. − Depending on the formation and growth of the condensate on the surface, condensation can be distinguished into two different modes, i.e., filmwise condensation (FWC) and dropwise condensation (DWC). Due to its, up to by an order of magnitude, higher heat-transfer coefficient, DWC is highly desired in all heat-transfer applications. − Most of the condenser surfaces (copper, aluminum, steel, etc.) used in the industry are naturally hydrophilic.…”

Nanoarray-Embedded Hierarchical Surfaces for Highly Durable Dropwise Condensation

“…Arrays. To gain insights into the physical mechanisms underlying stable dropwise condensation, we laid emphasis on the significant contribution of nanoscale vertical arrays VACNT-embedded surface Cu nanowire 14,23 CuO nanowire 13,50 Si nanowire 4,9,22 Cu porous surface 21 Graphene nanoscaffold 26 Maximum 𝜃 ⁎ in enabling efficient heat transfer. Figure 3(a) shows air pockets at the solid-liquid interface, demonstrating that the CNT array maintains the Cassie wetting state, as remarked in previous studies [30,43,44].…”

“…Therefore, the film-like droplets that pin on the surface will undergo the irreversible Cassie-Wenzel wetting transition, leading to the phenomenon of flooding that declines the heat transfer efficiency of the surface [19,20]. In efforts to maintain the Cassie state of the droplet, previous studies have focused on decreasing the solid-liquid contact area [21,22] or the number of droplet nucleation sites [23,24] by designing increasingly smaller arrays or approximate arrays, from micro to nanoscale size, such as pine needle shapes [6], microconical architectures [25], nanoscaffolds [26], microratchet arrays [27], and vertical arrays of carbon nanotube (CNTs) [28,29]. These surfaces indeed exhibit an enhancement in dropwise condensation by collecting a volume of water three times higher than that in the case of plate surfaces [30], achieving a 100% higher heat flux than that on the plane hydrophobic surface [31], and reaching a directional transport efficiency of approximately 80% for tiny droplets [27].…”

ANALISA TRANSFER PANAS PADA KONDENSASI LUAR DENGAN MENGGUNAKAN REFRIGERANT R-134a

“…Beberapa peneliti terdahulu menggunakan berbagai material untuk menciptakan permukaan dengan energi permukaan kecil sehingga dapat menciptakan droplet pada permukaan. Tripathy et al [8] melakukan penelitian kondensasi dengan menggunakan graphene sebagai promotor dan air sebagai fluida kerja dan dapat menghasilkan kondensasi dalam mode dropwise dengan kenaikan koefisien transfer panas hampir 3 kali lebih besar dibandingkan dengan kondensasi tanpa promotor dan menghasilkan droplet yang stabil pada permukaan selama 24 jam.…”