大部分冷凝器的熱傳表面具有高表面能的特性，所以比起滴狀冷凝而言更容易在熱傳表面上生成液膜形成膜狀冷凝。然而膜狀冷凝具有高熱阻的特性進而導致熱傳性能低落。而滴狀冷凝則會在表面上形成許多顆粒液滴而不會形成液膜熱阻，使滴狀冷凝的熱傳性能超過膜狀冷凝的四倍。所以可藉由將冷凝器表面改為疏水性表面產生滴狀冷凝的效果。 在冷凝器中經常將石墨烯濺鍍至熱傳表面上形成疏水性表面，因為石墨烯具有高化學穩定性及高耐久性的特點。不幸的是，對於低表面張力的液體，濺鍍石墨烯無法形成滴狀冷凝。可藉由R-245fa的接觸角來證明R-245fa在純銅及具有石墨烯塗層的銅上的接觸角幾乎沒有差異。但是實際上藉由濺鍍石墨烯仍有達到接觸角為小幅度提升或表面能降低的效果。 本實驗使用化學氣相層積法(CVD)，將石墨烯濺鍍至純銅圓鰭管表面上以提升冷凝熱傳性能。透過增加小幅度的接觸角，鰭管可在排水區域形成更少的冷凝液使傳熱面積增加。此外，接觸角的增強受到鰭片間距極大影響，這是因為鰭片間距與冷凝液形成及冷凝液的曲率有關。較大的鰭片間距顯示比起較小的鰭片間距有著更凹的半月形狀，並且接觸角也有著較大的提升。 ;Most of the heat exchanger materials in condensation system associate with high surface energy and prefer inducing film than droplet on the surface. This film condensation mode generates high thermal resistance and leads low heat transfer performance. Meanwhile, the yielded heat transfer performance by dropwise condensation exceeds almost four times higher than filmwise condensation due to providing faster re-nucleation with smaller departure drop size. The dropwise mode occurs due to functionalization of surface becomes hydrophobic surface. Graphene is frequently used in the condensation system as hydrophobic promoter since offering high chemical stability to induce droplet on the surface with long durability. Unfortunately, the critical surface energy of graphene is not low enough to induce droplet for low surface tension liquid. This is proved by the contact angle difference of R-245fa whose low surface tension, on the graphene coating and bare copper only has a little difference. Even though the contact angle of R-245fa on the graphene coating and bare copper show almost no difference but the contact angle enhancement must occur or at least the wettability on the surface decreases since decreasing surface energy after graphene coating. Furthermore, the experimental investigation has been conducted to enhance the heat transfer performance of R-245fa on the horizontal integral fin tube surface which is coated by chemical vapor deposition (CVD) graphene. The integral fin tube provides thinning condensate on the drainage area which leads higher chance to increase heat transfer area by enhancing contact angle. Moreover, the contact angle enhancement is immensely affected by fin spacing due to fin spacing controls the occupied condensate and condensate curvatures. Higher fin spacing shows more concave meniscus shape than smaller fin spacing and leads higher chance for contact angle enhancement than smaller fin spacing.
