Dropwise condensation enhancement on cylindrical tubes via external screen meshes

• External screen mesh with a small annular gap enhances dropwise condensation on tubes. • An optimal mesh open-area ratio (0.55 ratio) maximizes condensation heat transfer coefficient. • Smaller tube diameter (6 mm), revealing strong curvature effects that enhance heat transfer. • Mesh screen boosts droplet departure frequency, thereby sustaining dropwise condensation. Dropwise condensation enhancement is generally achieved through surface coating or chemical modification. These methods often involve complex fabrication, chemical instability, and long-term durability concerns. Therefore, a simple and passive alternative that enhances condensation without modifying the surface is desirable, particularly for cylindrical geometries. This experimental research investigates the enhancement of dropwise condensation on horizontal copper tubes surrounded by external polyethylene screen meshes. Three different mesh sizes (open area ratios of 0.49, 0.53, and 0.72) were positioned concentrically around 6 mm and 8 mm diameter tubes with a controlled vapor gap. Results establish a notable enhancement in heat transfer compared to simple tubes. For the 6 mm diameter tube, the intermediate mesh improved the heat transfer coefficient (HTC) by 36% (to ∼12 kW/m 2 K), while the coarse mesh increased it by ∼10% (to 13 kW/m 2 K). However, the finest mesh reduced performance (∼30% below that of the bare tube) due to excessive vapor resistance and restricted droplet mobility. The intermediate mesh also reduced droplet departure diameter by 70% (from 1.1 cm to 0.32 cm), promoting earlier detachment and higher surface renewal. Similar trends were observed for the 8 mm tube, with HTC increases of ∼25% and 18% for the intermediate and coarse meshes, respectively. However, their absolute values were lower. The enhancement arises from coupled capillary-driven drainage, improved near-wall vapor transport, and modified droplet dynamics. These results highlight that a non-contact screen mesh near and around a tube could be a novel approach for condensation enhancement.