Dynamic Behaviors of Droplet Impacts in Dropwise Condensation on Horizontal Tube Bundles.

Abstract

Dropwise condensation offers substantial heat transfer advantages over filmwise condensation, enhancing the industrial condenser efficiency and reducing energy losses. However, the dynamics of condensate droplets on horizontal tube bundles remains complex and insufficiently studied. This paper presents a detailed investigation of the impact of dynamic behaviors of condensate droplets by numerical simulation using the Volume of Fluid model. The droplet Weber number (We^d) between horizontal tube bundles determines the characteristics of droplet impact behaviors. This study examines the effects of tube pitch and contact angle on We^d and its distribution of detached droplets, revealing the transition process of the We^d-dominant factors. Based on visualization results, three dynamic behaviors of condensate droplets impacting the lower tube are identified: attachment, rebound, and breakup. The dominant behaviors of multiple droplets impacting the lower tube under various conditions are clarified through the We^d distribution, leading to the establishment of a droplet impact regime map. Breakup behavior results in a larger proportion of the renewal area, with a maximum exceeding 88.80%, enhancing the surface flushing effect. However, it is essential to mitigate liquid film spreading to prevent the onset of near-FWC. Rebound behavior, characterized by minimal contact times down to 15.40 ms, make it more suitable for tubes that can perform quick self-renew. Finally, based on the characteristics of droplet impact behaviors, guidelines for regulating droplet behavior under different conditions are proposed. The findings provide critical insights for the design of novel dropwise condensers.