Enhancing Condensation Heat Transfer on Three-Dimensional Hybrid Surfaces
Journal
Joule
Journal Volume
3
Date Issued
2019-11-20
Author(s)
Abstract
Given the self-unbridging phenomenon, the confined liquid-film thickness, and the dragging motion observed on the 3D hybrid surfaces, enhanced condensation heat transfer on the 3D hybrid surface over a large subcooling (ΔTsub) range was achieved. In addition, the obtained heat flux of 655 ± 10 kW·m−2 at ΔTsub ∼18 K exceeded the values in the literature regarding state-of-the-art micro/nanostructured surfaces. This suggests that the 3D hybrid surface can be applied to enhance the condensation in various applications. In recent years, micro/nanostructured surfaces have been applied to enhance condensation heat transfer. However, condensation heat transfer is greatly deteriorated by the flooding phenomenon that occurs at high subcooling temperatures. Here, we propose a three-dimensional (3D) hybrid surface to enhance the condensation at high subcooling temperatures. The 3D hybrid surface consisted of superhydrophobic (SHB) Si nanowire (SiNW) arrays and hydrophilic microchannels. The microchannels could confine the liquid-film thickness, and the liquid bridges formed on the 3D hybrid surfaces could be self-removed. Both of these characteristics prevent the surfaces from flooding. In addition, liquid droplets formed in the SiNW regions were dragged into the microchannels, which also improved the heat transfer. The heat transfer coefficient on the 3D hybrid surface could be enhanced over a large subcooling range. More remarkably, a record high heat flux of 655 ± 10 kW·m−2 was obtained on the 3D hybrid surface. Condensation is widely seen in various applications. Condensation can be enhanced by using micro/nanostructured surfaces. Most of the micro/nanostructured surfaces show enhanced condensation at low subcooling temperatures (ΔTsub), but the condensation performance deteriorates significantly at high ΔTsub due to the buildup of a liquid film on the structured surfaces as the ΔTsub increases. Nevertheless, many applications require operation at a high ΔTsub, including distillation plants, industrial refrigeration systems, and steam power plants. Thus, enhancing the condensation at high ΔTsub is necessary. Here, by using a three-dimensional (3D) hybrid surface, for the first time, the condensation heat transfer is enhanced over a wide range of ΔTsub from 2 to 18 K. In addition, a record high heat flux of 655 ± 10 kW·m−2 is obtained at ΔTsub ∼ 18 K. The concept of this work can be applied to improve the condensation performance in a wide range of applications involving condensation.
Type
journal article
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