Effect of Steam Flow Rate and Storage Period of Superhydrophobic-Coated Surfaces on Condensation Heat Flux and Wettability

Nataliia Fedorova,Lucia Helena Prado,Ana Zbogar-Rasic,Christian Lindner,Antonio Delgado,Sannakaisa Virtanen,Vojislav Jovicic

doi:10.3390/pr9111958

Abstract

The jumping-droplet phenomenon occurring on superhydrophobic (SHPhob) surfaces under special conditions may be beneficial for numerous systems using condensation, due to the reported increased heat transfer coefficients. One technique to create a SHPhob surface is coating, which can be applied to larger areas of existing elements. However, challenges are associated with coating stability and the realization of continuous dropwise condensation. This research examined the condensation of steam at different flow rates (2, 4 and 6 g/min) and its influence on heat flux and water contact angles on the SHPhob spray-coated aluminum samples. Special emphasis on the impact of time was addressed through a series of one and five-hour condensation experiments on the samples with different storage periods (coated either one year ago or shortly before testing). Over the experimental series at a higher steam flow rate (6 g/min), heat flux decreased by 20% through the old-coated samples and water contact angles transferred from the superhydrophobic (147°) to hydrophobic (125°) region. This can be attributed to the joint effects of the partial coating washout and the adsorption of the condensed water within the porous structures of the coating during steam condensation. The new-coated samples could sustain more than fifty hours of condensation, keeping the same heat fluxes and SHPhob characteristics.

Highlights

As the need for more efficient ways of condensation heat transfer grows, so does research interest in superhydrophobic (SHPhob) surfaces
The increase in the steam flow rate led to the increase in thebetween condensation heat flux lower thermocouple in the cooling block
The current study focused on examining the superhydrophobic-coated aluminium samples under steam condensation of various durations and at different steam flow rates

Summary

Introduction

As the need for more efficient ways of condensation heat transfer grows, so does research interest in superhydrophobic (SHPhob) surfaces. In comparison to conventional dropwise condensation, jumping-droplet condensation can occur on SHPhob surfaces, which is reported to increase heat flux up to 25% [1]. This may be beneficial for numerous systems, including heat exchangers, heating, ventilation and air conditioning, electronics cooling, heat pipes, thermal diodes, heat pumps and many others [1,2,3]. A variety of fabrication techniques exist to make a SHPhob surface, such as electrochemical deposition to create micro/nanostructured surfaces, coating (e.g., spraying or dipping), lubricant infusion, etching (chemical or physical), and combinations of different methods [4,5].

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