Liquid-Infused Surfaces for Boiling Heat Transfer Enhancement and Mitigation of Corrosion and Inorganic Scaling

Abstract

One of the key sustainable development objectives of the United Nations is to ensure a reliable and consistent supply of fresh water. However, the growing population, industrialization, and urbanization have made it increasingly difficult to access an adequate amount of potable water. Consequently, desalination of brackish and seawater, which accounts for 97% of the global water resources, has emerged as an effective solution to provide potable water. In recent years, advancements in desalination research have led to increased capacity in large-scale commercial desalination plants using traditional technologies such as membrane and thermal desalination. However, these methods consume significant amounts of energy, typically obtained by burning fossil fuels and coal, leading to inevitable environmental concerns. Therefore, desalination methods those work on alternative/renewable energy sources, such as solar still, holds great potential for replacing traditional methods on a large scale. Conventional solar still desalination works by evaporating fresh water from brackish sources, a process that is extremely slow. Research has been focused on enhancing the efficiency of solar stills. Historically, efforts were directed at maximizing the evaporation process to increase distillate output. A recent study suggested that instead of relying on evaporation, inducing nucleate boiling in the solar still basin by integrating it with tools that achieve concentrated solar power could significantly enhance distillate output. To maximize distillate output when nucleate boiling is induced, modifying the morphology of the solar still basin to enhance boiling heat transfer is necessary. Additionally, continuous and enhanced fresh water recovery from brackish sources poses challenges such as inorganic scaling and corrosion. In recent years, novel methods such as superhydrophobic surfaces and slippery liquid-infused surfaces have demonstrated excellent capabilities in inhibiting corrosion and inorganic scaling. However, concerns have been raised about their heat transfer capabilities due to insufficient liquid surface contact on these surfaces. In view of the above facts, the aim of this study was to demonstrate the effectiveness of a type of liquid-infused surface called binary surface (BiS) to inhibit scaling and corrosion without compromising the heat exchange efficiency. To this end, a highly-wetting Ultra-Omniphilic Surface (UOS) was prepared from a plain aluminum alloy surface (PS) using a bulk micro manufacturing approach. Later, the sub-surface micro/nanocavities of UOS were infused with a liquid lubricant to get BiS, which has two distinct superficial phases — solid phase as islands and liquid phase as puddles. Saturated boiling heat transfer experiments were conducted on the BiS and the critical heat flux (CHF) and the boiling heat transfer coefficient (HTC) were measured. The results were compared with the UOS and PS. In addition, high-speed visualization was employed for capturing the bubble dynamics at different heat fluxes and parameters such as bubble departure diameter (Dd), bubble departure frequency (f), and nucleation site density (NSD) were measured. The results revealed that the boiling heat transfer performance of water on the BiS surpasses both the PS and the UOS. The HTC on the BiS was 1.33 times and two times larger than those on UOS and the PS, respectively. The CHF obtained on the BiS was comparable to that on the UOS and 1.47 times larger than that on the PS even though a considerable portion of the BiS surface area was covered with the liquid lubricant and unavailable for boiling. Remarkably, an inspection of the high-speed videos has suggested the presence of the same liquid lubricant as the reason for the better boiling heat transfer performance of the BiS. The liquid lubricant that was spread over the BiS as puddles was found to prevent the growth of large vapor bubbles and extend the isolated bubble regime by delaying the lateral coalescence of adjacent bubbles. Lab-scale corrosion and scaling experiments were conducted on BiS in a simulated brackish water environment. Results indicated that BiS significantly outperformed PS and UOS in hindering scaling and corrosion. BiS exhibited nearly 50% less mass gain due to mineral deposition than on PS and UOS. Moreover, corrosion rates obtained from electrochemical and immersion tests showcased a notably slower metal degradation on BiS than on PS and UOS. This enhancement is attributed to well-distributed liquid puddles on BiS, promoting a smooth, defect-free surface that reduces foulants adhesion and shields the underlying metal from corrosion.