# Review of Hygroscopic Coating on Aluminum Fin Surface of Air Conditioning Heat Exchanger
## 5 Conclusions  
Conventional air conditioning has weak dehumidification capacity and high energy consumption, cannot meet people's requirements. In recent years, substantial research has been focused on improving the dehumidification capacity of air conditioners by optimizing the fins of air conditioner heat exchangers to achieve energy-saving and comfortable effects. This paper reviews two kinds of heat exchangers modified by coating, including desiccant-coated heat exchangers and hydrophobic/hydrophilic coated heat exchangers.  
Desiccant-coated heat exchangers have displayed the potential to provide superior dehumidification capacity. Different materials have been coated on desiccant-coated heat exchangers to achieve an efficient performance. Some latest studies show that the composite desiccants made by mixing LiCl salt with the pure silica gel have performed better than their pure counterparts. Besides, the influencing factors have also been discussed, such as  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Aluminum Sheet Types** & **Advantages** & **Disadvantages** \\ \hline Conventional & Simple production and low initial & Weak dehumidification capacity, low heat \\  & investment & transfer coefficient \\ Desiccant-coated & Strong dehumidification capacity, & High initial investment and difficult \\ Hydrophobic coated & High heat transfer coefficient & system control \\ Hydrophilic coated & Strong dehumidification ability & Weak dehumidification capacity \\ Hydrophobic/hydrophilic coated & High water droplet nucleation rate and & Low heat transfer coefficient \\  & & Expensive to fabricate and poor \\  & surface heat transfer efficiency & mechanical durability \\ \hline \hline \end{tabular}
\end{table}
Table 1: Types of aluminum fins and their characteristics.  
air velocity increased, the adsorption and desorption speeds also increased. Hydrophobic/hydrophilic coated heat exchangers are also widely used in air conditioning dehumidification. Moreover, many experiments have shown that hybrid hydrophobic-hydrophilic coated surfaces have better dehumidification performance than single hydrophobic or hydrophilic aluminum surfaces.  
Lastly, although desiccant-coated heat exchangers and hydrophobic/hydrophilic coated heat exchangers have extraordinary potential in indoor dehumidification, there are many challenges here that we need to continue to research and improve.  
Resources, S.H. and W.C.; investigation, W.C.; writing--original draft preparation, S.H.; writing--review and editing, S.H.; supervision, X.Z.; funding acquisition, W.Y. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Key R&D Program of China: Low Energy Dew Point Cooling for Computing Data Centres [2016 YFE0133300]; EUROPEAN COMMISSION: Horizon 2020-Research and Innovation Framework Programme: Low Energy Dew Point Cooling for Computing Data Centres [734340-DEW-COOL-4-CDC-MSCA-RIS. and \"The APC was funded by Hunan Provincial College Innovation and Entrepreneurship Education Base (REANG ECO-ENERGY Innovation and Entrepreneurship Education Base) Construction Fund\".  
The authors declare no conflict of interest.