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Ion-conducting polymers (Ionomers) are critical in catalyst layers (CLs) of proton exchange membrane (PEM) fuel cells and water/vapor-fed electrolyzers, serving essential roles in proton conduction, electronic insulation, and water absorption. This review summarized the physical, chemical and economic parameters of CL ionomers across various PEM modules, focusing on long- and short-side-chain perfluorosulfonic acid (PFSA) ionomers. It also outlines recent efforts in PEM air dehumidification. Characterization methods for ionomer morphology (e.g. rods, swollen clusters, networks) and mass transfer resistance (e.g. ionomer/gas interfacial, catalyst/ionomer interfacial and intra-ionomer) were summarized. Optimal ionomer distribution at electron-proton-gas interfaces is crucial, as proton transfer requiring a thick and connected distribution and gas transport requiring a thin and dispersed distribution. Adjusting ionomer equivalent weight and ratio to catalyst can enhance distribution. Besides, CL ionomer design should emphasize product escape for water electrolyzers and reactant diffusion for vapor ones. Integration of multidimensional and multifunctional techniques, such as visual characterizations of Transmission Electron Microscopy and Nanoscale X-ray computed tomography and numerical simulations of Molecular Dynamics and lattice Boltzmann methods, is recommended for accurate assessment of ionomer behavior. This comprehensive review provides insights into ionomers in CLs, highlighting characterization methods and manipulation strategies, offering guidance for next-generation PEM modules. [ABSTRACT FROM AUTHOR]

Proper catalyst coated membrane (CCM) methods are significant for membrane electrode assembly (MEA) of PEM-based electrolytic dehumidification. In this work, four CCM processes, doctor blade, decal, electrostatic spraying, and modified pneumatic spraying methods, were employed for fabricating dehumidifier assemblies with low-load (0.6 mg/cm2) IrO2 catalyst layers (CLs). The physical and electrochemical properties of the as-prepared CLs were characterized, and the mass transfer resistance and dehumidification rate of the MEA were tested during actual operations. The optimal hot-pressing parameters were also determined. Results showed that the modified pneumatic spraying method can significantly improve the pore distribution and CL flatness by promoting the evaporation of solvent from catalyst slurry. The charge-transfer and ohmic resistances of MEA was 25.3 and 27.8 mΩ/cm2, respectively, which are the best values for those prepared using the four methods. The dehumidification rate was also the highest (0.105 g/h), 20–40% higher than that of other methods. Although the overall mass transfer resistance of assembly prepared by the electrostatic spraying was low, the CL structure was obviously loose and unable to bind to the membrane surface tightly, leading to high electrochemical resistance (6.6-fold that of pneumatic spray method). Besides, catalyst particles tend to agglomerate using the doctor blade method. The pore size of the CL prepared using the decal method was found to be too small (<300 nm), hindering reactant transfer and resulting in a low overall mass transfer coefficient. This study provides a practical direction for the preparation of economical and high-performance dehumidifiers or electrolyzers. [ABSTRACT FROM AUTHOR]

PEM-based electrolyte dehumidification is suitable for small-space and high-precision occasions, but the influencing level of various operating conditions is still unclear. This paper investigated the four factors (air temperature, humidity, flowrate, and applied voltage) that affect the dehumidifier's performance (moisture removal rate and current density). Through orthogonal experiments, it was found that process air temperature was the most significant parameter affecting performance, followed by air humidity and applied voltage. The moisture removal rate and current density rose almost linearly as the air temperature increased. Through parameter analysis, the best working conditions of the dehumidifier were found as: applied voltage = 3 V, air flowrate = 2.7 × 10−2 g/s, air temperature = 35°C and air humidity = 90%. Then, by fitting empirical formulas of the PEM conductivity and water content difference on both sides of the membrane, an operation simulation of dehumidification process was established by MATLAB Simulink. Compared with experiments, the deviations (~10%) were acceptable. This simulation used a 100 L box and a 3.5 × 3.5 cm2 membrane dehumidifier as a case study, and the optimized parameters derived from the experiment were used. Under typical air conditions in Guangzhou, to reduce the inside humidity to 60%, the dehumidification time for the cabinet was the shortest in autumn, about 5.6 hours. Besides, dehumidification energy consumption was the highest in summer, at 39.4 kJ. And energy consumption was the lowest in winter under the same dehumidification time. This research contributes to the operation optimization of electrolyte dehumidifiers. [ABSTRACT FROM AUTHOR]

The liquid contact angle on a solid surface is important in evaporation processes, which characterizes the wettability, and the spread of liquid films or droplets on the working surface. Thus, it critically affects heat and mass transfer, and evaporation performance accordingly. The evaporating droplet contact angle is complicated, accompanied by internal flow, heat/mass transfer, and phase change, and has received considerable attention in recent years. This paper summarizes the recent research progress of the measurement and simulation methods for determining the liquid contact angles of evaporation processes, including experimental approaches such as the sessile droplet, Wilhelmy and inclined plate methods, as well as numerical approaches such as the molecular dynamics, computational fluid dynamics, and lattice Boltzmann methods. The principles, applicable conditions, and limitations of these methods are analyzed and compared. This paper also discusses the measurement methods and effects of influencing factors related to the evaporating droplet contact angle, such as temperature and velocity distribution. Besides, it is discussed to enhance liquid evaporation by changing the droplet contact angle. Finally, a brief summary and suggestions for future work are presented. [ABSTRACT FROM AUTHOR]

The article offers information on fifth International Symposium on Heat Transfer and Energy Conservation (ISHTEC2016) held on November 11-14, 2016 in Guangzhou, China. Topics discussed include new heat transfer theories, heat transfer enhancement technologies, micro/meso-heat transfer, and the heat transfer problems in energy use systems.

Packed liquid desiccant dehumidification systems are regarded as energy-saving and environmentally friendly technologies compared with conventional dehumidification technologies. The packing type plays a significant role in the system performance, but comparative studies of the different types are limited. First, this article investigates the dehumidification performance of liquid desiccant dehumidification with three packing types: corrugated structured, S-shaped polyvinyl chloride, and globular-shaped polypropylene. Then, the operation performance of solar-assisted liquid desiccant air-conditioning systems with different packings is simulated. A commercial building in Hong Kong was chosen as the case study. Results show that each specific packing surface area and structure determines the dehumidification performance by significantly influencing the liquid/air contact area and time. The enthalpy and moisture effectiveness of the corrugated structured packing were found to be 1.69 and 1.60 times those of S-shaped polyvinyl chloride packing, and 1.97 and 1.87 times those of globular-shaped polypropylene packing. The main reason is that the corrugated structured packing has a denser structure with a smaller volume of individual modules, which could provide a large specific surface area, but the dehumidification performance did not increase proportionally with the specific surface area. When the specific surface area increased from 81.8 to 537.3 m2/m3, the enthalpy and moisture effectiveness increased from 0.35 to 0.6 and from 0.38 to 0.61, respectively. Furthermore, the simulation results showed that for the commercial building, the maximum electricity savings percentage for globular-shaped polypropylene packing liquid desiccant air-conditioning systems, S-shaped polyvinyl chloride packing liquid desiccant air-conditioning systems, and corrugated structured packing liquid desiccant air-conditioning systems was 11, 21, and 42%, respectively. For globular-shaped polypropylene packing liquid desiccant air-conditioning systems, a minimum solar collector area of 219m2was required to avoid consuming more electricity. The authors also found that the dehumidification performance could be enhanced with an increase of desiccant/air mass flow rate ratio and inlet air temperature. This article will help researchers and engineers optimize the design of liquid desiccant air-conditioning systems with different packing types. [ABSTRACT FROM PUBLISHER]