Search

• Dehumidifier with PEM is suitable for the humidity control in refrigerators. • Performance of PEM dehumidifier under -10~10°C conditions was experimentally investigated. • The dehumidifier has a starting voltage, which is higher at lower air temperatures. • With the increase in applied voltage, the operating current first increases and then drops. • Performance changing rate with operating parameters is much lower under sub-zero temperatures, due to possible icing and swelling inside the membrane. • The low temperature performance is not as good as normal, but the efficiency is still competitive. Dehumidifier with Polymer electrolyte membrane (PEM) is suitable for high-accuracy, limited-space humidity control in refrigerators. This study experimentally investigated the performance of PEM-based dehumidifier under the temperature range of -10~10°C. Empirical equations of PEM water content at refrigerator temperatures were developed. Results showed that although the low-temperature performance of electrolytic dehumidifier is not as good as that of room temperature, the efficiency (~1.3 × 10−2 g·J−1·m−2) is still competitive to desiccant or electrochemical methods. The dehumidifier has a starting voltage, and the voltage is higher at lower air temperatures (i.e. 1.3V for 26.1°C and 2.3 V for -3.9°C). During dehumidification, the operating current first increases significantly and then drops as the applied voltage increases, leading to a first increase and then steady dehumidification rate. The peak of current occurs at a smaller voltage as the air temperature decreases, i.e. 1.8V for 0°C and 2.5V for 26°C. Furthermore, the dehumidification rate increases as the air temperature and flow rate increases, while the changing rate with operating conditions was lower at sub-zero temperatures. Dehumidification has little effect on the oxygen concentration or temperature increment of the supply air. Characterizations also indicated that there was no obvious physical change on the PEM surface after operating at low temperatures. However, there exists a starting temperature for the dehumidifier, i.e. -9.5°C for the 3V applied voltage, which is due to the possible icing and swelling problem within the membrane. This study provided a new method, and proved its feasibility for dehumidifying at refrigerator temperatures. [ABSTRACT FROM AUTHOR]

Electrolytic air dehumidification (vapor electrolysers) based on proton-exchange membrane (PEM) is competitive to conventional dehumidifiers, but serious degradation has been found in long-running applications. This study conducted the durability test of electrolytic dehumidifier, under continuous operation for more than 250 h. Changes in current and dehumidification rate were analyzed and compared to those for fuel cells and water electrolysers. Physicochemical and electrochemical changes of the materials before and after the test were investigated. Results show that higher applied potential or higher air humidity corresponds to a larger dehumidification amount, while performance attenuates more quickly over time. When the applied potential increased from 2 V to 4 V, the degradation rate increases from 23% to 67% at 90% air humidity. Simultaneously, the internal resistance of PEM element increased from 0.419 to 1.45 Ω and the reaction resistance changed from 1.13 to 2.17 Ω, indicating by in-situ and ex-situ EIS. By characterization analysis, it indicated that the corrosion of the anode-side catalyst IrO 2 is the main reason for the long-term attenuation. The grain size of almost all IrO 2 faces reduced after 250 h dehumidification, and the content of active metal of the catalyst lost by 54.3%. The dissolution rate of IrO 2 also increases with increasing applied potential. Besides, there is almost no physical or chemical damage on PEM or cathode catalyst before and after the durability test. This research clarifies the micro-scale changes of the materials during long-term operation, and discloses the degradation mechanism of PEM-based electrolytic dehumidifiers. • Durability of electrolytic air dehumidifiers under 250 h continuous operations is tested. • The higher the dehumidification rate, the faster the performance decays. • As applied voltage increases, the degradation rate and PEM resistance increase significantly. • The over-time decay is mainly due to the corrosion of anode-side catalyst IrO 2. • There is almost no physical/chemical damage on PEM or cathode catalyst after the test. [ABSTRACT FROM AUTHOR]

PEM-based electrolytic air dehumidification is innovative due to its high efficiency, compact size and cleanness. However, high polarization loss and severe performance degradation have been observed, especially at high applied voltages (>2.5 V). Understanding the V–I characteristics is critical to performance optimization. This study experimentally investigated the V–I characteristics and internal response of materials under various operating conditions, with in-situ Electrochemical Impedance Spectroscopy (EIS) methods. Real-time mass transfer, electrochemical polarization and reaction dynamics of PEM components during dehumidification were derived by EIS. Then, a fast prediction model was built to directly predict the dehumidification rate and attenuation without any iteration, suitable for online monitoring and adjustment. Compared to other models, this model can take a quick understanding of the impact of operating conditions on the material characteristics inside the PEM element. The deviations of current density, PEM proton conductivity and moisture removal were 3%, 11.2% and 15.3%, respectively, compared to experiment data. Results showed that when the applied voltage changed from 1.5 to 3.5 V, the high-frequency resistance of the PEM element increased from 1.69 to 2.69 Ω, and the PEM proton conductivity decreased by about 38 times. The sharp drop in PEM proton conductivity resulted in a current attenuation. With this model, requirements for key components of PEM dehumidification were also obtained. Analysis of the overpotential distribution showed that increasing the water retention and reducing the dependence of proton conductivity on water molecules of the PEM can effectively improve the performance. This research provides guidance for the performance optimization and material selection of PEM-based dehumidification. • V–I characteristics of electrolytic air dehumidifier were explored with in-situ EIS. • Decrease in PEM proton conductivity was the main reason for current attenuation. • A one-dimensional fast prediction model was built with acceptable deviations. • The model can quickly predict performance attenuation during dehumidification. • Guidelines for performance optimization and material selection was provided. [ABSTRACT FROM AUTHOR]

An electrochemical air dehumidification system with polymer electrolyte membrane (PEM) was developed. The system performance under various operating conditions was investigated experimentally. A semi-empirical prediction model was also developed with multi-parameter linear regressions. Results showed that the novel system could dehumidify the air flow, with a humidity decrease from 90% (inlet) to less than 30% RH (outlet) under a 3 V electric field, which is promising as it can achieve an independent, portable and energy-efficient moisture removal. The steady-state dehumidification performance derived was 80 kg/(kW h·m 2 ), or 54 kg/(h·V·m 2 ), which were advantageous to current electrochemical dehumidifiers. Specially, this simple element has a volume of only 0.001–0.01‰ of traditional ones, which is also suitable for cascading or multilevel assembly to satisfy various requirements for commercial and industrial applications. The moisture transfer, mainly caused by the electrolysis (+), electro-osmosis (+) and back diffusion (−), increased significantly with the increases in anode-side air humidity and flow rates. When the inlet air humidity increased from 70 to 90%, the dehumidification rate increased about 1.5–2 times. However, only 30% of total power input was effectively used in current element, and the rests were lost, leading to a relatively low system COP (≈0.33). The main reason was that the back-diffusion mass transfer was found to be up to 2.3 times larger than expected, causing by the high moisture content in cathode-side layers (mainly the diffusion layer), which seriously deteriorated the system performance. Therefore, enhancing the diffusion layer performance may help to optimize the dehumidification efficiency effectively. The suggested measures include improving the structure, changing the internal surface parameters or adding microporous layers, etc. [ABSTRACT FROM AUTHOR]

Humidity control is important in electronic manufactures as the equipment and components have increasing moisture sensitivity level in recent years. Electrolytic dehumidifier is an innovative independent dehumidification technology, as it is simple, compact, accurate, safe and environmentally friendly, etc. But previous research was very limited. In this paper, we developed an electrolytic dehumidifier element with polymer electrolyte membrane (PEM), and investigated the performance under various electric fields experimentally. Nafion 117 was used as the PEM. Experimental data showed that the energy efficiency was 1.5~1.8×10 -2 g/(J·m 2 ), which was competitive to other electrochemical dehumidifiers. The mass transfer increased effectively with the increase of electric field. When the supplied electric field increased from 1.5 to 3.8V, the removal rate increased around 3 times. The increase of applied voltage also caused a first increase and then decreased current, showing a maximum value at 2.5-2.9V. The possible reason was the increase of overpotentials deteriorated the system performance. Besides, the mass transfer and current also increased with the air mass flow rates. Therefore, this dehumidifier is a promising alternative for independent humidity control for precision manufactures. [ABSTRACT FROM AUTHOR]

Humidity control is necessary for a comfortable and healthy indoor environment. The electro-chemical dehumidification is promising recently due to its economical, space-flexible and en-vironmental-friendly characteristics. In this study, an electrolytic dehumidification system with polymer electrolyte membrane was developed, which size was as small as 10-5~10-6 m3. The dehumidification and energy performance were investigated under various operating conditions. Results showed that this method could dehumidify the air flows. The dehumidifi-cation rate increased significantly with the air temperature, which improved more than 2 times when the temperature increased from 22 to 41°C. It also increased significantly with air flow rates, which the growth trend could be divided into three phases. The current also increased with the air temperature and flow rates. Furthermore, the steady-state energy efficiency ob-tained was 0.43×10-2 g/(J•m2), which was competitive to current electrochemical methods. Therefore, the dehumidification method is promising for independent and portable humidity control. [ABSTRACT FROM AUTHOR]

Abstract: Electro-osmotic regeneration for the solid desiccant has been proved to have many merits such as regeneration without the heat source; energy-saving and simple structure. However; the previous work has revealed that its performance is seriously limited by the severe Joule heating effect and electrode corrosion; which demands further improvement to meet the practical requirement. In this paper; four possible improvement methods are investigated experimentally; including changing the material of anode; changing layout of cathode; applying the interrupted power and optimizing the electrical field strength. Through detailed experiments and analysis; we found that applying the platinum-plated titanium mesh as anode could improve the working lifetime from 6h to over 120h and effectively reduce Joule heating effect simultaneously; laying a piece of filter cloth under the cathode could enhance the EO regeneration rate up to 0.0021gs−1; the application of interrupted power could increase the regeneration rate up to 1.5 times; the optimal on–off-time was found at 30s:1.3s with 17Vcm−1 electric field strength and 30s:0.8s with 11Vcm−1; and the most suitable value of electric field strength was observed as ranging from 8.5 to 13Vcm−1 in our EO regeneration system. [Copyright &y& Elsevier]

Abstract Liquid desiccant air-conditioning systems are promising as they can achieve independent dehumidification. Non-metallic materials, such as plastics, are good internal working plate materials due to their natural anti-corrosion and easy-processing characteristics. However, poor wettability severely limits the application. In this study, the enhancement of surface wettability and mass transfer performance for liquid desiccant dehumidification with plastic internal plates was achieved, with a newly developed, durable, super-hydrophilic modified surface. The plastic plates were first etched into micro-rod structures to improve durability, and then the surfaces were prepared by adhering the super-hydrophilic SiO 2 particles to the microstructures. Results showed that the liquid desiccant could completely spread on the coated plastic surfaces within 2 s, and the contact angle could be as low as 0°. Durability tests showed that after immersing in 40 wt% LiCl solution for 15 days, the liquid desiccant could still completely spread in 3 s. Furthermore, after 48 h of high-speed scouring (more than 1000 times of common conditions), the contact angle of desiccant maintained 0° on the coated surface, and fully spread within 22 s. By comparing coated to uncoated surfaces through experiments with dehumidification rigs, the wetted area of desiccant could be effectively increased by 1.5–5 times when the novel plates were used. The average film thickness decreased by 1.4–2.4 times and the moisture removal rate increased by 1.3–1.8 times for super-hydrophilic surfaces relative to original surfaces. For a case study with a typical building in Hong Kong, the annual energy consumption of air-conditioning systems could be predicated to decrease about 1/3 by using coated plastic plates. Therefore, this durable super-hydrophilic surface could significantly enhance the wettability, and thus enhance the performance of plastic LDACS. The manufacturing process of the surfaces is cheap and facile for industrialization. This study helps the optimization of liquid desiccant dehumidifiers, and other plastic applications with liquid-gas flows. [ABSTRACT FROM AUTHOR]