Superhydrophilic surfaces were fabricated on copper substrates by an electrochemical deposition and sintering process. Superhydrophobic surfaces were prepared by constructing micro/nano-structure on copper substrates through an electrochemical deposition method. Conversion from superhydrophobic to superhydrophilic was obtained via a suitable sintering process. After reduction sintering, the contact angle of the superhydrophilic surfaces changed from 155° to 0°. The scanning electron microscope(SEM) images show that the morphology of superhydrophobic and superhydrophilic surfaces looks like corals and cells respectively. The chemical composition and crystal structure of these surfaces were examined using energy dispersive spectrometry(EDS) and X-ray diffraction(XRD). The results show that the main components on superhydrophobic surfaces are Cu, Cu2 O and Cu O, while the superhydrophilic surfaces are composed of Cu merely. The crystal structure is more inerratic and the grain size becomes bigger after the sintering. The interfacial strength of the superhydrophilic surfaces was investigated, showing that the interfacial strength between superhydrophilic layer and copper substrate is considerably high.
The methods were studied to improve the cooling performance of the absorption refrigeration system(ARS) driven by low-grade solar energy with ultrasonic wave, while the mechanism of ultrasonic wave strengthening boiling mass transfer in LiB r solution was also analyzed with experiment. The experimental results indicate that, under the driving heat source of 60–100 oC and the ultrasonic power of 20–60 W, the mass flux of cryogen water in Li Br solution is higher after the application of ultrasonic wave than auxiliary heating with electric rod of the same power, so the ultrasonic application effectively enhances the heat utilization efficiency. The distance H from ultrasonic transducer to vapor/liquid interface significantly affects mass transfer enhancement, so an optimal Hopt corresponding to certain ultrasonic power is beneficial to reaching the best strengthening effect for ultrasonic mass transfer. When the ultrasonic power increases, the mass transfer obviously speeds up in the cryogen water; however, as the power increases to a certain extent, the flux reaches a plateau without obvious increment. Moreover, the ultrasound-enhanced mass transfer technology can reduce the minimum temperature of driving heat source required by ARS and promote the application of solar energy during absorption refrigeration.
To enable the use of metallic components in direct methanol fuel cells(DMFCs), issues related to corrosion resistance must be considered because of an acid environment induced by the solid electrolyte. In this study, we report the electrochemical behaviors of metal-fiber-based porous sintered components in a simulated corrosive environment of DMFCs. Three materials were evaluated: pure copper, AISI304, and AISI316 L. The environmental factors and related mechanisms affecting the corrosion behaviors were analyzed. The results demonstrated that AISI316 L exhibits the best performance. A higher SO42- concentration increases the risk of material corrosion, whereas an increase in methanol concentration inhibits corrosion. The morphological features of the corroded samples were also characterized in this study.
Direct methanol fuel cell(DMFC)has great potential to replace the traditional battery in the field of portable power sources.This study investigates the operational and structural aspects of a vapor-feed semi-passive DMFC supplied with concentrated methanol.The effectiveness of using vaporous methanol to improve the cell performance is experimentally validated.Results indicate that there exits an optimal value of methanol concentration that favors both methanol supply and control of methanol crossover(MCO).With the increase in vaporization temperature,the cell performance can be enhanced.Based on the traditional structural design,a sintered porous metal plate is further used to depress the impact of MCO so that the cell performance can be significantly improved at a relatively higher methanol concentration.This is of great importance to enhance the energy density and operating duration for portable applications.The mechanisms related to the performance behaviors are discussed in detail.
