External humidifying

The results dearly show an improved performance when using humidified gases, because they keep the membrane well hydrated. Therefore, to increase the power density without increasing the size and complexity of the system, proper water management without an external humidifier is an important objective. 

Figure 19.9. Polarization curves and the corresponding power density curves of fuel cells with a Pt/C/Nafion-PTFE/C eatalyst cathode and a Pt/C/Nafion membrane-based cathode, respectively. Measured at 80 °C. The hydrogen and air reactant gases were externally humidified at 90 °C and 85 °C, respectively. The flow rates were 50 mL min for hydrogen and 200 mL min for air [49]. (Reprinted from Eleetroehemistry Communications, 8(7), Tian ZQ, Wang XL, Zhang HM, Yi BL, Jiang SP, Microwave-assisted sjmthesis of PTFE/C nanocomposite for polymer electrol)4e fuel cells, 1158-62, 2006, with permission from Elsevier.)...

A highly water-permeable PEM would facilitate water removal via liquid transport toward the anode, alleviating the problem of cathode flooding and anode dehydration. Erom a system perspective, it is deemed beneficial to make use of internal humidification of CLs and PEM by water that is produced at the cathode. This mode of internal water management obviates the need for external humidifiers. It demands, however, precise control of water permeation rates through the PEM and of vaporization rates in partially saturated porous electrodes. Therefore, it is cmcial to know how relevant parameters of water transport (diffusion, hydraulic permeation, electro-osmotic drag, vaporization, and condensation) depend on PEM morphology and thermodynamic conditions. 

Water may be supplied by externally humidifying the hydrogen supply... 

A commercial combustion turbine with the provision to inject, at any point upstream of the combustor, the externally supplied humidified and preheated supplementary compressed air. Engineering and mechanical aspects of the air injection for the compressed air injection plant concepts are similar to the steam injection for the power augmentation, which has accumulated significant operating experience. 

The concept of injecting humidified and heated compressed air just after the gas turbine compressor is another very interesting way to increase power and efficiency. In this system, compressed air is added to the compressed discharge air. The compressed air is about 5% of the main gas turbine air and this air after it has been compressed using an external compressor is then injected into an air saturation device where steam obtained from the HRSG unit is then injected into the device to saturate the air with water and the saturated air then is further heated in the HRSG before it is injected into the compressor discharge of the gas turbine. 

The respiratory system is responsible for mediating gas exchange between the external environment and the bloodstream. The upper respiratory tract conducts air to the lower respiratory passages and ultimately to the lungs. It also humidifies and conditions inspired air and serves to protect the lungs from harmful substances. In the lungs, gas exchange takes place between the alveoli and the pulmonary circulation. 

Figure 6.11. Nyquist plots for MEAs containing different proton-conducting ionomers at 0.85 V without external humidification catalyst loading = 0.4, 0.7 mg Pt/cm2 for anode and cathode, respectively TceU = 25°C Pressure = 1 atm and H2/02 flow = 400 cmVmin [8]. (Reprinted from Electrochimica Acta, 50(2-3), Ahn SY, Lee YC, Ha HY, Hong SA, Oh IH. Effect of the ionomers in the electrode on the performance of PEMFC under non-humidifying conditions, 673-6, 2004, with permission from Elsevier.)...

Cyclical Humidity Changes in the Tomb. The isothermal nature of the tomb simplifies its physicochemical description because one key variable is now fixed. The humidity data did not show the same degree of stability as the data for temperature did. Figure 6 shows that the external humidity peaks in July. The internal humidity follows this trend but peaks 1.5 months later at a value of 9.1 g of H20/m3 or 32% RH at 28 °C. These data suggest an annual cycle, and these results indicate that the tomb of Nefertari is not totally isolated, even if it is closed, but that it is weakly coupled to the external environment. Consequently, the tomb is progressively humidified, as is the entire Nile Valley. 

In most fuel cell operations, humidified gases are used to ensure proper membrane hydration. Hence, the ability to remove liquid water becomes the primary concern of GDL selection. PTEE is often used to increase the GDL hydrophobic-ity. Contact angle is commonly used to measure the hydrophobicity (typically in the range between 120 and 140°). However, Gurau et al. suggested that external contact angle measurements were more indicative of the GDL surface roughness than the capillary forces in the GDL pores (which reflects the real measurement of water removal capacity). They presented a new method for... 

On the other hand, the use of external humidification is essential at high temperatures, because the concentration gradient of H2O in the membrane of individual cells would be more uniform if both air and hydrogen streams were humidified externally. The external water supply helps to balance the combined effects of electro-osmotic drag and back diffusion permitting to maintain the performance of the membrane. External humidification is practically useful also below 60°C, at least for medium large-size FCS. 

A possibility is to saturate at different temperatures the reactants before they enter into the stack [33]. This approach can be accomplished by several procedures based on external dewpoint, external evaporation, steam injection with downstream condensers, or flash evaporation. High temperature values allow to absorb significant water amount in gas streams and then transport it inside the stack compensating the water losses due to internal fast evaporation. However, the main problem with external humidification is that the gas cools after the humidifier device, the excess of water could condense and enter the fuel cell in droplet form, which floods the electrodes near the inlet, thereby preventing the flow of reactants. On the other hand, internal liquid injection method appears preferable for example with respect to the steam injection approach because of the need of large energy requirement to generate the steam. 

The matured oocytes were visually judged on the basis of their external characteristics (e.g. expansion of the cumulus cells and presence of smaller and darker oocytes), as indicators of degree of maturity. The selected oocytes were then placed in a culture Petri-dish containing TALP-hepes medium, washed two times in TALP-hepes and one time in Fert-Talp medium. 15-20 oocytes were transferred into the 50p.l droplet of Fert-Talp media that was supplemented with caffeine and Heparin. Then a final volume of the prepared semen, containing 1-2 x 10 sperm cells/ml, was added to the 50pl droplet containing the matured oocytes. The in-vitro fertilization was performed in media supplemented with 20 pg of heparin/mL and 6 mg/mL of fatty Iree-acid BSA fraction, covered with mineral oil for 18 h in a humidified atmosphere of 5% CO2 and at 39 C in air. 

Because the lung functions in close contact with what is often a variable external environment, one of the important functions of the lung is to equilibrate inhaled air to a constant temperature (37°C) and humidity and to remove foreign objects and organisms from the air before they reach the systemic circulation. Most temperature equilibrium and humidification of the inhaled air oecurs in the upper nasal passages, where it initially comes in contact with the rich, warm vascular supply of the nasal cavities and is humidified by nasal secretions. In addition, the hairs and mucous coating of... 

The electrons are drawn to an external circuit through conductive backing layers to generate electricity, and the protons migrate through a humidified solid electrolyte (proton exchange membrane, PEM) and react with oxygen at the cathode ... 

Emulation cells, i.e. without MEA and in which water is supplied by external injection in a continuous air stream, such as that used by Chen (2010) or by Conteau et al. (2010), or by condensation of moisture contained in streaming humidified air. 

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