Air bleeding

Electrode insulators must also be designed for a particular service. The properties of the dust or mist and gas determine their design as well as the physical details of the installation. Conducting mists require specif lowances such as oil seals, energized shielding cups, or air bleeds. With saturated gas, steam coils are frequently used to prevent condensation on the electrodes. 

The function of the trap is to condense the hexane from the n-butyl-lithium solution. The checkers used a 1-L three-necked flask fitted with a short delivery tube (a quick fit air bleed tube was used), stopper, and rubber tubing connection. The submitters used a water aspirator and a 1-L filter flask with a drying tower between. 

A vacuum condenser has vacuum equipment (such as steam jets) pulling the noncondensibles out of the cold end of the unit. A system handling flammable substances has a control valve between the condenser and Jets (an air bleed is used to control nonflammable systems). The control method involves derating part of the tube surface by blajiketing it with noncondensibles that exhibit poor... 

Air bleed-in Openings at the end of a branch duct that provide increased flow rates for the transportation of heavy particulate matter. 

The air bleed is u.sed to maintain a constant condition. However, a control valve may be used instead. Control or hand valves in the lower pressure vapor lines to an ejector are not recommended, as they must be paid for in system pressure drop and ejector udlity requirements. 

Figure 6-32 illustrates ejector systems with large condensable loads which can be at least partially handled in the precondenser. Controls are used to maintain constant suction pressure at varying loads (air bleed), or to reduce the required cooling water at low process loads or low water temperatures [2]. The cooler W ater must not be throttled below the minimum (usually 30%-50% of maximum) for proper contact in the condenser. It may be controlled by tailwater temperature, or by the absolute pressure. 

However, the Pt anode is seriously poisoned by trace amounts of carbon monoxide in reformates (fuel gas reformed from hydrocarbon), because CO molecules strongly adsorb on the active sites and block the HOR [Lemons, 1990 Igarashi et ah, 1993]. Therefore, extensive efforts have been made to develop CO-tolerant anode catalysts and cell operating strategies to suppress CO poisoning, such as anode air-bleeding or pulsed discharging. 

The phosphite was being distilled under reduced pressure. At the end of distillation the air-bleed was opened more fully, when spontaneous combustion occurred inside the flask, probably of phosphine formed by thermal decomposition. 

Figure 14.16 the shows fuel cell stack performance of a 1 kWe atmospheric PEMFC stack using PtRu anodes, operating on various gas compositions. As can be clearly seen, already small concentrations of CO lead to a large decrease of fuel cell performance. An air-bleed of 1.5% air in hydrogen is able to mitigate this ef-... 

CO (6). Another approach is to develop a CO tolerant anode catalyst such as the platinum/ruthenium electrodes currently under consideration. Platinum/ruthenium anodes have allowed the cells to operate, with a low level air bleed, for over 3,000 continuous hours on reformate fuel containing 10 ppm CO (23). 

An open, split-shaft, air-bleed Brayton eyele as illustrated in Fig. 4.19 has the following information ... 

An open, split-shaft, air bleed Brayton cycle with two compressors (CMPl and CMP2), three turbines (TURl, TUR2, and TUR3), one intercooler (CLRl), one combustion chamber (HTRl), one reheater... 

The aqueous effluent from the parfait column was exposed to vacuum in a silanized 12-L flask on a high-capacity freeze dryer. The effluent was stirred with a magnetically coupled stirring bar and heated by immersion of the lower half of the flask in a 30 °C constant-temperature water bath. The rate of distillation was controlled to about 8 L/24 h with a needle-valve air bleed. Distillation was continued to a volume of about 500 mL. Then the concentrate was transferred to a smaller flask, and the volume was further reduced to 10 mL on a conventional rotary evaporator. 

Figure 3.5. Vacuum control with steam jet ejectors and with mechanical vacuum pumps, (a) Air bleed on PC. The steam and water rates are hand set. The air bleed can be made as small as desired. This can be used only if air is not harmful to the process. Air bleed also can be used with mechanical vacuum pumps, (b) Both the steam and water supplies are on automatic control. This achieves the minimum cost of utilities, but the valves and controls are relatively expensive, (c) Throttling of process gas flow. The valve is larger and more expensive even than the vapor valve of case (a). Butterfly valves are suitable. This method also is suitable with mechanical vacuum pumps, (d) No direct pressure control. Settings of manual control valves for the utilities with guidance from pressure indicator PI. Commonly used where the greatest vacuum attainable with the existing equipment is desired.

Mitigation approach Mitigation via. potential control air bleed, CO tolerant catalysts,, avoid potential contaminants in conduits and m new alloy catalysts new alloy catalysts, avoid OCV p 0 ten tial-cycling Surface modifica- tion Alternative material, increase compression avoid high T, dry RH- cycling... 

Du, B., Richard, P., and Elter, J.E., CO-air bleed interaction and performance degradation study in proton exchange membrane fuel cells, ECS Trans., 3, 705, 2006. 

Jusys, Z., Kaiser, J., and Behm, R.J., Simulated air bleed oxidation of adsorbed CO on carbon supported Pt. Part I. A differential electrochemical mass spectrometry study, J. Electroanal. Chem., 554/555, 427, 2003. 

Du, B., DDP 960 Pulsed Air Bleed for Improved Fuel Cell Performance, Plug Power internal report, April, 2005, Latham, NY. 

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