Sub-zero conditions

A wide range of degradation results have been reported due to exposure of fuel cells to sub-zero conditions, from no degradation to significant degradation (Kim and Mench, 2007, Patterson et al, 2007) including ... 

MEA design significantly influences the amount of degradation by increasing the ability of the MEA to handle water production upon start-up under sub-zero conditions when ice may quickly form. Factors that are important include (Kim et al, 2008, Mukundan et al, 2008) ... 

NorthFlex Cold Grip Gloves are insulated to provide comfort and warmth in sub-zero conditions, while maintaining dexterity and flexibility. Productivity stays up even when temperatures go down to -15°F. Foamed PVC coating extends to the knuckles to provide liquid protection, excellent dry and wet grip. Learn more by visiting North Safety at www.NorthSafety.com. Circle 333... 

Condensable hydrocarbon components are usually removed from gas to avoid liquid drop out in pipelines, or to recover valuable natural gas liquids where there is no facility for gas export. Cooling to ambient conditions can be achieved by air or water heat exchange, or to sub zero temperatures by gas expansion or refrigeration. Many other processes such as compression and absorption also work more efficiently at low temperatures. 

In most cases thermoplastic components are designed for use at room temperature. It might appear, therefore, that data on the impact properties at this temperature (approximately 20°C) would provide sufficient information for design. However, this approach would be rather naive since even indoors, temperatures may vary by an amount which can have a significant effect on impact behaviour. For components used outdoors of course, the situation can be much worse with conditions varying from sub-zero to tropical. In common with metals, many plastics exhibit a transition from ductile behaviour to brittle as the temperature is reduced. 

The ordinary mercury-in-glass thermometer as covered by ISO 177014 is in such common use that it is rather badly taken for granted. In practice, much of the variability associated with testing at a set temperature can be traced to the misuse of thermometers. They should be calibrated frequently, carefully inspected for separation of the mercury, and immersed to the correct depth. The worst errors are usually found with low temperature thermometers and, hence, particular care should be taken when conditioning or testing at sub-zero temperatures. Precision thermometers are covered by ISO 653 - 65615 18 and there is a British standard for laboratory thermometers19. 

Lyophilization employs sub-zero temperatures in combination with very low pressure to withdraw water from the protein solution typical values would be -80 °C and 1-3 mbar. In these conditions, as the water phase diagram reveals, water sublimes, leaving a fluffy porous enzyme powder. As typical run times are on the order of a day, lyophilization is not the method of choice for large-scale enzyme drying operations. On a laboratory scale, however, lyophilization is a very effective method. 

The study of hydrate and ice formation in gas saturated samples was carried out under conditions of cyclic temperature changes. At the beginning the temperature in a sample was lowered from room to low positive values ( +l +3 C) (cooling speed about 0.02 C/min), causing a hydrate accumulation in the pore space of soil, detected by a sharp pressure drop in the pressure chamber. Then, after the hydrate accumulation process, the chamber with the sample was cooled to sub-zero temperatures (-7 -8 C). In this step the... 

It s used in thallium-mercury alloys for applications in switches that are used at sub-zero temperatures, and it can be used in laboratories as a low temperature thermometer because it extends the freezing point of Hg to -60 C. This can be used by engineers to monitor conditions at such low temperatures. 

Cables used in mining, railways, shipbuilding and heavy industrial equipment have to be resistant to fire, oils, abrasion and other hazards, yet remain flexible across a wide temperature range from sub-zero to tropical and desert conditions. 

Difference between reversible and irreversible voltage degradation under open-circuit conditions Sub-zero operation effect on ice formation Driving cycle dynamic loading... 

As soon as the Urepan 600 has been compounded with the Desmodur TT, and filler or hydroquinone diethylol ether if required, the free isocyanate groups are capable of causing chain extension and crosslinking and the rate at which these reactions occur is dependent upon temperature. At room temperature these reactions proceed slowly and the material has a limited storage life. Provided that it is kept under cool dry conditions, storage times of several days are possible and at sub-zero temperatures this can be extended to 2 weeks. 

The various microporous products embody the thermal characteristics of the polyurethanes. Therefore they are thermally stable under normal conditions of use, but can be embossed or thermoformed at temperatures above 150°C. The true melting point (TJ is around IWC and at temperatures above this materials can be welded. The relatively low glass transition temperature (about -25" C for standard polymers) ensures that high flexibility is retained at sub-zero temperatures. 

To establish the top half and the bottom halP of a prostanoid molecule [21], the Ireland-Claisen rearrangement of the ester 2 was carried out at sub-zero temperature. The reaction conditions were so mild that the resulting Claisen product did not undergo a Cope rearrangement even though structurally it was feasible, as the latter rearrangement requires temperatures in excess of 100 °C (Scheme 5.1.10). 

The a of liquid water in equilibrium with ice at sub-zero (°C) temperatures is dependent only on the temperature, as the solute concentration will adjust such that the solution will have the same water activity as ice, if the ice-water equilibrium is maintained [39]. The a values of liquid water in equilibrium with ice at —20°C, and —40°C are 0.82 and 0.67, respectively. Microbes existing in these supercooled waters suffer the combined effects of the low temperature and loss of cellular water. Response to the latter may require expenditure of cellular energy for accumulation of intracellular compatible solutes as one example of a microbial response to such conditions. 

Elastomer epoxies generally contain nitrile rubber as the elastomeric component. This system is also referred to as a modified or toughened epoxy. One of the applications of widest use is in films and tapes. Elastomer epoxies cure at low pressures and low temperatures over a short time interval. This is achieved by adding a catalyst to the adhesive formulation. Bond strengths of elastomer epoxies are lower than those of nylon epoxies. However, the major advantage of elastomer epoxies is their sub-zero peel strengths, which do not decrease as fast as those of nylon epoxies. In addition, the moisture resistance of elastomer epoxies is better than that of nylon epoxies but not as good as that of vinyl-phenolics or nitrile-phenolics. Limitations to the use of elastomer epoxies include poor water immersion resistance and poor properties when exposed to marine conditions. 

---