Subfreezing temperatures

Freeze Point Depression. The slight heat-transfer penalty incurred when an antifreeze is added to the aqueous heat-transfer fluid is necessitated by the need for increased operating temperature range in most internal combustion engines. Because most parts of the world achieve temperatures below freezing during some time of the year, an antifreeze fluid is required to keep equipment operational in these subfreezing temperatures. 

WATER (LIQUID OR SUPERCOOLED) AND ICE VAPOR PRESSURES AND THEIR RATIO (WATER ACTIVITY BELOW FREEZING) AT 0°C AND SEVERAL SUBFREEZING TEMPERATURES... 

The above two examples serve to illustrate that more severe conditions of gas recovery require large expense in thermodynamic inhibitors. The high pressure and high water production at Canyon Express and the steeply upward sloping lines and subfreezing temperatures of Ormen Lange are harbingers of more severe conditions in the future. There are some cases in which the cost of hydrate inhibitors determine the project viability. 

Most recently, Gallagher et al.21 measured the water uptake of Nafion membrane under subfreezing temperatures, which showed a significant reduction in the maximum water content corresponding to membrane full hydration. The Nafion membrane with 1,100 equivalent weight, for example, uptakes A 8 of water at -25°C when it equilibrates with vapor over ice because of the low vapor pressure of ice compared to supercooled liquid water. They also found the electro-osmotic drag coefficient to be 1 for Nafion membrane under sub freezing temperatures. 

The electrolyte membrane presents critical materials issues such as high protonic conductivity over a wide relative humidity (RH) range, low electrical conductivity, low gas permeability, particularly for H2 and O2, and good mechanical properties under wet-dry and temperature cycles has stable chemical properties under fuel cell oxidation conditions and quick start-up capability even at subfreezing temperatures and is low cost. Polyperfluorosulfonic acid (PFSA) and derivatives are the current first-choice materials. A key challenge is to produce this material in very thin form to reduce ohmic losses and material cost. PFSA ionomer has low dimensional stability and swells in the presence of water. These properties lead to poor mechanical properties and crack growth. 

In areas where the air temperature remains below 0°C for prolonged periods of lime, the freezing of water in underground pipes is a major concern. Fortunately, the soil remains relatively warm during those periods, and it takes v/eeks lor the subfreezing temperatures to reach the water mains in the ground, Thus, the soil effectively serves as an insulation to protect the v ater from subfreezing temperatures in winter. 

The water main in the cities must be placed at sufficient depth belotv the earth s surface to avoid freezing during extended periods of subfreezing temperatures. Determine the minimum depth at which the water main must be placed at a location where the soil is initially at IS°C and the earth s surface temperature under the worst conditions is expected to remain at — lO C for a period of 75 days. Take the properties of soil at that location to be k = 0.7 W/m °C and a = 1.4 X 10 mVs. Answer 7.05 m... 

Citrus trees are very susceptible to cold weather, and extended e.xposure to subfreezing temperatures can destroy the Crop. In order to protect the trees from occasional cold fronts with subfieezing temperatures, tree growers in Florida usually install water sprinklers on the trees. WOien the tenipeiature drops below a certain level, the sprinklers spray water on the trees and their fruits to protect them against the damage the subfieezing temperatures can cause. Explain the basic mechanism behind this protection measure and write an essay on how the system works in practice. 

All lecithin grades should be stored in well-closed containers protected from light and oxidation. Purified solid lecithins should be stored in tightly closed containers at subfreezing temperatures. 

Ahluwalia RK, Wang X (2006) Rapid self-start of polymer electrolyte fuel cell stacks from subfreezing temperatures. J Power Sources 162 502-512... 

An additional challenge to the use of fuel cells for automobiles is response time. Currently, fuel cells have a response time of 15 seconds from 10 percent power to 90 percent. In order to be viable, this response time must drop to 1 second. Because they require liquid water to operate, a further challenge is to operate fuel cells in subfreezing temperatures. In addition, the current cost per kilowatt-hour for fuel cells must be reduced from 300 down to 45. 

The standard for a modem vehicle requires it to start within 2 seconds at worst. A fuel cell starts well within 1 second. However, fuel cells, including hydrogen fuel cells, do not operate well at subfreezing temperatures. This is because fuel cells are basically a liquid interface device and need liquid-phase water to operate. Running the system under the conditions of a highway environment is possible, but the current cost is too great for commercialization. 

Chemical Reactions in Proteins Irradiated at Subfreezing Temperatures... 

A temperature cycling study for drug products that may be exposed to subfreezing temperatures may consist of three cycles of 2 days at freezer temperature (-10° to -20°C) followed by 2 days under accelerated storage conditions (40°C). 

For inhalation aerosols, the recommended cycle study consists of three or four 6-hour cycles per day, between subfreezing temperature and 40°C (75%-85% RH) for a period of up to 6 weeks. 

E. Modulation of Energy Dissipation Against the Background of Sustained Xanthophyll Cycle Deepoxidation by Subfreezing Temperatures in the Winter... 

---