Operation at low ambient temperatures

Reserve batteries have been developed for appHcations that require a long inactive shelf period foUowed by intense discharge during which high energy and power, and sometimes operation at low ambient temperature, are required. These batteries are usually classified by the mechanism of activation which is employed. There are water-activated batteries that utilize fresh or seawater electrolyte-activated batteries, some using the complete electrolyte, some only the solvent gas-activated batteries where the gas is used as either an active cathode material or part of the electrolyte and heat-activated or thermal batteries which use a soHd salt electrolyte activated by melting on appHcation of heat. 

Special low temperature batteries were developed using low freezing-point electrolytes and a design that minimizes internal cell resistance, but they did not achieve popularity due to the superior overall performance of other types of primary batteries. For best operation, at low ambient temperatures, the Leclanch6 battery should be kept warm by some appropriate means. A vest battery worn under the user s clothing, employing body heat to maintain it at a satisfactory operating temperature was once used by the military to achieve reliable operation at low temperatures. 

The heat evolved improves the performance of immersion-type batteries it enables dunk-type batteries to operate at low ambient temperatures and forced-flow batteries to operate at high current densities. 

These requirements are usually met with two-pack paints based on hydroxyl-rich polyester or acrylic resins in the pigmented pack and aliphatic polyisocyanates in the activator pack. Cure with this type of finish is relatively fast and complete even at low ambient temperatures. An alternative finish is an acrylic lacquer, similar to the lacquer used for refinishing motor cars. These finishes are applied to the assembled aircraft by operators protected by air-fed hoods and using airless or conventional spray guns. High durability pigments are included. 

Starting of turbojet engines is more difficult at altitudes or at low ambient temperatures on the ground. Altitude ignition is required after flame-outs or with multiengine aircraft where all engines may not be operated at all times. 

The low cetane number of coal liquid fuels could lead to poor starting and warm-up characteristics at low ambient temperatures and to engine roughness at part load operation. 

The minimum operating temperature should include cold start ups at low-ambient temperatures where applicable (eg., mining equipment that normally does not require warm start ups) and upset conditions. 

Carbon dioxide is, by far, the most attractive SCF for many reasons It is inexpensive and abundant at high purity (food grade) worldwide and it is nonflammable, non-toxic, and environment friendly moreover, its critical temperature T = 31 °C) permits operations at near-ambient temperature which avoids product alteration and its critical pressure (= 74 bar) leads to acceptable operation pressure, generally between 100 and 350 bar. In fact, supercritical carbon dioxide behaves as a rather weak nonpolar solvent, but its solvent power and polarity can be significantly increased by adding a polar cosolvent that is chosen among alcohols, esters, and ketones. Ethanol is often preferred because it is not hazardous to the environment, not very toxic, and available pure at low cost. Hydro fluorocarbons (HFCs) are very costly and their specific properties rarely justify their use in the replacement of carbon dioxide. 

Liquid-liquid extraction (LLX) proved to be a highly attractive separation method for many of these applications due to low consumption of energy and of reagents, operation at about ambient temperature, avoidance of solid crystallization and purification, and reduction of the formation and treatment of by-products. 

Ambient-Temperature Removal. The vast majority of acid gas removal processes operate at high ambient temperatures (90-120°F). These systems are almost as efficient as cold systems, but have lower capital cost and are much simpler. These processes can reduce H2S to about 10-50 ppmv. The key operating cost is the large heat requirement for stripping. This cost is minor in most coal gasification plants because of the ample supplies of low-pressure steam and low-level process heat in the plants. Commonly used acid gas removal processes at these conditions include MDEA (methyldiethanolamines) and Sulfinol. 

To evaluate the availability performance of a skimmer, at first one needs to focus on its elements reliability performance, maintainability performance, and maintenance support performance (Barabady et al. 2010). Reliability of a system is defined as the probability that a system will perform a specified function within prescribed limits, under given environmental conditions, for a specified time (Stapelberg 2009). In other words, the failure rate of a skimmer depends on a number of parameters including environmental (operational) conditions. Low ambient temperature, wave height, current speed, sea ice concentration, and wind speed are some examples of operational conditions in the Arctic offshore. Figure 3 depicts some of the operational conditions that may affect the availability performance of the skimmers intended to be used in the Arctic offshore. 

A number of chemical and physical surface treatments have been developed for polymeric materials in recent years. Due to the disadvantage of chemical treatments, physical surface treatments are preferred to modify the surface of polymeric materials (Petrie 2006). Plasma surface treatment is often the preferred way to treat the surfaces as it offers more stable and longer-lasting surface-energy enhancement than any other treatments (Rotheiser 1999). However, conventional plasma treatment also has shortcomings. It requires a low pressure (partial vacuum), and thus the parts must be processed in a vacuum chamber, restricting the part size. Atmospheric-pressure plasma has been developed to operate at near ambient temperature and atmospheric pressure, eliminating the expensive vacuum systems. 

A viable electrocatalyst operating with minimal polarization for the direct electrochemical oxidation of methanol at low temperature would strongly enhance the competitive position of fuel ceU systems for transportation appHcations. Fuel ceUs that directiy oxidize CH OH would eliminate the need for an external reformer in fuel ceU systems resulting in a less complex, more lightweight system occupying less volume and having lower cost. Improvement in the performance of PFFCs for transportation appHcations, which operate close to ambient temperatures and utilize steam-reformed CH OH, would be a more CO-tolerant anode electrocatalyst. Such an electrocatalyst would reduce the need to pretreat the steam-reformed CH OH to lower the CO content in the anode fuel gas. Platinum—mthenium alloys show encouraging performance for the direct oxidation of methanol. 

This condition is of concern only when equipment operates in subzero ambient temperatures. Since diesel fuel extracted from crude oil contains a quantity of paraffin wax, at some low ambient temperatures this paraffin will precipitate and create wax crystals in the fuel. This can result in plugging of the fuel filters, resulting in a hard or no-start condition. Any moisture in the fuel can also form ice ciystals. Cloud point temperatures for various grades of diesel and other fuels should be at least 12°C (21.6°F) below the ambient temperature. In cases where cloud point becomes a problem, a fuel water separator and a heater are employed. 

The major requirement for a reliable hydrogen sensor operation in the fuel cell environment is in 100% condensing humidity Most of the fuel cells have abundant humidity and the sensor needs to operate continuously in humid environments. In some cases, the hydrogen sensor can also be operated at very low temperatures (as low as —40°C). The fuel cells regularly have a cold start, when operated from a very low ambient temperature the sensor needs to attain ambient temperature quickly (<30 s) and continue operation well below ambient temperature before the fuel cell itself reaches the ambient temperature. 

In order to study cathode flooding in small fuel cells for portable applications operated at ambient conditions, Tuber et al.81 designed a transparent cell that was only operated at low current densities and at room temperature. The experimental data was then used to confirm a mathematical model of a similar cell. Fig. 4 describes the schematic top and side view of this transparent fuel cell. The setup was placed between a base and a transparent cover plate. While the anodic base plate was fabricated of stainless steel, the cover plate was made up of plexiglass. A rib of stainless steel was inserted into a slot in the cover plate to obtain the necessary electrical connection. It was observed that clogging of flow channels by liquid water was a major cause for low cell performance. When the fuel cell operated at room temperature during startup and outdoor operation, a hydrophilic carbon paper turned out to be more effective compared with a hydrophobic one.81... 

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