Cold environments

Many industrial workplaces are located in cold environments, such as cold storage, meat packing areas, and outdoor sites. In cold environments, clothing is the 

TABLE 6.8 Reference Values for the Different Criteria of Thermal Stress and Strain 

TABLE 6.9 Required Sweat Rate Index SW q W/m, and Wettedness (w q) as a Function of Clothing, Temperature, Air Speed, and Humidity at an Activity Level M Equal to 70 W/m  

Clothing ci. c o Relative humidity, % Operative temperature t °C 0 Air velocity v , m/s  

3 TARGET VALUES FOR THERMAL FACTORS AN OVERVIEW OF INTERNATIONAL STANDARDS 

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In extremely cold environments, engines can quickly become difficult, sometimes nearly impossible, to start. If ordinary gasoline- or diesel-oil-fired heaters are used, the coolant circulation pump, air fan, etc, must be powered from the vehicle s batteries, thus curtailing the time the system can be used, especially at very low temperatures when it is needed the most. By adding PbTe thermoelectrics to such heater systems, about 2% of their thermal output can be turned into electricity to mn the heater s electronics, fuel pump, combustion fan, and coolant circulation pump, with stiH sufficient power left over to keep the vehicle s battery fliUy charged. The market for such units is in the hundreds of thousands if manufacturing costs can be reduced. 

Hydration at Ordinary Temperatures. Pordand cement is generally used at temperatures ordinarily encountered in constmction, ie, from 5 to 40°C. Temperature extremes have to be avoided. The exothermic heat of the hydration reactions can play an important part in maintaining adequate temperatures in cold environments, and must be considered in massive concrete stmctures to prevent excessive temperature rise and cracking during subsequent cooling. 

ISO TR ENV 1 1079 Thcrivial stress evaluation in cold environments Evaluation of cold environments DetcTini-nation of required clothing insulation, 1,... 

ISO DIS 12894 Selection of an appropriate system of medical supervision for different types of thermal exposure EIrgonomics of the thermal environment Medical supervision of individuals exposed to hot or cold environment ... 

ISO CD 15265 Assessment of risk in moderate, hot and cold environments Risk assessment... 

ISO EN 9886 presents the principles, methods, and interpretation of measurements of relevant human physiological responses to hot, moderate, and cold environments. The standard can be used independently or to complement other standards. Four physiological measures are considered body core temperature, skin temperature, heart rate, and body mass loss. Comments are also provided on the technical requirements, relevance, convenience, annoyance to the subject, and cost of each of the physiological measurements. The use of ISO 9886 is mainly for extreme cases, where individuals are exposed to severe environments, or in laboratory investigations into the influence of the thermal environment on humans. 

The flow field created within the protection zone depends mainly on the density difference between supply air and room air (Fig. 10.90). With vertical flow the supply air should be isothermal or cooler than ambient air. If it were warmer, the extension of the controlled flow would be reduced due to buoyancy effects, resulting in the supply air not reaching the operator s breathing zone. As the. supply air cannot be used for heating, the operator s thermal comfort should be maintained, preferably with radiant heaters in cold environments. If the supply air temperature is lower than the room air, the denser supply air accelerates down to the operator, and for continuity reasons the supply flow contracts. Excessive temperature differences result in a reduced controlled flow area with thermal discomfort, and should only be used in special cases. 

In general, transitions from a hot to a cold environment are more likely to produce failure than those in the opposite direction since they tend to induce tensile stresses at the surface. 

In practical situations, if permeation through a hose lining, for example, is being considered, and the hose is exposed externally to a cold environment (such as the sea) while hot fluid passes through the hose (e.g., hot oil in the offshore production industry), a temperature gradient — Ti will apply across the lining. To cover this situation, for a representative permeation coefficient Campion and Thomas developed from Tick s laws... 

Bradley PM, FH Chapelle (1995) Rapid toluene mineralization by aquifer microorganisms at Adak, Alaska implications for intrinsic bioremediation in cold environments. Environ Sci Technol 29 2778-2781. 

Concrete exposed to deicer salts, or to a marine environment is subjected to chloride and sodium loading. The ability of concrete to resist the penetration of chlorides and sodium is a primary design consideration in marine or cold environments. The ingress of chlorides into concrete is a major problem due to chloride-induced corrosion of the reinforcing steel and deicer salt scaling [a process by which a thin layer (< 1 mm) of concrete deteriorates from the surface of the concrete]. The penetration of sodium from sea water or deicer salts is generally... 

A global Thomthwaite PET surface was calculated from the temperature surface data for a 0.5° resolution grid. The Thomthwaite method is known systematically to underestimate PET for dry conditions and to overestimate values for moist and cold environments. Consequently, an empirical adjustment factor was derived by CRU and applied to the data to bring the values closely in line with those of the Penman method. 

Precipitating factors include exercise, cold environment, walking after a meal, emotional upset, fright, anger, and coitus. Relief occurs with rest and within 45 seconds to 5 minutes of taking nitroglycerin. 

Most of the generated vapour is condensed in spray condensers which are equipped with circulation pumps and an EG cooler. The vapour that is still uncondensed is withdrawn from the gas phase with the help of a vapour jet which is located down-stream behind the spray condenser and generates the necessary vacuum in the reaction zone. The most critical part of the spray condenser system is the end of the pipe leading the vapour from the prepolycondensation reactors and the finishers into the spray condenser. The transition from a hot to a cold environment causes deposition of solid material onto the cold walls which has to be removed manually or by means of a mechanical scraper. 

For example, thermodynamic calculations will provide a value for the maximum voltage of a storage battery—that is, the voltage that is obtained when no current is drawn. When current is drawn, we can predict that the voltage will be less than the maximum value, but we cannot predict how much less. Similarly, we can calculate the maximum amount of heat that can be transferred from a cold environment into a building by the expenditure of a certain amount of work in a heat pump, but the actual performance will be less satisfactory. Given a nonequilibrium distribution of ions across a cell membrane, we can calculate the minimum work required to maintain such a distribution. However, the actual process that occurs in the cell requires much more work than the calculated value because the process is carried out irreversibly. 

Typically, the liquidus lines of a binary system curve down and intersect with the solidus line at the eutectic point, where a liquid coexists with the solid phases of both components. In this sense, the mixture of two solvents should have an expanded liquid range with a lower melting temperature than that of either solvent individually. As Figure 4 shows, the most popular solvent combination used for lithium ion technology, LiPFe/EC/DMC, has liquidus lines below the mp of either EC or DMC, and the eutectic point lies at —7.6 °C with molar fractions of - 0.30 EC and "-"0.70 DMC. This composition corresponds to volume fractions of 0.24 EC and 0.76 DMC or weight fractions of 0.28 EC and 0.71 DMC. Due to the high mp of both EC (36 X) and DMC (4.6 X), this low-temperature limit is rather high and needs improvement if applications in cold environments are to be considered. 

The resistance to freeze-thaw cycling which may be experienced during the winter months in many countries. This will not be a function of the average wintertime temperatures of the various countries because, in fact, the very cold environments will have only a small number of freeze-thaw cycles. In countries such as Great Britain, the winter daytime temperatures are often above 0°C and the night-time temperature below. In view of this, more freeze-thaw cycles would be experienced than in countries such as Scandinavia or North America where daytime temperatures in the winter tend to remain below 0°C. 

Fuel volatility is an extremely important factor related to fuel combustion and burning efficiency. Evaporation, vaporization, and vapor pressure of fuel can all be reduced in cold environments. Poor startability and warmup of gasoline and diesel engines can be directly related to fuel volatility. Also, cold kerosene will not vaporize and bum as efficiently in wick-fed systems. 

Also, separate compounds known to perform as effective metal chelators can be blended into stabilizer formulations. Compounds such as IVJV -disalicylidene-1,2-propanediamine, as shown in FIGURE 6-4, and lV V -disalicylidene-l,2-cyclohexanediamine are commercially available and quite effective. Care must be taken when using these compounds in cold environments. These metal chelators... 

Additional low-temperature fuel filterability information is often required to confirm whether fuel will pass through fuel filters in cold environments. Two tests are commonly used to determine this performance value, ASTM D-4539 and IP 309. The method ASTM D-4539 is termed the Low-Temperature How Test (LIFT) and is used to determine the low-temperature filterability of diesel fuel. 

CFPP (Cold Filter Plugging Point) A measure of the ability of a distillate fuel to be filtered satisfactorily in cold environments. This test measures the temperature at which fuel wax crystals can reduce or halt the flow of fuel through a standardized test filter. 

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