Air circulation

Figure 7 gives the results of an experiment in which freestanding films were exposed to constant elevated temperatures in air-circulating ovens for periods of weeks to months the failure criterion was a 50% loss in tensile strength. Because the test is destmctive, each data point (failure time at a given... 

Prolonged soldering in confined spaces with restricted air circulation requires ventilation. A small duct fan is recommended for hot-wire stripping. Tefzel articles should not be exposed to welding conditions. 

Provisions must be made for allowing residues of the stefilant absorbed by the product to dissipate by using aeration cabinets that have forced-air circulation at elevated temperatures. The amount of remaining absorbed stefilant should be determined before releasing the sterilized articles. If, as in the case of hospital sterilization, such studies are not feasible, the recommendations of the manufacturers of the articles sterilized or of the aeration equipment should be obtained. The permissible residue concentrations are 10—250 ppm, depending on the type of article and on its intended use. 

Fermentation. The term fermentation arose from the misconception that black tea production is a microbial process (73). The conversion of green leaf to black tea was recognized as an oxidative process initiated by tea—enzyme catalysis circa 1901 (74). The process, which starts at the onset of maceration, is allowed to continue under ambient conditions. Leaf temperature is maintained at less than 25—30°C as lower (15—25°C) temperatures improve flavor (75). Temperature control and air diffusion are faciUtated by distributing macerated leaf in layers 5—8 cm deep on the factory floor, but more often on racked trays in a fermentation room maintained at a high rh and at the lowest feasible temperature. Depending on the nature of the leaf, the maceration techniques, the ambient temperature, and the style of tea desired, the fermentation time can vary from 45 min to 3 h. More highly controlled systems depend on the timed conveyance of macerated leaf on mesh belts for forced-air circulation. If the system is enclosed, humidity and temperature control are improved (76). 

Process Description. Reactors used in the vapor-phase synthesis of thiophene and aLkylthiophenes are all multitubular, fixed-bed catalytic reactors operating at atmospheric pressure, or up to 10 kPa and with hot-air circulation on the shell, or salt bath heating, maintaining reaction temperatures in the range of 400—500°C. The feedstocks, in the appropriate molar ratio, are vaporized and passed through the catalyst bed. Condensation gives the cmde product mixture noncondensable vapors are vented to the incinerator. 

After being removed from the neutralizing solution, the ware is transferred to a dryer maintained at about 110—120°C that has good air circulation. This ensures quick and complete drying without msting of the metal. After being dried, the sheet ware is ready for apphcation of enamel. 

Theoretical possible heat removal per pound of air circulated in a cooling tower depends on the temperature and moisture content of air. An indication of the moisture content of the air is its wet-bulb temperature. Ideally, then, the wet-bulb temperature is the lowest theoretical temperature to which the water can be cooled. Practically, the cold-water temperature approaches but does not equal the air wet-bulb temperature in a coohng tower this is so because it is impossible to contact all the water with fresh air as the water drops through the wetted fill surface to the basin. The magnitude of approach to the wet-bulb temperature is dependent on tower design. Important factors are air-to-water contact time, amount of fill surface, and breakup of water into droplets. In actual practice, cooling towers are seldom designed for approaches closer than 2.8°C (5°F). 

They would require a larger storage area, which should be dustproof but well ventilated to provide for sufficient air circulation. 

Check for underventilation caused by obstructed vents, faulty dampers or other HVAC system malfunctions, or from problems within the occupied space. Furniture, papers, or other materials can interfere with air movement around thermostats or block airflow from wall or floor-mounted registers. If office cubicles are used, a small space (i.e., two to four inches) between the bottom of the partitions and the floor may improve air circulation. 

Lift a ceiling tile and examine the plenum for potential problems. Walls or full-height partitions that extend to the floor above can obstruct or divert air movement in ceiling plenums unless transfer grilles have been provided. If fire dampers have been installed to allow air circulation through walls or partitions, confirm that the dampers are open. Construction debris and damaged or loose material in the plenum area may become covered with dust and can release particles and fibers. 

Figure 7. Diurnal air circulation effects associated with valleys.

Air cooled heat exchangers will continue to operate (but at reduced capacity) due to radiation and natural convection air circulation should a power failure occur. 

Most vapors condense inside tubes eooled by a falling curtain of water. The water is eooled by air circulated through the tube bundle. The bundles ean be mounted directly in a cooling tower or submerged in water. 

Compartment driers are closets or even rooms in which the material is spread on trays or in shallow pans. The operation is often discontinuous in order to make it continuous, the pans may be placed on trucks traveling on rails, and these are pushed through a tunnel in which warm air circulates. Belt driers and chain driers have similar goals. 

Drying Rooms For drydng materials that cannot be agitated, the drying room, and tray drier (which there are many varieties) can be used. In the former, the material may be spread on pans and these stacked in a rack, which leaves a space between the trays for air circulation. The room has loosely fitted side walls of plaster board, or similar material, or even canvas, and contains a steam radiator. The natural circulation of the warm air removes the moisture the drying period is generally long, for example, one or two days. 

Air circulation with a parallel jet supply is illustrated in Fig. 7.45. Jets are located at distance t from each other, and each jet forms return flow similar to that induced by a single jet in the room with a width B = t. Thus, in the case of M parallel jets, the room should be considered divided into several zones with a width B = B /N, separated from each other by airtight walls. 

Sadovskaya, N. N. 1950. Studies of air circulation in the. spaces with heating and ventilating by concentrated air jet supply. Ph.D. thesis. VNIIOT VtsSPS, Leningrad. 

Sadovskaya, N. N. 1955. Air circulation in spaces with concentrated air jet supply. In Proceedings of the Conference Concentrated Air. Supply, issue 4. I.IOT, Leningrad. 

The evaporation test had been performed to see the loss of polymeric UV absorbers compared to their counterpart monomeric stabilizers, by placing the films in an air-circulating oven at 80°C for 200 to 1000 h (Fig. 13, 14, and 15). 

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