Air disturbances

The value of the coefficient of turbulent diffusion, D, depends upon the air change rate in the ventilated space and the method of air supply. Studies by Posokhin show that approximate D values for locations outside supply air jets is equal to 0.025 m-/s. Air disturbance caused by operator or robot movement results in an increase in the D value of at least two times. Studies by Zhivov et al. showed that the D value is affected by the velocity and direction of cross-drafts against the hood face, and the presence of an operator e.g., for a cross-draft directed along the hood face with velocity u = 0.5 m/s with D = 0.15 m-/s (with the presence of an operator), an increase to = 1.0 m/s results in D = 0.3 m-/s. 

The influence of air disturbances on performance can be minimized by locating the supply air device as close to the operator s breathing zone as practical to improve protection and by using walls or side baffles near the contaminant source. 

A primary explosion occurs in part of a plant, causing an air disturbance. 

The air disturbance disperses dust and causes a secondary explosion, which is often more destructive than the primary explosion. 

In dust explosions the combustion process is very rapid. The flame speed is high compared to that in gas deflagrations. However, detonations normally do not occur in dust explosions in industrial plants. In a serious industrial dust explosion, two steps often occur. First, a primary explosion occurs in part of a plant, causing an air disturbance. Second, the air disturbance disperses dust and causes a secondary explosion. The secondary explosion is often more destructive than the primary explosion. There is a great deal of literature on dust explosions, which is available to the process designer. See, for example, Lees (1980) for a bibliography on dust explosions. 

Airshear nozzles are used on motorised mistblowers with a centrifugal fan that creates a high-velocity airstream. Users perceive that the ability to project the spray over several metres is an advantage, and air disturbance within the crop canopy is expected to improve the spray distribution. However, successful application with this equipment depends very much on how they are operated. The air velocity should not be adjusted, as the engine should always be used at the... 

The uptake of organic contaminants by plants from biosolids-amended soil depends on the physicochemical properties of organic compoimds and the physiology of plants [92-95]. Plant uptake of organic chemicals and their distribution within plants have been shown to be affected by (1) the organic chemicals physicochemical properties, including solubility, vapor pressure, octanol-water partition coefficient Kow)> and Henry s law constants (iC ), (2) environmental conditions such as temperature, air disturbance and soil organic matter content, and (3) plant characteristics, for example the shape of the leaves, type of root system, and lipid and cuticle characteristics and contents [94]. 

Ozone plays important roles in atmospheric chemistry and physics. Up to 5 x 10 molecules cm or 4-5 ppmv (10 mixing ratio by volume) of ozone is found in the stratosphere where the solar radiation intensity of shorter wavelengths is high. Ozone in the stratosphere has made it possible for animals to live on land by preventing harmful 200-300 nm UV radiation from reaching the Earth s surface. The absorption of UV radiation by ozone, however, heats the air, disturbing air convection and creating a layered structure in the stratosphere. As some useful and stable chemicals like chlorofluorocarbons (Fre-ons) and other substances were found to decompose in the stratospheric environment and to destroy the... 

As shown in Figure 20.1, the top and side nozzles of the anti-rollback system are arranged for low reach (about 300 mm or 12 in.) from the cutting head. This location prevents overspray that would increase rollback. Flat spray patterns, as opposed to cone spray patterns, are better because the entire flow from the nozzle can be directed to the cutting head. On the boom top, horizontal flat spray patterns near the cutting head cause the least air disturbance on the sides, vertical flat spray patterns are best. 

Fig. 22.14 Commonly used gas distributirai concept for rotary spraying device. The fast air flow red arrows) serves to prevent the spray from wall deposition in the spray tower. The high relative velocity between the threads and the air disturbs the breakup process [11]. The thick red line represents the air velocity profile...

Laser Raman diagnostic teclmiques offer remote, nonintnisive, nonperturbing measurements with high spatial and temporal resolution [158], This is particularly advantageous in the area of combustion chemistry. Physical probes for temperature and concentration measurements can be debatable in many combustion systems, such as furnaces, internal combustors etc., since they may disturb the medium or, even worse, not withstand the hostile enviromnents [159]. Laser Raman techniques are employed since two of the dominant molecules associated with air-fed combustion are O2 and N2. Flomonuclear diatomic molecules unable to have a nuclear coordinate-dependent dipole moment caimot be diagnosed by infrared spectroscopy. Other combustion species include CFl, CO2, FI2O and FI2 [160]. These molecules are probed by Raman spectroscopy to detenuine the temperature profile and species concentration m various combustion processes. 

When the adsorbent has been introduced into the tube, the latter is fitted into a filter flask (see Fig. 77, 46, 2) to which a pump is attached the pump is run slowly and the column is again pressed down gently with the wooden pestle. The circumference of the upper surface is gently and uniformly tapped, especially where it is in contact with the glass surface, for about one minute air bubbles and channels are thus avoided when the solution is poured in. Some workers place a loose plug of cotton wool or a circle of filter paper at the top of the column in order to protect the solid from disturbance when the liquid is introduced. 

This procedure offers the possibiUty of remote noncontact velocity measurement, where no probes disturb the flow. It is thus compatible for use with hot or corrosive gases. Commercial laser velocimeters have become weU-developed measurement tools. Examples of laser velocimetry include remote measurement of wind velocity, measurement of vortex air flow near the wing tips of large aircraft, and in vivo measurement of the velocity of blood flow. 

Inhalation. The threshold limit value of HCN is 4.7 ppm. This is defined as the maximum average safe exposure limit for a 15-min period by the Occupational Safety and Health Administration. Exposure to 20 ppm of HCN in air causes slight warning symptoms after several hours 50 ppm causes disturbances within an hour 100 ppm is dangerous for exposures of 30 to 60 min and 300 ppm can be rapidly fatal unless prompt, effective first aid is adininistered. There is always a small concentration of cyanide (0.02 to 0.04 mg/L) in the blood, and the body has a mechanism for continuous removal of small amounts, such as from smoking, by converting it to thiocyanate, which is discharged in the urine. 

Peroxide Formation. Except for the methyl alkyl ethers, most ethers tend to absorb and react with oxygen from the air to form unstable peroxides that may detonate with extreme violence when concentrated by evaporation or distillation, when combined with other compounds that give a detonable mixture, or when disturbed by heat, shock, or friction. Appreciable quantities of crystalline soHds have been observed as gross evidence for the formation of peroxides, and peroxides may form a viscous Hquid in the bottom of ether-fiHed containers. If viscous Hquids or crystalline soHds are observed in ethers, no further tests for the detection of peroxides are recommended. Several chemical and physical methods for detecting and estimating peroxide concentrations have been described. Most of the quaHtative tests for peroxides are readily performed and strongly recommended when any doubt is present (20). 

Vacuum is applied to the chamber and vapor is removed through a large pipe which is connected to the chamber in a manner such that, if the vacuum is broken suddenly, the inrushing air will not greatly disturb the bed of material being dried. This line leads to a condenser where moisture or solvent that has been vaporized is condensed. The noncondensable exhaust gas goes to the vacuum source, which may be a wet or diy vacuum pump or a steam-jet ejector. 

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