Air speed

Conditions that are warmer than the applicable still-air comfort zone of Fig. 5.7b can often be made comfortable by increasing the air speed. If the conditions are 1 to 6 °C warmer than the still-air comfort zone of Fig. 5.7b, the necessary air speed v) to restore thermal balance and comfort can be estimated from Fig. 5.8, where Tis the temperature difference between the environment and the still-air comfort temperature. Though the increased air speed will bring the whole-body thermal sensation to the comfort level, air motions above 0.8 m/s or so may cause other kinds of discomfort frojn... 

FIGURE 5.8 Air speed necessary at temperature T for the same thermal response as air environment (SO.2 m/s). 

Ar higher air speeds > h convective heat loss becomes greater than radiation and approaches Tj. For such conditions Eq. (5.20) is recommended... 

ISO EN 7730 standardizes the PMV-PPD index as the method for evaluation of moderate thermal environments. To quantify the degree of comfort, the PMV (predicted mean vote) index gives a value on a 7-point thermal sensation scale -t-3 hot, +2 warm, +1 slightly warm, 0 neutral, -I slightly cool, -2 cool, -3 cold. An equation in the standard calculates the PMV index based on the six factors (clothing, activity, air and mean radiant temperatures, air speed, and humidity). 

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 ... 

Air quality requirements may be set as content of particles and as content of chemical substances. Other requirements for temperature, humidity, and air speed could be set. One example is the spray painting process, which is very dependent on a minimum relative humidity (RH) level to... 

Where the product shape is irregular, the only way to extract its heat will be by using a cold fluid surrounding it. The most common of these is air. The air temperature will be of the order of - 40°C and the air speed over the product will be high, to get good heat transfer. 

In order that consistent conditions can be obtained, the air speed over the thermometers should be not less than 1 m/s. This can be done with a mechanical aspiration fan (the Assmann psychrometer) or by rotating the thermometers manually on a radius arm (the sling psychrometer). If the thermometers cannot be in a moving airstream, they are shielded from draughts by a perforated screen and rely only on natural convection. In this case the wet bulb... 

Convective heat loss will depend on the area of skin exposed, the air speed, and the temperature difference between the skin and the... 

In the first of these methods, the reduction in air mass flow is limited by considerations of distribution velocities within the rooms, so at light load more air may need to be used, together with more re-heat, to keep air speeds up. Within this constraint, any proportion of sensible and latent heat can be satisfied, to attain correct room conditions. However, full humidity control would be very wasteful in energy and a simple thermostatic control is preferred. 

Experimentally measured dielectrophoretic augmentation factor DAF as a function of air speed and applied voltage for a glass-fiber filter (HP-100, Farr Co.). Cf Fielding, Thompson, Bogardus, and Clark, Dielectrophoretic Filtration of Solid and Liquid Aerosol Particulates, Prepr. 75-32.2, 68th ann. meet.. Air Pollut. Control Assoc., Boston, June 1975. 

Performance of Art for Air Speed Drop (Fast Ramp) absd... 

Vulcanisation using hot air systems remains the most important production system for profile production. Hot air can be used alone but can also be supplemented by the addition of infrared heaters. The systems usually consist of modular units which can be built up into the required length. Air speed can usually be controlled and the compound throughput can be adjusted from speeds of 2.5 m/sec up to 20 m/sec. These systems are sufficient for thin section profiles, but thicker articles will require slower transport speeds. Addition of microwave systems to these units... 

Although the use of enclosures is conceptually the simplest approach, some particular problems arise in their use in studies of NH3 loss. These are associated with the chemical reactivity of the gas, particularly its reactivity with water, and to the strong influence of environmental factors on the volatilization process (11). Matching conditions within the enclosure to those prevailing outside is a difficult task and much of the data obtained using enclosures is open to question. However, the problems associated with enclosures can be overcome if the air speed through the enclosure is controllable to within the same range as that of wind speed at the experimental site (9, 12). 

Fig. I. Relationship between concurrent measurements of the rate of ammonia loss made using the wind tunnel and micrometeorological mass balance methods during an experiment in which the mean air speed through the tunnels was adjusted to maintain a value within 20% of the mean ambient wind speed. Rates of loss measured using the wind tunnels are the means of four replicates, the bars around each point indicating the 95% confidence limits (reproduced from ref. 12).

In order to keep the operating costs as low as possible the filter is dimensioned in such a way that the air resistance will be low. Naturally, the flow resistance is highly dependent on the filter material and the air speed through the filter. According to Zeisig, the filter area should be 25m2 per 100 pigs. The filter material should consist of peat mixed with heather. A suitable mixture is considered to be ca 50% peat and 50% heather calculated... 

In some experiments, volunteers were exposed to CS aerosols through gasmasks arranged for air-agent passage in and out. Typically, men were exposed in a large wind tunnel in which CS concentration, air speed, and temperature were controlled. Table 4-14 shows test conditions. 

Aircraft Parachute Flare, M26A1. shown on Figs 2-24 2-25, is intended for illumination in night bombardment. It is parachute-supported type which burns with a yellowish light and casts circular usable illumination upon the terrain 1500 feet in diam. By use of an MT fuze of the Mill Series the flare may be released from altitudes 2500 to 25000 feet at 350 mph true air speed... 

To demonstrate that air speed is homogeneous in each section of the tunnel (entrance, heating, cooling). The air speed values and homogeneity are important for uniform heating (sterilization) and uniform cooling of glass containers. 

---