Airflow rate requirements

The load in the room will be primarily sensible. This will require a fairly high airflow rate as compared to comfort applications. High airflow rates require a high degree of care with air distribution devices in order to avoid drafts. One way to alleviate this problem is to utilize underfloor distribution where a raised floor is provided for computer cable access. A typical computer-room arrangement is shown in Fig. 3.28. Major obstructions to air flow below the floor must be minimized so as to avoid dead spots. 

Specificalions for airflow rate requirements for MBRs are based on experience rather than theoretical analyses, although there is a growing hterature on the effect of bubble flow on fouling control [see reviews by Cui et al. (2003) and Le Clech et al. (2006)]. Judd (2006) has summarized a wide range of available data for submerged MBRs as the specific air demand (SAD) and defines two parameters ... 

Design Methods The size of the agitated flash dryer is based on the evaporation rate required. The operating temperatures are product-specific. Once established, they determine the airflow requirements. The diyiug chamber is designed based on air velocity (approximately 3 m/s) and residence time (product-specific). 

Natural ventilation design allows one to size the inlets, and outlets, / p based on their pressure loss characteristics, Cp, and on the airflow rate, G , required to maintain the occupied zone within desired limits. The reverse design procedure is commonly used to evaluate the airflow rate through the building given the sizes, characteristics, and locations of inlets and outlets and the heat load and characteristics of heat sources. 

It will be appreciated that if 30 kW is required for such a small air quantity, it is important to reduce the airflow rate to a value as low as possible in order to save energy. 

An exhaust hood requires an adequate supply airflow rate (direct supply or indirect from another room and transported through a transfer opening) inside the room where the exhaust is situated. This means that the supply airflow rate should be approximately equal to the exhaust rate and that the supply devices should be placed in such a way that the incoming air does not... 

Finally, the required hood airflow rate is calculated as the sum of the plume airflow and the inward airflow through the rest of the hood ... 

An increase of the capture airflow rate normally results in increased capture efficiency, but the relationship between these quantities is not linear. A case-by-case evaluation is necessary to establish this relationship. In every case an increase of the airflow rate causes an increase of the operating costs. Analogously, a decrease in airflow rate leads to a decrease in capture efficiency and in some cases, a total breakdown of the capture effect (e.g., capture dev ices working with the vortex principle require minimum airflow rates). 

In the low-momentum supply system, the contaminants are emitted within the low -momentum airflow blown from the supply inlet and they are transported to near the exhaust opening. If the contaminants diffuse into the whole of the supply airflow, the exterior hood must exhaust the whole of the airflow. To diminish the exhaust flow rate, some methods to prevent the contaminants from diffusing into the whole of the airflow are required. One possible method is to supply the air as slowly as possible but with enough velocity to reach the exhaust outlet and to control the surrounding air motion. Another method is to blow supply air with uniform... 

These combinations are possible without too detailed design of the combined jet and exhaust, since the wide jet itself will act as a separator between inside and outside and the consequences of an imbalance of supply and exhaust airflow are small. The relative mixing of outside and inside air into the jet is less than for a thin air jet, which also makes it easier to design fan(s) and ducts. The high velocity needed requires a high airflow rate and, with heating, can be expensive to operate. 

With particles, the contaminant concentration in the duct is determined by isokinetic sampling with subsequent laboratory analysis use of a calibrated direct reading instrument. If the concentration distribution in the duct is uneven, a complete survey of the concentration distribution with the corresponding duct velocities and cross-sectional area is required. National and ISO standards provide information on isokinetic sampling and velocity measurements. In the case of particles, the airborne emission differs from the total emission, for example in the case of granular particulate. The contaminant settling on surfaces depends on particle distribution, airflow rates, direction in the space, electrical properties of the surfaces and the material, and the amount of moisture or grease in the environment. 

Outdoor air is warmer than inside temperature. This is, of course, possible only for such a hall where the air volume is very large in comparison to the required airflow rate. 

Adjustable pitch fan A fan in which the pitch angle can be set to provide the required airflow rate. The pitch angle may be preset or controlled with the fan running. 

Fan energy The energy required by a fan in order for it to provide a given airflow rate against a set resistance. 

Minimum ventilation requirements The lowest possible airflow rates that will ensure all obnoxious products are removed from the air by the introduction of fresh air. 

Maintenance of a PSVE system is expected to cost 2% of the installed capital cost of the system per year. Operation and waste disposal costs are a function of concentration of contaminants and the airflow rate and will therefore vary widely (D14489S, p. 26). Once a system is installed, no utilities are generally required. If a valve and differential pressure control system are used, these could be run by solar-cell-powered batteries (D18119L, p. 384). 

A nominal result of this technique is that the required airflow rate and equipment size is about two-thirds of that when evaporative cooling is not used. See Sec. 20 for equipment available. 

Not all loose-fitting respirators move the air at the same rate. Most pesticide handling tasks require a minimum airflow rate of 4 cubic feet per minute. If you are doing physically strennous work, nse a respirator with an airflow rate of at least 6 cubic feet per minute. 

Stability test ( Swift test Vactive oxygen method) gives an indication of the oil s resistance to oxidation during storage. The test gives the time in hours required for a sample of oil to reach a peroxide value of 100 when subjected to aeration under specified conditions of temperature and airflow rate. The period of time in hours is determined by interpolation between two peroxide value determinations, which must fall between 75 meq and 175 meq. 

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