Airflow velocity

The basic fluid-bed unit consists of a refractory-lined vessel, a perforated plate that supports a bed of granular material and distributes air, a section above the fluid bed referred to as freeboard, an air blower to move air through the unit, a cyclone to remove all but the smallest particulates and return them to the fluid bed, an air preheater for thermal economy, an auxiUary heater for start-up, and a system to move and distribute the feed in the bed. Air is distributed across the cross section of the bed by a distributor to fluidize the granular soflds. Over a proper range of airflow velocities, usually 0.8-3.0 m/s, the sohds become suspended in the air and move freely through the bed. 

By experimentation, it is possible to measure the lift and drag forces for all values of airflow velocity, angles of incidence, various airfoil shapes. Thus, for any one airfoil the acting forces can be represented as shown in Figure 7-6a. Using such observed values, it is possible to define relations between the forces... 

The quantity aAp is defined separately for each type of cooling tower. It depends on many variables jet pressure, jet division, airflow velocity, and others. The total energy balance for a cooling tower is (see Fig. 4.19)... 

Mean airflow velocities approach zero as the inspired airstream enters the lung parenchyma, so particle momentum also approaches zero. Most of the particles reaching the parenchyma, however, are extremely fine (< 0.5 pm MMAD), and particle buoyancy counteracts gravitational forces. Temperature gradients do not exist between the airstream and airway wall because the inspired airstream has been warmed to body temperature and fully saturated before reaching the parenchyma. Consequently, diffusion driven by Brownian motion is the only deposition mechanism remaining for airborne particles. Diffusivity, can be described under these conditions by... 

Nozzle Static Pressure Loss Overall nozzle static pressure loss (SPN) was tested for all of the experimental LVHV nozzles.Experimental testing has confirmed what would be expected, that nozzle shape and size variation can cause great differences in overall static pressure loss, especially at high airflow velocities. Figure 10.25l/ compares SPN versus Vq (cm Hg versus m s" inch Hg versus fpm) characteristics for five circular nozzles. The plain wedge had the steepest rising curve, followed by the plain circular nozzle. Both of... 

In order to maintain a high level of air qualit), it is necessary to test airflow velocities and HEPA filters for integrity. These tests are described in a variety of standards and recommended practices depending on the use of the airflow bench. 

Large Car-C were aged up to eight weeks at 70°C. The ovens were calibrated per ASTM E 145 with an A2LA approved, modihed, method for temperature uniformity, consistency, airflow exchanges, and airflow velocity. 

Instruments are available for measuring the airflow velocity at specific points of the hood window opening. Testing is an OSHA requirement. 

The airflow velocity is a function of the sash height and the blower speed. Arrows are frequently used to indicate the proper sash height to ensure a specified face velocity. 

The compressed air introduced from the atmosphere through the air-intake is termed ram air , and the associated pressure is termed ram pressure . Ram pressure is built-up when the airflow velocity is decelerated in flow fields. The air-intake is designed as an aerodynamic tool to obtain maximum ram pressure.lh Air-intakes are designed to decelerate supersonic flow to subsonic flow by the formation of shock waves in front of them. The combustor in which the fuel gas is burned with the ram air is termed a ramburner . 

When the back-pressure in the difTuser is optimized, a normal shock wave is set up at the hp of the diffuser and the pressure behind the shock wave is increased. No air spill-over occurs at the lip of the diffuser and the airflow velocity is as shown in Fig. D-2 (b). The pressure in the diffuser increases and the airflow velocity decreases along the flow direction. When the back-pressure is lower than the design pressure, a normal shock wave is swallowed inside of the diffuser, as shown in Fig. D-2 (c). Since the flow velocity in front of the normal shock wave in the diffuser is increased along the flow direction, the strength of the normal shock wave inside of the diffuser becomes higher than that in the case of the diffuser at the optimized back-pressure shown in Fig. D-2 (b). Thus, the pressure behind the shock wave is lowered due to the increased entropy. 

Typically, either airflow velocity or air flow volume testing will be performed. Total volume may in turn be used to determine the air exchange rate (room air volume changes per hour) for the clean room. 

From Eq. (8.2) it is obvious that the Stokes number Stk and thus the deposition efficiency by impaction increase with increasing particle size and airflow velocity. Impaction occurs most frequently in the upper respiratory tract (pharynx, larynx, and main trachea), where particles larger than 5 p,m are trapped because of their size and the fast and turbulent airflow exerted. Also in the upper tracheobronchial region, impaction is the most prominent mechanism (Hinds 1998). 

Two sets of typical data experimentally measured are illustrated in Figs. 5.3(a) and (b), in which the curves represent the results calculated by Eq. (5.2) with properly regressed parameters Q. It should be noted that u.d in the figures is the airflow velocity at the exits of the nozzles which is quite different from the impinging velocity, u , in both the nature and the order of magnitude. 

Fume hood fulfilling the present internationally recognized requirements set for fume hoods, such as DIN, OSHA (US) and BS standards. Normal linear airflow velocity at the face should be over 0.5 m/s (measured in compliance with BSI DD80 or equivalent) with approx, size 90 x 90 x 90 cm. 

Q5 Measurement of peak expiratory flow this is a simple measure of expiratory function. The peak flow meter measures the velocity of expired airflow and is suitable for both adults and children. The patient breathes out a short blast of air, as fast as possible, into the device. Normal individuals can achieve airflow velocity of 450-6501 min-1. The peak flow meter is a cheap device which is used by patients at home to monitor their asthma. If a patient s peak flow diminishes below a certain level which has been set by their nurse practitioner or family doctor, they can adjust their own treatment, within specified limits, and control their condition better. 

Airflow velocity exiting an unobstructed workstation should be maintained at 90 LFPM average with a uniformity within 20% across the entire area of the exit. 

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