Airflow horizontal

The conventional top spray method shown in Figure 2 has been used for layering and coaling for decades. It evolved from the fluidized bed dryers commercialized more than 40 years ago. The substrate is placed in the product container, which is typically an unbaffled. inverted, truncated cone with a fine retention screen and an air or gas distribution plate at its base. Perforated plates such as a Conidur or Gill plate may also achieve air distribution and product retention. These types of plates may have directed holes for guiding the airflow horizontally in the product container (for side discharge as an example). Process air is drawn through the distribution plate and into the product. 

FIGURE 7.6 Flow patterns in rooms with horizontal air supply along the ceiling surface (a) primary airflow in a short room (b) primary airflow (c) secondary and tertiary eddies in long rooms. ... 

FIGURE 7.7 Schematics of air supply (o) with inclined jets toward the occupied zone (b) with horizontal jets and occupied zone ventilated by reverse flow (c) with vertical jets. Shaded areas show the effect of buoyant forces on airflow pattern when supply air is excessively heated over the room air" ... 

To create unidirectional low-turbulence flow, air is supplied with a low velocity supply diffusers and exhaust openings have large surfaces (e.g., filter mats). Airflow can be either vertical (air supplied from the ceiling and exhausted through the floor or vice versa (Fig. 7.1 la)), or horizontal (air supplied through... 

Experimental Studies of Isothermal Horizontal Jets in Confined Spaces Airflow Pattern, Throw, Velocities... 

Similar studies were conducted by Troyanovsky, who concluded that to maintain the airflow pattern in rooms with heated or cooled air supply as in isothermal conditions, it is necessary that the rise of horizontally supplied jet does not exceed Ay = 0.1 BH at the distance from the outlet X = 0.15K BH) -. From this assumption the following equation for the maximum air temperature difference was derived ... 

When the width of the jet (calculated for free conditions) is less than the width of the room, airflow after jet impingement on a floor is similar to that in noncon-fined conditions. When the horizontally directed flow (along the particular line) reaches the wall, it is divided into two branches one following the direction of the branch with a maximum airflow and another flowing in the opposite direction. 

FIGURE 7.80 CDF-predicted values of maximum velocity V, temperature differential, ( C), and airflow, q (Us), in the horizontal cross-section of the buoyant plume above the heated cube (0.66 m x 0.66 m X 0.66 m, 22SW).i ... 

Perforated sheets are, however, much more vulnerable to uneven pressure distributions and tilted inflow of air, as illustrated in Fig, 8,26. The supply air entering horizontally alxive the perforated sheet partly maintains its horizontal velocity component when being discharged through the holes in the perforated sheet. Thus, it leaves the perforated sheet at an angle less than 90°. The suction between the small outflowing jets also makes the airflow stick to the perforated sheet and flow along the sheet instead of perpendicular to (t. 

The influence of airflows from ventilating systems must also be considered. Processes using mediums of different physical qualities when mixed will have separation into different layers. Transmission of energy between molecules in flowing mediums takes place in the direction of the velocity. This strengthens the separation into parallel layers. The level of fluid in containers and tanks is due to stratification of horizontal temperature layers, while airflow after batteries, heat-recovery systems, and humidifiers or dehumidifiers will separate into parallel layers. 

Slots or holes are placed into a horizontal work surface to exhaust air downward in such a way that the surface can also be used as a table. The amount of open area for airflow varies depending on use. 

Low-momentum air supply systems designed for local ventilation purposes mainly use vertically downward airflow. Some systems with an inlet of low-momentum horizontal airflow for a whole workroom are on the borderline between general and local ventilation and are therefore briefly described here. A more complete description will be found in chapters 7 and 8 dealing with general ventilation. 

The purpose of open unidirectional airflow benches is to protect products from particulate contaminants by creating a controlled environment. These benches are used, for example, in electronic, biological, pharmaceutical, and food industries. It should be mentioned that within pharmaceutical production, aseptic sterile processes must be carried out in a Class 100 environment (U.S. Federal Standard 209 E, Airborne Particulate Cleanliness Classes in Cleanrooms and Clean Zones). To avoid particle contamination in the bench, horizontal or vertical airflow with high-efficiency particulate air (HEPA)-filtered air is used. The air velocity is normally 0.4-0.5 ra s". Some examples of typical arrangements of open unidirectional airflow benches are shown in Fig. 10.51. 

For a push-pull system, the source is usually an open surface tank and the airflow acts as a horizontal curtain above the surface. In this case, the person could be anywhere as long as the system works as intended and the curtain is not broken. The curtain will be broken when parts or material are lifted out of or placed into the bath and the contaminants could be spread either through convection or because the supply air blows against the material or part. 

For these rooms, the air should flow horizontally from one end to the other with a velocity greater than 1.3 m s"T The necessary airflow rate is of course calculated as the volume times the number of air changes per hour. 

The exhaust flow rate influences the flow of the jets and some reports recommend a ratio of supply airflow rate to exhaust airflow rate of approximately 0.3. A ratio of 0.2 is unsteady and ratios larger than 0.4 have not been studied. In the cases that have been studied, the exhaust opening was 80 mm in diameter, the distance between the horizontal planes was 750 mm, the tubes were placed in a square w ith side length equal to 670 mm, and the inward angles of the jets were 10 degrees. This configuration resulted in better capture of hot gases than use of an exhaust system alone. 

A Similar aphical presentation of the spatial distribution of a tracer g is or a real contaminant and thereby to some extent the airflow in the studied area is based on the use of computed tomography and optical remote sens-jt]g I2.M beams are sent out horizontally and reflected back to an IR analytical instrument, analyzing the average concentration of the contaminant along the IR beam. By combining data from several measured tines it is possible ro present data in a similar way to Fig. 12.8. Those methods presuppose access ro an expensive and complicated sampling/data processing system. 

Figure 46.1 Horizontal duct with adequate carrying velocity. Ducting of increasing size to accommodate increasing airflow...

Filtered air may be used to purge a complete room, or it m be confined to a specific area and incorporate the principle of laminar flow, which permits operations to be carried out in a gentle current of sterile air. The direction of the airflow may be horizontal or vertical, depending upon the type of equipment being nsed, the type of operation and the material being handled. It is important that there is no obstruction between the air supply and the exposed product, since this may resnlt in the deflection of microorganisms or particulate matter fiom a non-sterile surface and canse contamination. Airflow gauges are essential to monitor that the correct flow rate is obtained in laminar flow units and in complete suites to ensure that a positive pressure fiom clean to less clean areas is always maintained. 

The greatest risk of contamination of a pharmaceutical product comes from its immediate environment. Additional protection from particulate and microbial contamination is therefore essential in both the filling area of the clean room and in the aseptic unit. This can be provided by a protective work station supplied with a unidirectional flow of filtered sterile air. Such a facility is known as a laminar airflow unit in which the displacement of air is either horizontal (i.e. from back to front) or vertical (i.e. from top to bottom) with a minimum homogenous airflow rate of 0.45 ms" at the working position. Thus, airborne contamination is not added to the work space and any generated by manipulations within that area is swept away by the laminar air currents. 

Figure 14.1 presents the main components of a typical in situ SVE system.910 Vertical extraction wells are installed inside the contaminated zone at appropriate distances from one another. The SVE wells are typically constructed of PVC pipe, with a screened interval, which is placed within the contaminated zone. The wells are connected to blowers or vacuum pumps, which induce a continuous airflow through the pores of the unsaturated zone. The soil surface is sometimes covered with an impermeable seal, made from high density polyethylene (HDPE) or bentonite clay for example, to prevent the vertical influx of air from the surface, which might cause short-circuiting problems, and promote horizontal gas flow through the contaminated area. The airstream, which contains the contaminant vapors, passes initially through an air-water separation unit to remove the entrained moisture and is then directed to the gas treatment unit, where the contaminants are thermally destroyed or removed by adsorption. 

Horizontal blades installed at air inlets on towers to control splash-out of water and promote uniform airflow, esp. cross-flow towers. 

A is the area of the clean room of clean air controlled space in m2. In the case of unidirectional perpendicular airflow, the area A may be considered as the cross section of air horizontal to the airflow. 

Kuts et al. [88, 89] patented a spray dryer with rotating impinging streams for solutions or suspensions of thermal sensitive materials, as shown in Fig. 6.2. The drying chamber is a horizontal cylinder, 1.2 m in diameter and 4 m long. The main airflows at 150°C enter axially the drying chamber from the two sides with the sprayed... 

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