Air impingement

FIG. 12-46 Example of the use of air impingement in drying secondary heat source on a doiihle-dnim dryer. [Chem. Eng., 197, (June 19, 1967).]... 

Air impingement is commonly employed for drying sheets, film, thin slabs, and coatings. Another application in which it is used is as a secondary heat source on drum and can diyers (see Fig. 12-46). 

A continuous conveyor diyer employing a combination of air impingement and through circulation is shown in Fig. 12-57. 

The basic purpose of an oil separator is to clean the pressurized air of any oil contamination, which is highly detrimental to pneumatically controlled instrumentation. A separator consists of an inlet, a series of internal baffle plates, a wire mesh screen, a sump, and an outlet. The pressurized air enters the separator and immediately passes through the baffle plates. As the air impinges on the baffle plates it is forced into making sharp directional changes as it passes through each baffle section. As a result, the oil droplets separate from the air and collect on the baffles before dropping into the separator s sump. 

External-mixing air-assist atomizers. Derived from ethanol (glycerin)-air spray data with initial thickness of flat circular sheet up to 0.7 mm and varied air impingement angles Sampled with oil-coated slides... 

Cloths used to apply linseed oil to laboratory benches were not burned as directed, but dropped into a waste bin. A fire developed during a few hours and destroyed the laboratory. Tests showed that heating and ignition were rapid if a draught of warm air impinged on the oil-soaked cloth. Many other incidents involving ignition of autox-idisable materials dispersed on absorbent combustible fibrous materials have been recorded [1], Practical tests on the spontaneous combustion of cotton waste soaked in linseed oil and other paint materials had been reported 40 years previously [2],... 

Ion chromatography has also been used in air pollution studies to measure anions and cations in an air impinger solution and air particulate extracts. 

Figure 4.2 (cont.) (b) Dry spinning a stream of hot air impinges on the jets of solution emerging from the spinneret, evaporates the solvent, and leaves the solid filaments. 

Regardless of placement of an aerobiological sampler in a laminar airflow work zone, it can at best measure the effect of the process at some point downstream from the product. For example, the mouth of a flask may be situated in first air issuing from the HEPA filter, while air impinging on the surface of a plate adjacent to it will be affected by disruptions of the airstream caused by the flask. Contamination found on the plate then results from a different set of conditions than those to which the product is subjected and does not exactly parallel the product contamination mechanism. Only a media-fill process simulation can fulfill this function. Aerobiologic sampling immediately downstream of the critical orifice can, however, detect downward shifts in the overall cleanliness of the critical process air, which in turn may indicate increased contamination potential near the product. 

Another well-known correlation has been used to predict heat-and mass-transfer coefficients for air impinging on a surface from arrays of holes (jets). This correlation uses relevant geometric properties such as the diameter of the holes, the distance between the holes, and the distance between the holes and the sheet [Martin, Heat and Mass Transfer Between Impinging Gas Jets and Solid... 

These methods, typically HPLC, must detect the chemical under evaluation at or below the acceptance criteria limits. The methods must be validated with samples from the swabs, rinses, and air impingers to prove limit of detection, specificity, range, sample preparation, sample stability, and reproducibility. A quick method, like UV spectrophotometry or conductivity, should also be developed and validated for the routine cleaning verification of wash rinse samples. 

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