Wide air curtains

There are many different combinations of supply inlets and exhaust hoods, where these have to be designed together. Some of these are described in some detail. Two examples of using air jets for special purposes are described and the use of wide air curtains is also described. 

TABLE 10.16 Airflow Rates for Heated Wide Air Curtains (Pressure Difference between Inside and Outside Is 15 Pa)... 

A wide air curtain is usually directed downward from above. The air is blown along the width of the entire door and the jet has a large depth. The ex haust, which could be connected to the inlet (recirculation), is then situated in the floor. The supply air is usually heated, by a heat regenerator, to increase the comfort of people passing through the opening. 

Air Curtain and Exhaust Off-Take Air curtain design and exhaust offtake location are very important considerations. The air curtain is applied on roof openings that are typically 2 to 3 m wide and used for crane rope access. The opening may extend over the length of the enclosure and should, therefore, be served by two sets of independently operated doors— one for tapping and one for charging. This feature minimizes the pen area when one of the two events occurs. 

In industrial ventilation the majority of air velocity measurements are related to different means of controlling indoor conditions, like prediction of thermal comfort contaminant dispersion analysis adjustment of supply airflow patterns, and testing of local exhausts, air curtains, and other devices. In all these applications the nature of the flow is highly turbulent and the velocity has a wide range, from O.l m in the occupied zone to 5-15 m s" in supply jets and up to 30-40 m s in air curtain devices. Furthermore, the flow velocity and direction as well as air temperature often have significant variations in time, which make measurement difficult. 

Eggleston, Herrera, and Pish 1976 To provide needed data about the use of air entrained by a water spray to dilute flammable vapor releases below the lower flammability limit. Absorption/adsorption effects are insignificant in the case of ethylene and vinyl chloride. Sprinklers and water-spray nozzles vary widely in their efficiency as air movers. Flame quenching was not affected in any of the experiments Water sprays increased the rate of flame propagation. The air-pumping action of a water curtain can be used to set up a barrier to the horizontal flow of vapors. 

Most films are produced by extrusion. Thermoplastic materials are heated and pushed through a die to form a flat tube. Warm air is blown into the extruded tube to produce a balloon which is then cut open and laid flat. Calendering can also be employed to produce film. Hot thermoplastic is passed through a series of temperature-controlled metal rolls with progressively smaller gaps to produce a continuous sheet (Figures 3.27 and 3.28). The technique is used to make shower curtains, food wrap films, carrier bags and protective films. The most widely used films are polyethylene, nylons, polypropylene, cellulose acetate, PVC and polyesters. 

While smoke screens on land and sea were not new at the time of World War II, air screens were an innovation. Such screens, or curtains as they were frequently called, were set up by low-flying airplanes spraying liquid smoke-producing chemicals into the air. As the droplets floated to earth they reacted with moisture in the atmosphere and formed white smoke that hung suspended in the sky like a high, wide curtain. 

---