Cooling surface foaming

Air-cooled surfaces may be cleaned by brushing off the accumulation of dust and fluff where the air enters the coil, by the combination of a high-pressure air hose and a vacuum cleaner, or, with the obvious precautions, by a water hose. Foaming detergents are also used. 

Flame lamination is another hot-air bonding process that is used mainly to continuously join fabric to foam. A foam sheet is passed over an open flame to create a thin layer of molten polymer on the foam surface, which is then mated with a fabric by passing the assembly through a set of rollers (Figure 13.5). The molten foam surface acts as an adhesive when it cools. PU foam is the most frequently used material in flame lamination. 

Stabilization of the Cellular State. The increase in surface area corresponding to the formation of many ceUs in the plastic phase is accompanied by an increase in the free energy of the system hence the foamed state is inherently unstable. Methods of stabilizing this foamed state can be classified as chemical, eg, the polymerization of a fluid resin into a three-dimensional thermoset polymer, or physical, eg, the cooling of an expanded thermoplastic polymer to a temperature below its second-order transition temperature or its crystalline melting point to prevent polymer flow. 

Provide adequate fixed fire protection for tanks and vessels containing flammable, unstable or reactive materials. This can include fire loops with hydrants and monitors in the storage area, foam systems for individual tanks, and deluge spray systems to keep the exposed surfaces of tanks cool in case of fire in an adjacent tank. 

Foam extinguishing system-Available in automatic and manual systems, foam has the ability to adhere to surfaces, and thus provide a blanketing as well as cooling effect. 

Another type of probe is based on the principle of the sudden cooling of the heated element. When foam comes in contact with a heated electrical element, the hot surface detects sudden cooling, which is translated to an output signal. The major problem with the use of a heated element is fouling of the media the sensitivity decreases while it is used, so such detectors may not be reliable in practice. 

These agents are effective on small spill fires. If there is risk of re-ignition from embers or hot surfaces, these ignition sources should be quenched or cooled with water and secured with foam, or the source of fuel should be shut off before attempting extinguishment. An example of a dry chemical system is shown in Figure 7-36. 

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