Cooling foam insulated containers

Cooling is most effectively accomplished with a tandem arrangement of two extmders, as shown in Figure 12, wherein the first extmder ensures complete dissolution of the blowing agent, and the second extmder is operated at slow speed for optimum cooling. Additional information on extmsion of foams is contained in Reference 28 (see Foamed plastics Insulation, thermal). 

The most suitable containers for cooling baths are plastic bowls (ice baths), Pyrex dishes (solid CO2 baths) and Dewar flasks (solid CO2 and liquid nitrogen baths). If Pyrex dishes are to be used below —20 °C, an insulated container can be prepared by placing a smaller Pyrex dish inside a larger one and filling the space between with an insulating material such as cotton wool, cork chips or polyurethane foam chips. Remember that foam chips will dissolve if they come into contact with many organic solvents. 

In polystyrene, a benzene ring replaces one hydrogen atom of each ethylene monomer unit. Because such a ring is bulky, atactic polystyrene does not crystallize to any significant extent. The most familiar application of this polymer is in the polystyrene foam used in disposable containers for food and drinks and as insulation. A volatile liquid or a compound that dissociates to gaseous products on heating is added to the molten polystyrene. It forms bubbles that remain as the polymer is cooled and molded. The gas-filled pockets in the final product make it a good thermal insulator. 

The outside of this condenser is packed with enough dry ice to keep it good and cold, in the vicinity of O0F. He insulates this dry ice packing so that it does not evaporate too quickly. He attaches the vacuum adapter to the condenser, then connects a section of plastic tubing to the vacuum nipple to carry fumes of ammonia outside. He attaches a 500 ml round bottom flask to the vacuum adapter. This flask is cooled by placing it in a styro foam container. He pours in alcohol until the rubbing alcohol is halfway up the sides of the flask. He adds dry ice to this alcohol bath until its... 

Foams, in addition to being useful as cushioning, can be used to provide thermal insulation for products. A frozen product, for example, might be packaged with ice (or dry ice or gel packs) to provide cooling, and encased in a foam container to help reduce the conduction of heat from the surroundings into the container. Often the temperature inside and outside the container can be regarded as relatively constant, and the heat transfer process can considered essentially one-dimensional. In such cases, Fourier s law of heat conduction reduces to its one-dimensional steady-state form ... 

Pumice is a natural porous ceramic. It is produced by volcano eruptions and the gas is trapped inside the solid as it rapidly cools. The matrix is mainly glass, but it can contain small crystals. Synthetic ceramic foam is illustrated in Eigure 15.15. Uses for ceramic foam are summarized in Table 15.3. One of the best-known applications for a porous ceramic is the space shuttle tile. An SEM image of such a tile is shown in Eigure 15.16. Notice that in this case, the ceramic consists mainly of fiber (pressed not woven), so the principle is the same as for ceramic (glass) fiber for house insulation. 

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