Extended surfaces condensing

Method 1. Fit a 500-ml. three-necked flask with a thermometer (the bulb of which is within 2 cm. of the bottom), and inlet tube extending to the bottom of the flask, and a double surface condenser. Use old ... 

Into a 1-litre three-necked flask, equipped with a reflux (double surface) condenser, a mechanical stirrer (preferably of the Hershberg type. Fig. II, 7, 8) and a gas lead-in tube extending to near the bottom of the flask, place 200 g. (227 ml.) of dry benzene, 20 g. of paraformaldehyde (1) and 20 g. of finely-pulverised, anhydrous zinc chloride. Support the flask on a water bath so arranged that the level of the water in it is about... 

Improved and redesigned rotors of modem compressors save considerable power. The ethylene fractionator and the propylene refrigeration condensers can be replaced with extended surface tube bundles instead of conventional tube bundles. 

Air-cooled condensers are used mostly in air-conditioning and for smaller-refrigeration capacities. The main advantage is avauability of cooling medium (air) but heat-transfer rates for the air side are far below values when water is used as a coohng medium. Condensation always occurs inside tubes, while the air side uses extended surface (fiusy... 

Gases or vapours that are not water soluble but are slowly reactive, with absorbing agent Condensation Freezing traps or low temperature condensers Glass or metal Dry 1-5 90-100 (depends on vapour pressures at reduced temperature) Can be packed with glass beads or other extended surfaces... 

Above this size, the flow of air over the condenser surface will be by forced convection, i.e. fans. The high thermal resistance of the boundary layer on the air side of the heat exchanger leads to the use, in all but the very smallest condensers, of an extended surface. This takes the form of plate fins mechanically bonded onto the refrigerant tubes in most commercial patterns. The ratio of outside to inside surface will be between 5 1 and 10 1. 

The heat-transfer coefficient of an air cooler (Btu, per hour, per square foot of finned area, per degree Fahrenheit), is not particularly good. It might be 3 to 4, for cooling a viscous liquid, or 10 to 12 for condensing a clean vapor. The low heat-transfer coefficients are off-set by the large extended surface area. 

Air finfan overhead condensers. Table 8.34 gives the modular cost of the overhead condensers and product coolers. Since this plant is to be installed in Saudi Arabia, cooling tower water is not available. Also, cooling water is not necessary since the products will be stored in spherical tanks requiring 150 to 180°F cooling. This is easy to obtain, even in Saudi Arabia, with air finfan coolers. The square feet of surface area shown in Table 8.34 is the bare tube surface area of each cooler. Please note this is not the extended surface of the outside tube area, but rather the outside bare tube surface area in square feet. Figure 8.4 was used to find the base cost of these air coolers. 

Water flows inside the tubes, and vapors condense on the shell side. Cooling water is normally chilled, as in a cooling tower, and reused. Air-cooled surface condensers and some water-cooled units condense inside the tubes. Air-cooled condensers are usually constructed with extended surface fins. 

Forced Convection 186 Condensation 187 Boiling 187 Extended Surfaces 188... 

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