Cooling media

The heat duty on the heating/cooling medium is given by... 

IK as a cooling medium for nuclear reactors, and as a gas for supersonic wind tunnels. 

Aqueous media, such as emulsion, suspension, and dispersion polymerization, are by far the most widely used in the acryUc fiber industry. Water acts as a convenient heat-transfer and cooling medium and the polymer is easily recovered by filtration or centrifugation. Fiber producers that use aqueous solutions of thiocyanate or zinc chloride as the solvent for the polymer have an additional benefit. In such cases the reaction medium can be converted directiy to dope to save the costs of polymer recovery. Aqueous emulsions are less common. This type of process is used primarily for modacryUc compositions, such as Dynel. Even in such processes the emulsifier is used at very low levels, giving a polymerization medium with characteristics of both a suspension and a tme emulsion. 

Quenching. After solution treatment, the product is generally cooled to room temperature at such a rate to retain essentially all of the solute in solution. The central portions of thicker products caimot be cooled at a sufficient rate to prevent extensive precipitation in some alloys. Moreover, some forgings and castings are dehberately cooled slowly to minimize distortion and residual stress produced by differential cooling in different portions of the products. Cold water, either by immersion or by sprays, is the most commonly used cooling medium. Hot water or a solution of a polymer in cold water is used when the highest rates are not desired. Dilute Al—Mg—Si and Al—Mg—Zn extmsions can be effectively solution heat treated by the extmsion process therefore, they may be quenched at the extmsion press by either air or water. 

There are a number of ways to provide the heating or cooling medium at temperatures closer to the optimum level. One is by use of double-effect distillation, which uses the overhead vapor from one column as the heat source for another column such that the second column s reboiler becomes the first column s condenser. This basically cuts the temperature differential in half, and shows up as an energy saving because external heat is suppHed to only one of the units. 

Cooling-in-Tank or Jacketed Vessel Isothermal Cooling Medium... 

Contactive (Direct) Heat Transfer Contactive heat-transfer equipment is so constructed that the particulate burden in solid phase is directly exposed to and permeated by the heating or cooling medium (Sec. 20). The carrier may either heat or cool the solids. A large amount of the industrial heat processing of sohds is effected by this mechanism. Physically, these can be classified into packed beds and various degrees of agitated beds from dilute to dense fluidized beds. 

Liquid Coolers and Condensers Dirty water can be used as the cooling medium. The top of the cooler is open to the atmosphere for access to tubes. These can be cleaned without shutting down the cooler by removing the distributors one at a time and scrubbing the tubes. 

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... 

Cmb (°C) = ambient temperature (or temperature of condenser cooling medium). 

Condenser cooling medium Brine Chilled water Tower water Chilled water... 

Scraped-Surface Crystallizer For relatively small-scale apph-cations a number of ciystallizer designs employing direct neat exchange between the shiny and a jacket or double wall containing a cooling medium have been developed. The heat-transfer surface is scraped or agitated in such a way that the deposits cannot build up. 

Condensation Equipment There are two basic types of condensers used for control contact and surface. In contact condensers, the gaseous stream is brought into direct contact with a cooling medium so that the vapors condense and mix with the coolant (see Fig. 25-15). The more widely used system, however, is the surface condenser (or heat exchanger), in which the vapor and the cooling medium are separated by a wall (see Fig. 25-16). Since high removal efficiencies cannot be obtained with low-condensable vapor concentrations, condensers are typically used for pretreatment prior to some other more efficient control device such as an incinerator, absorber, or adsorber. 

Use heating/cooling medium which does not react with or inhibit reactor contents... 

Use lower pressure heating or cooling medium to avoid flow into reactor in the event of a leak... 

Limit maximum utility temperature by choosing different heating/cooling medium (e.g.. tempered water in atmospheric loop vs. high pressure steam)... 

Each cooling circuit is then identified for the primary cooling medium by a letter A, H or W etc. which specifies the coolant as noted below ... 

The motor may be tested at any convenient value of cooling medium temperature less than 40°C. But whatever the value of this cooling-medium temperature, the permissible rise of temperature during test should not exceed those shown in Table 11.1. 

For assemblies using the surrounding air as the insulation and cooling medium... 

---