Bulk cooling

Such contact measurements of temperature are appealing because they provide a direct measure of the bulk-cooling element temperature. Furthermore, the extraction of heat from an attached sensor is in itself a demonstration of cooling a thermal load. However, the use of thermocouples becomes difficult because of fluorescent heating and heat conduction through the wires. These drawbacks can be avoided with some of the noncontact thermometry methods reviewed in the following. 

Glasses and crystals doped with Yb represent the majority of laser-cooUng materials studied to date. Table 1 summarizes the systems in which net laser-induced bulk cooling has been observed experimentally. The dominance of... 

TABLE 1 Yb +-Doped Materials for Which a Net Laser-Induced Bulk-Cooling Effect Has Been Reported... 

If the solid does not dissolve in the cold solvent gently heat the mixture over a micro-Bunsen burner or in a small water-ba until the liquid boils. Continue to add o-i ml. portions of solvent until the solid dissolves. [If more than about i ml. of solvent is required, the solvent is considered unsatisfactory.] If a clear solution is obtained, cool the tube and scratch it below the surface of the solution with a very fine glass rod and proceed as suggested on p. 16. In general, the products from the choice of solvent investigation are not discarded but added to the main bulk of the crude product for recrystallisation. 

The oxime is freely soluble in water and in most organic liquids. Recrystallise the crude dry product from a minimum of 60-80 petrol or (less suitably) cyclohexane for this purpose first determine approximately, by means of a small-scale test-tube experiment, the minimum proportion of the hot solvent required to dissolve the oxime from about 0-5 g. of the crude material. Then place the bulk of the crude product in a small (100 ml.) round-bottomed or conical flask fitted with a reflux water-condenser, add the required amount of the solvent and boil the mixture on a water-bath. Then turn out the gas, and quickly filter the hot mixture through a fluted filter-paper into a conical flask the sodium chloride remains on the filter, whilst the filtrate on cooling in ice-water deposits the acetoxime as colourless crystals. These, when filtered anddried (either by pressing between drying-paper or by placing in an atmospheric desiccator) have m.p. 60 . Acetoxime sublimes rather readily when exposed to the air, and rapidly when warmed or when placed in a vacuum. Hence the necessity for an atmospheric desiccator for drying purposes. 

B) Methiodi s. Members of Classes (i), (ii) and (iv) combine wdth methyl iodide (some very vigorously) to form quaternary methiodides. It is best to add the amine to an excess of methyl iodide dissolved in about twice its volume of methanol, allow any spontaneous reaction to subside, and then boil under reflux for 30 minutes (extend to 1 hour for Class (iv) except pyridine and quinoline). The methiodide may crystallise when the reaction-mixture cools if not, evaporate the latter to small bulk or to dryness, and recrystallise, (M.ps., pp. 553-554 )... 

Place in a dry test-tube 0 -5 g. of the compound and an equal bulk of pure phthahc anhydride, mix well together, and add 1 drop of concentrated sulphuric acid. Stand the tube for 3-4 minutes in a smah beaker of concentrated sulphuric acid or oil previously heated to 160°, Remove from the bath, allow to cool, add 4 ml. of 5 per cent, sodium hydroxide solution and stir until the fused mass has dissolved. Dilute with an equal... 

Method 1. Dissolve 76 g. of thiourea in 200 ml. of warm water in a 750 ml. or 1 litre round-bottomed flask. Dilute the solution with 135 ml. of rectified spirit and add 126-5 g. of benzyl chloride. Heat the mixture under reflux on a water bath until the benzyl chloride dissolves (about 15 minutes) and for a further 30 minutes taking care that the mixture is well shaken from time to time. Cool the mixture in ice there is a tendency to supersaturation so that it is advisable to stir (or shake) the cold solution vigorously, when the substance crystallises suddenly. Filter off the sohd at the pump. Evaporate the filtrate to about half bulk in order to recover a further small quantity of product. Dry the compound upon filter paper in the air. The yield of hydrochloric acid filter off the sohd which separates on cooling. Concentrate the filtrate to recover a further small quantity. The yield of recrystalhsed salt, m.p. 175° is 185 g. some of the dimorphic form, m.p. 150°, may also separate. 

A schematic of a continuous bulk SAN polymerization process is shown in Figure 4 (90). The monomers are continuously fed into a screw reactor where copolymerization is carried out at 150°C to 73% conversion in 55 min. Heat of polymerization is removed through cooling of both the screw and the barrel walls. The polymeric melt is removed and fed to the devolatilizer to remove unreacted monomers under reduced pressure (4 kPa or 30 mm Hg) and high temperature (220°C). The final product is claimed to contain less than 0.7% volatiles. Two devolatilizers in series are found to yield a better quaUty product as well as better operational control (91,92). 

If condensation requires gas stream cooling of more than 40—50°C, the rate of heat transfer may appreciably exceed the rate of mass transfer and a condensate fog may form. Fog seldom occurs in direct-contact condensers because of the close proximity of the bulk of the gas to the cold-Hquid droplets. When fog formation is unavoidable, it may be removed with a high efficiency mist collector designed for 0.5—5-p.m droplets. Collectors using Brownian diffusion are usually quite economical. If atmospheric condensation and a visible plume are to be avoided, the condenser must cool the gas sufftciendy to preclude further condensation in the atmosphere. 

Texturing. The final step in olefin fiber production is texturing the method depends primarily on the appHcation. For carpet and upholstery, the fiber is usually bulked, a procedure in which fiber is deformed by hot air or steam jet turbulence in a no22le and deposited on a moving screen to cool. The fiber takes on a three-dimensional crimp that aids in developing bulk and coverage in the final fabric. Stuffer box crimping, a process in which heated tow is overfed into a restricted oudet box, imparts a two-dimensional sawtooth crimp commonly found in olefin staple used in carded nonwovens and upholstery yams. 

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