Heat heads

The light scattering measurements were performed with a Sofica photogoniometer. The temperature was controlled by a special bath, which was mounted around the index vat, in which benzene was stirred to achieve a good temperature uniformity in the measuring cell. By means of a heated head-piece, which was kept at bath temperature, the temperature remained constant to 0.01 °C. 

Electrically heated head of a probe with a solid-electrolyte disk [58]. 

If there is an operation bottleneck because of lack of heating capacity of a furnace in this temperature range, control techniques are available to increase capacity by raising the temperature of the furnace above the final product temperature. If bright metals such as stainless steel or titanium are to be heated, the rate of radiation will be low because of their lower emissivity (eq. 2.6) therefore, convection velocity should be increased. An excess of furnace or gas temperature over the desired final load temperature is permissible with steel provided the hottest location has a T-sensor to automatically control heat head. A fiue gas temperature somewhat higher than the final load temperature can be used with aluminum because of its lower absorptivity and higher thermal conductivity. 

To attain an even more effective heat head control of a preheat zone, relocate the control measurement near the charge door, for example, 2 or 3 ft (0.7 to 0.9 m) into the zone. Such a measurement will require greater firing rates to achieve the same set points. The relocation will not be dangerous to the strip because the strip temperatures in preheat zones are several hundred degrees below final temperature. In addition, during a line stop, the relocated measurement will sense the rapid temperature rise and reduce energy input. (See accordian effect discussed earlier in this section.)... 

The two controllers should operate through a low-select device to gain heat head without damage to the product, yet providing automatic heat head adjustment to maintain constant product temperature. 

Heat head (temperature) should be automatically added or subtracted as needed to hold product surface temperatures as desired. Heat heads to 100°F above normal furnace setpoints may be desirable. Holding the product at a near-constant distance from the thermocouple is necessary for the control to hold the product temperature near constant therefore, the product should be charged at a fixed distance from the outside wall of the furnace chamber. 

Air velocities can be measmed by a variety of instruments but vane anemometers and heated head (hot wire or thermistor) air meters are the most common. Vane anemometers Figure 3.6.7) have a rotating windmill type head coupled to a meter and are most suitable for use in open... 

Figure 3.6.8 Heated head air meter (Courtesy Airflow Developments Ltd)...

Compression of gases and air to achieve high pressures with relatively low volumes is by positive displacement compressors of either the piston or rotary type, while for large volumes at lower pressures centrifugal compressors are used as for example in gas turbines. Gas flows can be measured by means of a vane or hot wire (heated head) anemometer, by measuring the pressure difference across an orifice, or through the use of pitot tubes. 

Figure 10.4 Comparison of recovery by 3 heated head-space enrichment methods. Sample Fire debris sample, gasoline on a charred matrix of carpet and carpet padding (Instrument 1). Top SPME, Car-boxen/PDMS fiber (70°C, 3 min extraction). Middle Static headspace enrichment (90°C,...

A second instrament has been developed in an ambient-to-573 K C-80 model by Mathonat et al. (94MAT1) to measure the enthalpy of Mxing or reachon of two fluids (gas + liquid or liquid + liquid). The details are siMlar to those of the above calorimeter, the main difference is that the reference cell was not used. The pure component liquids were brought to the temperature of the calorimeter by passing them through an electrically heated head maintained at the temperature at which it was required to make the measurements. The calorimeter was tested with both liquid-hquid Mxtures (ethanol + water) and gas-liquid Mxtures (CO2 + toluene). The overall imcertainty was foimd to be 2% for liquid-liquid systems and 4% for gas-liquid systems. Measurements are possible up to 573 K and at pressures up to 20 10 Pa (File Number LB2338, p. 2-375). 

Pour the mixture into a 500 ml. flask fitted with a steam-distillation head, and with a steam-inlet tube reaching almost to the bottom of the flask. First distil off the benzene in steam. Then place the flask in an oil-bath heated to 165-170 ", and continue the steam-distillation (2-3 hours). The /)-bromobiphenyl passes over and forms orange crystals in the water-condenser therefore run the water out of the condenser for a short while from time to time to melt the orange deposit and allow it to run into the receiver containing the distilled water. 

Add 23 g. of powdered (or flake ) sodium hydroxide to a solution of 15 ml. (18 g.) of nitrobenzene in 120 ml. of methanol contained in a 250 ml. short-necked bolt-head flask. Fix a reflux water-condenser to the flask and boil the solution on a water-bath for 3 hours, shaking the product vigorously at intervals to ensure thorough mixing. Then fit a bent delivery-tube to the flask, and reverse the condenser for distillation, as in Fig. 59, p. 100, or Fig. 23(D), p. 45). Place the flask in the boiling water-bath (since methanol will not readily distil when heated on a water-bath) and distil off as much methanol as possible. Then pour the residual product with stirring into about 250 ml. of cold water wash out the flask with water, and then acidify the mixture with hydrochloric acid. The crude azoxybenzene separates as a heavy oil, which when thoroughly stirred soon solidifies, particularly if the mixture is cooled in ice-water. 

Prepare a mixture of 30 ml, of aniline, 8 g. of o-chloro-benzoic acid, 8 g. of anhydrous potassium carbonate and 0 4 g. of copper oxide in a 500 ml. round-bottomed flask fitted with an air-condenser, and then boil the mixture under reflux for 1 5 hours the mixture tends to foam during the earlier part of the heating owing to the evolution of carbon dioxide, and hence the large flask is used. When the heating has been completed, fit the flask with a steam-distillation head, and stcam-distil the crude product until all the excess of aniline has been removed. The residual solution now contains the potassium. V-phenylanthrani-late add ca. 2 g. of animal charcoal to this solution, boil for about 5 minutes, and filter hot. Add dilute hydrochloric acid (1 1 by volume) to the filtrate until no further precipitation occurs, and then cool in ice-water with stirring. Filter otT the. V-phcnylanthranilic acid at the pump, wash with water, drain and dry. Yield, 9-9 5 g. I he acid may be recrystallised from aqueous ethanol, or methylated spirit, with addition of charcoal if necessary, and is obtained as colourless crystals, m.p. 185-186°. 

Oxidation, (i) Dissolve 5 g. of potassium dichromate in 20 ml. of dil. H2SO4 in a 100 ml. bolt-head flask. Cool and add 1 ml. of methanol. Fit the flask with a reflux water-condenser and warm gently a vigorous reaction soon occurs and the solution turns green. The characteristic pungent odour of formaldehyde is usually detected at this stage. Continue to heat for 3 minutes and then fit the flask with a knee-tube (Fig. 59, p. 100) and distil off a few ml. Test the distillate with blue litmus-paper to show that it is definitely acid. Then apply Test 3 p. 350) for formic acid. (The reflux-distillation apparatus (Fig. 38, p. 63) can conveniently be used for this test.)... 

Fig. II, 17, 2 illustrates a fractional distillation unit f for use with glass helices. The column is provided with an electrically-heated jacket the resistance shown in the Figure may be replaced by a variable transformer. The still head is of the total-condensation variable take-off type aU the vapour at the top of the column is condensed, a portion of the condensate is returned to the column by means of the special stopcock (permitting of...

Attention is directed to the fact that ether is highly inflammable and also extremely volatile (b.p. 35°), and great care should be taken that there is no naked flame in the vicinity of the liquid (see Section 11,14). Under no circumstances should ether be distilled over a bare flame, but always from a steam bath or an electrically-heated water bath (Fig.//, 5,1), and with a highly efficient double surface condenser. In the author s laboratory a special lead-covered bench is set aside for distillations with ether and other inflammable solvents. The author s ether still consists of an electrically-heated water bath (Fig. 11, 5, 1), fitted with the usual concentric copper rings two 10-inch double surface condensers (Davies type) are suitably supported on stands with heavy iron bases, and a bent adaptor is fitted to the second condenser furthermost from the water bath. The flask containing the ethereal solution is supported on the water bath, a short fractionating column or a simple bent still head is fitted into the neck of the flask, and the stUl head is connected to the condensers by a cork the recovered ether is collected in a vessel of appropriate size. 

The Stedman-type column is shown in Fig. 11, 56, 25. The characteristic features are (i) the use of a fine stainless steel wire cloth formed into conical discs, and (ii) an accurately fitting Pyrex glass jacket, produced by shrinking Pyrex glass on mandrels to the required inside dimensions. Modifications incorporating a silvered vacuum jacket and an electrically-heated jacket are marketed. This column is said to possess high efficiency but is expensive. It is generally employed in conjunction with a total-condensation variable take-off still head. 

Sulphuric acid method. Place 20 g. of commercial cycZohexanol and 0-6 ml. of concentrated sulphuric acid in a 150 or 200 ml. round-bottomed or bolt head flask, add 2-3 chips of porous porcelain, and mix well. Fit the flask with a fractionating column, a Liebig condenser, adapter and filter flask receiver as in Section 111,10 (1). Heat the flask in an air bath (Fig. II, 5, 3) at such a rate that the temperature at the top of the column does not rise above 90° alternatively, an oil bath, heated to a temperature of 130-140°, may be used. Stop the distillation when only a small residue remains and the odour of sulphur dioxide is apparent. Transfer the distillate to a small separatory funnel. 

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