Cooling foaming

The burning object should be blanketed by the foam. It acts both by smothering and cooling. Foam extinguishers are suitable for burning liquids which exert no breaking effect on the foam (alcohols, esters, ethers, etc. may preclude the formation of a continuous foam blanket). 

Zhang et al. [21] experimentally investigated the fluid flow and heat transfer of liquid-cooled foam heat sinks (FHS). As indicated in Fig. 7, eight open-cell copper foam materials with two pore densities of 60 and 100 PPI (pores per inch) and four porosities varying from 0.6 to 0.9 were... 

Zhang HY, Pinjala D, Joshi YK, Wong TN, Toh KC, Iyer MK (2005) Fluid flow and heat transfer in liquid cooled foam heat sink for electrraiic packages. IEEE Trans Cmnptui Packag Technol 28(2) 272—280... 

For generations, attempts have been made to heat and cool foams, emulsions, dispersions, and heterogeneous colloidal systems, and to learn about the stability of the systems through their thermal behavior. Differential scanning calorimetry (DSC) and differential thermo gravimetry (DTG) are classical instruments that... 

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°. 

Place 84 g. of iron filings and 340 ml. of water in a 1 - 5 or 2-litre bolt-head flask equipped with a mechanical stirrer. Heat the mixture to boiling, stir mechanically, and add the sodium m-nitrobenzenesulphonate in small portions during 1 hour. After each addition the mixture foams extensively a wet cloth should be applied to the neck of the flask if the mixture tends to froth over the sides. Replace from time to time the water which has evaporated so that the volume is approximately constant. When all the sodium salt has been introduced, boU the mixture for 20 minutes. Place a small drop of the suspension upon filter paper and observe the colour of the spot it should be a pale brown but not deep brown or deep yellow. If it is not appreciably coloured, add anhydrous sodium carbonate cautiously, stirring the mixture, until red litmus paper is turned blue and a test drop upon filter paper is not blackened by sodium sulphide solution. Filter at the pump and wash well with hot water. Concentrate the filtrate to about 200 ml., acidify with concentrated hydrochloric acid to Congo red, and allow to cool. Filter off the metanilic acid and dry upon filter paper. A further small quantity may be obtained by concentrating the mother liquid. The yield is 55 g. 

Dinitroaniline from 3 5-dinItrobenzoic acid. Place a solution of 50 g. of 3 5-dinitrobenzoic acid (Section IV, 168) in 90 ml. of 10 per cent, oleum and 20 ml. of concentrated sulphuric acid in a 1-litre three necked flask equipped with a reflux condenser, mechanical stirrer, adropping funnel, and thermometer (FUME CUPBOARD ). Add 100 ml. of clJoroform and raise the temperature to 45°. Stir rapidly and add 17 -5g. of sodium azide in small portions whilst maintaining the temperature at 35-45°. The reaction is accompanied hy foaming, which usually commences after about 3 g. of sodium azide has been introduced. After all the sodium azide has been added raise the temperature so that the chloroform refluxes vigorously and maintain this temperature for 3 hours. Then cool the reaction mixture, pour it cautiously on to 500 g. of crushed ice, and dilute with 3 litres of water. After 1 hour, separate the yellow solid by filtration at the pump, wash well with water and dry at 100°. The yield of 3 5-dinitroaniline, m.p. 162-163°, is 39 g. The m.p. is unaffected by recrystallisation from dilute alcohol. 

In a 500 ml. Pyrex round-bottomed flask, provided with a reflux condenser, place a mixture of 40 g. of freshly-distUled phenylhydrazine (Section IV.89) and 14 g. of urea (previously dried for 3 hours at 100°). Immerse the flask in an oil bath at 155°. After about 10 minutes the urea commences to dissolve accompanied by foaming due to evolution of ammonia the gas evolution slackens after about 1 hour. Remove the flask from the oil bath after 135 minutes, allow it to cool for 3 minutes, and then add 250 ml. of rectified spirit to the hot golden-yellow oil some diphenylcarbazide will crystallise out. Heat under reflux for about 15 minutes to dissolve the diphenylcarbazide, filter through a hot water funnel or a pre-heated Buchner fuimel, and cool the alcoholic solution rapidly in a bath of ice and salt. After 30 minutes, filter the white crystals at the pump, drain well, and wash twice with a little ether. Dry upon filter paper in the air. The yield of diphenylcarbazide, m.p. 171 °, is 34 g. A further 7 g. may be obtained by concentrating the filtrate under reduced pressure. The compound may be recrystallised from alcohol or from glacial acetic acid. 

Stabilization of the Cellular State. The increase in surface area corresponding to the formation of many ceUs in the plastic phase is accompanied by an increase in the free energy of the system hence the foamed state is inherently unstable. Methods of stabilizing this foamed state can be classified as chemical, eg, the polymerization of a fluid resin into a three-dimensional thermoset polymer, or physical, eg, the cooling of an expanded thermoplastic polymer to a temperature below its second-order transition temperature or its crystalline melting point to prevent polymer flow. 

Extmded stmctural foams are produced with conventional extmders and a speciaUy designed die. The die has an inner, fixed torpedo located at the center of its opening, which provides a hoUow extmdate. The outer layer of the extmdate cools and soHdifies to form soHd skin the remaining extmdate... 

Poly(vinylchloride). Cellular poly(vinyl chloride) is prepared by many methods (108), some of which utili2e decompression processes. In all reported processes the stabili2ation process used for thermoplastics is to cool the cellular state to a temperature below its second-order transition temperature before the resia can flow and cause coUapse of the foam. 

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