Cooling techniques

Sometimes it is necessary to cool a reaction mixture either to avoid undesired side reactions or to moderate the temperature of exothermic reactions that could become uncontrollable. Cooling is also often used to maximize the recovery of solid 

Reaction vessels (a) assorted shapes of standard-taper ground glassware and sealable glass tubes (courtesy CEM Corporation) (b) array of special reaction tubes for multiple, simultaneous reactions (courtesy of CEM Corporation). 

The most common cooling medium in the undergraduate laboratory is an ice-water bath. Liquid water is a more efficient heat transfer medium than ice, because it covers the entire surface area of the portion of the vessel that is immersed in the bath. Consequently, when preparing this type of bath, do not use ice alone. 

An ice-water bath has an equilibrium temperature of 0 °C. For lower temperatures, an ice-salt bath can be prepared by mixing ice and sodium chloride in a proportion of about 3 1 to generate a temperature of approximately -20 C. As the ice melts, the excess water should be removed and more ice and salt added to maintain this temperature. Still lower temperatures are possible using combinations of organic liquids and either dry ice (solid carbon dioxide) or liquid nitrogen directions for preparing these types of baths can be found in Reference 5 of Chapter 1. 

Immersing a vessel containing a warm reaction mixture in a container of tap water is useful for rapid cooling to room temperature so long as the glassware you are using is Pyrex. Consult with your instructor to ensure that this is the t)q e of glass you have. 

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Fig. 8. Equipment to prepare microporous membranes by the polymer precipitation by cooling technique (23).

Improved materials, coatings, and cooling techniques permit newer machines to operate at higher turbine inlet temperatures, yielding both increased output and efficiency. Further efficiency gains result from improved aerodynamics in the hot gas path, compressor, and turbine sections. Use is also made of variable inlet guide vanes (IGV). 

Moffitt, T.P., Prust, H.W. Jr., Szanca, E.M., and Schum, H.J., Summary of Cold-Air Tests of a Single-Stage Turbine with Various Stator Cooling Techniques, NASA, TM X-52969, 1971. 

Cooling techniques Various methods have been developed to cope with high temperature and heating problems. They are based on absorptive, dissipative, and mass... 

Bajugam and Flitsch [217] have described the synthesis of glycosylamines from mono-, di-, and trisaccharides by direct microwave-assisted Kochetkov amination (Scheme 6.110). The reaction was found to be effective with just a fivefold excess (w/w) of ammonium carbonate with respect to the sugar, as compared to the 40-or 50-fold excess needed under thermal conditions. All transformations were completed within 90 min in dimethyl sulfoxide as solvent, maintaining the vessel temperature at an apparent 40 °C using the heating-while-cooling technique (see Section 2.5.3). 

Figure 3. The regions of pressure and temperature accessible by joining static compression methods to heating and cooling techniques are compared to the Earth geotherm and to Jupiter and Uranus isentropes.

Figure 13. Thickness of InGaAsP epitaxial layers versus growth time for growth by the step-cooling technique with 10 °C supersaturation. (Reproduced with permission from reference 100. Copyright 1980 American Institute of...

In order to control the reaction course and so avoid a runaway incident, it is essential to understand how heating-cooling systems of reactors work and what their performance is. These topics are reviewed in this chapter, where different heating and cooling systems are reviewed from the particular implications on process safety. In the first section, the different heating and cooling techniques... 

Figure 3.16 Equipment to prepare microporous membranes by the polymer precipitation by cooling technique [37]. Reprinted with permission from W.C. Hiatt, G.H. Vitzthum, K.B. Wagener, K. Gerlach and C. Josefiak, Microporous Membranes via Upper Critical Temperature Phase Separation, in Materials Science of Synthetic Membranes, D.R. Lloyd (ed.), ACS Symposium Series Number 269, Washington, DC. Copyright 1985, American Chemical Society and American Pharmaceutical Association...

The need to cool patients quickly while at the same time reducing complication rates has led to the development of simpler methods of rapidly inducing and maintaining hypothermia. More modest hypothermia can now be achieved in awake patients with acute stroke by surface cooling with the forced air method in combination with pethidine to treat shivering (75), and several intravenous vascular cooling techniques look encouraging (48-50). 

Reports on the clinical experience with the latest cooling techniques... 

Conditions of crystal growth of selected materials by Bridgman and slow cooling techniques... 

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