Cooling techniques, advanced

Turbine-Blade Cooling The turbine inlet temperatures of gas turbines have increased considerably over the past years and will continue to do so. This trend has been made possible by advancement in materials and technology, and the use of advanced turbine blade-cooling techniques. The blade metal temperature must be kept below 1400° F (760° C) to avoid hot corrosion problems. To achieve this cooling air is bled from the compressor and is directed to the stator, the rotor, and other parts of the turbine rotor and casing to provide adequate cooling. The effect of the coolant on the aerodynamic, and thermodynamics depends on the type of cooling involved, the tem-... 

When the conventional cooling techniques discussed in the previous sections cannot be used, then the physical designer may want to use some advanced techniques. These include thermoelectric, jet impingement, heat pipes, and microchannel cooling. 

The isolation of f. is performed on the basis of their high solubility in hot water, and similar techniques as in the beet sugar diiliision step are used. The polysaccharides will precipitate on cooling. An advanced process, immediately leading to fhic-tose syrups, consists of in-situ hydrolysis of the sliced bulbs by acids or fhictanases. 

In advancing-front or layer melt crystallizations, mother Hquor flows over a cooled surface on which material is crystallized. The advancing front of crystals grows in the direction from the cooled surface into the mother Hquor. A variety of techniques can be used to take advantage of this type of Operation. 

Low-temperature research requires hard work and imagination, but successful advances are richly rewarded. Seven Nobel Prizes in physics and chemistry have been awarded for low-temperature research. The first, in 1913, went to the Dutch physicist Heike Kamerlingh Onnes, who discovered how to cool He gas to 4.2 K and convert it into a liquid. The American William Giauque received the 1949 prize in chemistry and the Russian Pyotr Kapitsa won the 1978 prize in physics. Each was honored for a variety of discoveries resulting from low-temperature research, and each developed a new technique for achieving low temperature. 

More advanced techniques are now available and section 4.2.1.2 described differential scanning calorimetry (DSC) and differential thermal analysis (DTA). DTA, in particular, is widely used for determination of liquidus and solidus points and an excellent case of its application is in the In-Pb system studied by Evans and Prince (1978) who used a DTA technique after Smith (1940). In this method the rate of heat transfer between specimen and furnace is maintained at a constant value and cooling curves determined during solidification. During the solidification process itself cooling rates of the order of 1.25°C min" were used. This particular paper is of great interest in that it shows a very precise determination of the liquidus, but clearly demonstrates the problems associated widi determining solidus temperatures. 

HPLC-UV-NMR can now be considered to be a routine analytical technique for pharmaceutical mixture analysis and for many studies in the biomedical field. HPLC-UV-NMR-MS is becoming more routine with a considerable number of systems now installed worldwide, but the chromatographic solvent systems are limited to those compatible with both NMR spectroscopy and mass spectrometry. The increased use of HPLC-UV-IR-NMR-MS is possible, but it is unlikely to become widespread, and the solvent problems are more complex. The future holds the promise of new technical advances to improve efficiency, and to enhance routine operation. These approaches include the use of small-scale separations, such as capillary electrochromatography, greater automation, and higher sensitivity and lower NMR detection limits through the use of NMR detectors cooled to cryogenic temperatures. 

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