Rapid heating and cooling

If food can be heated quickly to a temperature of I3I°C a lethaUty equivalent to 6 min at I2I°C can be accumulated in 36 s. This rapid heating and cooling of hquid foods, such as milk, can be performed in a heat exchanger and is known as high temperature—short time (HTST) processing. HTST processing can yield heat-preserved foods of superior quahty because heat-induced flavor, color, and nutrient losses are minimized. 

The evolution of T, is just an exercise in mesoscale thermodynamics [13]. These expressions, in combination with (7.54), incorporate concepts of heterogeneous deformation into a eonsistent mierostruetural model. Aspects of local material response under extremely rapid heating and cooling rates are still open to question. An important contribution to the micromechanical basis for heterogeneous deformation would certainly be to establish appropriate laws of flow-stress evolution due to rapid thermal cycling that would provide a physical basis for (7.54). 

Modern low-density insulation such as those based on ceramic fibers can be used to save energy in plant operating on a batch basis. The low thermal mass permits a rapid heating and cooling period that can save a substantial amount of energy. With continuously operating plant the advantages are not so pronounced. 

Several exploratory experiments were made with unlabeled 1,2-dihydronaphthalene, either neat or with 10% dibenzyl, at 450°C. The runs were made using an agitated 10 cc reactor which was immersed in a preheated sand bath to achieve rapid heating and cooling. It is first noted that the products from... 

Phenylacetamides were prepared in the MBR from the corresponding styrene or acetophenone derivatives by Willgerodt reactions (Scheme 2.8) [44]. Yields were comparable with those obtained by others with conventional heating. At similar temperatures, the microwave-heated reactions were completed within minutes rather than hours. Optimization was readily accomplished through the capabilities of the MBR for rapid heating and cooling. The substantially shorter reaction times probably re-... 

As demonstrated above with examples, the CMR and MBR offer many advantages for synthetic processes that benefit from rapid heating and cooling. These systems are less useful and may be inappropriate when the reaction requires low temperature conditions throughout, when materials or reactions that are incompatible with microwave energy (e. g. reactions involving predominantly nonpolar organics) are to be employed or for reactions with dry media. 

For capillary GC, the split/splitless inlet is by far the most common and provides an excellent injection device for most routine applications. For specialized applications, there are several additional inlets available. These include programmed temperature vaporization (PTV) cool on-column and, for packed columns, direct injection. PTV is essentially a split/splitless inlet that has low thermal mass and a heater allowing rapid heating and cooling. Cool injection, which can be performed in both split and splitless mode with the PTV inlet, reduces the possibility of sample degradation in the inlet. Capabilities of the commonly available inlets are summarized in Table 14.3. 

The heating and cooling system ensures rapid heating and cooling of the heat-transfer medium. The installation of additional intermediate silos for cooling the final polymer shortens the residence time of the polymer in the reactor and helps to increase its capacity. 

Small-volume ovens (100-500 cubic inches) for portable units and for single column isothermal units. These ovens seldom have the capability of rapid heating and cooling. 

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