Quasi-isothermal mode

In general, the quasi-isothermal mode in turbulent plug flow reactors will emerge, if the criteria in Equations 1.42,1.43 and 1.51 are met. 

There is a correlation between the reactor design, reactor geometry and process kinetics, and hydrodynamics as well as the final product yield. There is a critical device radius R, indicating transition from a torch to a planar reaction mode and conditions, for carrying out fast reactions in the quasi-isothermal mode. 

This disadvantage does not apply to an isothermal device based on electrical compensation. Nevertheless, calorimeters of the latter type operate only in a quasi-isothermal mode, since electronic control systems depend for their response upon small deviations from an established set point, and a certain amount of time is required for changing the prevailing temperature. The use of modem circuits and components ensures that errors from this source will be negligible, however. Electrical compensation makes it possible to follow both endothermic and exothermic processes. In both cases the compensation power is readily measured and recorded or processed further with a computer. Isothermal calorimeters are used quite generally for determining heats of mixing and solution. Commercial devices are available that al.so support the precise work required for multiphase thermo-... 

One peculiarity of electrical compensation should be mentioned, too every electronic temperature controller needs a minimal but nonzero temperature difference to react. Furthermore, the heat produced by the sample and that produced by the electrical heater are not at the same place, and there must be some temperature gradient to allow a heat exchange between them. Therefore, such calorimeters operate not in a strictly isothermal but in a quasi-isothermal mode. The temperature is generally kept constant but may differ locally. The deviations depend on the heat flow rate as well as on the quality of the compensation controller. Normally, these differences can be neglected in practice. 

Isoperibolic instruments have been developed to estimate enthalpies of reaction and to obtain kinetic data for decomposition by using an isothermal, scanning, or quasi-adiabatic mode with compensation for thermal inertia of the sample vessel. The principles of these measuring techniques are discussed in other sections. 

The next important step in the study of the regularities of the autowave modes of cryochemical conversion was to perform a series of experiments with thin-film samples of reactants. The changeover to such objects, characterized by the most intense heat absorption, allowed the realization of quasi-isothermal conditions of the process development and thus favored the manifestation of the abovementioned isothermal mechanism of wave excitation, which involves autodispersing the sample layer by layer due to the density difference between the initial and final reaction products. The new conditions not only not suppressed the phenomenon, but made it possible to reveal some details of the traveling-wave-front structure, which will be discussed here and also in Section X. 

Quasi-plug-flow mode in turbulent flows as a key to realization of fast chemical processes in quasi-isothermal conditions... 

The combination of Equations 1.49 and 1.50 provides us with summarising criteria, determining a quasi-isothermal process mode in turbulent displacement reactors ... 

Thus, even in an adiabatic mode of tubular turbulent chlorination reactor operation (without heat removal), the temperature growth in the reaction zone in the case of BR chlorination (12-15% solution) with molecular chlorine in a tubular reactor, operating in the optimum plug-flow mode in turbulent flows, does not exceed 2 1 °C. The process can be thought to proceed under quasi-isothermal conditions and does not require external or internal heat removal, or special stirring devices for heat and mass exchange intensification. 

Formation of the quasi-plug flow mode in the reaction zone in turbulent flows, due to the intensive convective heat exchange in proximity to the reactor walls and resulting quasi-isothermal conditions, allows efficient control of the thermal mode of the neutralisation process by external cooling. In order to decide whether it is reasonable to use external cooling for the neutralisation reaction in a tubular turbulent reactor of cylinder form, it is necessary to estimate the amount of heat which is released in the reaction zone under conditions of adiabatic heating. If the density and thermal capacity of the reaction mixture in the first approximation correspond to the values for water, then [15] ... 

Next, a mathematical description of T is given for a quasi-isothermal run. This type of run does not only simplify the mathematics, it also is a valuable mode of measuring Cp as described in Sect. 4.4.5. In addition, standard TMDSC with y O is linked to the same analysis by a pseudo-isothermal data treatment as described in Sect. 4.4.3. 

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