Heat Transfer in Nonagitated Vessels

It is not practical to stir all reaction systems, for example, bulk polymerizations, postpolymerization reactions, fixed-bed catalytic reactors, and plug-flow reactors. Although multipoint temperature sensing is often used as a key solution to determine a runaway in nonagitated vessels, the occurrence of hot spots may not always be detected. 

A criterion to avoid thermal decomposition in nonagitated cases in the top layer of the core (the likely hot spot) of a vertical cylindrical vessel is to assure that the maximum temperature difference between the reacting bulk fluid and the bulk fluid of die coolant (perhaps the ambient air) is always less than shown in Equation (3-14) [173,179]  

Equation (3-14) is similar to Equation (3-12) for the well-agitated reactor, where the ATmax is given as RT /Ea in which T is the temperature of the stirred reaction mass. A version of Equation (3-14) which applies to unstirred liquids without convection is  

The calculated ATmax for most reactions is not very large. For a reaction at 100°C that doubles in rate with an increase of 10°C, the value of ATmax is only 14°C. 

To get an idea of the possible effects of a runaway, it is useful to calculate or to determine experimentally the adiabatic temperature rise, and to consider the effect of this temperature increase on the system. An adiabatic temperature rise of 150°C or above is considered a strongly exothermic situation that could result in loss of containment. 

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