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Physical Chemistry 3: — Chemical Kinetics — - Christian-Albrechts ...

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9.2 Heat explosions 208<br />

• positive feedback effect:<br />

reaction rate increases<br />

y temperature ↑<br />

y reaction rate ↑<br />

y heat explosion !!<br />

I<br />

Figure 9.4: Heat explosions.<br />

I Heat removal: At constant temperature in the stirred reactor, we use Newton’s law<br />

<br />

= ( − 0 ) (9.25)<br />

where<br />

: heat conduction coefficient (depends on material)<br />

: reactor surface area<br />

: temperature<br />

0 : wall temperature<br />

(9.26)<br />

As we see, the heat removal increases (becomes steeper), when we increas the reactor<br />

surface area (at constant reactor volume).<br />

I<br />

Stability limits:<br />

(1) 0 = 1 : Heat removal wins over heat production y negative feedback y stable.<br />

(2) 0 = 2 : Heat removal wins over heat production y negative feedback y stable.<br />

(3) 0 = 3 : Heat production wins over heat removal y positive feedback y heat<br />

explosion, but the system should never reach point [3].<br />

(4) 0 = 4 : tangent y stability limit, the system runs away upon the smallest<br />

perturbation!<br />

(5) 0 = 5 : always unstable!

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