Continuous flow reactor variable density

The classical CRE model for a perfectly macromixed reactor is the continuous stirred tank reactor (CSTR). Thus, to fix our ideas, let us consider a stirred tank with two inlet streams and one outlet stream. The CFD model for this system would compute the flow field inside of the stirred tank given the inlet flow velocities and concentrations, the geometry of the reactor (including baffles and impellers), and the angular velocity of the stirrer. For liquid-phase flow with uniform density, the CFD model for the flow field can be developed independently from the mixing model. For simplicity, we will consider this case. Nevertheless, the SGS models are easily extendable to flows with variable density. 

Note that Eqs. 10.2.b-l, 7, and 10 do not explicitly contain the residence time, just as was the case for the continuity equations for the plug flow reactor in Chapter 9. They could be reformulated (e.g., see Levenspid [3]) but, again as in Chapter 9, there is no advantage, and it is simpler to just use the directly manipulated variables Fao, y> and Cao It is only in constant density systems that the residence time, V/F, directly appears, as is illustrated by Eq. 10.2b-4. 

BWRs do not operate with dissolved boron like a PWR but use pure, demineralized water with a continuous water quality control system. The reactivity is controlled by the large number of control rods (>100) containing burnable neutron poisons, and by varying the flow rate through the reactor for normal, fine control. Two recirculation loops using variable speed recirculation pumps inject water into the jet pumps inside of the reactor vessel to increase the flow rate by several times over that in the recirculation loops. The steam bubble formation reduces the moderator density and... 

The primary process variables affecting the economics of sulfuric acid alkylation are the reaction temperature, isobutane recycle rate, reactor space velocity, and spent acid strength. To control fresh acid makeup, spent acid could be monitored by continuously measuring its density, the flow rate, and its temperature. This can reduce the acid usage in alkyla-tion units. 

In addition to phase behaviour, it is also important to evaluate the density of the reaction mixture. This variable plays a major role in both reaction equilibrium and kinetics. The control of density is more complex in supercritical reactors, where it can change dramatically with small perturbations in temperature, pressure or composition. The more direct application of density, in the case of continuous reactors, is to calculate the residence time of the reaction mixture for a given operating pressure and temperature. It is important to keep in mind that the volumetric flow measured downstream of the reactor can be very different from the flow inside the reactor due to the high variability of the density at supercritical conditions. In the case of batch reactors there are two... 

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