Double-pipe reactors radius ratio

Properties of the reactive fluid within the inner tube are identified by the subscript Rx, and represents the kinetic rate law that converts reactant A to products. Only one independent variable is required to simulate reactor performance because axial coordinate z and average residence time for the reactive fluid trx are related by the average velocity of the reactive fluid j)rx. In comparison with the single-pipe reactor discussed earlier, the double-pipe reactor contains two additional design parameters that can be manipulated to control thermal runaway radius ratio k and average velocity ratio x/f, defined as follows ... 

Obviously, thermal runaway occurs in the previous example if the flow rate ratio is unity. However, it is possible to control a double-pipe reactor with = I by decreasing the radius ratio. This is illustrated in Table 4-4 for conditions described in the previous example. Thermal runaway occurs when k > /Ccriticai and the critical radius ratio lies somewhere between 0.10 and 0.15. 

Figure 4-8 Effect of higher flow rate ratios on the conversion of an exothermic reactive fluid in a plug-flow reactor with endothermic cocurrent cooling in a concentric double-pipe configuration with radius ratio k =0.5. Both fluids enter the double-pipe reactor at 340 K.

Figure 4-5 Sensitivity of reactant conversion to changes in flow rate ratio for nonisother-mal plug-flow tubular reactors with exothermic chemical reaction and cocurrent cooling in a concentric double-pipe configuration with radius ratio k = 0.5. The inlet tempoatures are 340 K for the reactive fluid and 335 K for the cooling fluid.

TABLE 4-3 Summary of Parametric Sensitivity Results for Nonisothermal Plug-Flow Tubular Reactors with Cocurrent Cooling in a Double-Pipe Configuration with Radius Ratio ic = 0.5 ... 

The outer wall of the double-pipe configuration at radius Routside is thermally insulated from the surroundings. Identify the acceptable range of the flow rate ratio parameter xj/ that corresponds to a well-behaved novel reactive system which does not exhibit thermal runaway. The appropriate reactor design equations are summarized in Table 4-6. 

Reactant A is converted irreversibly and exothermically to products in a 2-in.-inner-diameter tubular reactor via first-order chemical kinetics. The reactive mixture in the inner pipe is cooled using a concentric double-pipe heat exchanger. The nonreactive cooling fluid in the annular region flows countercurrently with respect to the reactive fluid. The radius ratio of the double-pipe configuration is If = Rinside/ outside = 0.5, the inlet temperature of the reactive fluid is 340 K,... 

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