Laminar-Flow Reactor LFR

A laminar-flow reactor (LFR) is rarely used for kinetic studies, since it involves a flow pattern that is relatively difficult to attain experimentally. However, the model based on laminar flow, a type of tubular flow, may be useful in certain situations, both in the laboratory and on a large scale, in which flow approaches this extreme (at low Re). Such a situation would involve low fluid flow rate, small tube size, and high fluid viscosity, either separately or in combination, as, for example, in the extrusion of high-molecular-weight polymers. Nevertheless, we consider the general features of an LFR at this stage for comparison with features of the other models introduced above. We defer more detailed discussion, including applications of the material balance, to Chapter 16. 

Some consequences of the model described in the seven points above are as follows  

The most important results obtained in this chapter for ideal reactor models, except the LFR, are summarized in Table 2.1. The relationships for the items listed in the first 

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Laminar-flow reactor (LFR), based on laminar flow. 

In a laminar flow reactor (LFR), we assume that one-dimensional laminar flow (LF) prevails there is no mixing in the (axial) direction of flow (a characteristic of tubular flow) and also no mixing in the radial direction in a cylindrical vessel. We assume LF exists between the inlet and outlet of such a vessel, which is otherwise a closed vessel (Section 13.2.4). These and other features of LF are described in Section 2.5, and illustrated in Figure 2.5. The residence-time distribution functions E(B) and F(B) for LF are derived in Section 13.4.3, and the results are summarized in Table 13.2. 

Fig. 7.1. Measured hysteresis in our reaction system [1]. Plot of the redox potential of Br, Fpt, as a function of the flow rate coefficient fct (in units of reciprocal residence times, the time spent by a volume element in the laminar flow reactor (LFR)). Filled dots represent one of the stable stationary states (the oxidized state) and empty dots the other stable state, the reduced state. Prom [1]...

Fig. 7.2. Schematic diagram of the apparatus. Each solution, one corresponding to one stable stationary state and the other to the other stationary state, is stored in one of two continuous-stirred tank reactors (CSTR) and pumped at a determined and variable rates through the laminar flow reactor (LFR), where they are brought in contact with each other in a sharp well-defined boundary. For the remainder of the definitions see the text. Prom [1]...

The first experiment on the relative stability in a bistable multi-variable system is reported in [36]. The apparatus consists of two continuously stirred tank reactors (CSTR), and a different stable stationary state of a bistable bromate-ferroin reaction is established in each CSTR with same set of influx of reactant solutions into the reactors. The reaction solution from each tank is then pumped quickly into a laminar flow reactor (LFR) where the solutions... 

Develop the E(t) profile for a 10-m laminar-flow reactor which has a maximum flow velocity of 0.40 m min-1. Consider t = 0.5 to 80 min. Compare the resulting profile with that for a reactor system consisting of a CSTR followed by a PFR in series, where the CSTR has the same mean residence time as the LFR and the PFR has a residence time of 25 min. Include in the comparison a plot of the two profiles on the same graph. 

Fig. 7. Schematic diagram of the apparatus LFR, laminar flow reactor CSTR, continuous-flow stirred tank reactor. Reprinted from [36].

Since laminar flow itself occurs at low values of Re( = Dupl/x), the most likely situations are those characterized by low velocity (u) or high viscosity (p,), such as those involving the slow flow of polymers in extrusion reactors, or of blood in certain organs in animals. Even if not a close approximation in some cases, the predictable performance of an LFR may serve as a limiting model for actual performance. 

P13-i0a An irreversible first-order reaction takes place in a long cylindrical reactor. There is no change in volume, temperature, or viscosity. The use of the simplifying assumption that there is plug flow in the tube leads to an estimated degree of conversion of S6.55 . What would be the actually attained degree of conversion if the real state of flow is laminar, with negligible diffusion P13-1 1a Consider a PFR, CSTR. and LFR. 

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