Laminar plug flow reactor

Roesler, J. F., An Experimental and Two-Dimensional Modeling Investigation of Combustion Chemistry in a Laminar Non-Plug-Flow Reactor, Proc. 27th Symp. (Int.) Combust., 1, 287-293 (1998). 

For a few highly idealized systems, the residence time distribution function can be determined a priori without the need for experimental work. These systems include our two idealized flow reactors—the plug flow reactor and the continuous stirred tank reactor—and the tubular laminar flow reactor. The F(t) and response curves for each of these three types of well-characterized flow patterns will be developed in turn. 

Calculate the volumes of a plug flow reactor and a laminar flow reactor required to process 0.5 m3/ksec of feed containing 1.0 kmole/m3 of species A to 95% conversion. The liquid phase... 

Plug flow reactors. Laminar flow. 102 Figures 102a... 

In a plug flow reactor, or along a stream line in the laminar flow unit,... 

FlameMaster v3.3 A C+ + Computer Program for OD Combustion and ID Laminar Flame Calculations. FlameMaster was developed by H. Pitsch. The code includes homogeneous reactor or plug flow reactors, steady counter-flow diffusion flames with potential flow or plug flow boundary conditions, freely propagating premixed flames, and the steady and unsteady flamelet equations. More information can be obtained from http //www.stanford.edu/group/pitsch/Downloads.htm. 

For fairly high degrees of conversion, with both first- and second-order reactions, the volume of a tubular reactor in which laminar flow occurs is about 30—50% greater than that of the plug-flow reactor in... 

Comparison of the volumes of laminar flow and plug-flow reactors giving the same conversion when operating under the same conditions... 

A graphical representation of the cumulative residence time distribution function is given in Figure 4.97 for a structured well, a laminar flow reactor and an ideal plug flow reactor assuming the same average residence time and mean velocity in each reactor. 

Obviously the characteristic distribution of the structured square, as expected, is much closer to the ideal plug flow reactor than to the laminar flow reactor. This desired behavior is a result of the channel walls, which are flow-guiding elements and pressure resistors to the flow at the same time. Two of the streamlines are projecting with a residence time of more than 0.4 s. These are the streamlines passing the area close to the wall of the distribution area, which introduces a larger resistance to these particles due to wall friction. This could, for example, be accounted for by a different channel width between the near wall channels and the central channels. 

Figure 4.97 Calculated cumulative residence time distribution function for a multi-channel well, a laminar flow reactor and a plug flow reactor [147] (by courtesy of VDI-Verlag GmbH).

Fig. 11.9 Types of linear continuous-flow reactors (LCFRs). (a) Continuous plug flow reactor (CPFR) resembling a batch reactor (BR) with the axial distance z being equivalent to time spent in a BR. (b) A tabular flow reactor (TFR) with (tq) miscible thin disk of reactive component deformed and distributed (somewhat) by the shear field over the volume, and (b2) immiscible thin disk is deformed and stretched and broken up into droplets in a region of sufficiently high shear stresses, (c) SSE reactor with (cj) showing laminar distributive mixing of a miscible reactive component initially placed at z = 0 as a thin slab, stretched into a flat coiled strip at z L, and (c2) showing dispersive mixing of an immiscible reactive component initially placed at z — 0 as a thin slab, stretched and broken up into droplets at z — L.

In addition to the CSTR and batch reactors, another type of reactor commonly used in industry is the tubular reactor. It consists of a cylindrical pipe and is normally operated at steady state, as is the CSTR. For the purposes of the material presented here, we consider systems in which the flow is highly turbulent and the flow field may be modeled by that of plug flow. That is, there is no radial variation in concentration and the reactor is referred to as a plug-flow reactor (PFR). (The laminar flow reactor is discussed in Chapter 13.)... 

The use of monoliths as catalytic reactors focuses mainly on applications where low pressure drop is an important item. When compared to fixed beds, which seem a natural first choice for catalytic reactors, monoliths consist of straight channels in parallel with a rather small diameter, because of the requirement of a comparably large surface area. The resulting laminar flow, which is encountered under normal practical circumstances, does not show the kinetic energy losses that occur in fixed beds due to inertia forces at comparable fluid velocities. Despite the laminar flow, monolith reactors still may be approached as plug-flow reactors because of the considerable radial diffusion in the narrow channels [1]. 

Examples of chemical process units in this category include plug flow reactors, laminar flow reactors, turbulent flow reactors, plasma reactors, and separation units that are described in terms of the mass transfer concept. To develop a numerical algorithm, the time and spatial derivatives are replaced by finite difference approximations. In general, the time derivative is represented by a forward difference, whereas the second order spatial derivatives are approximated by central differences as follows for the dependent variable Y in Cartesian coordinates ... 

For reactors with known mixing characteristics the response curve and the RTD can be predicted no experiments are necessary. As an illustration let us deyelop the RTD for the plug-flow reactor, a single ideal stirred-tank reactor, and a tubular reactor with laminar flow. 

J d) is plotted against d/d in Fig. 6-7 also shown are the curves for the two ideal reactors, taken from Fig. 6-5. The comparison brings out pertinent points about reactor behavior. Although the plug-flow reactor might be expected to be a better representation of the laminar case than the stirred-tank reactor, the RTD for the latter more closely follows the laminar-reactor curve for 6/6 from about 0.6 to 1.5. However, there is no possibility for 6 to be less than 0.5 in the laminar-flow case. Hence the stirred-tank form is not applicable at all in the low 6 region. At high 6 the three curves approach coincidence. Conversions for these reactors are compared in Sec. 6-7. 

For calculating conversion in this laminar-flow reactor the RTD for a stirred-tank reactor is more appropriate than that for a plug-flow reactor. This is not apparent from a comparison of the three RTDs shown in Fig. 6-7. 

We can consider that if the flow along the micro-defect is laminar and the convection flow between the bubble and the electrolyte behaves as a plug-flow reactor, we can say that [75]... 

If k /k is 0.8, the laminar-flow reactor would have to be 1/0.8, or 1.25, times longer than a plug flow reactor with the same conversion. Values of k jk are given in Table 6.1. 

In a large incinerator operating at high Reynolds number, about 1 % of the gas flows in the laminar boundary layer near the wall, where the average velocity and temperature are mueh lower than the midstream values. The conversion in the boundary layer is decreased, because the temperature effect is more important than the increase in residenee time. The predicted effect of boundary-layer flow on toluene destruction in a large incinerator is shown in Figure 6.9 [26]. There is little effect at 99% conversion, but for X > 0.999, the nonideal reactor requires more than twice the residence time of an ideal plug-flow reactor. 

J. M. Castro, S. D. Lipshitz, and C. W. Macosko [AIChE J., 28, 973 (1982)] modeled a thermosetting polymerization reaction in a laminar flow reactor under several different operating conditions. Demonstrate your ability to simulate the performance of a plug flow reactor for this reaction under both isothermal and adiabatic reaction conditions. In particular, determine the reactor space times necessary to achieve 73% conversion for both modes of operation and the following parameter values for a (3/2)-order reaction (r = kc - ). 

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