Mixing continued perfect

Preferential Removal of Crystals. Crystal size distributions produced ia a perfectiy mixed continuous crystallizer are highly constraiaed the form of the CSD ia such systems is determined entirely by the residence time distribution of a perfectly mixed crystallizer. Greater flexibiUty can be obtained through iatroduction of selective removal devices that alter the residence time distribution of materials flowing from the crystallizer. The... 

The name continuous flow-stirred tank reactor is nicely descriptive of a type of reactor that frequently for both production and fundamental kinetic studies. Unfortunately, this name, abbreviated as CSTR, misses the essence of the idealization completely. The ideality arises from the assumption in the analysis that the reactor is perfectly mixed, and that it is homogeneous. A better name for this model might be continuous perfectly mixed reactor (CPMR). 

If the mixing is "perfect," tlie estuary behavior may be approximated by what chemical engineers define as a continuous stirred tank reactor (CSTR) (5). However, accurately estimating the time and spatial beliavior of water quality in estuaries is complicated by the effects of tidal motion as just described. The upstream and downstream currents produce substantial variations of water quality at certain points in the estuary, and tlie calculation of such variation is indeed a complicated problem. How ei er, the following simplifications provide some reiiitirkably useful results in estimating the distribution of estuarine water quality. 

The perfectly mixed, continuous-how stirred tank reactor (CSTR)... 

Setting f = Tout, H = Hout, and so on, specializes the integral energy balance of Equation (5.14) to a perfectly mixed, continuous-flow stirred tank ... 

If three perfectly mixed continuous stirred tank reactors of equal volume were used in series flow instead, what would the required volume be ... 

Sometimes useful information and insight can be obtained about the dynamics of a system from just the steadystate equations of the system. Van Heerden Ind. Eng. Chem. Vol. 45, 1953, p. 1242) proposed the application of the following steadystate analysis to a continuous perfectly mixed chemical reactor. Consider a nonisothermal CSTR described by the two nonlinear ODEs... 

The same consecutive reactions considered in Prob. 6.18 are now carried out in two perfectly mixed continuous reactors. Flow rates and densities are constant. The volumes of the two tanks (P) are the same and constant. The reactors operate at the same constant temperature. 

J1. An isothermal, first>oidei, liquid-phase, reversible reaction is carried out in a constant-volume, perfectly mixed continuous reactor. 

For the perfectly mixed continuous reactor, the CSTR, the ratio VT/ Fy only represents the mean residence time, /p,av however, it is still possible to compare the performance of the CSTR with the performance of the BR by letting the mean residence time fp av = t. Interestingly, when the reaction rate shows a positive dependence on reactants concentration, the BR is more effective than the CSTR. This is because the batch reactor experiences all the system compositions between initial and final values, whereas the CSTR operates at the final composition, where the reaction rate is smaller (under the above hypotheses). Finally, one can compare the two continuous reactors under steady-state conditions. The CSTR allows a more stable operation because of back-mixing, which however reduces the chemical performance, whereas the PFR is suitable for large heat transfer but suffers from larger friction losses. 

In this chapter we study the steady-state design of perfectly mixed, continuously operating, liquid-phase reactors. The effects of a wide variety of reaction types, kinetics, design parameters, and heat removal schemes are explored. The important elfects of design conversion and design temperature on heat transfer area and other process parameters are quantitatively studied. 

FIGURE 16 Typical population density plot from perfectly mixed, continuous crystallizer. 

Note PF = plug flow PM = perfect mixing (continuous stirred lank)... 

The reactors treated in the book thus far—the perfectly mixed batch, the plug-flow tubular, and the perfectly mixed continuous tank reactors—have been modeled as ideal reactors. Unfortunately, in the real world we often observe behavior very different from that expected from the exemplar this behavior is tme of students, engineers, college professors, and chemical reactors. Just as we must learn to work with people who are not perfect, so the reactor analyst must learn to diagnose and handle chemical reactors whose performance deviates from the ideal. Nonideal reactors and the principles behind their analysis form the subject of this chapter and the next. 

Example 2.2 is also a Markov chain. It deals with a pulse input of some dye introduced into a perfectly-mixed continuous flow reactor. Here the system is a fluid element containing some of the dye-pulse. The state of the system is the concentration of the dye-pulse in the reactor, which is a continuous function of time. The change of system s concentration with time is the state transition given by... 

The differential Eqs.(3.13-2) were solved numerically [59] for the case of a continuous perfectly mixed reactor. 

In [57] the equations were integrated numerically for the case where the reactions take place in a continuous perfectly mixed reactor. 

Randolph and Larson showed that for a continuous crystallizer with a (perfectly) mixed suspension, (perfectly) mixed product removal (MSMPR) crystallizer. 

These are systems where the state variables describing the system are lumped in space (invariant in all space dimensions). The simplest chemical reaction engineering example is thp perfectly mixed continuous stirred tank reactor. These systems are described at steady state by algebraic equations while in the unsteady state they are described by initial value ordinary differential equations where time is the independent variable. 

In writing the material balance equations for a compartment, several assumptions are made. The transport terms between each of the subcompartments are defined, the binding of drug in each subcompartment is quantified and incorporated into the equations, and additional terms are included where necessary to account for liver clearance, kidney clearance, and intestinal absorption. Each subcompartment, i.e., the vascular, the interstitial, and the intracellular, is considered to be a perfectly mixed continuous-stirred-tank reactor (CSTR). This means the concentration of each subcompartment has no spatial dependence. 

As a matter of fact, the problem of radioactive decay is exactly the same as the problem of washout of particles from a perfectly mixed, continuous flow vessel. Thus, Eq. (124) of the text can be applied to yield the well-known law of radioactive decay. 

---