Circulation time distribution measurement

The pumping capacity of the stirrer or the liquid throughput of the stirrer is the liquid flow rate that is displaced through the area swept by the stirrer. For axial flow stirrers, q is determined from the circulation time of particles with Ap = 0. For radial flow stirrers, it is obtained from the integral value of the measured velocity distribution of the flow. 

If recirculation rates are 10 to 15 times the feed rate, the reactor would tend to operate nearly isothermally. High velocities past the bed of particles could eliminate almost completely any external mass-transfer influence on the reactor performance. By varying the circulation rates, the reaction condition for which the mass transfer effect is negligible can be established. Except for the rapidly-decaying catalyst system, steady state can be achieved effectively. Sampling and product analysis can be obtained as effectively as in the fixed-bed reactor. Residence-time distributions for the fluid phases can be measured easily. High fluid velocities would cause less flow-maldistribution problems. 

A measurement technique for determining mean circulation times and their distribution, is available. A scale-up correlation for mean circulation time, ( ,., applicable to zero or low gas hold-up with the standard vessel con-flgu ration, is... 

White [23,24] observed the circulatory flow behavior using markers with flow visualization technique in the R-R handed screw and double-flighted rotors mixer (Figure 8). This makes possible measurement of the circulation time as a criteria of mixing. Since the flow visualization experiments have limitations in observing the overall flow motion in the mixer, the following experiment was carried out to determine the distribution of elastomers. 

Measurement of the circulation time in the mixer was carried out to characterize the distributive mixing. The results indicated that void region shortens circulation time. The circulation time of R-R screw rotor is shorter than that of double-flighted rotor. The shorter circulation time represents a good distributive mixer. 

Harris AT, Thorpe RB, Davidson JF. The measurement of particle residence time distributions in circulating fluidized beds. In Grace JR, Zhn J, de Lasa HI, eds. Circulating Fluidized Bed Technology VII. Ottawa CSChE, 2002, pp. 145-152. 

Another class of time-dependent problems of concern to the reactor physicist are questions on fuel burnup, poison production and burnup, breeding ratio, and the like. These problems differ from those on reactor stability in that they involve time scales measured in hours (or years) in contrast to stability problems which are concerned with fractions of a second. Reactor-analysis problems, such as the determination of critical mass and neutron-density distributions, are based on the steady-state operating condition of the reactor. The day-to-day operation of the reactor at steady state involves, however, long-time changes in the fuel concentration. Except in the case of circulating-fuel reactors, the fuel is introduced into the reactor according to some predetermined cycle. As the fuel is consumed, some gradual adjustments can be made by means... 

The content of the material in a carbon reservoir is a measure of that reservoir s direct or indirect exchange rate with the atmosphere, although variations in solar also create variations in atmospheric content activity (Stuiver and Quay, 1980, 1981). Geologically important reservoirs (i.e., carbonate rocks and fossil carbon) contain no radiocarbon because the turnover times of these reservoirs are much longer than the isotope s half-life. The distribution of is used in studies of ocean circulation, soil sciences, and studies of the terrestrial biosphere. 

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