Flow residence times

The three main types of reactors shown in Fig. 27-6 are in aclual commercial use the moving bed, the fluidized bed, and the entrained bed. The moving bed is often referred to as a. fixed bed because the coal bed is kept at a constant height. These differ in size, coal feed, reactant and product flows, residence time, and reaction temperature. 

MIXFLOl and MIXFL02 - Mixed-Flow Residence Time Distribution Studies... 

Example MIXFLOl MIXED FLOW RESIDENCE TIMES CASEl... 

Example MIXFL02 MIXED FLOW RESIDENCE TIMES CASE 2... 

Level (3) global e.g., reactor model some key parameters reactor volume, mixing/flow, residence time distribution, temperature profile, reactor type... 

From the table, the plug flow residence time at f =0.2 is... 

To elucidate the possible causes of the decrease in suppression potential, the effects of flow residence time and relative pulsating fuel amount were examined. One possible explanation for the above trend is the reduction in flow residence time as the flow rate was increased. At these conditions some of the larger fuel droplets that persisted in the downstream may not have had enough time to react completely if the residence time became very short. When the residence time was estimated by the reference time scale which is the combustor length divided by inlet velocity (Fig. 21.12), the general trend appears to be consistent with the expectation. The scatter in the plot reflects the crudeness of the estimation larger droplets do not follow the carrier flow very well. 

Figure 21.12 Effect of flow residence time on control effectiveness...

The combustion of ethyl acetate in a flow system was studied by Fish and Waris [96]. Below 250 °C there was no oxidation under the conditions employed, (equimolar fuel and oxygen flows, residence time... 

The independent variable t is either the batch time or the plug flow residence time. 

A comparison of the laminar-flow residence time distribution with corresponding plug flow and perfect mixing results is shown in Figure 4.9. 

Figure 4.9 Comparison of plug flow, perfect mixing, and laminar flow residence-time distributions.

Compact tubular turbulent apparatus of cylindrical design with da S 0,03m are characterized by comparatively low rate of longitudinal mixing E <4-10 m /sec, relative flows residence time 0r2 1, narrow reagents residence times distribution, that allows realization of fast chemical reactions with Tch 0,01 sec in quasi-plug-flow mode ... 

Comparison of mixing characteristic times calculated by (3.24)-(3.26) with chemical reaction characteristic time Tch or liquid flows residence time in apparatus Tr allows calculation of optimal construction of tubular turbulent apparatus for both fast chemical reactions realization and flows mixing with the aim of their homogenization. 

Olefin polymerization in batch reactors is not common. Laboratory-scale high-throughput reactors are perhaps one of the few examples of such reactors applied to olefin polymerization. Some olefin polymerization tubular reactors can also be treated as batch reactors, where a polymerization-time to reactor-length transformation can be made and directly applied to the equations derived above if the tubular reactor has plug-flow residence time. 

We expect to be able to conduct LES with over billions grid points and over tens of billions of Monte Carlo particles. These simulations are proposed to be conducted for prototype reactors with variable physical length and time scales. In this case, the effects of the flow residence time and the Damkohler number will be the primary subject of the investigations. In addition, the spatial and the compositional structures of the reacting flow field will be assessed. 

By pyrolysis of polyolefins, waxy, liquid, and gaseous products are obtained their yields depend on the working conditions such as heating rate, temperature, gas flow, residence time, type of reactor, mode of heat supply, etc. High temperatures favor gas formation, while increased residence time leads to charring [326] (Fig. 13). 

COMMENTS What we have solved for is the maximum possible uptake of water vapor into the anode flow stream, which may not acmally be achieved. Depending on the design, it is quite possible that the flow residence time in the fuel cell is not long enough to achieve the equilibrium condition. We have also assumed constant pressure, temperature, and flow rate to simplify the problem. In reality, there are often variations in these values through the fuel cell, which can even be used to help control the water uptake in advanced designs. Finally, in this problem we only considered the anode, while the complete water balance must include the cathode as well. 

---