High-flow-rate regime

At higher gas flow rates an annular regime is found as in vertical flow. At very high flow rates the liquid film may be very thin, the majority of the liquid being dispersed as droplets in the gas core. This type of flow may be called the spray or mist flow regime. 

CSTR for most reactions. These conditions are best met for short residence times where velocity profiles in the tubes can be maintained in the turbulent flow regime. In an empty tube this requires high flow rates for packed columns the flow rates need not be as high. Noncatalytic reactions performed in PFRs include high-pressure polymerization of ethylene and naphtha conversion to ethylene. A gas-liquid noncatalytic PFR is used for adipinic nitrile production. A gas-solid PFR is a packed-bed reactor (Section IV). An example of a noncatalytic gas-solid PFR is the convertor for steel production. Catalytic PFRs are used for sulfur dioxide combustion and ammonia synthesis. 

Increasing the flow rate of water results in its spreading in stratified fashion as the velocity forces dominate the interfacial one. The oil flow in this case forms either a pearlike drop flow when it is at low flow rate or a stratified oil stream at high flow rate. The inlet junction has an influence on the flow pattern regime as well. To prove this, water flow was introduced from the central inlet and the oil from the two external inlets. Under conditions of high flow rates, similar flow patterns were observed as those shown in Figure 4.16 but in a reverse fashion. Well-defined aqueous droplets were attained at high-water flow rate combined with low-oil flow rate and no pear-... 

In order to approach idea PFR behavior, the flow must be turbulent. For example, with an open tube, the Reynolds number must be greater than 2100 for turbulence to occur. This flow regime is attainable in many practical situations. However, for laboratory reactors conducting liquid-phase reactions, high flow rates may not be achievable. In this case, laminar flow will occur. Calculate the mean outlet concentration of a species A undergoing a first-order reaction in a tubular reactor with laminar flow and compare the value to that obtained in a PFR when kV)/u = 1 ( = average linear flow velocity). 

At relatively low flow rates, the convective component is negligible, and the diffusion component is dominant. As shown in Figure 2.3, at high flow rates, the diffusion component is negligible, and the convective component is dominant. Between these exttemes, both components contribute to the overall dispersion process, and this is the regime commonly encountered in reservoir flow processes. Note that the dimensionless Peclet number is defined in Figure 2.3 as... 

When immiscible fluid streams are contacted at the inlet section of a microchannel network, the ultimate flow regime depends on the geometry of the microchannel, the flow rates and instabilities that occur at the fluid-fluid interface. In microfluidic systems, flow instabilities provide a passive means for co-flowing fluid streams to increase the interfacial area between them and form, e.g. by an unstable fluid interface that disintegrates into droplets or bubbles. Because of the low Reynolds numbers involved, viscous instabilities are very important At very high flow rates, however, inertial forces become influential as well. In the following, we discuss different instabilities that either lead to drop/bubble breakup or at least deform an initially flat fluid-fluid interface. Many important phenomena relate to classical work on the stability of unbounded viscous flows (see e.g. the textbooks by Drazin and Reid[56]and Chandrasekhar [57]). We will see, however, that flow confinement provides a number of new effects that are not yet fully understood and remain active research topics. 

At high flow rates (7a > 400) the flow becomes turbulent, characterised by random and rapid fluctuations of velocity. Theoretical analyses of this regime agree in general with experimentally obtained correlations, and in particular with the extensive data of Eisenberg and collaborators for a range of Re (defined as 2r ujv) of 100-160,000. Their correlation for an annular space of >8 mm is ... 

---