Fluid falling film reactor

Microstructured devices for fluid-fluid systems exist in a number of configurations. They can be roughly classified into three types based on the contacting principles [ 1] micromixer, microchannels, and falling film microreactors. The first two types of devices are used for all fluid-fluid applications while the microstructured falling film reactor is used only for gas-liquid systems. Depending on the application, these microstructured devices can also be used in series, for example. 

The problems discussed here are basic in the description of absorption in falling films, performance of wetted-wall towers, operation of tubular reactors, and fluid blending. 

The transfer of mass within a fluid mixture or across a phase boundary is a process that plays a major role in various engineering and physiological applications. Typical operations where mass transfer is the dominant step are falling film evaporation and reaction, total and partial condensation, distillation and absorption in packed columns, liquid-liquid extraction, multiphase reactors, membrane separation, etc. The various mass transfer processes are classified according to equilibrium separation processes and rate-governed separation processes. Fig. 1 lists some of the prominent mass transfer operations showing the physical or chemical principle upon which the processes are based. 

Fluid phase only Countercurrent flow Absorber Countercurrent flow Absorber Countercurrent flow Spray tower Co-current or countercurrent Bubble column Absorber or Reactor Venturi Static mixers Falling film, etc. 

Continuous phase contacting, where the fluid phases are separated. Examples are microstructured falling film and mesh reactors. 

In the gas-liquid-solid MSR, catalyst is incorporated either as a packed bed or as a coating. In the packed bed reactors, standard porous catalysts are incorporated and the fluid streams are brought into contact. In the falling film MSR, the catalyst is incorporated as thin nonporous films or as particles in alumina-coated walls [4]. 

L h for the falling film microreactor. The authors explain the increase in selectivity with the fact that in the micro reactor the concentration of chlorine radicals can be kept lower due to its large surface-to-volume ratio. In the microreactor, the entire fluid film can be penetrated by the inddent light, in contrast to the batch reactor, where only a thin film of the fluid is irradiated in the vicinity of the light... 

Since we do not want to consider the fluid mechanics of this reactor in detah, we will assume that the hquid falls with a constant average velocity and forms a hquid film of thickness R — R, with / j the radius in the tube at the surface of the hquid film. If these assumphons hold, then and R — i j are independent of the position z in the tube of length L (actually the height, since the tube must be vertical). Similarly, if the hquid film thickness is constant, then the cross section occupied by the gas is constant, and the velocity of the gas is also independent of z if the density of the gas is constant. These distances are sketched in Figure 12-8. 

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