Baffles configurations, types

Heat transfer can occur in either batch or continuous configurations. Both types of processes require fluid motion to obtain an effective heat transfer to the bulk of the fluid. In batch processing using jacketed vessels, helical coils, or coils in a baffle configuration, for example, sufficient agitation is required for heat transfer through the medium while continuous systems rely on flow rate to achieve effective heat transfer to satisfy process requirements. Effective heat transfer in batch operations for structured liquid detergents may require scrapers or anchor-type impellers to increase heat transfer coefficients in jacketed vessels. 

Evaporators of this general type with dry expansion circuits will have the refrigerant within the tubes, in order to maintain a suitable continuous velocity for oil transport, and the liquid in the shell. These can be made as shell-and-tube, with the refrigerant constrained to a number of passes, or maybe shell-and-coil (see Figure 7.4). In both these configurations, baffles are needed on the water side to improve the turbulence, and the tubes maybe finned on the outside. Internal swirl strips or wires will help to keep liquid refrigerant in contact with the tube wall. 

Figure 7.7, also taken from the work of RUSHTON et shows Np v.v Re data for a 150 mm diameter turbine with six flat blades. In addition, this figure also shows the effect of introducing baffles in the tank. BlSSELL et a/.(lSl have studied the effect of different types of baffles and their configuration on power consumption. 

Finally, the reactor vessel has been assumed to be perfectly mixed. Imperfect mixing and a flow pattern created by different types of agitators, baffles, feed locations and other reactor vessel configurations will cause the performance to be below that indicated by perfect mixing. 

Figure 5.9 Design of a generalized microbial cell fermentation vessel (a) and an animal cell bioreactor (b). Animal cell bioreactors display several structural differences compared with microbial fermentation vessels. Note in particular (i) the use of a marine-type impeller (some animal cell bioreactors-air lift fermenters-are devoid of impellers and use sparging of air-gas as the only means of media agitation) (ii) the absence of baffles (iii) curved internal surfaces at the bioreactor base. These modifications aim to minimize damage to the fragile animal cells during culture. Note that various additional bioreactor configurations are also commercially available. Reprinted with permission from Proteins Biochemistry and Biotechnology (2002), J. Wiley Sons...

The power required for a given stirrer type and associated vessel configuration depends on the speed of rotation N, the stirrer diameter du the density p, and the kinematic viscosity v of the medium. In vessels without baffles, the liquid vortex, and therefore the acceleration due to gravity, g, is immaterial, as long as no gas is entrained in the liquid. Thus, P = f(N, dt,p, v), and in the dimensionless form, Ne = /(Re), a relationship generally known as the power characteristics of the stirrer. Here, Ne = P/(pN3df) is the Newton or Power number, and Re s Ndf/v the Reynolds number. This relationship was described in Sections II and III for gas-liquid and gas-liquid-solid systems. 

In the case of a ball-type regenerator, dirt and dust tend to accumulate in the balls but their cleaning method is simple and straightforward as fhe ceramic balls can be easily removed, washed, or cleaned. With these features, ball-type regenerators can well be employed for dirty gases that contain scale and dust. For normal configuration, a burner nozzle is installed in the longitudinal center axis of fhe burner and a baffle-fype burner is used. 

A four blade glass rectangle, specially made to fit the reactor, was used as a baffle system when desired. Figure 3 shows the reactor mixing configuration and the dimensions of the two types of impellers tested. A Sage Instruments model 355 syringe pump was used to feed the reaction solution to the quench reactor at a... 

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