Pressure drop overall

The overall pressure drop is expressed as the sum of a laminar term proportional to FT/DT and a turbulent term proportional to FP/DI to yield the Ergun equation (1) ... 

Use screens (Fig. 6-35) to increase overall pressure drop across the slot. 

Where D, is bulk density. An equation for the overall pressure drop of the system based on the area of the bed, A, is ... 

We ehoose to earry out only few numerieal experiments to seleet the solution parameters. Detailed optimization of the solution parameters is diffieult and often expensive eomputationally, so we do not reeommend it. Finally, we must validate the model. Though detailed experimental data for the veloeity and pressure profiles are not available for this partieular RFR, we ean employ the data on the overall pressure drop aeross the bed to validate the model to some extent. We find that the predieted overall pressure drop aeross the bed (10 kPa) shows good agreement with the available data. 

The orifice meter, in which the fluid is accelerated at a sudden constriction (the orifice) and the pressure developed is then measured. This is a relatively cheap and reliable instrument though the overall pressure drop is high because most of the kinetic energy of the fluid at the orifice is wasted. 

It should be noted that Equations 13.9 and 13.10 apply to smooth pipes, whereas the pipes used for transmission of fluids usually have some surface roughness, which increases the friction factor. However, for short fluid transmission pipes, the overall pressure drop is usually dominated by the pressure drop in the pipe fittings (valves, bends, etc). Thus, for short transmission pipes, there is little point in calculating the straight pipe pressure drop accurately. If the transmission pipe is long (>100 m) and straight, then the Fanning friction factor can be correlated as7 ... 

Table 13.4 gives some typical values of the loss coefficient for various fittings9. It should be noted that values for loss coefficient will vary for the same fitting, but from different manufacturers, as a result of differences in geometry. Table 13.5 gives head losses for sudden contractions, sudden expansions and orifice plates. Note that the relationship for orifice plates in Table 13.5 relates to the overall pressure drop and not the pressure drop between the pressure tappings used to determine the flowrate. 

Instrumentation shall be required to monitor and control the airflow through the filter system. Instrumentation shall provide a means to monitor overall pressure drop as well as the pressure drop between each filter element. 

Pipe entrance and exit pressure losses should also be calculated and added to obtain the overall pressure drop. The loss in pressure due to sudden expansion from a diameter dtl to a larger diameter dl2 is given by the equation... 

The first pass at the adsorber sizing is now complete and a check on the overall pressure drop expected can be obtained from the Ergun equation. An adjustment in the bed diameter may be required and then the bed size can be fixed using one more pass through the sizing process outlined above. 

Surface Area and Mesh Size. 20/40 mesh sorbent is generally used to minimize the pressure drop across a sorbent tube. Some sorbents, such as Tenax-GC, are not available in these mesh sizes, but can still be used by increasing the cross-sectional area of the sampling tube to lower the overall pressure drop for these smaller sorbent particles. Surface areas vary from very low in Tenax-GC to over 1000 m2/g in activated charcoal. In some cases, the greater surface area may increase the capacity of the sorbent. 

The pressure drop in simultaneous flow of gas and solid particles is made up of contributions from each of the phases. When the particles do not interact significantly, as in dilute transport, the overall pressure drop is represented by... 

The pressure drops between Points A and C, between Points A and C, between Points A and B, and between Points A and B , denoted by -ApAC, -ApA C, -ApAB, and -A/Evb, respectively, are measured with inclined U-shape tubes filled with colored kerosene. The average of -ApAB and -ApA B- is taken as the pressure drop through the accelerating pipes, while that of -Ap v and -ApA c as the overall pressure drop across the impinging stream contactor, -ApT. Consequently, there should be... 

Combining the results of the theoretical analysis and the experimental investigation above, the overall pressure drop across the whole impinging stream contactor can be represented by... 

A comparison between the data measured for the overall pressure drop across the impinging stream contactor and the corresponding values calculated with Eq. (4.25) is illustrated in Fig. 4.6. Good agreement between the results measured and calculated can be observed clearly, suggesting that the total pressure drop model established is reasonable and feasible for application. In addition, it has the advantages of universal applicability and convenience in calculation. 

Figure 4.6 Comparison between measured data and results calculated with Eq. (4.25) for the overall pressure drop cross the IS contactor. u0, m-s n9.48 011-06 ol2.64 A14.22 xl5.60...

Solution The overall pressure drop is a combined result of flow parallel to the fibers and flow perpendicular to the fibers. The pressure drop of flow parallel to the fibers is estimated from Eq. (7.45) as... 

For a flow through a random assemblage of fibers, it is necessary to give twice the weight to the pressure drop from the flow perpendicular to fibers as that from the flow parallel to fibers therefore, the overall pressure drop is obtained as... 

Consider a clean house bag filter filled with randomly assembled fibers. The porosity of the filter is 0.97, and the fibers have an effective diameter of 10 pm. The length of the filter is 0.1 m. The viscosity of air is 1.8 x 10-5 kg/m s. For a velocity of the dust-laden air of 0.2 m/s, and a collection efficiency of a single fiber of 1.50 percent, estimate the overall efficiency of the filter. To reach a collection efficiency of 99.99 percent, what is the minimum length of this type of filter At this minimum length, what is the overall pressure drop ... 

Indirect heating by a start-up burner through a dedicated flow path avoids the direct contact of the catalysts with combustion off-gases. Here micro structured channel systems offer unique possibilities at low overall pressure drop of the start-up system. 

From a practical point of view the chemical engineer is very often interested in obtaining a relation between the overall pressure drop across a pipe, fitting, or piece of processing equipment and the bulk or mean velocity of flow through it. On occasion the details of the velocity, temperature, or concentration profile are important, but most frequently it is the gross pressure drop-flow rate behavior that is important to a chemical engineer. 

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