Experimental pressure drop

A simple additive model is normally used to predict the total pressure drop. The total is taken as the sum of the pressure drop calculated for the flow of vapour through the dry plate (the dry plate drop hj) the head of clear liquid on the plate (hw + how) and a term to account for other, minor, sources of pressure loss, the so-called residual loss hr. The residual loss is the difference between the observed experimental pressure drop and the simple sum of the dry-plate drop and the clear-liquid height. It accounts for the two effects the energy to form the vapour bubbles and the fact that on an operating plate the liquid head will not be clear liquid but a head of aerated liquid froth, and the froth density and height will be different from that of the clear liquid. 

Downcomer and Draft Tube Pressure Drop. Typical experimental pressure drops across the downcomer, AP, 4, and the draft tube, AP2 3, show that they are essentially similar. Successful design of a recirculating fluidized bed with a draft tube requires development of mathematical models for both downcomer and draft tube. 

There are few reported comparisons to experimental pressure drop data taken by the same workers. An exception is Calis et al. (2001) who compared CFD, the Ergun correlation and experimental data for N — 1-2. They found 10% error between CFD and experimental friction factors, but the Ergun equation... 

This equation can be derived by supposing that the wall is in contact with liquid only, and that shearing forces are equal at the gas-liquid interface. Experimental pressure drops were predicted to +50% to —30% on the average, although larger individual variations existed. An attempt was made by Marchaterre (Ml) to refine this method by expressing the mechanical-energy balance in terms of... 

Figure 5.2-23. Predicted values of the pressure drop (Eqn. 5.2-24) versus the experimental pressure drop data (after Wammes et al. [33]).

Interpolation of actual experimental data circumvents the systematic correlation limitations, gives reliable and accurate pressure drop prediction, is difficult to computerize, and requires that suitable interpolation charts are available. This saction deals with predicting pressure drop by correlation. Section 8,2.9 describes interpolating experimental pressure drop data. 

Figure 8.19 (Contin usd) The latest version of the GPDC pressure drop correlation, (rf) Superimposing experimental pressure drop data for a given pecking generates a GPDC interpolation chart for this packing.

By selecting a factor that gives the best fit of available experimental pressure drop data to the GPDC correlation curves (81b, 60). This method biases the packing factor toward the regions on the chart for which experimental data exist. 

Since packing factors are derived from experimental pressure drop data, they are affected by the inherent limitations of the experimental data (Sec. 8.2.5). 

From a practical point of view, the parameter 4> is obtained from the determination of few experimental pressure drops at different fluid velocities. 

Figure 7-6 Comparison of experimental pressure-drop data with data obtained using the correlation of Tallmadge.22...

Figure 23 compares, for various L/d ratios, the experimental pressure drop and the numerical radial stress difference along the wall (between 10 nun upstream from the contraction and die exit), as a faction of the apparent shear rate (in the reservoir, the wall radial stress On- is quite equivalent to the mean... 

FIGURE I 3.8 Comparison of predicted and experimental pressure drop for three Pall rings (from Yin et o/ 2000). 

Figure 20 shows the calculated pressure drop factor and the experimental values. We observe that the model of Liu et al. (32) predicts the experimental pressure drop both in the Darcy s flow regime, the transition, and the Forchheimer regimes. The two-dimensional model gives a much better prediction than that using the one-dimensional model. The Ergun equation significantly overpredicts the experimental data. 

The monolith data were taken from Kreutzer et al. [15]. In exactly the same setup, we have also measured the pressure drop, and data in Fig. 6.4 were obtained by calculating the power input from the experimental pressure drop data. The monolith data are consistently higher than the data for the turbulent systems at equal power input. There is significant scatter in the monolith data. The mass transfer was measured at steady state for two lengths of monohth columns. The measured outlet concentration of the short column was used as the inlet concentration for the rest of the longer column, and with the measured outlet concentra-hon the mass-transfer group was determined from... 

Besides the pressure drop inside the columns there can be an additional pressure loss due to the piping and the valves between the columns. In experiments, a large pressure drop was found in an SMB-SFC apparatus due to these flow resistances [55]. Taking into account the pressure drop as a function of mass flow rates, a pressure-loss coefficient f for the total flow resistance (analogous to pipeline construction) between two columns is determined by fitting to experimental pressure drops. Then the pressure drop can be calculated from ... 

Figure 11.3 Comparison between trickle-bed slit model and experimental pressure-drop (a) and liquid-holdup (b) data for an air-water system for various gas and liquid superficial velocities. Magnetic field OFF, 1-mm glass beads.

Figure 5.13 Experimental pressure drop superficial velocity curve and determination of minimum fluidisation velocity...

Fig. 4.20 Experimental pressure drop during liquid-liquid plug flow as a function of the mixture velocity in 4 dififerent channels at flow rate ratio equal to 1...

It is next possible to compare the increase in experimental pressure drop across the advancing surface, AP, with that which would exist for spherical geometry, (AP ), using the maximum radius of curvature given by equation (6b), i.e.. 

For micromixers for which experimental pressure drop data are available, it is possible to estimate the specific power dissipation from Equation (6.4) between the inlet and the outlet pressure measurement points. It is assumed here that the estimated specific power contributes to mixing, which is a rough estimation because of the pressure drop induced by the micromixer pipe connections. In Figure 6.9 is plotted the mixing time with respect to the specific power dissipation for several mixers. The experimental mixing times scale fairly well as a power law of the... 

Power input, a decisive parameter for benchmarking technical reactors, has been investigated using the experimental pressure drop and compared with conventional contactor as shown in Table 15.5. The comparison reveals that the liquid-liquid slug flow microreactor requires much less power than the alternatives to provide large interfacial area - as high as a = 5000 m m in a 0.5 mm capillary microreactor, which is way above the values in a mechanically agitated reactor (a 500 m m ). 

The close match between experimental and simulated data does not continue when the same fractional flow curve is used to simulate the experimental pressure drop results at a slower frontal advance rate (2 m/day, oil free). A new fractional flow curve had to be constructed to give a closer match. In Figure 10 the experimental pressure drops are compared to the simulated curves and in Figure 9 the contrast between the new and old fractional flow curves is made clear. Due to the shear thinning nature of the foam, at slower frontal advance rates a steeper fractional flow curve is required at the same critical water saturation, = 0.35. 

Qian et al. (1998) found that when a sintered metal distributor plate was used for gas distribution, the experimental pressure drop could be predicted fairly well with the theoretical equation mentioned above. However, when a distributor with slotted openings... 

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