Pressure-drop measurements

Hydrodynamics, pressure drop, and mass transfer during liquid-liquid flows were investigated in two different systems, viz. in glass microchannels with circular cross section of 0.2 mm ID (Fig. 3.3a, b) using an ionic liquid and deionised water, and in Teflon channels of different sizes, i.e. 0.2-2 mm ID (Fig. 3.3c) using either different TBP/ionic liquid mixtures (30 %, v/v) (Table 3.2) and aqueous nitric acid solutions, relevant to spent nuclear fuel reprocessing, or ionic Uquid and deionised water. The internal diameter of the microchannels was measured using a microscope (Nikon Eclipse ME 600). 

For aU the experiments the aqueous phase was seeded with 1 or 3.2 pm fluorescent polymer micro-beads suspension at 1 % concentration by weight, depending 

For the pressure drop measurements, a differential pressure meter Comark C9555 (range 0- 200 kPa, accuracy 0.2 %) was used, connected to two pressure ports before and after the microchannel, as illustrated in Fig. 3.5. To measure the pressme drop in the glass microchannel, two side channels (referred as t2 in Fig. 3.5), with a length of 5 cm each, were added to connect the main channel to the pressure ports. For pressure drop measurements in the Teflon microchannels the pressure ports 

A mixing zone B, E pressure port CD test section BC 5cm DH 5 cm 

In order to separate the two phases online an in-house flow splitter was connected at the end of each test section (Fig. 3.6). The splitter had two side channels made of stainless steel and PTFE that have different wettabilities for the two liquids used. The internal diameter and the length of the side channels were chosen based on the pressure drop that was created on the flow splitter [similar to (Scheiff et al. 2011)]. With this configuration pure ionic liquid phase was obtained from the PTFE outlet and aqueous solution from the stainless steel outlet. However, at high mixture velocities the separation was not always 100 % efficient and a mixture of ionic liquid and aqueous solution was collected from the steel outlet. 

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Example 3 Venturi Flowmeter An incompressible fluid flows through the venturi flowmeter in Fig. 6-7. An equation is needed to relate the flow rate Q to the pressure drop measured by the manometer. This problem can he solved using the mechanical energy balance. In a well-made venturi, viscous losses are neghgihle, the pressure drop is entirely the result of acceleration into the throat, and the flow rate predicted neglecting losses is quite accurate. The inlet area is A and the throat area is a. 

The continuity equation gives V2 = V AJa, and Vj = Q/A. The pressure drop measured by the manometer is pi —p2= (p — p)gA . Substituting these relations into the energy balance and rearranging, the desired expression for the flow rate is found. 

An equation for use with venturi meters was given by Chisholm [Br Chem. Eng., 12, 454—457 (1967)]. A procedure for determining steam quahty via pressure-drop measurement with upflow through either venturi meters or sharp-edged orifice plates was given By Colhus and Gacesa [J. Basic Eng., 93, 11-21 (1971)]. 

For column analysis and troubleshooting it is important to have pressure drop measured with a DP cell. The differential pressure can also be used to control column traffic. A good way to do this would be to let the differential pressure control the heating medium to the reboiler. The largest application for differential pressure control is with packed columns where it is desirable to run at 80 to 100% of flood for best efficiency. 

Support plate manufactured at 60% open area vs. normal 80-100-1-%. Poor separation. Taps were not available to obtain accurate pressure drop measurements. Manufacturing error. 

Strigle [139] reports that Kister and Gill s [93] tests indicate that from over 3,000 pressure drop measurements the results fit Figure 9-21-G for 80% (excellent) and another 15% (reasonable) fit. 

Figure 9-63A. Flooding data for structured packings obtained by pressure drop measurements as well as by efficiency measurements (see Ref. 108 for sources). Reproduced by permission of the American Institute of Chemical Engineers, Fair, J. R. and Bravo, J. L., Chemical Engineering Progress, V. 66, No. 1 (1990) p. 19 all rights reserved.

The surface shear stress t is a consequence of the velocity difference between the metal surface and the fluid velocity. For tubular geometries it can be obtained from pressure drop measurements or calculated ... 

One of the reasons for developing the parallel plate catalyst was to reduce the pressure drop across the catalyst bed and consequently to reduce power costs for circulating the recycle gas. For pressure drop measurements across the 2-ft long catalyst beds, see Table X. These data show that the pressure drop across the parallel plates is about 1/15 of that across the pelleted catalyst bed. 

Hewitt, G. F., King, I. and Lovegrove, P. C. Brit. Chem. Eng. 8 (1963) 311-318. Holdup and pressure drop measurements in the two phase annular flow of air-water mixtures. 

Pressure drop measurements. For the majority of experiments the instrumentation was relatively similar. Due to limitations associated with the small size of the channels, pressures were not measured directly inside the micro-channels. To obtain the channel entrance and exit pressures, measurements were taken in a plenum or supply line prior to entering the channel. It is insufficient to assume that the friction factor for laminar compressible flow can be determined by means of analytical predictions for incompressible flow. 

Pfund D, Rector D, Shekarriz A (2000) Pressure drop measurements in a micro-channel. AIChE J 46 1496-1507... 

The Lockhart-Martinelli model can correlate the data obtained from pressure drop measurements in gas-liquid flow in channels with hydraulic diameter of 0.100-1.67 mm. The friction multiplier is 0l = 1 + C/X - -1 /X. ... 

A summary of the nine batch reactor emulsion polymerizations and fifteen tubular reactor emulsion polymerizations are presented in Tables III IV. Also, many tubular reactor pressure drop measurements were performed at different Reynolds numbers using distilled water to determined the laminar-turbulent transitional flow regime. 

Other schemes have been proposed in which data are fit to a lower, even order polynomial [19] or to specific rheological models and the parameters in those models calculated [29]. This second approach can be justified in those cases when the range of behavior expected for the shear viscosity is limited. For example, if it is clear that power-law fluid behavior is expected over the shear rate range of interest, then it would be possible to calculate the power-law parameters directly from the velocity profile and pressure drop measurement using the theoretical velocity profile... 

Tippets, F. E., J. A. Bond, and J. R. Peterson, 1965, Heat Transfer and Pressure Drop Measurements for High Temperature Boiling Potassium in Forced Convection, Proc. Conf. on Applied Heat Transfer Instrumentation to Liquid Metal Experiments, ANL-7100, p. 53-95, Argonne National Lab., Argonne, IL. (3)... 

When one of the three draft tube velocities was increased to simulate upset conditions, stable operations were still possible. These upset conditions could also be detected by pressure drop differences among various draft tubes and downcomers when differences in draft tube velocities were large. For severe upset conditions, where some of the draft tubes become downcomers, pressure drop measurement alone could not distinguish the solids flow pattern inside the draft tubes. 

Calculate tw from the pressure drop measurements using equation 2.3 and the corresponding values of the flow characteristic (8u/d, = AQhnj) from the flow rate measurements. 

The flow rate-pressure drop measurements shown in Table 3.1 were made in a horizontal tube having an internal diameter d, = 6 mm, the pressure drop being measured between two tappings 2.00 m apart. The density of the fluid, p, was 870 kg/m3. Determine the wall shear stress-flow characteristic curve and the shear stress-true shear rate curve for this material. 

As stated earlier, CEP and CC are the most common materials used in the PEM and direct liquid fuel cell due fo fheir nature, it is critical to understand how their porosity, pore size distribution, and capillary flow (and pressures) affecf fhe cell s overall performance. In addition to these properties, pressure drop measurements between the inlet and outlet streams of fuel cells are widely used as an indication of the liquid and gas transport within different diffusion layers. In fhis section, we will discuss the main methods used to measure and determine these properties that play such an important role in the improvement of bofh gas and liquid transport mechanisms. 

This second method does not lend itself to the development of quantitative correlations which are based solely on true physical properties of the fluids and which, therefore, can be measured in the laboratory. The prediction of heat transfer coefficients for a new suspension, for example, might require pilot-plant-scale turbulent-flow viscosity measurements, which could just as easily be extended to include experimental measurement of the desired heat transfer coefficient directly. These remarks may best be summarized by saying that both types of measurements would have been desirable in some of the research work, in order to compare the results. For a significant number of suspensions (four) this has been done by Miller (M13), who found no difference between laboratory viscosities measured with a rotational viscometer and those obtained from turbulent-flow pressure-drop measurements, assuming, for suspensions, the validity of the conventional friction-factor—Reynolds-number plot.11 It is accordingly concluded here that use of either type of measurement is satisfactory use of a viscometer such as that described by Orr (05) is recommended on the basis that fundamental fluid properties are more readily determined under laminar-flow conditions, and a means is provided whereby heat transfer characteristics of a new suspension may be predicted without pilot-plant-scale studies. 

Fig. 35. Analysis of the 3-D standard deviation maps calculated from data acquired with the bed operating at a constant gas velocity of (a) 25 and (b) 3l ll l iiiin s as a function of liquid velocity. The number of independent liquid pulses identified at each liquid velocity ( ), and the standard deviation in the pressure drop measurements made over the length of the bed, recorded at 0.5 s intervals over a 10-min period (x), are shown. All data derived from the 3-D MRI standard deviation maps are averaged over six maps acquired for each set of operating conditions.

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