The measurement of flow

Methods Dependent on Reletionship Between Pressure Drop end Flowrete 

Instruments which are employed to measure flow often use the relation between rate of flow and pressure drop along a section of pipe, around some obstruction or across a restriction within the pipe. The more widely employed flow measuring devices (or flowmeters) are discussed in Volume 1, Chapter 6. These are as follows  

Other sensors which are described in Volume 1 (Sections 6.3.7-6.3.9) are the variable area meter, the notch or weir, the hot wire anemometer, the electromagnetic flowmeter and the positive displacement meter. Some of these flowmeters are relatively less suitable for producing signals which can be transmitted to the control room for display (e.g. weir, rotameter) and others are used in more specialist or limited applications (e.g. magnetic flowmeter, hot wire anemometer). The major characteristics of different types of flow sensor are summarised in Table 6.1. Brief descriptions follow of the principles underlying the more important types of flowmeter not described in Volume 1. In many instances such flow sensors are taking the place of those more traditional meters which rely upon pressure drop measurement. This is for reasons of versatility, energy conservation and convenience. 

---

A hot-wire anemometer, working in the CT mode, is capable of measuring rapid velocity fluctuations. This is an advantage in the measurement of flow turbulence and is also the main area of application for the hot-wire anemometer. It is an instrument mainly for scientific purposes. 

The complete LDA system includes the appropriate transmission and detection optoelectronics, traverse mechanisms, computer-controlled signal processing, and a data acquisition and evaluation system. The LDA equipment is a powerful tool for the measurement of flow velocity and velocity fluctuation, as well as the local concentration of particles or droplets transported in the airflow. 

In this chapter we will illustrate and analyze some of the more common methods for measuring flow rate in conduits, including the pitot tube, venturi, nozzle, and orifice meters. This is by no means intended to be a comprehensive or exhaustive treatment, however, as there are a great many other devices in use for measuring flow rate, such as turbine, vane, Coriolis, ultrasonic, and magnetic flow meters, just to name a few. The examples considered here demonstrate the application of the fundamental conservation principles to the analysis of several of the most common devices. We also consider control valves in this chapter, because they are frequently employed in conjunction with the measurement of flow rate to provide a means of controlling flow. 

For polymer melts another type of apparatus has been designed in order to measure flow birefringence in the same plane (17). This apparatus is of the cone-and-plate type. In this apparatus the light beam is directed in a radial direction. The principles of other arrangements, which were designed for the measurement of flow birefringence in a plane perpendicular to the plane of flow, will receive special attention in Section 1.5. 

As already mentioned in Chapter 1, there are mainly three geometries suitable for the measurement of flow birefringence, viz. those of the concentric cylinder apparatus, the adapted cone-and-plate apparatus and the slit-capillary with a rectangular cross-section. The general principles of the pertinent techniques have been described in the same chapter. The purpose of the present chapter is to give details of the design and construction in order to enable the reader to form a judgement as to the efficiency of the proposed methods, i.e. the relation between information and experimental effort. 

As has already been pointed out in Sections 1.3 and 1.5, the slit-geometry is interesting for two reasons. First, it enables the measurement of flow birefringence in the 1—3 plane. Second, it furnishes the possibility to investigate polymer melts at high shear rates, where the cone-and-plate geometry fails. In the present section it remains to give a short description of the apparatus. 

Fig. 6.7. Slit-apparatus for the measurement of flow birefringence in the 1—3 plane. (A) outer body, (V) conical member enclosing the slit with a rectangular cross-section (this part is split into pieces), (E) entrance, (Wt, IV2) windows, (Hlt Ht, Ha)...

The turbine flow-meters are suitable for use at high pressure up to 4000 bar. The measuring device could be easily mounted into high-pressure tubes. For this purpose, small instruments have been developed [56]. The use of turbines is limited to the measurement of flow of extremely clean components. Fig.4.4-2 shows an example of such a device. Other devices are so-called helical- and gear flow meters which are in use up to pressures of approx. 400 bar [56]. 

C. Flow Measurement by Pressure Drop across an Orifice. Another common scheme for the measurement of flow is based on the determination of the pressure drop on either side of a constriction, such as an orifice or venturi. Either a liquid-filled differential manometer or a pressure transducer with associated digital readout may be used for this pressure measurement. The flow rates determined by these meters are in units such as cm3/s, and it is necessary to make a correction for total pressure to convert these to standard cm3/s or mol/s. 

Cardiac output can be measured using dye- or thermal-dilution techniques or by placement of an electromagnetic flow probe around the pulmonary artery. Insertion of a pressure transducer or fluid-filled catheter into the pulmonary artery and pulmonary vein allows for the calculation of pulmonary vascular resistance. The measurement of flow through the proximal aorta may also be useful but does not include coronary blood flow and as such is not equivalent to... 

Munoz-Ruiz, A.J. Jimenez-Castellanos, M.R. Integrated system of data acquisition for the measurement of flow characteristics. Pharm. Technol. Int. 1993, 21-26. 

The Bernoulli theorem can also be applied to the measurement of flow rate. The passage of an incompressible fluid through a constriction results in an increase in velocity from Ui to uj, which is associated with a decrease in pressure from Pi to P2, which can be measured directly. The volumetric flow rate Q = Mifli = M2fl2 by algebraic rearrangement (which is not shown). The final linear velocity M2 can be described by Eq. (5). 

The primary factors that affect the flowability of the final blend (or almost any powder), such as moisture content, particle shape/size/distribution, temperature/humidity and others, are discussed in more detail later in this chapter. Note that the measurement of flow properties and the design parameters they provide can also be applied to troubleshooting and developing corrective actions for flow problems in the preblending steps. 

Prior to beginning the discussion of the measurement of flow properties, it is beneficial to review how bulk solids are different than liquids. Since one of our primary concerns with bulk solids handling is flow, a term that is commonly associated with liquids, it is often assumed that the principles of fluid mechanics may be used to describe the behavior of... 

The MW obtained in this way, M, is higher that and lower than sometimes My can reach values very close to My,. An advantage of obtaining this average MW with capillary viscosimetry is that the equipment used (the viscometer) is very inexpensive in comparison to those used in other sophisticated techniques, and the measurements of flow time are very simple the only drawback is the time consumed to prepare the samples at different concentrations and to run the samples in the glass viscometer, repeating the measurements a certain number of times. 

The measurement of the flow velocity by introduction of radioactive substance or electrolyte into a cross section, followed by measurement of the radioactivity or electric conductivity in cross sections further downstream, has gained wide acceptance in different branches of engineering and, in particular, in physiology (the measurement of flow velocity of blood in arteries). The main difficulty associated... 

The measuring of flow speed in any point of industrial apparatus is very complicated, and sometimes practically impossible. So, one can determine hydrodynamic structure of reaction mixture movement indirectly, in particular by studying of fluid particles distribution by their residence times in reaction zone. For measuring of aleatory variable, i.e. particle residence time in apparatus, this particle should be marked in some way allowing to register its entering and coming out of apparatus and to receive concentration curve of flow at the outlet. This curve is called output curve or response curve [14, 15]. 

Pressure measurement is a critical factor not only in the oil and gas industry but also for the operation of process equipment including reactors, distillation columns, pipelines, and for the measurement of flow rate. It is a scalar quantity and equals the perpendicular force exerted on a surface with the units of force per surface area ... 

Whereas the transport of water to major centers allowed civilizations to flourish, the measurement and control of fluid flow has been a critical aspect of the development of industrial processes. Not only is metering flow important to maintaining stable and safe operating conditions, it is the prime means to account for the raw materials consumed and the finished products manufactured. While pressure and temperature are critical operating parameters for plant safety, the measurement of flow rate has a direct impact on process economics. For basic chemicals (as opposed to specialty chemicals or pharmaceuticals) like ethylene, propylene, methanol, sulfuric acid, etc. profit margins are relatively low and volumes are large, so high precision instruments are required to ensure the economic viability of the process. 

The measurement of flow rate is one of main subjects in experimental fluid mechanics. However, the thermocapacitive flow sensor may have electronic and semiconductor components, such as a capacitor, an n-channel MOS transistor, an oscillation circuit, and a microfabrication. Therefore, the thermocapacitive flow sensor is a multidisciplinary tool and some of its electronic and semiconductor components need to be explained. 

This relation can be written only if the distance between the section of injection and the section of measure is rather big so that in this last one there is good mixture of the tracer, condition which we represent by C = constant, whatever is the point of sampling in the section. This technique is ideal for the measure of flow in open channels such as sewers and mouths of rivers (the range of measure is very wide flows of rivers of several thousand cubic meters per second can be measured). The precision is among the best which we can obtain ( 1 % or better). A precision of 0.5 % can be reached for regular flows with adequate distances of mixture. 

The capacity factor k is essentially a corrected retention time (Equation [3.18]) that takes into account variations in mobile phase flow rate and thus provides a more robust indicator of analyte retention for a given combination of stationary and mobile phases. As is a unique property of a given solute A for a given stationary-mobile phase combination, the adjusted (corrected) retention volume V,a (Equation [3.15] (or the corresponding retention time) can be used as a tag for analyte identification. Thus the precision and accuracy of measurement of Vja become important and depend on those of the measurement of flow rate U since in practice retention times rather than volumes are the measured quantities. In response to this limitation of the V,a parameter, the capacity ratio of a solute (k) ) was defined as the ratio of its distribution (partition) coefficient to the phase ratio (Vm/V s) of the column with respect to analyte A ... 

---