Flow measurements flowing fluid

Gup and Vane Anemometers. A number of flow meter designs use a rotating element kept in motion by the kinetic energy of the flowing stream such that the speed is a measure of fluid velocity. In general, these meters, if used to measure wind velocity, are called anemometers if used for open-channel Hquids, current meters and if used for closed pipes, turbine flow meters. 

Measurement of Fluid Flow hy Means of Orifice Plates, Nobles and Venturi Tubes Inserted in Circular Cross Section Conduits Punning Full, ISO 5167-1980(e), International Organization for Standardization, Geneva, Switzerland, 1980. 

There are do2ens of flow meters available for the measurement of fluid flow (30). The primary measurements used to determine flow include differential pressure, variable area, Hquid level, electromagnetic effects, thermal effects, and light scattering. Most of the devices discussed herein are those used commonly in the process industries a few for the measurement of turbulence are also described. 

Temperature. Temperature sensor selection and installation should be based on the process-related requirements of a particular situation, ie, temperature level and range, process environment, accuracy, and repeatabiHty. Accuracy and repeatabiHty are affected by the inherent characteristics of the device and its location and installation. For example, if the average temperature of a flowing fluid is to be measured, mounting the device nearly flush with... 

Not all elements of the industrial thermocouple need to be wine. For example, if a copper pipe contains a flowing fluid whose temperature is to be measured, a constantan wine attached to the pipe will form a T, or copper—constantan, thermocouple. Such arrangements ate difficult to caUbrate and requite full understanding of the possible inherent problems. For example, is the copper pipe fully annealed Homogeneous Pure, or an alloy Many ingenious solutions to specific measurement problems ate given in Reference 6. 

Static temperature is the temperature of the flowing fluid. Like static pressure, it arises because of the random motion of the fluid molecules. Static temperature is in most practical instaUations impossible to measure since it can be measured only by a thermometer or thermocouple at rest relative to the flowing fluid that is moving with the fluid. Static temperature will increase in a diffuser and decrease in a nozzle. 

This subsertion deals with the techniques of measuring pressures, temperatures, velocities, and flow rates of flowing fluids. 

Since this temperature requires the thermometer or thermocouple to be at rest relative to the flowing fluid, it is impractical to measure. It can be, however, calculated from the measurement of total temperature and total and static pressure. 

The laser-Doppler anemometer measures local fluid velocity from the change in frequency of radiation, between a stationary source and a receiver, due to scattering by particles along the wave path. A laser is commonly used as the source of incident illumination. The measurements are essentially independent of local temperature and pressure. This technique can be used in many different flow systems with transparent fluids containing particles whose velocity is actually measured. For a brief review or the laser-Doppler technique see Goldstein, Appl. Mech. Rev., 27, 753-760 (1974). For additional details see Durst, MeUing, and Whitelaw, Principles and Practice of Laser-Doppler Anemometry, Academic, New York, 1976. 

Temperature gradient normal to flow. In exothermic reactions, the heat generation rate is q=(-AHr)r. This must be removed to maintain steady-state. For endothermic reactions this much heat must be added. Here the equations deal with exothermic reactions as examples. A criterion can be derived for the temperature difference needed for heat transfer from the catalyst particles to the reacting, flowing fluid. For this, inside heat balance can be measured (Berty 1974) directly, with Pt resistance thermometers. Since this is expensive and complicated, here again the heat generation rate is calculated from the rate of reaction that is derived from the outside material balance, and multiplied by the heat of reaction. 

Another pitfall in pressure measurement, partieularly important in flow measurement, is the potential for liquids in gauge lines. All too often gauge lines eoming from overhead pipes have no provision for maintaining a liquid-free status, even though the flowing fluid may be eondensible at gauge-line temperatures. 

ISO 3966. Measurements of fluid flow in closed conduits—Velocity area method using Pitot static tube. 1977, p. 39. 

ISO Standard 3966. Measurement of Fluid Flow in Closed Conduits—Velocity Area Method Using Pitot Static Tubes. International Organisation fot Standardisation, 1977. 

ISO 5167-1 1991. Measurement of Fluid Flow by Means of Pressure Differential Devices-Fart 1 Orifice Plates, Nozzles and Venturi Tubes Inserted in Circular Cross-section Conduits Running Full. International Organisation for Standardisation, 1991. 

ISO/TR 5168 1998. Measurement of Fluid Flow—Evaluation of Uncertainties. International Organi-sation fot Standardisation, 1998. 

Hot wire anemometer An instrument for the measurement of fluid velocity by measuring the resistance of a fine platinum or nichrome wire, which may or may not be shielded by a silica tube. The wire resistance is proportional to the temperature and the fluid flow rate. 

Hot wire microphone anemometer An instrument for the measurement of fluid flow. 

Historically, viscosity measurements have been the single most important method to characterize fluids in petroleum-producing applications. Whereas the ability to measure a fluid s resistance to flow has been available in the laboratory for a long time, a need to measure the fluid properties at the well site has prompted the development of more portable and less sophisticated viscosity-measuring devices [1395]. These instruments must be durable and simple enough to be used by persons with a wide range of technical skills. As a result, the Marsh funnel and the Fann concentric cylinder, both variable-speed viscometers, have found wide use. In some instances, the Brookfield viscometer has also been used. 

The measurement of viscosity is important for many food products as the flow properties of the material relate directly to how the product will perform or be perceived by the consumer. Measurements of fluid viscosity were based on a correlation between relaxation times and fluid viscosity. The dependence of relaxation times on fluid viscosity was predicted and demonstrated in the late 1940 s [29]. This type of correlation has been found to hold for a large number of simple fluid foods including molten hard candies, concentrated coffee and concentrated milk. Shown in Figure 4.7.6 are the relaxation times measured at 10 MHz for solutions of rehydrated instant coffee compared with measured Newtonian viscosities of the solution. The correlations and the measurement provide an accurate estimate of viscosity at a specific shear rate. 

The addition of a flux results not only in a mixture of silica and flux having a lower melting temperature than that of the silica, but also in the melt being less viscous, flowing more easily than silica (viscosity is a measure of the resistance of fluids, liquids, and also gases, to flow fluids with high viscosity flow more slowly than do those with low viscosity). As a consequence of its relatively low viscosity, the hot molten mixture of silica and flux, a type of early glass, can be shaped with relative ease. 

That is, the total increase in entropy (which is a measure of disorder ) comes from heat transferred across the system boundary (Sq). However, a flowing fluid is in a dynamic, or irreversible, state. Because entropy is proportional to the degree of departure from the most stable (equilibrium) conditions, this means that the further the system is from equilibrium, the greater the entropy, so for a dynamic (flow) system... 

The shape of the response curve is strongly influenced by the way tracer is introduced into the flowing fluid, and how it is measured. You may inject or measure the tracer in two main ways, as shown in Fig. 15.5. We therefore have four combinations of boundary conditions, as shown in Fig. 15.6, each with its own particular E curve. These E curves are shown in Fig. 15.7. 

Measurement of fluid flow by means of orifice plates, nozzles etc. 1980... 

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