Access flow, measurement

Kertzscher, U., Seeger, A., Affeld, K., Goubergrits, L., and Wellnhofer, E. (2004), X-ray based particle tracking velocimetry - A measurement technique for multi-phase flows and flows without optical access, Flow Measurement and Instrumentation, 15(4) 199-206. 

Fig. 3. Access flow measurement by means of duplex Doppler ultrasonography.

Flow measurements using tracers are performed in all piping systems carrying oil, gas or water including separators, compressors, injector systems, and flares. Calibration of elsewhere difficult accessible flow meters is regularly performed by the tracer methods, which are based on international standards. Tracer flow measurements are also well suited for special purposes... 

PIV has become the most popular technique to measure velocity and turbulent properties (Figure 15.1). The movement of seed particles in a millimeter-thick laser sheet is measured by correlating two photos taken a few milliseconds apart. With two cameras, it is also possible to obtain a 3D vector of the velocity in that plane. The method gives, in general, very good resolution of the flow, but it requires optical access. Also, measurement close to walls can be problematic due to light reflections that disturb the measurements. One extension of PIV is the micro-PIV that uses fluorescent tracer particles, which allows all direct light, for example, reflections at the walls, to be filtered out [1]. 

The transfer flow for 2-stage dilution could be measured only after partially dismantling the olfactometer, which is a clear disincentive to regular calibration. WSL s portable olfactometer included an orifice plate and micro-manometer for measuring this flow, which could thus be checked and adjusted at any time. This investigation has therefore demonstrated the value of using in situ, non-interfering flow measurement devices that are accessible to the operator at all times. 

In the process industries, flow measurement devices are the largest market in the process instrumentation field. Two web sites for process equipment and instrumentation, www.globalspec.com, and www.thomasnet.com, both list more than 800 companies that offer flow measurement products. There are more than one hundred types of flowmeters commercially available. The aforementioned web sites not only facilitate selection and specification of commercial flowmeters, but also provide electronic access to manufacturers technical literature. 

In order for cryoenzymology experiments to provide mechanistically significant information, it is important that the reaction at low temperature be analogous to that under normal conditions, that is, aqueous solution and ambient temperature. One definitive way to demonstrate this is to take the kinetic data for a particular intermediate at subzero temperatures and to calculate the expected rates of formation and breakdown under normal conditions. If these rates are accessible to measurement (e.g., by stopped-flow techniques) then comparison can be made between the low-temperature and high-temperature data. 

U.S. Bureau of Reclamation. 1997. Water Measurement Manual. Washington, D.C. U.S. Government Printing Office. A useful handbook on methods of water flow measurement, and so on, available for downloading at http //www.usbr.gov/pmts/hydraulics lab/pubsl wmm/ (accessed November 3,2010). 

The access flow should be measured in a straight vascular segment without excessive dilatation by the longitudinal section. It is based on multiplying the... 

Quick RC Predicting arteriovenous fistula maturation with intraoperative blood flow measurements. J Vase Access 2008 9 241-247. 

For AVG, NFK-KDOQI recommends PE for access monitoring. It lists use of intra-access flow, direct or derived static venous pressures and US as preferred techniques for access surveillance. For AVF, direct flow measurements, physical findings of persistent swelling of the arm, presence of collateral veins, prolonged bleeding on needle withdrawal, altered characteristics of pulse or thrill in the outflow vein and US are preferred techniques of surveillance [17]. 

Most emphasis in recent times has been in the development of nonintrusive flow measurement techniques for measuring vector as well as scalar quantities in ihe flow. These techniques have been mostly optically based, but when fluid opaqueness prohibits access, other techniques are available. A quick overview of several of these nonintrusive measurement techniques is given for completeness in the next few sections. More extensive discussion on these techniques can be found in the references cited. 

In the cathodic protection of storage tanks, potentials should be measured in at least three places, i.e., at each end and at the top of the cover [16]. Widely different polarized areas arise due to the small distance which is normally the case between the impressed current anodes and the tank. Since such tanks are often buried under asphalt, it is recommended that permanent reference electrodes or fixed measuring points (plastic tubes under valve boxes) be installed. These should be located in areas not easily accessible to the cathodic protection current, for example between two tanks or between the tank wall and foundations. Since storage tanks usually have several anodes located near the tank, equalizing currents can flow between the differently loaded anodes on switching off the protection system and thus falsify the potential measurement. In such cases the anodes should be separated. 

In the corrosion protection of marine structures, it is often found that the corrosion rate decreases strongly with increasing depth of water, and protection at these depths can be ignored. Investigations in the Pacific Ocean are often the source of these assumptions [7], However, they do not apply in the North Sea and other sea areas with oil and gas platforms. Figure 16-1 is an example of measurements in the North Sea. It can be seen that flow velocity and with it, oxygen access, is responsible for the level of protection current density. Increased flow velocity raises the transport of oxygen to the uncoated steel surface and therefore determines the... 

Cathodic protection of water power turbines is characterized by wide variations in protection current requirements. This is due to the operating conditions (flow velocity, water level) and in the case of the Werra River, the salt content. For this reason potential-controlled rectifiers must be used. This is also necessary to avoid overprotection and thereby damage to the coating (see Sections 5.2.1.4 and 5.2.1.5 as well as Refs. 4 and 5). Safety measures must be addressed for the reasons stated in Section 20.1.5. Notices were fixed to the turbine and the external access to the box headers which warned of the danger of explosion from hydrogen and included the regulations for the avoidance of accidents (see Ref. 4). 

In addition to regulatory requirements, the practical matters associated with maintaining product and personnel flow to and from operating facilities must be addressed. For example, it may be difficult to remove a rail spur for remediation of a contaminated bed, if the only means to deliver a feedstock into the facility or ship a product from the facility is this rail line. In-situ flushing or some other form of non-invasive treatment would be required to address such a problem. Similarly, jjersonnel access may have to be addressed in the planning for a corrective measures program. This is especially true in older or... 

Convenient methods of studying flow characteristics related to structural elements that are accessible with difficulty for traditional measurement devices... 

A simple quantity meter which is used for the measurement of the flow of gas in an accessible duct is the anemometer (Figure 6.29). A shaft carrying radial vanes or cups... 

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