Flow measurements special tubes

The Coriolis meter is commonly used to measure liquid flow rates. The coriolis meter utilizes the coriolis effect to directly measure the mass flow rate of liquids. The meter is equipped with a specially shaped vibrating tube through with the liquid flows. When a fluid flows through the tube it alters the manner in which the tube vibrates. The mass flow rate of the fluid is then... 

Viscosity can also be measured with viscometers where the movement or the developed force is due to gravity, by the fluid s own weight. Such a system is developed when the fluid flows in special glass tubes (capillary tubes). In this case, the kinematic viscosity (qj or v) is measured, and the measurement unit is in square millimetres per second. This unit is also known as centistoke (cSt). However, when the fluid is forced to flow under negative pressure (vacuum), then the dynamic viscosity (Pa-s) is measured. 

As the viscosity of a liquid varies greatly with the temperature (roughly a per cent, per degree), the tube and liquid must be kept at a constant temperature during the measurement. The tube is therefore suspended in a bath, the temperature of which can be regulated to within o i°. As it is necessary to watch the flow of liquid, the thermostat must be transparent, or have transparent sides. We may therefore use a large beaker fitted with a thermo-regulator (p, 72) and stirrer, preferably a turbine or tube stirrer (p. 77) or a metal bath with transparent sides (p. 69). The viscosity tube must be supported in a perpendicular position, and should be so far immersed in the liquid of the thermostat that the upper mark c is well beneath the suiface. As a support for. the tube, one may employ either an ordinary retort clamp, or a special clamp attached to the side of the thermostat. A simple holder for the tube can also be made as follows —... 

Katz and Scott used equation (7) to calculate diffusivity data from measurements made on a specially arranged open tube. The equation that explicitly relates dispersion in an open tube to diffusivity (the Golay function) is only valid under condition of perfect Newtonian flow. That is, there must be no radial flow induced in the tube to enhance diffusion and, thus, the tube must be perfectly straight. This necessity, from a practical point of view, limits the length of tube that can be employed. 

An industrial standard method has been developed to test the lightfastness of polymers in accelerated test equipment [103]. The apparatus consists of a quartz-xenon tube with a special optical filter between the light source and the specimen to produce light that resembles window glass-filtered daylight [104], Samples are mounted at a specific distance from the arc and are supported on a frame which revolves around the arc 1 to 5 times per minute for uniform exposure. A blower unit in the base provides a flow of air which makes it possible to maintain a black panel temperature of 45°C, measured by a black panel thermometer which is positioned at level with the samples. A black panel unit consists of a bimetallic thermometer mounted on a steel frame. Both faces of the frame plate and also the stem of the thermometer are coated with a heat-resistant glossy black enamel. The relative humidity level in the exposure cabinet is closely controlled. 

Pump tubes are available in different materials depending on the liquid to be pumped, e.g. for solvents or concentrated acids. Flow rates for these other materials will be different than for standard PVC. Pump tubes may also be available in a specially calibrated or measured flow rate quality at extra cost. Unless specified for medical purposes or to meet regulations, the standard quality is normally adequate. See Chapter 1, Peristaltic pumps. ... 

Differential Pressure Meters Differential pressure meters or head meters measure the change in pressure across a special flow element. The differential pressure increases with increasing flow rate. The pitot tubes described previously work on this principle. Other examples include orifices [see also Eqs. (6-111) and (8-102), and Fig. 10-14], nozzles (Fig. 10-19), targets, venturis (see also Sec. 8 and Fig. 10-17), and elbow meters. Averaging pitot tubes produce a pressure differential that is based on multiple measuring points across the flow path. 

In the case of a tube packed with particles, such as a chromatographic column, the diameters of all of the flow paths cannot be measured, but the average diameter of the packing particles (dp) can be measured. The spaces between particles are proportional to the average size of the particles. Therefore, columns packed with large particles hold a greater mass of mobile phase than those packed with smaller particles. Equation (10.2) describes a special case (Re ) of the Reynolds number for columns packed with particles ... 

The meter is not suited to measure gas-liquid mixtures or low-pressure gases and develops high pressure drops when the gas velocity is high. To keep the tubes full, they should be installed in vertical pipes with an upward flow direction. Besides their relatively high cost, CMF limitations also include their relatively small sizes (up to 150 mm, or 6 in.), their vibration sensitivity, and the limitation of standard designs to 205°C (400°F) and special ones to 425°C (800°F). The Coriolis-based mass flowmeters are popular in fuel cell, fuel flow, reactor feed, and in other applications where mass flowmeters are needed. 

Let us consider some of the special problems encountered in the operation of a radioisotope detector and the compromises that must be considered. Like any chromatographic detector, a carbon-14 detector should have a small volume and a short hold-up time in order to minimize band spreading and loss of resolution. Unfortunately radioisotopes are measured with an inherent time factor - disintegrations per minute. Therefore, the smaller the cell and the shorter the hold-up, the lower will be the sensitivity, a circumstance which is totally at odds with the first requirement. In practice, we have found that a U-tube with a cross-section diameter of 2mm is generally satisfactory. This gives a cell with a void volume of 200-300 yl, which is high compared to the 2-10 yl volumes of many UV flow cells, and may introduce some band spreading when used with the best new HPLC columns. 

In addition to a proper choice of collecting material (filter paper), a reliable measurement of flow rate is required. Flow meters are classified into rotameters and integrating flow meters. The latter are further classified into wet-gas meters and dry-gas meters. A rotameter has a specially graduated vertical tube, whose diameter increases in the ascending direction, containing a spinning top-shaped or spherical float. A gas-stream is admitted into the bottom of the tube and the float is held at a vertical position which varies in proportion to the flow rate of gas. 

The HOTCR is operated at several temperature levels up to 1000 C. The carrier gas flow rate and the reactor tube diameter are chosen to ensure a mean gas residence time below 0.5 s. Such low residence times are needed to determine the kinetics of homogeneous tar conversion without oxidants, cf. [1]. Before and after the HOTCR, tar samples are taken and the concentrations of non-condensable gases (CO, COj, CH4, H2) are measured on-line. The gas volume flows before and after the HOTCR are measured by a special-designed Pitot-tube system. 

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