Flow meters sizing

Valves and pressure meters are installed on the inlet lines to the tube to permit adjustment of flow and measurement of pressure drop, respectively. A pressure meter and check valve are employed in the outlet line. In addition, a flow meter, sized in accordance with the tube data sheet, and a thermometer are included in the outlet line of each coolant course. These flow meters are equipped with automatic interlock switches, wired into the system electrical controls, so that the tube will be completely deenergized in the event of a loss of coolant flow in any one of the coolant passages. In some tubes, filament power alone is sufficient to damage the tube structirre in the absence of proper water flow. 

Wedg e Meters. The wedge flow meter consists of a flanged or wafer-style body having a triangular cross section dam across the top of the fluid conduit. Pressure taps are on either side of this restriction. Overall meter sizes range from 10 to 600 mm. Within each size several restrictions are available to provide the range of differential pressure desired for the appHcation. 

Vortex-shedding flow meters typically provide 1% of flow rate accuracy over wide ranges on Hquid, gas, and steam service. Sizes are available from 25 to 200 mm. The advantages of no moving parts and linear digital output have resulted in wide usage in the measurement of steam, water, and other low viscosity Hquids. 

Turbine flow meters range in size from 5 to 600 mm in diameter, are suitable for temperatures of between 20 and 750 K at pressures of up to 300 bar. A normal range of flows falls between 0.02 litre/s and 2000 litre/s (2m Vs) and a diagram showing a section of an axial turbine flow meter is shown in Figure 6.32. 

Fig. 1.5.3 Aerosol generator assembly for the production of composite or coated particles (a) carrier gas (e.g., helium) tank, (b) drying column containing silica gel and molecular sieve, (c) Millipore membrane of 0.1 p.m pore size, (d) flow meters, (e) nuclei (e.g., NaCI, AgCI) generator, (f) and (m) boilers containing different reactant liquids, (g) and (n) condensation chambers, (h) heater, (i) chamber for recondensation of droplets, (q) and (e) coreactant containers, (k) and (p) vapor injection ports, (I) and (g) reaction chambers, (r) powder collector. (From Ref. 39.)...

Simulation of Mouth Conditions for Flavor Analysis The RAS is not intended to simulate the size or structure of the mouth. The conditions in the mouth expected to affect volatility—i.e., temperature, breath flow, mastication, and salivation—are simulated. Temperature iscontrolled with a waterjacket (37°C). Gas (N2 or purified air) flow is controlled with a variable-area needle-valve flow meter (20 ml/sec). The shearing resulting from mastication is implemented with blender blades and a high-torque variable-... 

The most important relationship in designing flow systems is the macroscopic mechanical-energy balance, or Bernoulli s equation. Not only is it required for calculating the pump work, but it is also used to derive formulas for sizing valves and flow meters. Bird, et al. [6] derived this equation by integrating the microscopic mechanical-energy balance over the volume of the system. The balance is given by... 

However, if the net is equipped with a suitable flow meter or if the volume of water filtered tlirough the net is carefully noted, accuracy can be improved. Fig. 5 shows a typical result of aparticle size analysis of a netplankton sample of reservoir water during a bloom of dominant Dmtoma and Asterionella. Within a particle size range 7.0—30.0 jUm, different maxima in the particle size distribution were observed caused by the presence of both individual cells and of 2—5 celled colonies. A correlation coefficient of = 0.67 was found between the netplankton count by microscopy and the netplankton count by particle counter (cf. Fig. 6). 

The type of meter used for water flow depends on the flow rate and velocity. Meter types include Venturi, propeller, turbine, and magnetic. The manufacturer of each should be consulted for their limitations, which include pipe size, up- and downstream straight pipe available at flow meter installation, minimum and maximum velocity through meter, and calibration requirements. Unfortunately, meters are usually selected by pipe size, not flow rate, so the water meter is often grossly oversized for the flow rate through it. Because most meters are least accurate at the low velocity end of their measurement range, the result is that water flow is not accurately measured. 

The remedy is to select a meter no larger than necessary to handle the minimum flow rates expected, even if the pipe and meter sizes do not match. The velocity through the meter at minimum flow should have range between 2 and 5 fps and at maximum flow have a range of 8-12 Ips (1 fps = 1 ft/s = 0.3048 m/s). In some cases, this may involve the use of pipe reducers to adapt the water line to the meter size a practice which is acceptable provided that the resulting pressure loss is not excessive. Manometers (measuring pressure differential) can be used to calibrate Venturi type meters, whereas only controlled water tests can be used to accurately calibrate propeller, turbine, and magnetic type meters. 

The carrier gas was helium flow rate was approximately 5 mL/min, as measured by a homemade 9 mL bubble flow meter. Because of its small size, the helium diffu-sional loss, as discussed by Munk et al. (2), was deter-... 

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