Mass-flow measurement

Mass flow measurement has been shown to be efficient as a mole ratio control, even where S03 mass flow was not measurable with sufficient accuracy in the diluted gas stream. 

MASS FLOW MEASUREMENT. The use of collectors for the determination of aerosol mass flow rates is reported. La Mer and Hochberg (10D) pass the mixture through a glass wool filter. Burgoyne and Cohen (5D) use a similar technique. A discussion of the efficiency of collector screens is given by Berly, First, and Silverman (3D). 

Equation 3.23 gives the velocity of the local C-frame with respect to the V-frame (i.e., the velocity of local mass flow measured by the velocity of an embedded inert marker relative to the ends of a diffusion couple such as in Figs. 3.3 and 3.4). The measurement of and D at the same concentration in a diffusion experiment thus produces two relationships involving Di and D2 and allows their determination. In the V-frame, the diffusional flux of each component is given by a simple Fick s-law expression where the factor that multiplies the concentration gradient is the interdiffusivity D. In this frame, the interdiffusion is specified completely by one diffusivity. 

Barolo et al. (1998) developed a mathematical model of a pilot-plant MVC column. The model was validated using experimental data on a highly non-ideal mixture (ethanol-water). The pilot plant and some of the operating constraints are described in Table 4.13. The column is equipped with a steam-heated thermosiphon reboiler, and a water-cooled total condenser (with subcooling of the condensate). Electropneumatic valves are installed in the process and steam lines. All flows are measured on a volumetric basis the steam flow measurement is pressure- and temperature-compensated, so that a mass flow measurement is available indirectly. Temperature measurements from several trays along the column are also available. The plant is interfaced to a personal computer, which performs data acquisition and logging, control routine calculation, and direct valve manipulation. 

Mass flow measurements are required for several control circuits and for balancing the experiments. For a maximum flexibility, gauges have been installed which measure the mass flow via the Coriolis-forces. The mass of the feed vessel is continuously measured by a weighing cell The integrated weight loss is used to control the frequency of the feed pump. 

Yan, Y., Mass flow measurement of bulk solids in pneumatic pipelines, Meas. Sci. Technol. 7, pp. 1687-1706, 1996. 

Mann, D.B., et al, Gas Orifice Meter Discharge Coefficients as Determined by Mass Flow Measurement, NBSIR 83-1685, August 1983. 

Enoksson, P. Stemme, G. Stemme, E. A silicon resonant sensor structure for Coriolis mass flow measurement. J. MEMS 1997, 6 (2), 119-125. 

The device should be suitable whenever large quantities of bulk solids have to be measured downstream of mechanical conveyor systems and should be accurate even in case of large flows and high ambient temperatures. It should be possible to install the instmment on round pipes or ducts and should operate with the latest microprocessor technology. It should be dustproof and can be installed at an angle if required. The mass flow measurement should be independent of flow characteristics, and with no moving parts in the system, maintenance is not required. 

The balance calculation starts from directly measured values. In the sequel, we are mainly interested in mass and energy flows and their inventories. But note that the mass flow measurement system usually comprises not only flowmeters, but also further instruments (in practice, mass flows are very often computed, e.g., using the data Of a volume flowmeter along with the density). In general, we speak about pre-processing of data. A sj cial part of pre-processing is so-called compensation of directly measured flows (for pressure, temperature, etc.). 

Mass flow measurement Electrical/magnetic measurement Capacitance measurement... 

Yan, Y, Barratt, IR, Ma, J, Reed, AR, On-Line Continuous Mass Flow Measurement of Particulate Solids in Gas Streams , Int. Symp. on Reliable flow of Particulate Solids, Porsgrunn, Norway, 1999... 

The use of downstream heat transfer for mass flow measurement does directly relate to the mass flow rate, as the heat transfer mechanism relies on the mass and velocity of each individual particle, However the technique does rely on the injection of heat uniformly to all sections of the pipe and a uniform sensing throughout the pipe cross section. The requirements for a uniform excitation and sensing field are not peculiar to this application however. 

Arko A., Waterfall R.C., Beck M.S., Dyakowski T., Sutcliffe P. and Byars M., Development of Electrical Capacitance Tomography for Solids Mass Flow Measurement and Control of Pneumatic Conveying Systems, Proceedings of the C World Congress on Industrial Process Tomography, 140 - 146, 1999. 

Boeck Th., Mass flow measuring systems for pneumatically conveyed solids, Bulk Solids Handling, 7,181-187,1987. 

The discharge coefficient is in general determined experimentally by the valve manufacturer for a fixed nominal lift. It corresponds to the average value of the ratio from mass flows measured and calculated with the nozzle flow model [1]. At least... 

These equations are of increasing interest to the process control engineer because online charge balance models combined with Coriolis mass flow measurements of influent and reagent flows can provide online fast and reliable pH estimators per Chapter 8. The pK in these models closest to... 

The principal advantages of this mass flowmeter in cryogenic service is that it requires no moving parts in the fluid stream, requires no flow straighteners, and can be used with two-phase flow. Its major disadvantage is that it is an inferential mass flow measurement with slow response time. Additionally, the screen and honeycomb open area may be insufiicient to allow free passage of solid particles. 

Electromagnetic flowmeters offer the advantage of no moving parts in the flow stream, possible two-phase fluid capability, direct mass flow measurement, good time response, and linear calibration. For reproducible results, the flow velocity profile must be symmetric with respect to the axis of the pipe. Problems with this flowmeter include zero point drift with temperature, complex electronics, and difficulty in maintaining a hydrogen leak-proof flow tube. 

The error in a measurement is often roughly proportional to the absolute value of the measured variable. This is used in Appendix lOA to show that the error in the value of rj calculated from the three mass flows is by far the lowest if the overflow fraction is one of the two mass flows measured. 

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