Mass flow measurement indirect

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. 

Paper II presents a hypothetical method to indirectly measure the key quantities of a PBC, that is, the mass flow and the stoichiometry of the conversion gas, as well as the air excess numbers of the conversion and combustion system, defined in paper I. It also includes a measurement uncertainty analysis. 

However, it is possible to directly or indirectly measure the mass flux (mass flow) of conversion gas. Several authors have measured the mass loss of the fuel bed as function of primary air velocities and biofuel [12,33,38,53] by means of a balance. Most of them have used the over-fired batch conversion concept. They utilise the relationship illustrated by Eq. 16 (formulised in amounts instead of flows) above and the assumption that no ash is entrained. As a consequence, the mass loss of the batch bed with time equals the conversion gas. In the simple three-step model [3], an assumption of steady state is made, which is not relevant for batch studies. If it is practically possible, the method of using a balance to measure the conversion gas rate is especially appropriate for transient processes, that is, batch processes. 

One class of flow measurement which is becoming of increasing importance (particularly in the form of sensors for control systems) is the monitoring of mass flow. This is rapidly superseding the measurement of volumetric flow—especially where it is required to determine accurately the transfer of large quantities of gas and liquid in the oil, gas and water industries. Two principal approaches are employed to measure mass flow. One is indirect and uses a combination of volumetric flow and density and the other is direct in that it involves the measurement of properties which are sensitive to variations in the mass rate of flow itself. 

The condition for the practical implementation of such a feed control is the availability of a computer controlled feed system and of an on-line measurement of the accumulation. The later condition can be achieved either by an on-line measurement of the reactant concentration, using analytical methods or indirectly, by using a heat balance of the reactor. The amount of reactant fed to the reactor corresponds to a certain energy of reaction and can be compared to the heat removed from the reaction mass by the heat exchange system. For such a measurement, the required data are the mass flow rate of the cooling medium, its inlet temperature, and its outlet temperature. The feed profile can also be simplified into three constant feed rates, which approximate the ideal profile. This kind of semi-batch process shortens the time-cycle of the process and maintains safe conditions during the whole process time. This procedure was shown to work with different reaction schemes [16, 19, 20], as long as the fed compound B does not enter parallel reactions. 

There are many other types of flow meters that can be used such as venturi meters, vortex shedder flow meters, and Coriolis flow meters. Any of these may be preferred depending on the application. Fluid flow can also be measured indirectly using chemical analysis and mass and energy balance calculations. Air flow measurements are commonly made this way since an oxygen analyzer is generally more accurate than a thermal mass flow meter. 

The complete description of a flame requires the specification of the pressure, the mass flow rate or burning velocity, the initial gas composition, and the appropriate transport coefficients and thermodynamic data. The remaining information is contained in a set of one-dimensional profiles of composition, temperature, and gas velocity as a function of distance (Fig. 2). Other independent variables than distance could have been used, e.g., temperature or time, but distance is common in experimental studies. Not all of these profiles are independent since there are a number of relations between the variables such as the equation of state, conservation of mass, etc. As an example, gas velocity can be obtained both by direct measurement and from temperature measurements using geometrical and continuity considerations. In the example given the indirect determinations of velocity are the more reliable and were used in the analysis. It is general practice to measure as many variables as convenient because the redundant profiles provide a check on the reliability of the measurements. 

It is important to realise that mass spectrometric measurements in TG-MS are not performed directly on the polymer but only evolved gases are detected and identified. Factors influencing component loss from polymeric matrices are volatility, rate of diffusion, solubility in the polymeric matrix, flow-rate, temperature, AT, sample thickness, etc. Therefore, information about the polymeric matrix is obtained in an indirect way, and concerns especially the thermal stability, degradation mechanism and kinetics, performance behaviour, reactivity, and analysis of volatile additives, residuals, monomer occlusions... 

An ion beam causes secondary electrons to be ejected from a metal surface. These secondaries can be measured as an electric current directly through a Faraday cup or indirectly after amplification, as with an electron multiplier or a scintillation device. These ion collectors are located at a fixed point in a mass spectrometer, and all ions are focused on that point — hence the name, point ion collector. In all cases, the resultant flow of an electric current is used to drive some form of recorder or is passed to an information storage device (data system). 

The technique offers a known interfacial area under convective flow conditions that are quite well-defined, with mass transport rates that are enhanced compared to the Lewis cell and its analogs. However, in common with many other approaches, interfacial fluxes must be determined indirectly from bulk solution measurements. 

The required concentration of detergency is extremely important in the field of washing machines and detergency. Two kinds of monitoring methods can be distinguished - direct determination of active substances in the washing liquor and indirect methods, which rely on the measurement of masses and flows. 

To meet the requirements of fuel consumption and emissions, modern fuel-injection systems require precise metering of the intake air mass. There are two main approaches direct and indirect measurement. In the indirect method the density of the air upstream of the intake valves is determined by measuring pressure and temperature, volumetric flow is determined from engine speed and displacement, including the volumetric efficiency of the engine. With direct measurement the disadvantages of the indirect method (adulteration due to exhaust gas recirculation and changes in the volumetric efficiency) can be avoided. 

The earliest experimental studies of heat transfer to flowing molten or thermally softened polymers were the papers of Beyer and Dahl [31] and Schott and Kaghan [32]. These dealt mainly with determining the radial point at which temperature approximated the mass average fluid temperature. Later Bird [33] measured a few experimental points that did not check well with theory. Gee and Lyon [19] also indirectly checked their theory by showing that calculated and experimental average flow rates of a thermally softened polymer undergoing heat transfer compared favorably. 

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