Mass flow measurement flowmeter, direct

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.). 

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. 

General Principles There are two main types of mass flowmeters (1) the so-called true mass flowmeter, which responds directly to mass flow rate, and (2) the inferential mass flowmeter, which commonly measures volume flow rate aud flmd density separately. A variety of types of true mass flowmeters have been developed, including the following (a) the Maguus-effect mass flowmeter, (b) the axial-flow, transverse-momentum mass flowmeter, (c) the radial-flow, transverse-momentum mass flowmeter, (d) the gyroscopic transverse-momentum mass flowmeter, aud (e) the thermal mass flowmeter. Type b is the basis for several commercial mass flowmeters, one version of which is briefly described here. 

Coriolis Mass Flowmeter This type, described in Sec. 8, offers simultaneous direct measurement of both mass flow rate and fluid density. The Coriolis flowmeter is insensitive to upstream and downstream flow disturbances, but its performance is adversely affected by the presence of even a few percent of a gas when measuring a liquid flow. 

In this approach a gas flowmeter is used to determine the amount adsorbed. It can be of a differential type, as in Figure 3.7 (e.g. with a differential catharometer or a differential pressure drop flowmeter) or a simple form with either a sonic nozzle (Figure 3.8) or a thermal detector (Figure 3.9). The last provides a signal which depends on the heat capacity, thermal conductivity and mass flow of the gas it is usually referred to as a mass flowmeter although there is no direct measurement of mass. 

A few types of flowmeters measure the mass flow rate directly, but the majority measure the volumetric flow rate or the average fluid velocity, from which the volumetric flow rate can be calculated. To convert the volumetric rate to the mass flow rate requires that the fluid density under the operating conditions be known. Most meters operate on all the fluid in the pipe or channel and are known as full-bore meters. Others, called insertion meters, measure the flow rate, or more commonly the fluid velocity, at one point only. The total flow rate, however, can often be inferred with considerable accuracy from this single-point measurement. 

In industry, it is often more important to measure mass flow rate than to monitor volumetric flow rate. To determine the mass flow rate of a mixed-phase flow, one must measure the velocity and concentration of each phase. This becomes a very difficult task and none of the current techniques can accomplish it. In practice, most mass flowmeters measure the relative change of a physical parameter like capacitance. To relate this measurement to solids concentration, the flowmeters must be calibrated against other, direct, methods... 

In an actual flowmeter, therefore, it is evident that the moment about the y axis must be measured or, more realistically, the reaction R at bearings 1 and 2 must be measured. Note that the magnitude of the reaction vector R is directly proportional to mass flow rate m, and that vector R rotates at an angular speed equal to oj. This flowmeter is capable of measuring bidirectional flow. The flowmeter must be provided with rotating seals and suitable bearings. 

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. 

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