Flow meter times time measuring

Consider now a situation in which the bias limits in the temperature measurements are uncorrelated and are estimated as 0.5 °C, and the bias limit on the specific heat value is 0.5%. The estimated bias error of the mass flow meter system is specified as 0.25% of reading from 10 to 90% of full scale. According to the manufacturer, this is a fixed error estimate (it cannot be reduced by taking the average of multiple readings and is, thus, a true bias error), and B is taken as 0.0025 times the value of m. For AT = 20 °C, Eq. (2.9) gives ... 

It is obvious that the flow rate must be precisely controlled. The pressure from the compressed gas cylinder of carrier gas, while sufficient to force the gas through a packed column, does not provide the needed flow control. Thus a flow controller valve is built into the system. The flow rate of the carrier gas, as well as other gases used by some detectors, must be able to be carefully measured so that one can know what these flow rates are and be able to optimize them. Flow meters are commercially available. However, a simple soap bubble flow meter is often used and can be constructed easily from an old measuring pipet, a piece of glass tubing, and a pipet bulb. See Figure 12.10. With this apparatus, a stopwatch is used to measure the time it takes a soap bubble squeezed from the bulb to move between two graduation lines, such as the 0- and 10-mL lines. The commercial version uses an electronic sensor to measure the flow rate based on the bubble movement. See Workplace Scene 12.3. 

Flow Rate Accuracy. One of the key performance requirements for the pump module is the ability to maintain accurate and consistent flow of the mobile phase. This is necessary to provide stable and repeatable interactions between the analytes and the stationary phase [8,9]. Poor flow rate accuracy will affect the retention time and resolution of the separation. The flow-rate accuracy of the pump can be evaluated simply by calculating the time required to collect a predetermined volume of mobile phase at different flow rate settings. For example, the flow-rate accuracy at 2 mL/min can be verified by using a calibrated stopwatch to measure the time it takes to collect 25 mL of effluent from the pump into a 25-mL volumetric flask. A calibrated flow meter can be used to determine the flow rate as well. The typical acceptance of the flow rate accuracy is listed in Table 11.1. A steady backpressure may be required, depending on the requirement of the system. 

Injector and detector temperatures were maintained at 150 and 200°C, respectively. Nitrogen carrier flow rates were measured with a Gasmet flow meter and were maintained between 22 and 24 ml min-1. Gas holdup times were measured with 20 1 injections of methane. 

A. Flow Measurement by Displacement. A variety of flow meter designs are based on the positive displacement of a small amount of easily visualized material which does not alter the flow rate. A simple and easily constructed mass flow meter of this type, the soap-film meter, is based on timing the displacement of a soap film up a buret tube (Fig. 7.11). This type of flow meter is often placed at the exit of a gas chromatograph or small flow reactor. It is very... 

Hydroformylation of 1-hexene was studied at 80 °C under 30 bar of CO/H2 (1 1) with the in-situ generated catalyst 7. The reaction was monitored via the CO/H2-uptake which was measured with mass flow meters. The polymer-bound catalysts possessed moderate activities in methanol (200-400 TO/h), and the activity was approx. 4-times higher when non polymer-bound TPPMS was used as the ligand. The activity of the catalyst 7 decreased in recycling experiments (entries 2a-2b in Table 2), which can presumably be attributed to a partial oxidation of the phosphine ligands. Moreover, the activity of the complex was not significantly affected by the change of P Rh... 

In multiphase flow metering, it is usually required to distinguish hydrocarbon from water. If the liquid phase is "oil continuous," the water fraction can be determined by dielectric constant measurement at microwave frequencies because the dielectric constant of dry hydrocarbon is on the order of 2 to 4 and that of water is 82. Naturally, density measurement can also distinguish water from oil. The next requirement is to distinguish the flow of liquid from the flow of gas in a system where the two will try to separate and travel at different velocities. Cross-correlation by nuclear techniques can measure the density of the stream twice (a short vertical distance apart) and correlate the fluctuations in density with time to determine velocity. Multiphase flow metering is a new and evolving technology,... 

Transit-time flowmeters measure the time taken for an ultrasonic energy pulse to traverse a pipe section both with and against the flow of the liquid within the pipe (Figure 3.97). The flow rate is the difference in transit times. Transit-time flowmeters are widely used in water treatment and chemical plant applications. This type of ultrasonic meter is considerably more expensive than the Doppler version, but it offers better accuracy. Unlike the Doppler meter, it is usable only on relatively clean fluid applications. Its advantages... 

In concurrent downward-flow trickle beds of 1 meter in height and with diameters of respectively 5, 10 and 20 cm, filled with different types of packing material, gas-continuous as well as pulsing flow was realized. Residence time distribution measurements gave information about the liquid holdup, its two composing parts the dynamic and stagnant holdup and the mass transfer rate between the two. 

The carbon/molecular sieve bed was temperature-controlled at 293 K. The volumetric flow rate was Q = 5.19 dm3 min-1 (1.0 dm3 min 1 cm2), resulting in the linear flow rate vL = 1000 cm min-1. The gas flow was controlled by several flow meters. The outlet concentrations were analyzed in cycles of 3 min with a CP 9001 CHROMPACK gas chromatograph with a flame ionization detector. The breakthrough time was determined at the outlet by a TBB concentration (behind the carbon bed) cx = 10 5 mg dm-3 (cx/c0 = 10 5). To study the water influence on TBB breakthrough, water vapour was added to reach 50% relative humidity (RH) of the air flow. The measurements were performed with dry carbon/molecular sieve beds using dry or wet air. 

Retention time and the peak efficiency depend on the carrier gas flow rate retention time is also directly proportional to column length, while resolution is proportional to the square root of the column length. For packed columns, the carrier gas flow rate is usually expressed in milliliters per minute at atmospheric pressure and room temperature. It is measured at the detector outlet with a soap film flow meter while the column is at operating temperature. Unless otherwise specified in the individual monograph, flow rates for packed columns are 60 to 75 mL/min for 4-mm id columns and 30 mL/min for 2-mm id columns. 

A steady gas flow calibrating a flow meter of this kind can be obtained from a needle valve attached to a regulator set to 5- 10 psi gauge pressure or more (to avoid perturbations due to small variations in outlet pressure). At small flow rates the volume of gas flow over an interval of time measured with a timer can be determined with a gas burette a three-way stopcock can be used to switch the gas burette in and out of the system. For larger flow rates a water-filled inverted graduated cylinder or volumetric flask, its mouth held under the surface of a water bath, can be used to collect gas from a rubber tube held underneath it for a time interval measured with a timer. For precise work, a correction should be made for the partial pressure of water vapor in the gas collected. 

The adjustment of organic vapor concentration is carried out from manipulating the valves installed in the line of gas flow. The flow rate of mixed gas flow during frequency measurement is maintained at 0.4 L/min. all the time by controlling the valve installed at the bottom of the flow meter. Experiment is conducted at room temperature. 

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