Soap-film flow meter

The schematic diagram of the experimental setup is shown in Fig. 2 and the experimental conditions are shown in Table 2. Each gas was controlled its flow rate by a mass flow controller and supplied to the module at a pressure sli tly higher than the atmospheric pressure. Absorbent solution was suppUed to the module by a circulation pump. A small amount of absorbent solution, which did not permeate the membrane, overflowed and then it was introduced to the upper part of the permeate side. Permeation and returning liquid fell down to the reservoir and it was recycled to the feed side. The dry gas through condenser was discharged from the vacuum pump, and its flow rate was measured by a digital soap-film flow meter. The gas composition was determined by a gas chromatograph (Yanaco, GC-2800, column Porapak Q for CO2 and (N2+O2) analysis, and molecular sieve 5A for N2 and O2 analysis). The performance of the module was calculated by the same procedure reported in our previous paper [1]. 

Soap-film flow meter A modified form of the soap film flow meter used by Krishnamurthi, Kumar, Datta, and Kuloor (K10) for collecting bubbles at atmospheric pressures is shown in Fig. 2. This device, which makes use of the movement of a soap film in a burette, can also be employed to calibrate low rate gas flow meters. Gas enters the apparatus from the top. A soap film is formed at the tip of the calibrated burette by raising a metallic loop dipped in soap solution. A water-seal is used to prevent the gas from escaping through... 

Fig. 2. Modified form of soap film flow meter.

Fig. 7.11. Soap-film flow meter. Soap solution is poured into the rubber bulb so that the solution level is just below the level of the sidearm. After attaching the flexible lubing to the flowing gas source, the rubber bulb is gently squeezed. This allows the flowing gas to percolate through the soap solution, picking up a thin film of soap which will travel up the burel. By noting how long it takes for the film to travel between two points on the buret, the flow may be determined.

The flow at the outlet, F0, is usually measured at ambient temperature with a soap film flow meter. In that case, several corrections must be applied to get the desired flow Fc. 

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. 

Figure 2 Atmospheric pressure g.l.c. apparatus. (A) Carrier gas cylinder , (B) pressure regulator, (C) injection block, (D) column , (E) manometer , (F) katharometer detector, (G) soap-film flow meter. The dotted lines refer to the thermostat...

First, measure the flow rate out of the split vent using a suitable flow meter (soap film flow meter or electronic flow meter). Then, inject a 5 microliter sample of methane and record its retention time. 

Figure 2.33 On-line coupled simultaneous DTA/DSC-EGD apparatus. 1, Gas cylinder 2, reducer valve 3, gas drying 4, governor valve 5, buffer 6, float meter 7, preheater 8, controlled temperature unit 9, bridge 10, fourway valve 11, gas conduit 12, crucible 13, furnace 14, infrared lamp 15, controlled temperature programmer 16, power compensation unit 17, DTA amplifier unit 18, three-way valve 19, soap film flow meter 20, rrxrorder for DTA/DSC 21, recorder for EGD 22, selective switch 23, tail gas...

Figure 2.37 Schematic diagram of the DTA-EGD-GC online coupled simultaneous apparatus (reproduced by permission of Tian Ping Instrumental Factory, China). 1, Gas cylinder for DTA system 2, carrier gas (or GC system 3, reducer valve 4, gas drying 5, governor valve 6, float meter 7, six-way valve 8, gasifier, 9, 5A molecular sieve 10, 401 organic support 11, soap film flow meter 12, sampling valve 13, infrared lamp 14, recorder for DTA/T 15, recorder for EGD-GC 16, tail gas...

A soap film flow meter is used almost exclusively to measure the flow rate. The gas is usually passed through the column at a rate of 40-80 cm /mlnute. 

Solutions of the complexes were prepared in spectral grade benzene or carbon tetrachloride solvents, which were deaerated with prepurified nitrogen before use in order to minimize oxidation of the chromium complexes. The flow rate for the SCOT column was determined by injecting 40 to 50y 1 of methane and measuring the time of elution. The resultant linear gas velocity in ft/sec was then converted to volume flow rate in ml/min by the appropriate conversion factors. Flow rates for the packed column were determined by use of a soap-film flow meter. 

The single gas permeation system is illustrated in Fig. 5.5. Pure O2 and pure N2 are introduced into the system at feed pressures of 1-5 bar at ambient temperature. The permeate side of membrane is maintained at atmospheric pressure. A soap film flow meter is used to measure the gas permeation rate. 

A2.1 Column flow rate can be measured directly on some instruments at the flame ionization detector jet using a soap film flow-meter. This is the preferred way as long as all other gas flows can be turned off during the measurement. 

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