Flow control and measurement

The hydrogenation of isophorone and ethyl pyruvate was carried out in methanolic solution at 25 C and 1-50 bar hydrogen pressure in a conventional apparatus or in a Biichi BEP 280 autoclave equipped with a magnetically driven turbine stirrer and a gas-flow controlling and measuring unit. Before hydrogenation the reaction mixtures were stirred under nitrogen for 10 minutes in the reaction vessel. 

The moisture content of the gas entering the chimney shall be <0.1% (m/m) and the variation in oxygen concentration rising in the chimney, below the level of the test specimen, is <0.2% (VAO. The flow control and measuring devices shall he such that the volmnetric flow of each gas into the colmnn is within 1% of the range being used. 

M G Guvenc V-Groove capillary for low flow control and measurement, Micromachimng and Micropackaging of Transducers, Elsevier Amsterdam(1985) 215-223... 

Many of the earlier studies of mass transfer involved measuring the rate of vaporisation of liquids by passing a turbulent air stream over a liquid surface. In addition, some investigations have been carried out in the absence of air flow, under what have been termed still air conditions. Most of these experiments have been carried out in some form of wind tunnel where the rate of flow of air and its temperature and humidity could be controlled and measured. In these experiments it was found to be important to keep the surface of the liquid level with the rim of the pan in order to avoid the generation of eddies at the leading edge. 

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]. 

An experimental fluidized bed reactor has a 2.5 cm in diameter and 230 cm in height, and the distributor has 32 holes and each hole was 2 mm in diameter. 200 mesh net was put on the distributor to prevent particles from falhng down. The cyclone was made by standard proportion to collect fine particles. Air flow rate was controlled by a flow meter, CO2 (99.9%) flow rate was controlled by mass flow controller and then 10% CO2 inlet concentration was maintained by mixing in a mixing chamber. CO2 outlet concentration was also measured by CO2 analyzer (CD 95, Geotechnical instruments, England). 

The catalysts were tested for their CO oxidation activity in an automated microreactor apparatus. The catalysts were tested at space velocities of 7,000 -60,000 hr . A small quantity of catalyst (typically 0.1 - 0.5 g.) was supported on a frit in a quartz microreactor. The composition of the gases to the inlet of the reactor was controlled by mass flow controllers and was CO = 50 ppm, CO2 = 0, or 7,000 ppm, HjO = 40% relative humidity (at 25°C), balance air. These conditions are typical of conditions found in spacecraft cabin atmospheres. The temperature of the catalyst bed was measured with a thermocouple placed half way into the catalyst bed, and controlled using a temperature controller. The inlet and outlet CO/CO2 concentrations were measured by non-dispersive infrared (NDIR) monitors. 

Basic Process Control System (BPCS) - Pneumatic, electronic, hydraulic or programmable instruments and mechanisms that monitor and/or operate a facility or system to achieve a desired function, i.e., flow control, temperature measurement, etc., which are supervised by human observation. 

The problems associated with the measurement and control of the flowrate of solids are much more complicated than those in the corresponding situation with liquids. The flow characteristics will depend, not only on particle size, size range and shape, but also on how densely the particles are packed. In addition, surface and electrical properties and moisture content all exert a strong influence on flow behaviour, and the combined effect of these factors is almost impossible to predict in advance. It is therefore desirable to carry out a preliminary qualitative assessment before making a selection of the, most appropriate technique for controlling and measuring flowrate for any particular application. 

The physical properties of a tracer gas must also be considered since control and measuring devices usually respond to mass flow rates or thermal conductivity. Thus, the response to pure C02 or methane would differ substantially from air, although correction factors can often be calculated. 

When chemists talk about an analytical method or when instrument vendors tout their products, they often quote the standard deviation that is achievable with the method or instrument as a measure of quality. For example, the manufacturer of an HPLC pump may declare that the digital flow control for the pump, with flow rates from 0.01 to 9.99 mL per minute, has a RSD less than 0.5%, or a chemist declares that her atomic absorption instrument gives results within 0.5% RSD. The most fundamental point about standard deviation is that the smaller it is, the better, because the smaller it is, the more precise the data (the more tightly bunched the data are around the mean) and, if free of bias, the greater the chance that the data are more accurate. Chemists have come to know through experience that a 0.5% RSD for the flow controller and, under the best of circumstances, a 0.5% RSD for atomic absorption results are favorable RSD values compared to other comparable instruments or methods. 

Nevertheless, in laboratory batch tests on the (multi-)sequential chemical/biological treatment suspended biomass is normally used to determine the biological fraction of DOC since the amount of biomass added to each batch is easier to control and measure (and indeed no washout is possible) (Karrer et al., 1997 Jochimsen, 1997). In most cases the operation of a continuous-flow sequential ozonation/biodegradation unit cannot be recommended without having performed batch tests before. 

The higher concentrations of the sample needed for the NMR method compared with other physical methods is a drawback, as also is the lower precision in the determination of rate constants. The latter is usually because the temperature of the sample in the NMR probe is controlled by a flow of heated or cooled nitrogen which does not normally provide highly accurate temperature control and measurement. Sometimes, the need for isotopically labelled substrates and solvents can be an additional drawback. 

The numerous reasons which can account for various deviations from the ideal FFF retention theory were discussed in the corresponding sections. Here, additional problems are treated which can complicate FFF measurements and significantly distort the results obtained. General requirements for a successful FFF measurement include precise flow control and flow rate precise temperature measurement precise determination of t0 and tr correct relaxation procedure control of sample overloading and integrity and control of mixed normal and steric retention effects as well as wall adsorption control. Some of these complications cannot be avoided so one must correct for these effects, usually in a sem-iempirical and partially very complicated fashion. 

Both of these control structures have the slight disadvantage cf lacking a single direct handle to set production rate, i.e., a one-to-one relationship with product flow. Desired throughput must be achieved by changing the setpoint of the reactor concentration controller, the reactor level controller, the reactor effluent flow controller, and/or the recycle flow controllers (one or both). Structure CS4 has another disadvantage since it requires a composition measurement, which can be very expensive and unreliable in many systems. 

The specific surface area of eement is eommonly determined directly by air. permeability methods. In the Lea and Nurse method (LI 5). a bed of cement / of porosity 0.475 is eontained in a cell through which a stream of air is f passed, and steady flow established. The specific surface area is caleulated ( from the density of the eement, the porosity and dimensions of the bed of j powder, the pressure differenee aeross the bed, and the rate of flow and ] kinematie viscosity of the air. In the Blaine method (B36), a fixed volume of I air passes through the bed at a steadily deereasing rate, whieh is controlled / and measured by the movement of oil in a manometer, the time required i being measured. The apparatus is ealibrated empirically, most obviously / using a cement that has also been examined by the Lea and Nurse method. The two methods gave elosely similar results. The Blaine method, though not absolute, is simpler to operate and automated variants of it have been devised. 

Calculated RON values corresponded to engine values of debutanized reformate samples (25 samples) with a standard deviation of 0.55 RON units, which is close to the accuracy of engine measurements. By carrying out a number of repeated test runs, the reproducibility taken as the standard deviation for the measured reformate and hydrogen yields were determined as 0.25 and 0.02 wt%, respectively, and 0.25 units for RON. In order to achieve this a detailed calibration of the GC system was carried out, and the reactor thermocouples, the hydrogen mass flow controllers and naphtha feed pumps were thoroughly calibrated between each test run. 

Now, we shall present an inexpensive means to meter small flows of gas. Accurately controlling and measuring such flowrates is often difficult. Control valves with small trims coupled to differential-pressure transmitters having small orifices (or long capillaries) are prone to plugging and calibration troubles. On the other hand, most mass flowmeters are expensive for small-scale uses. 

---