Flow rate parameters

Rheodynamics of non-linear viscous fluids flowing in circular channels with moving walls is described most comprehensively in 1S-34). With respect to the above conclusion (see sect 2.2.1) that the high elasticity of a melt influences insignificantly flow rate parameters of a flow, the combined shear is discussed in 24128-30,341 on the basis of a general approach to the analysis of viscosimetric flows developed by B. Colleman and W. Noll. 

Contrary to expectations based on qualitative explanations commonly found in textbooks, that q represents a fundamental (molecular level) flow rate parameter, the q values show an enormous variation, not only between different polymers, but often also for data collected by different workers on the same polymer. For example, the 0 values obtained for PMMA... 

Vielstich and co-workers [99] modified the analysis of Blaedel and Klatt [66] to derive the steady-state current-potential relationship at the microtubular electrode under turbulent flow conditions. Their analysis assumed that the electrode/cell/flow rate parameters were such that mass transport to the electrode could be considered to be controlled by the laminar sublayer. In terms of the parameter... 

Arbitrarily chosen volumetric flow rate parameter of the variable volume... 

On the drying gas stream interface, one can specify pressure, one of the three temperature parameters (either dry-bulb temperature, wet-bulb temperature, or dew-point temperature), and one of the two humidity parameters (either absolute humidity or relative humidity) then all the other thermal physical property variables are automatically calculated by Simprosys and displayed on the interface. Whenever one of the flow rate parameters (either mass flow rate wet basis, mass flow rate dry basis, or volume flow rate) is specified and the state of the moist air is determined, the other flow rates are automatically calculated and displayed on the gas stream s interface. 

In conclusion, all of these observations indicate that there is still much room to improve ADAFC performance by developing novel materials and, on the other hand, by optimizing the operational conditions of the fuel cell. Future work should look into a wider range of potential low-cost materials and composites with novel structures and properties, presenting catalytic activity comparable to that of noble metals. The development of new catalyst systems is more likely in alkaline media because of the wide range of options for the materials support and catalyst, as compared to acidic media which offer more limited materials choice. Moreover, efforts have to be addressed to meet the durability targets required for commercial application. More work is needed to optimize the operational fuel cell conditions, by achieving suitable chemical (OH concentration, hydroxyl/alcohol ratio in the fuel stream) and physical (temperature, pressure, flow rate) parameters. 

Based on simulation results,i the authors concluded that it is possible to obtain conversions higher than the thermodynamic equilibrium value, for a given set of operating conditions related with the pressure difference between the retentate and permeate sides, Thiele modulus (ratio between a characteristic intramembrane diffusion time and a characteristic direct reaction time), and contact time (ratio between the maximum possible flux across the membrane for a reference component and the total molar feed flow rate) parameters. For a given stoichiometry, the authors found a possible conversion enhancement when, globally, the diffusion coefficients of the reaction products were higher than the ones of the reactants, or vice versa for the sorption coefficients (that is, the ones for the reactants higher than the ones for the reaction products). Also, it was found that an enhancement or a detriment of the conversion could be obtained based solely on the pressure difference between the two sides of the membrane. 

For calculation of the volumetric flow rate only the cross section area of the pipe is to be known. In order to give flow under standard conditions the temperature and pressure must be measured, and for conversion to mass flow the composition or density of the gas must be determined. These process parameters are often monitored by calibrated instrumentation. 

Figure A3.14.3. Example bifurcation diagrams, showing dependence of steady-state concentration in an open system on some experimental parameter such as residence time (inverse flow rate) (a) monotonic dependence (b) bistability (c) tristability (d) isola and (e) musliroom.

The packing parameter ( ) (m) reflects the influence of the Hquid flow rate as shown in Figure 20. reflects the influence of the gas flow rate, staying at unity below 50% of the flooding rate but beginning to decrease above this point. At 75% of the flooding velocity, = 0.6. Sc is the Schmidt number of the Hquid. 

Accuracies of the flow meters discussed herein are specified as either a percentage of the full-scale flow or as a percentage of the actual flow rate. It may be convenient in some appHcations to compare the potential inaccuracies in actual volumetric flow rates. For example, in reading two Hters per minute (LPM) on a flow meter rated for five LPM, the maximum error for a 1% of full-scale accuracy specification would be 0.01 x 5 = 0.05 LPM. If another flow meter of similar range, but having 1% of actual flow rate specification, were used, the maximum error would be 0.01 x 2 = 0.02 LPM. To minimize errors, meters having full-scale accuracy specifications are normally not used at the lower end of their range. Whenever possible, performance parameters should be assessed for the expected installation conditions, not the reference conditions that are the basis of nominal product performance specifications. 

Whereas there is no universally accepted specification for marketed natural gas, standards addressed in the United States are Hsted in Table 6 (8). In addition to these specifications, the combustion behavior of natural gases is frequently characteri2ed by several parameters that aid in assessing the influence of compositional variations on the performance of a gas burner or burner configuration. The parameters of flash-back and blow-off limits help to define the operational limits of a burner with respect to flow rates. The yeUow-tip index helps to define the conditions under which components of the natural gas do not undergo complete combustion, and the characteristic blue flame of natural gas burners begins to show yellow at the flame tip. These... 

The quahtative flow distribution in a manifold can be estimated by examining a streamline plot. Figure 13 shows the streamline plot for the manifold having AR = 4. Note that the same amount of fluid flows between two consecutive streamlines. The area ratio is an important parameter affecting the flow distribution in a manifold, as shown in Figure 14a, which shows the percent flow rate in each channel for three cases. As the area ratio increases, the percent flow rate increases in channels no. 1 and no. 8, whereas the percent flow rate decreases in the middle channels. 

Adaptive Control. An adaptive control strategy is one in which the controller characteristics, ie, the algorithm or the control parameters within it, are automatically adjusted for changes in the dynamic characteristics of the process itself (34). The incentives for an adaptive control strategy generally arise from two factors common in many process plants (/) the process and portions thereof are really nonlinear and (2) the process state, environment, and equipment s performance all vary over time. Because of these factors, the process gain and process time constants vary with process conditions, eg, flow rates and temperatures, and over time. Often such variations do not cause an unacceptable problem. In some instances, however, these variations do cause deterioration in control performance, and the controllers need to be retuned for the different conditions. 

The optoelectronic properties of the i -Si H films depend on many deposition parameters such as the pressure of the gas, flow rate, substrate temperature, power dissipation in the plasma, excitation frequency, anode—cathode distance, gas composition, and electrode configuration. Deposition conditions that are generally employed to produce device-quahty hydrogenated amorphous Si (i -SiH) are as follows gas composition = 100% SiH flow rate is high, --- dO cm pressure is low, 26—80 Pa (200—600 mtorr) deposition temperature = 250° C radio-frequency power is low, <25 mW/cm and the anode—cathode distance is 1-4 cm. 

AH three parameters, the cut size, sharpness index, and apparent bypass, are used to evaluate a size separation device because these are assumed to be independent of the feed size distribution. Other measures, usually termed efficiencies, are also used to evaluate the separation achieved by a size separation device. Because these measures are dependent on the feed size distribution, they are only usefiil when making comparisons for similar feeds. AH measures reduce to either recovery efficiency, classification efficiency, or quantitative efficiency. Recovery efficiency is the ratio of the amount of material less than the cut size in the fine stream to the amount of material less than the cut size in the feed stream. Classification efficiency is defined as a corrected recovery efficiency, ie, the recovery efficiency minus the ratio of the amount of material greater than the cut size in the fine stream to the amount of material greater than the cut size in the feed stream. Quantitative efficiency is the ratio of the sum of the amount of material less than the cut size in the fine stream plus the amount of material greater than the cut size in the coarse stream, to the sum of the amount of material less than the cut size in the feed stream plus the amount of material greater than the cut size in the feed stream. Thus, if the feed stream analyzes 50% less than the cut size and the fine stream analyzes 95% less than the cut size and the fine stream flow rate is one-half the feed stream flow rate, then the recovery efficiency is 95%, the classification efficiency is 90%, and the quantitative efficiency is 95%. 

There are relationships between the independent size separation device parameters and the dependent size separation efficiencies. For example, the apparent bypass value does not affect the size distribution of the fine stream but does affect the circulation ratio, ie, the ratio of the coarse stream flow rate to the fine stream flow rate. The circulation ratio increases as the apparent bypass increases and the sharpness index decreases. Consequendy, the yield, the inverse of the circulating load (the ratio of the feed stream flow rate to the fine stream flow rate or the circulation ratio plus one), decreases hence the efficiencies decrease. For a device having a sharpness index of 1, the recovery efficiency is equal to (1 — a). 

The two steps in the removal of a particle from the Hquid phase by the filter medium are the transport of the suspended particle to the surface of the medium and interaction with the surface to form a bond strong enough to withstand the hydraulic stresses imposed on it by the passage of water over the surface. The transport step is influenced by such physical factors as concentration of the suspension, medium particle size, medium particle-size distribution, temperature, flow rate, and flow time. These parameters have been considered in various empirical relationships that help predict filter performance based on physical factors only (8,9). Attention has also been placed on the interaction between the particles and the filter surface. The mechanisms postulated are based on adsorption (qv) or specific chemical interactions (10). 

In the context of chemometrics, optimization refers to the use of estimated parameters to control and optimize the outcome of experiments. Given a model that relates input variables to the output of a system, it is possible to find the set of inputs that optimizes the output. The system to be optimized may pertain to any type of analytical process, such as increasing resolution in hplc separations, increasing sensitivity in atomic emission spectrometry by controlling fuel and oxidant flow rates (14), or even in industrial processes, to optimize yield of a reaction as a function of input variables, temperature, pressure, and reactant concentration. The outputs ate the dependent variables, usually quantities such as instmment response, yield of a reaction, and resolution, and the input, or independent, variables are typically quantities like instmment settings, reaction conditions, or experimental media. 

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