Rate measurements accuracy

Electromagnetic flow meters ate available in essentially all pipe si2es, ie, 1 mm to 3 m, and provide measurement accuracy of 1% of rate or better over wide ranges. The meters are obstmctionless, have no moving parts, and are extremely mgged. Pressure loss is that of an equivalent section of pipe. 

An eluted solute was originally identified from its corrected retention volume which was calculated from its corrected retention time. It follows that the accuracy of the measurement depended on the measurement and constancy of the mobile phase flow rate. To eliminate the errors involved in flow rate measurement, particularly for mobile phases that were compressible, the capacity ratio of a solute (k ) was introduced. The capacity ratio of a solute is defined as the ratio of its distribution coefficient to the phase ratio (a) of the column, where... 

In principle, pulsed excitation measurements can provide direct observation of time-resolved polarization decays and permit the single-exponential or multiexponential nature of the decay curves to be measured. In practice, however, accurate quantification of a multiexponential curve often requires that the emission decay be measured down to low intensity values, where obtaining a satisfactory signal -to-noise ratio can be a time-consuming process. In addition, the accuracy of rotational rate measurements close to a nanosecond or less are severely limited by tbe pulse width of the flash lamps. As a result, pulsed-excitation polarization measurements are not commonly used for short rotational periods or for careful measurements of rotational anisotropy. 

Visual proof of linear kinetics, making obvious the occurrence of undesirable conditions such as substrate depletion or lag phase non-linearity. Visual display of changes in the reaction rate. Maximum accuracy as the measurement can be made in the region of maximum linear velocity. 

The advantage of using the time lag method is that the partition coefficient K can be determined simultaneously. However, the accuracy of this approach may be limited if the membrane swells. With D determined by Eq. (12) and the steady-state permeation rate measured experimentally, K can be calculated by Eq. (10). In the case of a variable D(c ), equations have been derived for the time lag [6,7], However, this requires that the functional dependence of D on Ci be known. Details of this approach have been discussed by Meares [7], The characteristics of systems in which permeation occurs only by diffusion can be summarized as follows ... 

The versatility and accuracy of the oxygen consumption method in heat release measurement was demonstrated. The critical measurements include flow rates and species concentrations. Some assumptions need to be invoked about (a) heat release per unit oxygen consumed and (b) chemical expansion factor, when flow rate into the system is not known. Errors in these assumptions are acceptable. As shown, the oxygen consumption method can be applied successfully in a fire endurance test to obtain heat release rates. Heat release rates can be useful for evaluating the performance of assemblies and can provide measures of heat contribution by the assemblies. The implementation of the heat release rate measurement in fire endurance testing depends on the design of the furnace. If the furnace has a stack or duct system in which gas flow and species concentrations can be measured, the calorimetry method is feasible. The information obtained can be useful in understanding the fire environment in which assemblies are tested. 

Selected entries from Methods in Enzymology [vol, page(s)] Analysis of GTP-binding/GTPase cycle of G protein, 237, 411-412 applications, 240, 216-217, 247 246, 301-302 [diffusion rates, 246, 303 distance of closest approach, 246, 303 DNA (Holliday junctions, 246, 325-326 hybridization, 246, 324 structure, 246, 322-324) dye development, 246, 303, 328 reaction kinetics, 246, 18, 302-303, 322] computer programs for testing, 240, 243-247 conformational distribution determination, 240, 247-253 decay evaluation [donor fluorescence decay, 240, 230-234, 249-250, 252 exponential approximation of exact theoretical decay, 240, 222-229 linked systems, 240, 234-237, 249-253 randomly distributed fluorophores, 240, 237-243] diffusion coefficient determination, 240, 248, 250-251 diffusion-enhanced FRET, 246, 326-328 distance measurement [accuracy, 246, 330 effect of dye orientation, 246, 305, 312-313 limitations, 246,... 

In cases where an acceptable kinetic mechanism can be established, it may be possible to obtain expressions, such as those in Sect. 2, which predict concentration changes with time when the values for the rate coefficients are known. However, the use of these expressions to evaluate rate coefficients from experimental data is not always straightforward, particularly with coupled reaction systems where a key reactant participants in a reversible step. Initial rate measurements are often of insufficient accuracy and, with very complex sj stems, it becomes necessary to obtain a great deal of data from experiments in which initial concentrations can be varied. 

The first tests of this proposed method have been encouraging. On the basis of comparisons between rainfall rates measured with the differential reflectivity technique and with a network of rain gauges, Seliga et al. (1981) concluded that these first measurements of rainfall using the ZDR technique support the theoretical expectations... that rainfall rate measurements with radar can be made with good accuracy. So it may yet be possible to accurately measure rainfall with radar—provided that measurements are made with two orthogonally polarized beams. This exemplifies one of the principal themes of this book scattered polarized radiation contains information that may be put to good use. 

Here the vertical bars designate an absolute value. A relative accuracy of 5-10 % for the reaction rate measurements is satisfactory for practical purposes, so d = 0.05 - 0.1. 

To elucidate the significance of the accuracy of concentration and flow rate measurements, two ideal situations in the reactor which are usually assumed to occur in the experimental data collection are considered ... 

Several effects can play a role in the temperature measurement accuracy. Due to the small channel length, the temperature difference between the channel outlet and inlet can be as small as the sensor sensitivity. Thermocouples can have a size comparable to the channel dimensions and where is measured the temperature is questionable. Moreover, the heat flow rate through the thermocouple itself can be not negligible. The importance of these effects must be appreciated. 

Accuracy of the diaphragm gas meter is verified against either a wet test meter or a Sierra instruments 616 E-36 hot wire aneomemeter. On a yearly basis, a third party laboratory verifies chamber operation and air exchange rate measurements. The carbon monoxide decay is the method used to verify air exchange rate measurements(13). However, other researchers have reported using formaldehyde, propane, sulfur hexafluoride, and carbon dioxide as... 

The value of Eq. (2-8) rests substantially on the accuracy with which it represents experimental rate-temperature data (see Example 2-1). When measured rates do not agree with the theory it is usually found that the reaction is not an elementary step or that physical resistances are affecting the measurements. In other words, Eq. (2-8) correlates remarkably well the rate measurements for single reactions free of diffusion and thermal resistances. The Arrhenius equation provides no basis for discerning the value of E. However, Fig. 2-1 indicates that the activation energy must be greater than the heat of the overall reaction, AH, for an endothermic case. 

When the rate is measured for a catalyst pellet and for small particles, and the diffusivity is also measured or predicted, it is possible to obtain both an experimental and a calculated result for rj. For example, for a first-order reaction Eq. (11-67) gives directly. Then the rate measured for the small particles can be used in Eq. (11-66) to obtain k. Provided is known, d) can be evaluated from Eq. (11-50) for a spherical pellet or from Eq. (11-56) for a fiat plate of.catalyst. Then 7caic is obtained from the proper curve in Fig. 11-7. Comparison of the experimental and calculated values is an overall measure of the accuracy of the rate data, effective diffusivity, and the assumption that the intrinsic rate of reaction (or catalyst activity) is the same for the pellet and the small particles. Example 11-8 illustrates the calculations and results for a flat-plate pellet of NiO catalyst, on an alumina carrier, used for the ortho-para-hydrogen conversion. 

At the same time it is clear that such a setting makes accurate rate measurements difficult. The sticking coefficient is determined by [NJN — 1] and for N0jN 1 this ratio would have to be known with great accuracy. In the other extreme, when SF SE we can approximate a closed system. This maximizes the pressure drop in the cell on adsorption, but brings with it all the evils of a closed system. In practice, the adjustment of SE/SF must therefore be varied to suit each system. 

The measurement accuracy was experimentally determined by positioning the tracer in known locations inside the bed (Moslemian, 1987). The apparent tracer positions were calculated from the linear regression formulation Eq. 9.13, based on the measured detector count rates and the predetermined calibrations. Sufficient data were taken at each location to allow for statistical determination of mean and standard deviations of the tracer position and velocity. In general, the axial errors were often greater than the radial errors because of the longer axial distance of the bed that the detectors had to monitor. For an empty bed, the mean axial error in determining the tracer position was 4.7 mm and the mean radial error was 3.9 mm The corresponding standard deviations were 1.6 mm in the axial direction and 1.2 mm in the radial direction. These deviations were due to the statistical nature of the radiation detection and are the minimum deviations obtainable for the tracer position. The measured mean axial and radial velocities were approximately zero (<1 cm/s) at all locations inside the bed. However, the standard deviations of the velocities were 7.6 cm/s in the... 

The rotational speed of the rotor, or turbine, increases linearly with flow velocity within + 0.5% over a wide flow range from 10 1 to 20 1 [10]. The turbine speed is typically measured by detecting the pulse of each blade electrically, mechanically, or optically each pulse represents a certain volume of fluid. The flow rate of the fluid is determined by integrating the total number of pulses over a period of time. The accuracy of these meters is better than 1% over a wide range of flow rates [4]. Accuracy is compromised, however, with blade wear, bearing friction due to wear, and when a vapor enters the line for liquid flows [10]. 

Hornbaker, D. R., and Rail, D. L. "Thermal Perturbations Caused by Heat-Flux Transducers and Their Effect on the Accuracy of Heating-Rate Measurements." ISA Transactions 3 (1964) 123-30. 

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