SAMPLE CALCULATIONS 1 Unit Operations

In Fig. 30-25, representation of the fault detection monitoring activity, there appears to be two distinct time periods of unit operation with a transition period between the two. The mean parameter value and corresponding sample standard deviation can be calculated for each time. These means can be tested by setting the null hypothesis that the means are the same and performing the appropriate t-test. Rejecting the null hypothesis indicates that there may have been a shift in operation of the unit. Diagnosis (troubleshooting) is the next step. 

Quite a few years ago, Dr. Azbel and I analyzed the operational requirements for these machines and developed some design formulae. You can find this analysis on pages 646 through 665 in Fluid Mechanics and Unit Operations, David S. Azbel and Nicholas P. Cheremisinoff, Ann Arbor Science Publishers, 1983. There are some sample calculations and sizing criteria that you can follow for some practical exercises in this publication. 

This section presents sample calculations to aid the reader in understanding the calculations behind the development of a fuel cell power system. The sample calculations are arranged topically with unit operations in Section 10.1, system issues in Section 10.2, supporting calculations in Section 10.3, and cost calculations in Section 10.4. A list of conversion factors common to fuel cell systems analysis is presented in Section 10.5 ans a sample automotive design calculation is presented in Section 10.6. 

Knowledge of statistics (Chapter 26) is basic to effective handling of the last unit operation, evaluation of data. Many chemists rarely go beyond a calculation of the standard deviation for a set of determinations and have the erroneous notion that the use of more advanced statistical methods is restricted to enormous bodies of data. A point often overlooked is that a relatively small number of systematically planned observations may yield more information than a larger number of repeated identical observations. For example, in the simple matter of running triplicate analyses of a sample, it may be best to weigh three samples of substantially different sizes. The results obtained may reveal determinate errors that would be unsuspected with samples of equal size. 

There are many dcliniiions of aulomalion. bui (he practical meaning is the performance of operations without human intervention. In the context of analytical chemistry, automation may involve operations like the preparation of samples, the measurement of responses, and the calculation of results. Tigure 3,1-1 illustrates the common steps in a typical chemical analysis and the automation methods used. In some cases, one or more of the steps shown on the left of the figure can be omitted. For example, if the sample is already a liquid, the dissolution step can he omitted. Likewise, if the method is highly selective, the separation step may be unnecessary. The steps listed in Figure 33-1 are sometimes called unit operations. 

The above system of directly sensing a process stream without more is often not sufficiently accurate for process control so, robot titration is preferred in that case by means of for instance the microcomputerized (64K) Titro-Analyzer ADI 2015 (see Fig. 5.28) or its more flexible type ADI 2020 (handling even four sample streams) recently developed by Applikon Dependable Instruments20. These analyzers take a sample directly from process line(s), size it, run the complete analysis and transmit the calculated result(s) to process operation (or control) they allow for a wide range of analyses (potentiometric, amperometric and colorimetric) by means of titrations to a fixed end-point or to a full curve with either single or multiple equivalent points direct measurements with or without (standard) addition of auxiliary reagents can be presented in any units (pH, mV, temperature, etc.) required. 

Whereas the microprocessor controls an individual basic operation, the central computer, which has all the analytical procedures held in its memory, controls the particular analytical procedure required. At the appropriate time, the central computer transmits the relevant set of parameters to the corresponding units and provides the schedule for the sample-transport operation. All units are monitored to ensure proper functioning. If one of the units signals an error, a predetermined action, such as disposing of the sample, is taken. The basic results from the units are transferred to the central computer, the final results are calculated, and the report is passed to the output terminal. These results can also be transmitted to other data processing equipment for administrative or management purposes. The central control is, therefore, the leading element in a hierarchy of... 

Several companies supply density equipment which was considered suitable for automatic, continuous operation with sufficient precision for calculation of polymerization conversion. These break down into three classes based on mode of operation y-ray absorption, oscillatory frequency of a sample filled tube, and mass measurement at fixed volume. Only one of these, an oscillator-based system distributed by Mettler Instrument Corp. (representing Anton Paar Ag.) has models with dead volumes small enough for laboratory scale experimentation. The other units generally also suffered from narrow density spans when the precision was sufficient for conversion studies. Table... 

PCDD/PCDF in soil are the contaminants of concern for this project. The required information is the concentrations of PCDD/PCDF in soil, expressed in the units of 2,3,7,8-tetrachlorodibenzodioxin (2,3,7,8-TCDD) toxicity equivalents (TEQ). The TEQ is a calculated value, which contains all of the PCDD/PCDF homologue concentrations factored in according to their toxicity. YOCs are the contaminants of concern for this project. The required information is the VOC concentrations in the effluent water stream. To support decisions related to the treatment system operation, YOC concentrations in influent samples are also required. 

Before using the pH electrode, it should be calibrated using two (or more) buffers of known pH. Many standard buffers are commercially available, with an accuracy of 0.01 pH unit. Calibration must be performed at the same temperature at which the measurement will be made care must be taken to match the temperature of samples and standards. The exact procedure depends on the model of pH meter used. Modern pH meters, such as the one shown in Figure 5.8, are microcomputer-controlled, and allow double-point calibration, slope calculation, temperature adjustment, and accuracy to +0.001 pH unit, all with few basic steps. The electrode must be stored in an aqueous solution when not in use, so that the hydrated gel layer of the glass does not dry out. A highly stable response can thus be obtained over long time periods. As with other ion-selective electrodes, the operator should consult the manufacturer s instructions for proper use. Commercial glass electrodes are remarkably... 

An efficient slurry health monitoring tool should be able to provide both chemical as well as abrasive particle information on a continuous basis. There have been some efforts in this direction using an NIR absorption spectrum based analyzer [19]. This unit can provide oxidizer concentration and abrasive particle information in CMP slurry and operates on the principles of chemometrics, which is a two-phase process. In the first calibration phase, samples with known property values are measured by the system. A mathematical procedure then determines the correlation between the measured spectra and the true property values. The output of this phase is a model that optimally calculates the parameter values from the measured spectra of the calibration samples. In the second measurement phase, unknown samples are measured by the system, employing a model to produce estimates of the property values. 

There are two problems that must be anticipated, however. First sufficient cellulosic resin must be added. This may be determined by removing small samples of the solution and determining the amount of resin needed to bind as much protein as will bind. Once this has been done the amount of resin needed per unit weight of soluble protein may be calculated. In practice, this allows one to perform a simple biuret protein determination and calculate the quantity of resin needed. It is also advisable to spend a small amount of time determining which of the cellulosic resins (i.e., DEAE, CM, cellulose phosphate) and which experimental conditions yield the best results on a small scale before proceeding to large scale operations. 

A comprehensive report should be issued upon completion of the test procedures, which should include all values measured for compliance, a listing of all test equipment, calculations, conversions, and all appropriate statistical justification along with comments pertaining to system function and operation. A dated test-completion or certification sticker should be affixed to the LAP unit referring any examining authority to the completed test report. All reports should include floor plans or maps of the clean space, which identify sample locations, probe heights. 

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