Design of laboratory experiment

Although this issue will be discussed in Chapter 5 in the context of the design of laboratory experiments on biodegradation and biotransformation and in... 

In some upper-level courses and in undergraduate research laboratories, students start to participate in the design of laboratory experiments, usually under the watchful eye of an instructor or research mentor. For these experiences, it is very important to consider the safety of a procedure in the process of designing a new experiment. 

The design of subsequent experiments depends on one s early findings thus, care and skepticism must be exercised at the outset. From the first result in the laboratory, the investigator begins to formulate a model and to make plans to test it. Learning how to do so is a major goal for a person doing work in kinetics. 

Because of the difficulty in obtaining pure cultures of anaerobic bacteria, use has been made of anaerobic sediment slurries in laboratory experiments. In some of these, although no enrichment was deliberately incorporated, experiments were carried out over long periods of time in the presence of contaminated sediments and adaptation of the natural flora to the xenobiotic during exposure in the laboratory might therefore have taken place. The design of these experiments may also inevitably result in interpretative difficulties. A few illustrations are provided ... 

An experiment on toluene biodegradation under field and laboratory conditions provided results of value in the design of laboratory simulation experiments, and illustrated the caution required in assessing the fate of contaminants. Experiments were carried out under three conditions (i) in flow-through horizontal columns containing sediment and rocks, (ii) in shaking cultures containing sediments, rocks, or plant material, and (iii) in situ in a contaminated stream (Cohen et al. 1995). There were a number of important conclusions ... 

As will be discussed in the following section, a variety of experimental designs are available and have been described to conduct such transport studies. While these variations are all available, the choice of a system and design of the experiment will be dictated by the information desired from the study. However, as illustrated in the applications section, if the variables present in the experimental design are taken into proper consideration, it will be possible to extract mechanistic information which is essentially independent of the system used. In this way it should be possible to compare results from one system or laboratory with those of another. 

Example 2-3 Scale-Up of Pipe Flow. We would like to know the total pressure driving force (AP) required to pump oil (/z = 30 cP, p = 0.85 g/cm3) through a horizontal pipeline with a diameter (D) of 48 in. and a length (L) of 700 mi, at a flow rate (Q) of 1 million barrels per day. The pipe is to be of commercial steel, which has an equivalent roughness (e) of 0.0018 in. To get this information, we want to design a laboratory experiment in which the laboratory model (m) and the full-scale field pipeline (f) are operating under dynamically similar conditions so that measurements of AP in the model can be scaled up directly to find AP in the field. The necessary conditions for dynamic similarity for this system are... 

You want to determine the thickness of the film when a Newtonian fluid flows uniformly down an inclined plane at an angle 6 with the horizontal at a specified flow rate. To do this, you design a laboratory experiment from which you can scale up measured values to any other Newtonian fluid under corresponding conditions. 

Festing, M.F.W., Overend, P., Gaines Das, R., Cortina Borja, M., and Berdoy, M., Laboratory Animal Handbooks No. 14, The Design of Animal Experiments, Published for Laboratory Animals Ltd by Royal Society of Medicine Press Ltd, London, 2003, pp. 71-83. 

Vessels under vacuum do not explode but implode, and the consequences may be significantly worse than the pressure difference of 1 atm suggests. Implosions are, however, very rare and usually result from apparatus being incorrectly designed or handled. The author, with 40 years of laboratory experience, has never seen an implosion. 

Unfortunately, many of the chemical processes which are important industrially are quite complex. A complete description of the kinetics of a process, including byproduct formation as well as the main chemical reaction, may involve several individual reactions, some occurring simultaneously, some proceeding in a consecutive manner. Often the results of laboratory experiments in such cases are ambiguous and, even if complete elucidation of such a complex reaction pattern is possible, it may take several man-years of experimental effort. Whereas ideally the design engineer would like to have a complete set of rate equations for all the reactions involved in a process, in practice the data available to him often fall far short of this. 

Technique Selection. The design of an experiment is dictated by the nature of the analytical techniques available. The "alphabet soup" of surface methods provide many alternatives to the researcher, but they also add confusion because few workers have a complete array of methods at their laboratory nor do they have a working knowledge of the many possible techniques. Comparison charts, such as Table II (also see ref. 25) can help in selection of appropriate techniques, but operator experience, equipment style and accessories, and availability all make important differences. Frequently it is useful to apply two or more complimentary methods to solve a problem. The different types of data can be used to confirm or rule out any particular model or theory. 

FRANK and KOWALSKI [1982] also state Chemometric tools are vehicles that can aid chemists to move more efficiently on the path from measurements to information to knowledge . Another formulation is given by KATEMAN [1988] Chemometrics is the ... nonmaterial part of analytical chemistry . Expressed in other words [BRERETON, 1990] Chemometrics is a collection of methods for the design and analysis of laboratory experiments, most, but not all, chemically based. Chemometrics is about using available resources as efficiently as practicable, and arriving at as useful a conclusion as possible taking into account limitations of cost, manpower, time, equipment etc. . 

On scaling-up the equipment, the surface-to-volume ratio decreases, which limits the heat removal in production machines. Moreover, in production-size machines thermal inhomogeneities may occur that do not exist in laboratory equipment This requires a careful design of the experiments on laboratory scale in order to assure a reliable scale-up procedure. 

An experiment to study the effect of eight factors on blood-glucose readings made by a clinical laboratory testing device was described by Henkin (1986). The factor descriptions and levels are given in Table 1. One factor, A, has two levels whereas each of the other seven factors, B — H, has three levels. The design of the experiment had 18 runs and is shown, together with the data, in Table 2. 

Besides analyzing and correlating data by statistical means, the chemical engineer also uses statistics in the development of quality control to establish acceptable limits of process variables and in the design of laboratory, pilot plant, and process plant (evolutionary operation) experiments. In the latter application, statistical strategy in the design of experiments enables the engineer to set experimental variables at levels that will yield maximum information with a minimum amount of data. 

The quantitative description of these mechanisms is required for the construction of meaningful flow simulators that can be scaled up from the dimensions of laboratory experiments to the dimensions of field use, and for scientifically based surfactant design. 

The first order of business in the study of a new reaction in the context of process research and development is to measure reaction rates, establish approximate reaction orders for empirical power-law rate equations, and obtain values of their apparent rate coefficients. This chapter presents a brief overview of laboratory equipment, design of kinetic experiments, and evaluation of their results. It is intended as a tour guide for the practical chemist or engineer. More complete and detailed descriptions can be found in standard texts on reaction engineering and kinetics [G1-G7],... 

Since the effectiveness of a separate particle vanadium trap such as RV4+ depends on the ability of the vanadium to migrate from the catalyst to the trap, a number of laboratory experiments and commercial evaluations were designed to measure vanadium mobility. Vanadium mobility can be discussed in terms of intraparticle mobility, interparticle mobility from the catalyst to the trap, and interparticle mobility from the trap to the catalyst (irreversibility). These three areas are discussed below[6]. 

In recent years, it has become possible to extrapolate accurately using detailed chemical kinetic models to predict quantitatively the behavior of some rather complicated chemical systems. The most famous examples of this success are the detailed atmospheric chemistry models whose predictions underlie the Montreal Protocol on ozone-depleting chemicals. However, these atmospheric chemistry models were developed through a huge international effort over several decades, based heavily on a large number of laboratory experiments. Much more rapid and efficient methods of model development are required for detailed predictive chemical kinetics to become a practical everyday design tool for chemical engineering. 

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