Bench models

The water sample from the on-s1te test was subsequently deoiled using a bench model flotation unit in the laboratory. A much slower deoiling performance was obtained (Fig. 3). 

Figure 14.1 Atomic emission spectrometer. Basic concept and an example of a bench model of spectrometer, the Vista-Pro, CCD simultaneous ICP-OES (courtesy of Varian Inc, USA)...

As a first step in the development program, a single-stage bench model of the device as shown in Figure 3 was evaluated. 

Munz, Y. et al. "The benefits of stereoscopic vision in robotic-assisted performance on bench models." Surgical Endoscopy and Other Interventional Techniques 18.4 (2004) pp. 611-616. 

Limitations. The electrodeless conductivity technique using low-frecjuency inductive cells is available for analysis and control in the chemical process industries and in other continuous monitoring applications. Although its stability, freedom from maintenance, and accuracy, are superior to contacting conductivity techniques, lack of bench models of this type has hindered its laboratory use and application to date. 

Scott DJ, et al. Laparoscopic training on bench models better and more cost effective than operating room experience Am CoU Surg 2000 191(3) 272-83. 

Simulators are developed primarily for the procedure(s) they are designed to emulate. Surgical simulators can include animal models, cadavers, synthetic and tissue-based bench models, computer/web-based simulators, video box trainers, web-based interface simulators, VR (or computer driven) part-task trainers, VR simulators that can allow the user to mimic an entire surgical procedure (whole-task trainers), hybrid simulators... 

Figure 10.3 Reusable synthetic bench models for incisions, suturing, knot tying, and other types of part-task training simulations. ( McMaster University.)...

Haber s laboratory version of ammonia synthesis was indisputably effective, but even after Brunck made the decision that BASF should proceed with the commercialization of the discovery doubts persisted inside the company about the success of such a costly, and seemingly open-ended, exercise. Given the absence of any precedent for running continuous catalytic synthetic reactions at snch high pressures and temperatures, it was only reasonable to expect that even with intensive effort it would take a very long time to transform Haber s bench model to a smoothly operating commercial plant. ... 

In general, the desorptive behavior of contaminated soils and soHds is so variable that the requited thermal treatment conditions are difficult to specify without experimental measurements. Experiments are most easily performed in bench- and pilot-scale faciUties. Full-scale behavior can then be predicted using mathematical models of heat transfer, mass transfer, and chemical kinetics. 

One goal of catalyst designers is to constmct bench-scale reactors that allow determination of performance data truly indicative of performance in a full-scale commercial reactor. This has been accompHshed in a number of areas, but in general, larger pilot-scale reactors are preferred because they can be more fully instmmented and can provide better engineering data for ultimate scale-up. In reactor selection thought must be given to parameters such as space velocity, linear velocity, and the number of catalyst bodies per reactor diameter in order to properly model heat- and mass-transfer effects. 

Over 25 years ago the coking factor of the radiant coil was empirically correlated to operating conditions (48). It has been assumed that the mass transfer of coke precursors from the bulk of the gas to the walls was controlling the rate of deposition (39). Kinetic models (24,49,50) were developed based on the chemical reaction at the wall as a controlling step. Bench-scale data (51—53) appear to indicate that a chemical reaction controls. However, flow regimes of bench-scale reactors are so different from the commercial furnaces that scale-up of bench-scale results caimot be confidently appHed to commercial furnaces. For example. Figure 3 shows the coke deposited on a controlled cylindrical specimen in a continuous stirred tank reactor (CSTR) and the rate of coke deposition. The deposition rate decreases with time and attains a pseudo steady value. Though this is achieved in a matter of rninutes in bench-scale reactors, it takes a few days in a commercial furnace. 

Catalytic crackings operations have been simulated by mathematical models, with the aid of computers. The computer programs are the end result of a very extensive research effort in pilot and bench scale units. Many sets of calculations are carried out to optimize design of new units, operation of existing plants, choice of feedstocks, and other variables subject to control. A background knowledge of the correlations used in the "black box" helps to make such studies more effective. 

A schematic diagram of the version of the Aaberg slot exhaust (ASE) system is shown in Fig. 10.81. It consists of a horizontal bench to which a vertical flange is attached, housing a rectangular exhaust slot and jet nozzle. Figure 10.82 shows the two-dimensional geometry and the coordinate system of the ASE model. 

Potential Flow Model for a Bench Slot Exhaust... 

A similar mathematical model to that just described for bench slot exhausts can again be used, but in this case the Laplace equation should be employed in a cylindrical coordinate system (see Fig. 10.83), namely,... 

One goal of our experimental program with the bench-scale unit was to develop the necessary correlations for use in the ultimate design of large commercial plants. Because of the complexity inherent in the three-phase gas-liquid-solid reaction systems, many models can be postulated. In order to provide a background for the final selection of the reaction model, we shall first review briefly the three-phase system. 

This provides a very strong tool for communicating explanations, as the teacher can move between discussing the bench phenomena and the (sub-microscopic) explanatory models readily. By presenting an equation that describes the reaction (a macroscopic phenomena that students can see etc.) in a form that directly links to the molecules or other quanticles (ions, etc.) considered to be present at the sub-microscopic level, the symbolic representation acts as a referent to both levels and so at a meta-level also represents the relationship and mapping between substances and quanticles. 

Some experimenting nught be necessary if it turns out that quadratic terms such as improve the fit between the model and the data. However, the relevant point is that such a model is only a means to refine and speed up the process of finding optimal conditions. For this purpose it is counter-productive to try for a perfect fit, it might even be advantageous to keep the model simple and throw out all but the best five to 10 experiments, choose new conditions, and then return to the work bench. 

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