Scaling experiments

The experimental details for recrystallisation from mixed solvents (or solvent pairs) will be evident from the account already given the best proportions of the two solvents are determined by preliminary small-scale experiments. 

Properties. Silver difluoride melts at 690°C, bods at 700°C, and has a specific gravity of 4.57. It decomposes in contact with water. Silver difluoride may react violently with organic compounds, quite often after an initial induction period. Provisions must be made to dissipate the heat of the reaction. Small-scale experiments must be mn prior to attempting large-scale reactions. 

Acetylene traditionally has been made from coal (coke) via the calcium carbide process. However, laboratory and bench-scale experiments have demonstrated the technical feasibiUty of producing the acetylene by the direct pyrolysis of coal. Researchers in Great Britain (24,28), India (25), and Japan (27) reported appreciable yields of acetylene from the pyrolysis of coal in a hydrogen-enhanced argon plasma. In subsequent work (29), it was shown that the yields could be dramatically increased through the use of a pure hydrogen plasma. 

Process Economics. Relative economics of various ceU culture processes depend heavily on the performance of the ceU line in a system and on the cost of raw materials, particularly the medium. Models are usuaUy developed for the various processes using productivity data obtained from smaU-scale experiments (see Pilot AND MiCROPLANTs). Often, for high value products, the process which ensures the shortest time to market may be the process of choice because of other economic criteria. This is especially tme for pharmaceuticals (qv). RehabUity concerns also often outweigh economic considerations in choosing a process for a high value product. 

In addition, dimensional analysis can be used in the design of scale experiments. For example, if a spherical storage tank of diameter dis to be constmcted, the problem is to determine windload at a velocity p. Equations 34 and 36 indicate that, once the drag coefficient Cg is known, the drag can be calculated from Cg immediately. But Cg is uniquely determined by the value of the Reynolds number Ke. Thus, a scale model can be set up to simulate the Reynolds number of the spherical tank. To this end, let a sphere of diameter tC be immersed in a fluid of density p and viscosity ]1 and towed at the speed of p o. Requiting that this model experiment have the same Reynolds number as the spherical storage tank gives... 

The reaction is slightly exothermic, but no precaution is necessary for a small-scale experiment. It is advisable to cool the flask in a water bath when a large-scale synthesis is carried out. 

To examine sedimentation in greater detail, let us examine the events occurring in a small-scale experiment conducted batchwise, as illustrated in Figure 9. Particles in a narrow size range will settle with about the same velocity. When this occurs, a demarcation line is observed between the supernatant clear liquid (zone A) and... 

Scaling laws If a full-scale test is not possible, reduced-scale experiments are a good alternative. However, certain scaling laws must be observed (see Section 12.4, Scale model experiments ). Correct scaling for isothermal flows is usually possible. However, scaling of buoyant flows in large rooms may be difficult, if not impossible. Then numerical simulation is the better choice. 

Scale model experiments (.Section 12.4) In the case where there is no site to carry out full-scale measurements (planning phase), or it would be too expensive or space-demanding to construct a full-scale experiment (large lacdities/rooms/buildings). 

Measurements show that the velocity has a fairly constant level in the occupied zone even far downstream from the wall with the cooling device. The flow is plane, and general experience indicates that the velocity in a plane stratified flow is constant and independent of the distance from the inlet device. Prediction of the flow by coinpurational fluid dynamics shows a similar velocity level in the hall. - The full-scale measurements shown in Fig. 12.33 indicate a very low velocity in most of the hall due to the practical difficulties in obtaining a correct load during the full-scale experiment. 

The assumption of a self-similar flow (Reynolds number-independent flow) simplifies full-scale experiments and is also a useful tool in the formulation of simple measuring procedures. This section will show two examples of self-similar flow where the Archimedes number is the only important parameter. 

The epimeric 17 -methylandrost-5-ene-3, 17a-diol could be isolated as a by-product from larger scale experiments. Reaction of (49) with ethyl-magnesium halide affords the corresponding 17a-ethyl compound. In this... 

The model is able to predict the influence of mixing on particle properties and kinetic rates on different scales for a continuously operated reactor and a semibatch reactor with different types of impellers and under a wide range of operational conditions. From laboratory-scale experiments, the precipitation kinetics for nucleation, growth, agglomeration and disruption have to be determined (Zauner and Jones, 2000a). The fluid dynamic parameters, i.e. the local specific energy dissipation around the feed point, can be obtained either from CFD or from FDA measurements. In the compartmental SFM, the population balance is solved and the particle properties of the final product are predicted. As the model contains only physical and no phenomenological parameters, it can be used for scale-up. 

Accidental vapor cloud explosions do not occur under controlled conditions. Various experimental programs have been carried out simulating real accidents. Quantities of fuel were spilled, dispersed by natural mechanisms, and ignited. Full-scale experiments on flame propagation in fuel-air clouds are extremely laborious and expensive, so only a few such experiments have been conducted. 

A deflagration-detonation transition was first observed in 1985 in a large-scale experiment with an acetylene-air mixture (Moen et al. 1985). More recent investigations (McKay et al. 1988 and Moen et al. 1989) showing that initiation of detonation in a fuel-air mixture by a burning, turbulent, gas jet is possible, provided the jet is large enough. Early indications are that the diameter of the jet must exceed five times the critical tube diameter, that is approximately 65 times the cell size. 

Explosively Dispersed Vapor Cloud Explosions (Giesbrecht et al. 1981). The Giesbrecht et al. (1981) model is based on a series of small-scale experiments in which vessels of various sizes (0.226-10001) containing propylene were ruptured. (See Section 4.1.2, especially Figure 4.5.) Flame speed, maximum overpressure, and positive-phase duration observed in explosively dispersed clouds are represented as a function of fuel mass. 

Benedick, W. B., R. Knystautas, and J. H. S. Lee. 1984. Large-scale experiments on the transmission of fuel-air detonations from two-dimensional channels. Progress in Astronautics and Aeronautics. 94 546-555, AIAA Inc., New York. 

Small-scale experiments with fireballs have been carried out by a number of investigators, and can be roughly divided into two categories. The first includes experiments in which a spherical gas-air mixture contained by a thin envelope at ambient pressure was released, then ignited (soap bubble experiments). 

In view of the results from these small-scale experiments, and the increasing number of severe accidents involving large masses of fuel, there is a clear need for large-scale or full-scale experiments. Few large-scale test results are available, however. Table 6.3 gives an overview of some fireball experiments performed to date. 

Small-scale experiments by Schmidli et al. (1990) showed that, as degree of superheat increases, the quantity of fuel forming a pool decreases and droplet formation increases. These results support the proposition that more fuel is involved in a BLEVE than calculated from flash evaporation. 

Many small-scale experiments have been carried out to measure the durations and maximum diameters of fireballs. These experiments have resulted in the development of empirical relations among the total mass of fuel in the fireball and its duration and diameter. Fireball diameter estimates, as published by several investigators and modelers, are presented in Table 6.4. 

GrSsstwert, m. largest value, maximum value. Gross-verksuf, m. wholesale, -versuch, m. large-scale experiment. -zshlforschtmg, -zshluntersuchung, /. statistical research or analysis-... 

Kleinsteller, m. bypass (in Bunsen burner). kleinstmogUch, a. smallest possible. kleinstUcklg, a. in small pieces, small-sized Kleinstwerti m. minimum value, minimum. Klein-verkauf, m. retailing, retail, -versuch, m. small-scale experiment or test. 

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