Vessel Simulation Studies

FIGURE 11-4. A Ship Pilot Navigating a Scene on the ERDCANES Ship/ Tow Simulator. Courtesy qfU.S. Army Corps of Engineers. 

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NAVIGATION ENGINEERING PRACTICE AND ETHICAE STANDARDS 11.5 VESSEL SIMULATION STUDIES... 

In this chapter we discuss important issues as we move from laboratory to pilot plant and manufacturing. A review of batch process operation and pharmaceutical research is covered in Section 3.1.2, followed by laboratory vessels and reaction calorimetry in Section 3.1.3. In Section 3.1.4 heat transfer in process vessels is presented, including the effect of reactor type and heat transfer fluid on the vessel heat transfer capability. In Section 3.1.5 dynamic behavior based on simulation studies is discussed. 

If core debris in the lower plenum cannot be quenched quickly, it will eventually penetrate the reactor vessel. If the reactor coolant system is pressurised to levels above the pressurisation of the reactor containment, a pressure-driven expulsion of core debris will accompany vessel rupture. Studies of pressurised expulsion of simulant materials from a vessel suggest that 1-9% of the expelled material could be converted into aerosol by a combination of mechanical and vaporisation processes [S-15]. Interest in this source of radionuclides to the containment atmosphere has waned as procedures have been adopted to assure the reactor coolant system is depressurised during an accident. 

In many ports the restrictive rules cannot be obeyed if the large vessels are going to be operated. In these cases the exemptions given by maritime administration are based on the detailed navigational analyses mainly using simulation studies. 

The process of manoeuvring safety analysis based on real time simulation studies starts with modelling of the examined vessel, harbour and environment. In most cases the commercial full mission simulators are used to carry out the real time simulations in collaboration with local pilots and ship masters. 

The correct treatment of boundaries and boundary effects is crucial to simulation methods because it enables macroscopic properties to be calculated from simulations using relatively small numbers of particles. The importance of boundary effects can be illustrated by considering the following simple example. Suppose we have a cube of volume 1 litre which is filled with water at room temperature. The cube contains approximately 3.3 X 10 molecules. Interactions with the walls can extend up to 10 molecular diameters into the fluid. The diameter of the water molecule is approximately 2.8 A and so the number of water molecules that are interacting with the boundary is about 2 x 10. So only about one in 1.5 million water molecules is influenced by interactions with the walls of the container. The number of particles in a Monte Carlo or molecular dynamics simulation is far fewer than 10 -10 and is frequently less than 1000. In a system of 1000 water molecules most, if not all of them, would be within the influence of the walls of the boundary. Clecirly, a simulation of 1000 water molecules in a vessel would not be an appropriate way to derive bulk properties. The alternative is to dispense with the container altogether. Now, approximately three-quarters of the molecules would be at the surface of the sample rather than being in the bulk. Such a situation would be relevcUit to studies of liquid drops, but not to studies of bulk phenomena. 

One of the principal advantages of hydrides for hydrogen storage is safety (25). As part of a study to determine the safety of the iron—titanium—manganese metal hydride storage system, tests were conducted in conjunction with the U.S. Army (26). These tests simulated the worst possible conditions resulting from a serious coUision and demonstrated that the metal hydride vessels do not explode. 

Flow in stirred vessels was also investigated by Holmes et al. (H5), who simulated mass transfer in a diaphragm diffusion cell stirred by magnetic stirrer bars. This is a good example of a simple model study with a direct practical purpose. A minimum stirring speed in such cells is necessary to avoid appreciable errors in the cell constant. The experiment permits this stirring speed to be related to the solution properties. 

A further option is to forget about simulating the flow and the processes in the whole vessel and to zoom into local processes by carrying out a DNS for a small box. The idea is to focus on the flow and transport phenomena within such a small box, such as mass transport and chemical reactions in or around a few eddies or bubbles, or the hydrodynamic interaction of a limited number of bubbles, drops, and particles including their readiness to collisions and coalescence. Examples of such detailed studies by means of DNS are due to Ten Cate et al. (2004) and Derksen (2006b). 

Bakker, A., Oshinowo, L. M., and Marshall, E. M., The Use of Large Eddy Simulation to Study Stirred Vessel Hydrodynamics . Proceedings of the 10th European Conference on Mixing, Delft, Netherlands, 247-254 (2000). 

There are a number of different types of adiabatic calorimeters. Dewar calorimetry is one of the simplest calorimetric techniques. Although simple, it produces accurate data on the rate and quantity of heat evolved in an essentially adiabatic process. Dewar calorimeters use a vacuum-jacketed vessel. The apparatus is readily adaptable to simulate plant configurations. They are useful for investigating isothermal semi-batch and batch reactions, and they can be used to study ... 

Rotating culture vessels such as simulated microgravity systems are primarily used to study 3-D tumor growth and differentiation. However, mixed cell populations combined with matrix proteins can be used to generate a complex microenvironment in which cell-cell interactions and invasion can be measured (95). A similar system has also been described for the coculture of endothelial cells, myofibroblasts, and tumor cell clusters embedded in Matrigel . Differential labeling of the cell populations enables their invasion and the effects of inhibitors to be measured (96). 

Simulation of the process with analytical models can be used to evaluate the effects of changes in process parameters, providing the limiting assumptions of the model are noted [16]. These parametric studies can then be used to select critical experiments for selecting a cure cycle or to establish rules for process-cycle development [17]. If the simulation is true enough to the actual behavior of the material and processing vessel and provides the necessary predictions of material quality, it can even be used to select a cure cycle [15,18]. 

Artificial Maturation. Laboratory maturation studies provide a means to determine the influence of temperature on kerogen composition, since other variables (e.g. source input) can be eliminated. In order to study the behaviour of organically bound sulfur under these controlled conditions, Py-GC-FID/FPD was performed on a suite of solvent-extracted residues from sealed vessel (hydrous pyrolysis) experiments aimed at simulating maturation over the range involved in petroleum generation. 

The ethylbenzene CSTR considered in Chapter 2 (Section 2.8) is used in this section as an example to illustrate how dynamic controllability can be studied using Aspen Dynamics. In the numerical example the 100-m3 reactor operates at 430 K with two feedstreams 0.2 kmol/s of ethylene and 0.4 kmol/s of benzene. The vessel is jacket-cooled with a jacket heat transfer area of 100.5 m2 and a heat transfer rate of 13.46 x 106 W. As we will see in the discussion below, the steady-state simulator Aspen Plus does not consider heat transfer area or heat transfer coefficients, but simply calculates a required UA given the type of heat removal specified. 

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