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Numerical Analysis using Particle Method

A particle method is a technique of computational fluid dynamics (CFD) which does not require grid generation and which provides outstanding adaptability to phenomena with considerable flow field variations such as those involving free surfaces, solid-fluid coupling problems and moving boundary problems.

We have developed fluid analysis software dealing with free-surface phenomena using the moving particle semi-implicit (MPS) method known as a particle method. Figure 1 shows the computational results when a movable wall is instantly raised, thereby collapsing a column of water which then impacts against the far wall and splashes up to the initial height of the water column. Figure 2 shows the computational results when a wall is moved, thus generating waves which proceed to crash into a floating structure causing the wave to break apart and the floating structure to behave.

Numerical analysis using particle method is capable of dealing not only with fluid phenomena but deformation of structural objects as well, thus giving it a wide range of product applications. We are now working to further expand the applications of this numerical analysis technique in order to develop more sophisticated numerical simulation technologies.

<Fundamental Research Group>

Fig. 1 Collapse of water column

Fig. 2. Motion of floating structure
subjected to breaking waves

Rarefied Gas Flow Analysis Technology

Peaple tend to think of a vacuum as meaning nothing at all, but in industry, a vacuum denotes a rarefied gas flow state. At normal atmospheric pressure (105 Pa), one cubic meter of air holds around 1025 molecules. Even at 10-5 Pa, there are still around 1015 molecules present. In this state, molecules travel an average distance of 1 kilometer before a collision occurs—in other words, there are very few collisions. This state is called a rarefied gas flow, and it has quite different properties to continuous gas flow under normal atmospheric pressure.
Direct Simulation Monte Carlo (DSMC) is a technique for analysis of molecular behavior based on probability theory in which large numbers of molecules are treated as a molecule groups. DSMC can be used to perform advanced simulations of molecular behavior in rarefied gas flow on an ordinary high-spec computer.
At Hitachi Zosen, DMSC technology is used in the development of Organic LED (OLED) production systems (see Figure 1) and plasma CVD systems to improve the efficiency and reliability of product design processes. Figure 2 shows a DMSC rarefied gas flow analysis of molecules emitted from a nozzle under vacuum conditions. The molecules can be seen to spread out in radial fashion from the tip of the nozzle. This illustrates the unique characteristics of the rarified gas flow state; in a continuous gas flow under normal atmospheric conditions, the flowpattern would create a jet stream. In this way, we can evaluate the behavior of rarified gas flows for vapor deposition, and use this information to generate design data for optimal evaporator shapes.

<Plant & Energy Solution Technology Group, Technical Research Institute>

Figure 1 OLED production system

Figure 2 Rarefied gas flow analysis

Using CFD in Product Design

Computational Fluid Dynamics (CFD), a technique for solving and analyzing problems that involve fluid flows, is a valuable tool for investigating physical phenomena and generating comprehensive data for use in product design. A CDF program for simulating flows in the evaporator of the Multi-Stage Flash (MSF) desalination plant (see Figure1) has been successfully developed through ongoing research on CFD for gas-liquid two-phase flows. The MSF evaporator is characterized by complex flows involving a combination of vapor, product water and non-condensable gas (see Figure 2). Figure3 illustrates the adverse impact of non-condensable gas stagnating in the evaporator.
In this way, quantitative evaluation of the heat transfer performance of the evaporator is used to generate design guidelines that help to improve the efficacy of the MSF evaporator.

<Plant & Energy Solution Technology Group, Technical Research Institute>

Figure1 MSF desalination plant

Figure2 Flow in MSF evaporator

Figure3 Non-condensable gas volume fraction

Multi Effect Desalination

With water shortages reaching crisis levels in many countries, there is an increasing need around the world for systems capable of converting the inexhaustible supply of sea water into fresh water. Hitachi Zosen has been playing an important role in developing desalination systems since the 1970s through the continuous research. Recently Hitachi Zosen released the highly efficient Multi Effect Desalination (MED) with vapor compression process as shown in Figure 1.
Sea water is sprayed over the horizontal tube bundle and it forms a falling film on the outer surface of the heat exchanger tubes. The falling film is vaporized by heat of the steam in the tubes. The generated vapor is supplied into the tubes of next stage. This cycle is repeated until the last stage. At the final stage, some of the steam, now at relatively low temperature and low pressure, is compressed in the thermo ejector and made available as reheated steam. In this way, the vapor compression process is able to create fresh water at a high level of thermal efficiency.
Hitachi Zosen is committed to further refining and developing desalination technology and providing quality MED desalination plants which alleviate the world’s water shortages.

<Plant & Energy Solution Technology Group, Technical Research Institute>

Figure1 MED process