Simulation pressure

A further improvement in control response can be achieved by a variable gain of the controller. With this change, the simulated pressure fluctuation totals no more than 6 mbar. 

Figure 5 Effect of the number of marching sections on simulated pressure profiles, obtained using 64 triangles, 2.0 cc/s volumetric flowrate, and second order basis functions.

Comparison of simulated pressure drop for different filters (A-D) due to catalyst (solid lines) to the experimental data (points) (Karadimitra et al., 2004). 

Ion-exchange membranes also show some promise in the solution of waste problems, inter alia the treatment of spent pickle liquors by electrodialysis is discussed (80). A very high degree of deionization can be achieved with ion-selective membranes. P. Cohen investigated the electrodialysis of simulated pressurized water reactor coolant (34). The specific resistance of the treated water was as low as 0.5 to 3,0 Mi cm. 

Figures 7.13 and 7.14 give results using the FS2 flowsheet with the furnace for this hot-reaction case. Figure 7.13 shows that a 10% decrease in recycle flowrate can be handled, but a 20% decrease produces a reactor mnaway. This occurs despite the fact that the reactor inlet temperature increases only slightly ( 0.5 K) during the transient. Figure 7.14 gives results for changes in the setpoint of the reactor inlet temperature controller. Rather surprisingly, inlet temperature can be increased by 2 K without a runaway. This is unexpected since the isolated reactor (Fig. 7.12) showed a runaway with a +2 K change in Tm. The difference may be due to the effect of pressure. In the isolated reactor simulation, pressure is held constant at 50 bar. In the simulation of the whole process, pressure drops as reactor temperature increases due to the increased consumption of reactants. Since the reaction rate depends on the square of the total pressure (P2), the decrease in pressure lowers the reaction rates. However, a 3 K increase cannot be handled.

Fig. 10.67 Experimental and simulated pressure profiles obtained with kneading disk 5 of the 45/ 5/20 element sequence shown in Fig. 10.65(b). (a) Apex region and transducer (b) wide channel region and side port. [Reprinted by permission from V. L. Bravo, A. N. Hrymak, and J. D. Wright, Numerical Simulation of Pressure and Velocity Profiles in Kneading Elements of a Co-TSE, Polym. Eng. Set, 40, 525-541 (2000).]...

An example drawn from Deitrick s work (Fig. 2) shows the chemical potential and the pressure of a Lennard-Jones fluid computed from molecular dynamics. The variance about the computed mean values is indicated in the figure by the small dots in the circles, which serve only to locate the dots. A test of the thermodynamic goodness of the molecular dynamics result is to compute the chemical potential from the simulated pressure by integrating the Gibbs-Duhem equation. The results of the test are also shown in Fig. 2. The point of the example is that accurate and affordable molecular simulations of thermodynamic, dynamic, and transport behavior of dense fluids can now be done. Currently, one can simulate realistic water, electrolytic solutions, and small polyatomic molecular fluids. Even some of the properties of micellar solutions and liquid crystals can be captured by idealized models [4, 5]. 

The invidual components of the piping system like valves, branches, atomizing nozzles etc. are described by resistance coefficients. Furthermore the modeling of gas-charged dampeners and resonators is possible. The software simulates pressure losses in pipeline as well as radially expansion of pipes due to transition of pressure waves. 

A typical pressure profile obtained from the two transducers is presented in the Figure 2. Curve I along with points A, B and C illustrates the characteristic pressure prorile observed during the operation of the reactor. Meanwhile, curve II depicts the pressure profile inside the vacuum chamber. Point A of curve I indicates the pressure condition inside the Riser Simulator just prior to the hydrocarbon injection. Point B gives the Riser Simulator pressure at the end of the reaction period (just before evacuation commences) and Point C represents the equilibrium pressure once the pressures between the vacuum chamber and the Riser Simulator have stabilized. 

Figure 2. Curve I Riser Simulator Pressure. (A) Prior to Injection, (B) Before Evacuation, (C) Equilibrium Pressure. Curve II Vacuum Chamber Pressure.

Required number of grid points in DNS simulation Pressure, Pa... 

Gage et al. developed a three-dimensional CFD model to predict the pressure drop in a membrane BO [63]. They modified a commercial membrane BO to allow pressure measurement along the fiber bundle in all cardinal axes. Close agreement was obtained between experimental and simulated pressure drops at lower flow rates. However, the simulated pressure drops were lower than the experimental results at higher flows. 

Fig. 10. Flow simulation pressure history match. A simple block model was depleted by producing gas from a production well. The fault transmis-sibility varied to alter depletion rates in the non-producing block until a best-fit pressure history match was achieved. The resulting transmissibility could be related to the observed throw on the fault.

Duncan SL, Larson RG (2008) Comparing experimental and simulated pressure-area isotherms for DPPC. Biophys J 94 2965-2986... 

Figure 10.3 Measured (1 — pressure transducer and 2 — spectroscopic) and computed (3 — NRL simulation) pressures for detonation of stoichiometric C2H4/O2 mixture.

The concept of activation volumes has also become a valuable tool in studies of exchange reactions by ab initio computer calculations and in classical computer simulations. In these theoretical studies activation volumes can be estimated by bond-length variations or by calculating volume differences using Connolly surfaces. In MD simulations pressure can be applied by variation of the density of the simulated water box. In that way reaction volumes are accessible by following for instance the change in coordination number. 

Fig. 5. (b) Continued, (c) Simulated pressure against well data (present situation). 

Manage properly the pressure is a key aspect in dynamic simulation. As shown in Chapter 4, Aspen Dynamics offers two possibilities flow driven or pressure driven simulations. We selected the first possibility. We take care to specify all the items needed in dynamic simulation pressure change units (pumps, valves), mixers and heat... 

Figure 3 presents the simulated pore pressure versus time at the 6 points described above and the measured pore pressure at the P4 interval of the FEBEX.95002. The pore pressure measured in the P4 interval (0 = 14°) agree well with the numerical results obtained from the point located at 0 = 53°. This means that a good agreement between measured and simulated pressure response at P4 could be achieved merely by changing the orientation of the initial stress. 

Figure 4 shows the comparison carried out between the measured and simulated pressures. The general shape of the curves obtained with hydraulic simulation is quite similar to measurement results, except there is a constant difference of about 1 bar between the P4 measurements and the simulation. This point will be discussed in Section 4.5 below. Our simulation approach (a hydraulic steady flow analysis with four steady-state steps) was not able to reproduce pore pressure increase (led to a higher horizontal stress than vertical stress) as excavation neared the monitored borehole intervals and as post-tunnel face dissipation was completed. 

S. Yamazaki, Z. Lu, Y. Ito, Y. Takeda, T. Shoji, The effect of prior deformation on stress corrosion cracking growth rates of Alloy 600 materials in a simulated pressurized water reactor primary water, Cotros. Sci. 50 (2008) 835-846. 

For this project to work, the device had to be tested under controlled conditions. Bioengineers were struggling to build a mock loop to simulate pressures and flow conditions in the human body, so a mechanical engineer was invited to collaborate on this section of the project. The result was that the mock loop was built in... 

Figure 23.4 shows the effectiveness factor plotted against network Thiele modulus obtained for four simulation pressures in the range 27.5-27.8 bar, for which capillary condensation occurs. 

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