Instability dumping

Note that Figure 8-147 indicates the operating liquid minimum range is quite stable in the region of design for these trays. The vapor rate must never fall below the above values or instability will immediately set in and dumping will result. 

To demonstrate liquid-fueled active combustion control, instability suppression experiments were performed under several conditions. Figure 21.6 shows the dump combustor set-up used in the demonstration experiments. Three configurations in which naturally unstable oscillations were observed are shown. Table 21.1 lists the specific flow conditions where instabilities occurred. The case number in the table corresponds to the combustor configuration used. 

The present study was conducted in an effort to better understand ACC mechanisms and to design practical ACC based on pulsed liquid-fuel injection suitable for propulsion devices. The controller utilized a simple fixed phase-delay approach that has been studied previously, but the direct liquid-fuel injection and the novel use of vortex-droplet interaction made the present study unique. The demonstration experiment in a 102-millimeter dump combustor showed that combustion instabilities can be successfully suppressed using properly designed pulsed liquid-fuel injection. 

Network back propagation Generic combustion instability [15] Dump combustor [16] Boiler combustion systems [17] 2. Has similar algorithm in System ID 3. May be replaced by off-line ID plus Bode-Nyquist or observer-based controller... 

A comprehensive framework of robust feedback control of combustion instabilities in propulsion systems has been established. The model appears to be the most complete of its kind to date, and accommodates various unique phenomena commonly observed in practical combustion devices. Several important aspects of distributed control process (including time delay, plant disturbance, sensor noise, model uncertainty, and performance specification) are treated systematically, with emphasis placed on the optimization of control robustness and system performance. In addition, a robust observer is established to estimate the instantaneous plant dynamics and consequently to determine control gains. Implementation of the controller in a generic dump combustor has been successfully demonstrated. 

Dumping As gas velocity is lowered below the weep point, the fraction of liquid weeping increases until all the liquid fed to the tray weeps through the holes and none reaches the downcomer. This is the dump point, or the seal point. The dump point is well below the range of acceptable operation of distillation trays. Below the dump point, tray efficiency is slashed, and mass transfer is extremely poor. Operation below the dump point can be accompanied by severe hydraulic instability due to unsealing of downcomers. 

Fluxes must be specified during each phase of device operation including startup, heating, burn, fueling, shutdown and failure modes. Plasma failure modes, such as instabilities which cause much of the stored plasma energy to be dumped in a short time may result in large particle or photon fluences to selected small areas of surfaces exposed to the plasma. 

For smaller hydro power systems, such a solution is considered to be complex and additionally a danger exists of rapid control valve movement introducing damaging surge pressure waves in the pipelines or instability in the overall control system (Roberts, 2002). A preferable solution to maintain frequency close to its nominal value is the utilisation of load control. For the implementation of this scheme, secondary or even dump controllable loads are switched on and off, according to frequency-deviation measurements. 

J.-M. Samaniego, B. Yip, T. Poinsot, and S. Candel. Low-frequency combustion instability mechanism in a side-dump combustor. Combust. Flame, 94(4) 363-381, 1993. 

Use your audience analysis to help determine the types of information to include under each main point. For example, when talking about the synthesis of nonlinear optical polyimides for practical applications, mention the approaches that have been developed to tackle the instability problems. When talking about pollution in an area, refer to the dumping of chemicals in a nearby stream. 

Experiments are described using premixed prevaporized JP-10 in a dump combustor modified to accommodate counterflow control at the dump plane. The primary benefit of operation under prevaporized conditions is the careful regulation of the JP-lO/air stoichiometry, thereby providing independent assessment of flame speed modification using counterflow technology. Studies were also conducted to evaluate the fundamental nature of a planar nonreacting turbulent countercurrent shear layer. An abrupt transition in flow behavior at a counterflow level of U2/U1 w —0.13 provides the first evidence of global instability in a self-similar turbulent shear layer. 

Figure 8.2 Chemiluminescence images for JP-10 at = 0.9 (o) and corresponding instability modes in the dump combustor (fc).

Prevaporized JP-10 hcis been successfully burned in a dump combustor at nearly stoichiometric equivalence ratios. The flammability of the JP-lO/air mixture seems to be limited to fairly high equivalence ratios, which has led to what is believed to be a thermoacoustic instability, which flashes back into the combustor plenum if the equivalence ratio is slightly above 0.9. Although JP-10 will continue to be used in the dump combustor studies for future work, the potential limited range of equivalence ratio operation may motivate the use of another fuel in conjunction with JP-10, which can be used over a wider range. This would allow for a more thorough examination of the countercurrent dump combustor performance. 

Vortex shedding plays a significant role in maintaining self-sustained combustion instabilities in dump combustors. Vortices may entrain a large amount of hot recirculating products into fresh reactants, causing a substantial modification in... 

Zhang, C., W. Zhao, T. Ye, S. H. Frankel, and J. P. Gore. 2002. Parametric effects on combustion instability in a lean premixed dump combustor. AIAA Paper No. 02-4014. 

Ol ns Depropanizer Instability and fluctuations oocuned because of operation below the dumping loads in a section of the cohinm just below the feed. Ensure adequate hydraulics above rmd below alternate feed points. 

Micelles Small size should help avoid nonspecific uptake Can be made stimulus responsive Instability, dose dumping Only suitable for delivering hydrophobic drugs Burt eta/. (1999) Gaucher eta/. (2005) Y. Baeeta/. (2005)... 

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