Unstable operating condition

Supervision and diagnosis. For example, when it is necessary to supervise a microorganism concentration in a biofilm to avoid unstable operating conditions. 

The combustor is naturally unstable under certain operating conditions. Figure 16.7 shows combustor pressure oscillations and the Fast Fourier Transform (FFT) spectrum under atypical, unstable operating condition. The fundamental mode at 39 Hz and its higher harmonics were observed. The fundamental-mode frequency corresponds to the inlet quarter-wave mode of acoustic oscillations. During stable operation as shown in Fig. 16.8, the amplitude of pressure oscillations is much less. Also, no significant peak was observed in the pressure spectrum. 

Model analysis has revealed the existence of multiple unstable operational conditions (Hutchinson and Ray,... 

Pump Blockage wear Mass of the ash Ash concentration Fluid is not pumped Unstable operating conditions (variability of flow-rate, water infiltration) Day and Fisher, 1980 Blong, 1984... 

Either of the two stable operating conditions can be selected by adjusting the positions of the curves so that only one intersection is obtained. In a plant, long-time unstable operation is unlikely because of imprecise temperature control. 

The material charge of continuous mills called the holdup cannot be set directly but is indirectly determined by operating conditions. There is a maximum throughput rate that depends on the shape of the mill, the flow characteristics of the feed, the speed of the mill, and the type of feed and discharge arrangement. Above this rate the holdup increases unstably. 

It is worthwhile to note here that in Figs. 3 and 4 the current densities measured at a methanol and air flow rates of 2 ml/min and 2 L/min, respectively show the inconsistency even at the same operating conditions. The reason is expected to be due to the water produced at the cathode. Comparing Figs. 3 and 4, the measured current density response looks quite unstably scattered at low air flow rates in Fig. 3, while it seems to be stable even at the low methanol flow rates in Fig. 4. This instability of measured current density in Fig. 4 could have caused by the water formed at the cathode during the operation of the stack. In fact, it has been observed from the experiment that the water produced at the cathode looks accumulated in the cathode flow channels for a while and it bursts out intermittently to the cathode outlet. Based on the experimental observations, for the stable operation of the 5W... 

Process operating conditions. Some process conditions that may increase the frequency of an event include extremely high temperature or pressures or extremely low temperatures highly exothermic reactions processes handling highly corrosive, erosive, or unstable materials or processes subject to frequent pressure or temperature cycling. 

Most of the DSC equipment can be used in the temperature range of 25°C to 500°C. Most can be cooled as well, a feature required for investigating samples that are unstable at ambient conditions. DSC equipment is usually sufficient for indicating thermal hazards of stirred systems and small-scale unstirred systems provided the reaction is kinetically controlled under normal operating conditions, but the resulting data must be used with careful judgment if mixing or mass transport are important. 

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