Liquid instability problems

Often very large vertical and horizontal vibrations are seen in some speed intervals on decanters when they are started and stopped with liquid inside the bowl. The vibration frequencies in the instability intervals correspond to rigid body natural frequencies of the decanter, but the vibrations are not caused by unbalances. Rather, they are due to interaction between the liquid inside the bowl and the decanter. 

The vibrations which occur in some instability speed ranges are sub-synchronous, i.e. the vibration frequency is a fraction (normally about 0.7) of the actual operating speed. If, for example, the decanter is vibrating at an operating speed of 1000 rpm, the vibration frequency will be around 700 rpm. 

The complicated dynamic phenomenon, which is related to all rotating cylinders with an internal annulus of liquid, has been dealt with in a number of publications [25, 26], 

In general the bowl strength, the first rotor critical speed, and the maximum permissible speed of the main bearings control the maximum speed at which a decanter can be operated. 

When a decanter bowl, for calculation purposes, is approximated to a beam, its natural frequency is inversely proportional to the square of its length. In that g-force is proportional to the square of bowl speed, and it is necessary to keep resonance frequency above bowl speed, the maximum bowl speed is proportional to its length to the fourth power. To obtain g-forces in the range 20()0-3()()0, generally required for commercial decanters, the maximum length-to-diameter ratio, for the most frequently used designs, has to be restricted to a little over 4.0 [24]. 

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Chauvin and Olivier-Bourbigou (123) classified ionic liquids according to the complexing ability of their anions because they influence the solvation and complexing ability of ionic liquids. One problem is the instability of several ionic liquids in water, which reduces their potential for application in catalytic reactions. This subject is under investigation, and a series of novel air- and water-stable low-melting salts has recently been prepared (124). 

The successful combination of mass spectrometry with gas chromatography (GC-MS) and, subsequently, with liquid chromatography (HPLC-MS) allowed not only the determination of urea pesticides in food but also the identification of their residues at trace level. Mass spectrometry is a technique that can be used as a general detector, with cyclic scanning. The selectivity and sensibility of analysis can be enhanced using characteristic ions of the molecule, with selected ion monitoring (SIM). Urea pesticides have been determined by HPLC-MS directly (175-180), without the thermal instability problems of GC analysis. 

Char acts as a vapour cracking catalyst so rapid and effective separation from the pyrolysis product vapours is essential. Cyclones are the usual method of char removal and two are usually provided - the first to remove the bulk of the material and the second to remove as much of the residual fines as possible. However, some fines always pass through the cyclones and collect in the liquid product where they accelerate aging and exacerbate the instability problem, which is described below. 

Several immobilization techniques have been developed to overcome the instability problems of SLMs, such as by the gelation or microencapsulation of the liquid phase, covering the surface layers (contained liquid membranes). An overview on stabilization techniques for SLMs developed over the last 10 years can be found in Ref. [126]. 

All the aforementioned SILMs were prepared using microflltration membranes and operated with low varying pressure differential (<2 bar). To avoid the pitfaU of liquid instability associated with microporous membranes, nanofiltration membranes were used in SILMs, which greatly reduce the instability problem only at the expense of increased gas transport resistance provided by the nanofiltration (NF) membranes [87]. Experimental stability tests demonstrated that the impregnated ILs did not discharge from the NF membrane structure even under a high transmembrane... 

With single component cryogenic liquids LIN, LOX, LA, etc. in VI tanks, under isochoric conditions, there is no storage instability problem from refilling with colder liquid, which will settle below the wanner heel. If mixing is not complete, the stratification of warm layer above cold layer will take place as normal during isochoric, zero-loss storage, when the tank contents pressurise as usual within the tank volume. 

To achieve sufficient vapor pressure for El and Cl, a nonvolatile liquid will have to be heated strongly, but this heating may lead to its thermal degradation. If thermal instability is a problem, then inlet/ionization systems need to be considered, since these do not require prevolatilization of the sample before mass spectrometric analysis. This problem has led to the development of inlet/ionization systems that can operate at atmospheric pressure and ambient temperatures. Successive developments have led to the introduction of techniques such as fast-atom bombardment (FAB), fast-ion bombardment (FIB), dynamic FAB, thermospray, plasmaspray, electrospray, and APCI. Only the last two techniques are in common use. Further aspects of liquids in their role as solvents for samples are considered below. 

Because the facilitated transport process employs a specific reactive carrier species, very high membrane selectivities can be achieved. These selectivities are often far higher than those achieved by other membrane processes. This one fact has maintained interest in facilitated transport since the 1970s, but the problems of the physical instability of the liquid membrane and the chemical instability of the carrier agent are yet to be overcome. 

Significant industrial demand for a more practical stabilized liquid bromine product has been known for several years. Until the invention and commercial development of STABREX, there was no practical means to overcome the inherent instability, volatility, and handling hazards of liquid bromine. The new technology solves several longstanding technical problems that bromine manufacturers tried, unsuccessfully, to overcome for 15 years. The practical use of STABREX stabilized liquid bromine and its... 

Changes in the natures of individual phases of or phase separation within a formulation are reasons to discontinue use of a product. Phase separation may result from emulsion breakage, clearly an acute instability. More often it appears more subtly as bleeding—the formation of visible droplets of an emulsion s internal phase in the continuum of the semisolid. This problem is the result of slow rearrangement and contraction of internal structure. Eventually, here and there, globules of what is often clear liquid internal phase are squeezed out of the matrix. Warm storage temperatures can induce or accelerate structural crenulation such as this thus,... 

One additional problem at semiconductor/liquid electrolyte interfaces is the redox decomposition of the semiconductor itself.(24) Upon Illumination to create e- - h+ pairs, for example, all n-type semiconductor photoanodes are thermodynamically unstable with respect to anodic decomposition when immersed in the liquid electrolyte. This means that the oxidizing power of the photogenerated oxidizing equivalents (h+,s) is sufficiently great that the semiconductor can be destroyed. This thermodynamic instability 1s obviously a practical concern for photoanodes, since the kinetics for the anodic decomposition are often quite good. Indeed, no non-oxide n-type semiconductor has been demonstrated to be capable of evolving O2 from H2O (without surface modification), the anodic decomposition always dominates as in equations (6) and (7) for... 

As mentioned in the previous section, a major drawback of the simplex atomizer is the poor atomization quality at the lowest flow rate due to too-low pressure differential if swirl ports are sized to allow the maximum flow rate at the maximum injection pressure. This problem may be resolved by using dual-orifice, duplex, or spill-return atomizers. Alternatively, the atomization processes at low injection pressures can be augmented via forced aerodynamic instabilities by using air or gas stream(s) or jet(s). This is based on the beneficial effect of flowing air in assisting the disintegration of a liquid j et or sheet, as recognized in the application of the shroud air in fan spray and pressure-swirl atomization. 

Operation of cells at higher temperatures such as 80°C, as in membrane fuel cells, is not encouraged here because of the corrosion instability of the hardware, manufactured from titanium or titanium alloy. Even without such constraints, however, this high temperature would be unwelcome as the water produced is present as steam - without the conductive bridge of the liquid phase it would be necessary to bond the catalytic particles to the membrane with all the associated problems of technology and cost. 

Due to strict environmental regulations, turbine engine manufacturers and users are facing great challenges in reducing NO, SO , CO, and hydrocarbons to meet the compliance limits. To date, several innovative methods have been developed and introduced into the market to combat these problems. However, often, while reducing NOj, or other pollutants, new problems arise. These problems are lower turn-down ratio, poor thermal efficiency, flame instability, uneven temperature distribution in the combustor, and noise. These problems are even more pronounced in a liquid fuel fired turbine combustor. Therefore, the present research... 

In summary, all features of the liquid rocket engine combustion processes are extensively affected by injector design, and any simplified combustion model, in which the essential three-dimensional nature of the flow processes is ignored, can only be of qualitative significance. Nevertheless, these simplified models are useful in giving us some insight into the nature of the physicochemical phenomena that determine engine performance. In this connection, steady-state combustion rates and overall combustion efficiencies in propellant utilization are far less important practical problems than are control or elimination of instabilities, excessive heat transfer, and hard starts. 

The use of liquid gun propellants appears to be very attractive. However, the problems encountered such as gun design and ignition system along with combustion instability limit their application and at present no liquid gun propellant is in use. Therefore, solid gun propellants based on novel energetic ingredients are thought to be the ultimate choice for future applications [34, 49]. 

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