Motive media

The motive nozzle is shaped like a Laval nozzle. This means there is an enlargement of the diameter after the smallest cross section. This is necessary to achieve velocities higher than sonic speed. For steam an expansion pressure ratio of only Pi/Po = is sufficient to just achieve sonic velocity (critical pressure ratio). At higher expansion ratios (supercritical pressure ratios), the exact critical pressure and sonic speed is achieved in the smallest cross section. In these cases in the divergent part of the motive nozzle, a supersonic velocity results from a continuing expansion. Owing to the blocking of the velocity to the sonic speed in the smallest cross section, the mass flow rate of such a supersonic nozzle only depends on the state of the motive media in front of the nozzle and of course on the diameter d.. Here the mass flow rate is proportional to the motive pressurep. ... 

A further field of application for product vapour driven ejectors are in processes where the intrusion of water has to be avoided at all costs. In addition, the use of motive media other than steam can also be energy saving. 

Using the calculation methods of one dimensional gas dynamic shows how different motive media behave during the expansion in the motive nozzle. Depending on the expansion ratio ( = motive vapour pressure/suction pressure), the Mach number at the motive nozzle outlet for some vapours is charted in Figure 4.18. It can be seen, that the velocity is in the supersonic range and therefore the corresponding effects (expansion, compression and shock waves) have to be considered. 

Mechanical drive turbines, although designed for steam, can be adapted and modified to operate with high pressure gas as the motive power. This is particularly profitable where the gas is needed at reduced pressure. The driven applications can be the same as for the turbine when steam is the motive medium. 

The conversion of this principle to a practical purpose requires a simple apparatus, which normally consists of only three main parts the motive nozzle (1), the diffuser (2) and the head (3). There are three external connections to be designated the motive medium connection (A), the suction nozzle (B) and the pressure nozzle (C). 

Steam jet pumps are frequently used In the chemical industry for vacuum generation. The main reasons for this are their high operational reliability, their resistance to corrosion, their tolerance of fouling as well as their suitability for very large volume flows. However, when jet pumps are operated with steam as the motive medium, there will inevitably be waste water generated because the motive steam must be condensed. 

If jet pumps are driven by steam, waste water is generated when the motive steam is condensed. In this condensate, residuals of product from the suction flow can often be found. Even though this waste water flow rate is small and the costs for handling the effluents are similarly small, it should be an aim to reduce the waste water flow as far as possible. When the ejector is driven by a product vapour, this problem can often be avoided. Normally the motive medium condensate can again be evaporated and reused as motive vapour (Figure 4.17). 

The design of product vapour driven jet pumps needs a detailed analysis in order to find the best degree of efficiency. The main fluid dynamic processes in a vapour- or gas-driven ejector are firstly the expansion ofthe motive medium, then the mixing of motive and suction flows and finally the compression of the mixed flow to the required discharge pressure. These processes are influenced by the geometry of the ejector, the properties of the media employed and the prevalent pressures. 

The applicability of a substance to be used as a motive medium in a vapour jet vacuum pump is also considerably influenced by its vapour pressure diagram. It must be considered that the evaporation temperature is always below a possible... 

Figure 4.19 Example for a vapour jet vacuum pump with butanol vapour as motive medium.

The temperature of the available cooling water and the possible condensation pressure can preclude the use of a special motive medium. Also, the variation of the vapour pressure diagram by the addition of other components must be regarded. The example of the twin component system, ethylene glycol/water, makes this point more clearly. Even small parts of water lead to a distinct decrease of the necessary cooling liquid temperature. For example, at 2 mbar and a water content of 1% condensation is possible at 35 °C, but even at 3% water content the condensation temperature has decreased to about 15 C. 

Finally, Figure 4.19 shows the layout of a three-stage vacuum pump without waste water output. Here butanol is used as motive medium, as cooling liquid in the mixing condensers and also in the liquid ring pump which is not shown here. 

If still greater force is required, a positive pressure in excess of atmospheric can be applied to the suspension by a pump. This motive force may be in the form of compressed air introduced in a montejus, or the suspension may be directly forced through a pump acting against the filter medium (as in the case of a filter press), or centrifugal force may be used to drive the suspension through a filter medium as is done in screen centrifuges. 

Loss of motivity (dissipation of energy) is therefore accompanied by increase of entropy, but the two changes are not wholly co-extensive, because the former is less the lower the temperature T0 of the auxiliary medium, whilst the latter is independent of T0, and depends only on the temperature of the parts of the system. If T0 = 0, i.e., the temperature of the surroundings is absolute zero, there is no loss of motivity, whilst the entropy goes on increasing without limit as the heat is gradually conducted to colder bodies. 

A considerable amount of extracellular polysaccharides is produced in the process of cultivation of certain plant suspension cultures and the spent culture medium has proved to be an accessible source for their production (1-3). The interest in investigating these extracellular polysaccharides has been quite strong over the past 10-15 years, motivated by their biological activity (4,5). Plants of the Asteraceae family, as well as their cell cultures, have been established to contain polysaccharides with immunostimulating activity (1-6). The object of our research was Helianthus annuus 1805 cell culture (Asteraceae), which according to the preliminary investigation produces a considerable amount of exopolysaccharides. 

The leeway and motivations for substituting hazardous substances may indeed differ between small and medium-sized enterprises (SMEs) and large-scale enterprises. However, neither of the two types of enterprises appears to be more iimo-vative than the other per se. For example, the qualification of employees, the capital intensity of production, the availability of capital for research and development, the type of production and the competition strategy (mass or quality), the position on the supply chain as well as the corporate culture are at least just as decisive. 

The simplest example of a flame-supporting medium is a pure chemical compound which decomposes exothermically. The widespread interest in such flames is due to their possibilities as monopropellants. Many studies are motivated by purely fundamental considerations, since a decomposition flame can be a kinetically simple flame. The most widely used and studied combustion reactions are those between hydrocarbons or hydrocarbon derivatives and air or oxygen. However, many other chemical substances may be substituted for the common fuels and/or oxidizers. Flames of uncommon fuels and oxidizers are most important because of their possibility of surpassing ordinary hydrocarbon oxidation as a source of energy. Some unusual flames are discussed in reference (PI). 

The motivation for this work is the potential use of chiral (and maybe biisotropic) cylinders as rod antennas and scatterers. Accordingly, Lakhtakia investigated the boundary value problem relevant to the scattering of an incident oblique plane EM wave by an infinitely long homogeneous biisotropic cylinder. This medium is described by the so-called Fedorov representation through the monochromatic frequency-domain constitutive relations ... 

One common observation in patents and fundamental studies is that an acidic support promotes the selectivity. H202 is more stable in acid medium, but a strong acid could create problems of corrosion and further treatment of the solution. One of the motivations for the use of acidic supports was thus the reduction of the required concentration of inorganic acids in solution and hence minimization of... 

Our definition of the phases is mechanically motivated. A kinematical criterion on the other hand would sort species according to their velocities. Cartilage is viewed as a three-phase, multi-species, porous medium ... 

Nanosized ZnO particles are prepared by hydrolysis-condensation at moderate temperature (from 20 to 70°C) [27-29] of zinc-acetate precursors [30] in ethanolic medium. Besides the determination of local order around Zn and of the particle sizes during the nanosized ZnO preparation, the motivation of the combined investigation was also to clarify the occurrence of a Zn-based hydroxy double salt phase, Zn5(0H)8(0C0CH3)2.2H20 (labeled hereafter Zn-HDS) observed as final solid mixed with ZnO and zinc acetate phases [29]. In particular, we were interested in determining whether the formation of the Zn-HDS phase was concomitant to the ZnO formation or arose from the reaction of ZnO with zinc acetate precursors during ageing of the colloidal suspension before extraction of solids. 

Ringing Ears Due to severe tinnitus, the user of this drag or chemical agent has trouble hearing soft to medium volume sounds. As such, he suffers a -2 penalty on Listen checks and any other check related to hearing (such as Sense Motive to pick up a character s vocal intonation). 

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