Ejector Characteristics

Steam jet vacuum equipment is very reliable. However, unsatisfactory performance of an ejector can be caused by external or internal causes. Unsatisfactory performance can also be classified as sudden or gradual. The gradual loss of vacuum will normally suggest internal erosion or corrosion a sudden loss of vacuum will normally suggest external causes. Since it is easier to check external causes of trouble, all possible external causes should be checked first. 

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The ejector characteristics are determined by the following three important geometric parameters (i) the PR defined as (ii) suction chamber free area... 

Figure 5.43 shows a few of the ejector characteristics generated by the presented model and adequate experimental data for validation purposes. 

Dusts, particle sizes, 225 Dusts, hazard class, 521-523 Explosion characteristics, 524 Efficiency, centrifugal pumps, 200 Ejector control, 380 Ejector systems, 343, 344, 351 Air inleakage, table, 366, 367 Applications, 345 Calculations, 359-366 Chilled water refrigeration, 350 Comparison guide, 357, 375 Evacuation lime, 380, 381 Charts, 382 Example, 381 Features, 345... 

Rotational molding creates a wide variety of plastic products that cannot be made effectively, efficiently, or economically by other means. What sets this method apart from others is that it can create thin-walled, hollow parts that exhibit no weld lines or scarring from ejector pins and from the process itself. It also has the advantage of having little scrap and minimal molded-in stresses, due to the low pressure and low shear rate characteristics of the process. Finally, it can be used to make parts that are very large which would be impossible to manufacture by other methods. 

Similarly, vacuums can be created when a blower, fan, compressor, or jet ejector removes gases from equipment. The magnitude of the vacuum attainable will be governed by the performance characteristics of the device. Other mechanisms for generating a vacuum, which have been demonstrated by industry experience, include the following. 

The most commonly used steam is 100 psig with 10-15° superheat, the latter characteristic in order to avoid the erosive effect of liquids on the throats of the ejectors. In Figure 7.31 the steam consumptions are given as lb of motive steam per lb of equivalent air to the first stage. Corrections are shown for steam pressures other than 100 psig. When some portion of the initial suction gas is condensable, downward corrections to these rates are to be made for those ejector assemblies that have intercondensers. Such corrections and also the distribution of motive steam to the individual stages are problems best passed on to ejector manufacturers who have experience and a body of test data. 

The most commonly used vacuum pumps are steam-jet ejectors and several positive-displacement pumps, which are shown in Figures 5.1 and 5.2. Some of the characteristics of vacuum pumps are given in Table 5.1. A prime consideration when selecting a vacuum pump is the compatihility of a gas with a seal fluid. To avoid these problems, there is a trend toward using dry pumps where a seal fluid or lubricant is not used [60]. 

C. M. van Dierendonck, L. L., Hydrodynamics and mass-transfer characteristics of a loop-venturi reactor with a downflow liquid jet ejector. Chem. Eng. Sci. 1992, 47 (13/14), 3557-3564. 

Bhat et al. (1972) and Davies et al. (1963) studied the gas entrainment characteristics of gas-Uquid ejectors in the horizontal mode. The physical properties of the primary fluid were again represented by the Morton number M p = ( pp/ppCTp). The range of physical properties of the liquid phase covered in the investigation of Davies et al. was the same as that in the investigation of Ben Brahim et al. (1984). The viscosity range covered by Bhat et al. was relatively narrow. The dependences of mass ratio on the physical properties group observed by Davies et al. and Bhat et al. were... 

Cramers PHMR, Smit S, Leuteritz GM, van Dierendonck LL, Beenackers AACM. (1993) Hydrodynamics and local mass transfer characteristics of gas-liquid ejectors. The Chem. Eng. J., 53 67-73. 

Dutta NN, Raghavan KV. (1987) Mass transfer and hydrodynamic characteristics of loop reactors with down flow liquid jet ejector. The Chem. Eng. J., 36 111—121. 

Havelka P, Linek V, Sinkule 1, Zahradnik J, Fialova P. (1997) Effect of the ejector configuration on the gas suction rate and gas hold-up in ejector loop reactors. Chem. Eng. ScL, 52 1701-1713. Havelka P, Linek V, Sinkule 1, Zahradnik J, Fialova P. (2000) Hydrodynamic and mass transfer characteristics of ejector loop reactors. Chem. Eng. Sci., 55 535-549. 

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