Ring liquid

Furfural is obtained industrially (200000 t a-1) by dehydration of pentoses produced from hemicelluloses. Furfurylic alcohol is obtained by selective hydrogenation of the C=0 bond of furfural, avoiding the hydrogenation of the furan ring. Liquid phase hydrogenation at 80 °C in ethanol on Raney nickel modified by heteropolyacid salts resulted in a 98% yield of furfuryl alcohol [31]. 

TFE-fluorocarbon color O-Ring, liquid oxygen line seal 100.0 C... 

As the dimensions of the channel reduce, Taylor and annular flows dominate, while patterns specific to small channels appear (such as ring, liquid lump, Yakitori and rivulet flows). These can be considered to be variations of the Taylor and annular regimes. For a review of gas-liquid flow patterns in microchannels see Ghiaasiaan and Abdel-Khalik [2]. 

In contrast to other displacement compressors, liquid ring machines have a fluid piston . This is subject to a constant motion and deformation depending on effective forces. Potential differences are rapidly equalised by the motion of the fluid inside the piston. If the ring liquid plunges into the blade area, then the pressure of the enclosed medium is increased. 

The ring liquid has to fulfil further requirements depending on the field of application. These might be, for example,... 

The delivery characteristics of LRVPs are affected by the properties of the ring liquid and of the medium to be pumped. 

Contrary to the expenditures for compression (Eq. (3.1)) and pressure increase (Eq. (3.2)), power dissipation loss depends on the material data of the ring liquid. Eq. (3.3) refers to a proportional impact of the density pp on the power dissipation loss. The impact of other parameters such as the flow regime, the geometry and the viscosity is summarised in the pressure loss coefficient f. 

Because of the functional principle of LRVPs, an intensive phase contact exists bettveen the operating liquid and the medium to be compressed. Therefore, the available working chamber Vis partially filled by the vapour of the ring liquid V p in addition to the medium to be pumped. Thus, the suction capacity is reduced by the vapour of the ring liquid ... 

If one proceeds from the position of the equilibrium condition, the partial vapour pressure and the volume enclosed by the vapour of the ring liquid are determined by the temperature of the ring liquid. 

One can assume in a simplified manner that the gas and liquid temperature are identical at the pressure-side connection. If the suction medium is significantly colder than the ring liquid, then the cooling down of the ring liquid can also occur here. The energy balance around the LRVP reads... 

Heat input by inert gas Heat input by vapour Heat input by compression Heat input by the ring liquid... 

A regulation of the operating liquid temperature should take place in principle on the basis of the ring liquid escaping on the pressure side of the compressor stage, since otherwise energy inputs by gas and vapour as well as the variability of the amount of liquid remain unconsidered. 

However, one finds no hydraulic suction capacity in the catalogue. The characteristics described here apply mostly to the compression of dry air and of an operating water temperature of approximately 18 C(15"C- -3K heating). Thus, in these values, the modification of the suction capacity by the vapour of the ring liquid and by the temperatures of gas and ring liquid are already considered. 

LRVPs should be operated with suction pressures below the double vapour pressure of the ring liquid delivered on the pressure side with a gas ejector. With the aid of the ejector, the gas to be sucked off is compressed and the LRVP is fed with higher pressure. The result is an increase in the suction capacity of the working point. Furthermore, the noise developments are prevented by flow separations. 

A cause of the noise emissions most frequently to be encountered are separation noises via the operation close to the vapour pressure of the ring liquid or with a pressure difference which is too great. Previous experiences in numerous applications have shown that over wide ranges of two-stage LRVPs tend less to separation noises. However, they were replaced in numerous applications for lack of space and for reasons of economy by single-stage closed coupled pumps. 

Due to the intensive phase contact between the ring liquid and the medium to be absorbed, the compression takes place almost isothermally, that is the temperature gas changes only marginally. Thus, almost the entire shaft power supplied as well as the heat brought in via the incoming media must be discharged in the form of heat via the operating liquid. 

If no open cooling circuit is possible due to the structural conditions of the procedural processes, then the ring liquid is completely returned. The heat is then to be dissipated via an additional heat exchanger. It is now a matter of a closed circuit cooling (Figure 3.33). 

Due to the principle of operation, the working range of LRVPs is hmited by the vapour pressure of the ring liquid. However, if a vacuum is necessary below the double vapour pressure of the operating liquid, then a further compressor must be connected upstream, with the aid of which one can realise lower intake pressures. 

The use of gas ejectors for precompression is the simplest variant for the generation of a vacuum below the double vapour pressure ofthe ring liquid (Figure 3.34). 

With further divergence of the boiling pressure of the ring liquid, the gas entering via the propellant nozzle as well as the restrictor losses in the narrow mixing tube produces a decrease in the suction capacity of the combination, so that an operation without gas ejector makes sense. 

It is to be taken into account that with the employment of rotary piston vacuum pumps, the temperature of the fluid fed to the liquid ring compressor is higher than with the other combinations. In addition, this heat is to be dissipated by the ring liquid, so that the temperature of the liquid ring will be higher and with it the suction capacity will be lower. 

Similar to the descriptions in Figure 3.41, the ring liquid is accelerated by the cavitation into the space which is becoming open due to the condensation. Thus, the liquid ring reaches the hub before the conclusion of the volume decrease and almost fills the whole area between the blades. 

Ferrofluid (sealing) A suspension of colloidal (approx. 10 nm) magnetic particles (Fe304) in a fluid. See also Ferrofluidic seal 0-ring, liquid. 

O-ring, liquid (vacuum technology) A ferrofluid seal used in rotary motion feedthroughs. 

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