Lekce 1: Liquid ring compressors
Kapitola 1: Liquid ring compressors
A liquid ring compressor is a type of a vane compressor, which works on a similiar principle as liquid ring pumps. It expels liquid with a centrifugal force and thus creates a liquid ring that forms a seal. Liquid ring compressors are dust free and do not need any oil but, but they are not as efficient as other types of compressors. Because water is the most often used liquid, they are often also called water ring compressors.
Description
The rotor is usually positioned centrally in a casing of an oval shape. When it rotates, a ring of liquid, usually water, is formed. The ring adapts the shape of the casing and moves with the rotor. There are two places where the rotational axis is nearest to the casing and here the liquid completeley fills the chambers of the rotor.
Operation
During the rotation the liquid follows the profile of the casing and recedes from the chambers, leaving an empty space behind, which is filled by gas. Thus the gas is sucked into the compressor. The rotation continues and the liquid is pushed to the chambers again, which compresses the gas. The gas is expelled and leaves the compressor, and the whole process can start again. The liquid in the compressor seals the clearances between inlet and discharge port and prevents the gas from leaking. At the same time it cools the compressor.
The liquid has to be supplied to the compressor during the process, because it is expelled together with the compressed gas. Both the gas and the liquid are separated in a discharge separator.
Vocabulary
Liquid ring compressor, water ring compressor – vodokružný kompresor
Liquid ring pump – vodokružná vývěva
Liquid – kapalina
Vane – lopatka
Expel – vytlačit
Centrifugal force – odstředivá síla
Seal – těsnění
Dust – prach
Efficient – výkonný
Casing – obal, kryt
Oval – oválný
Shape – tvar
Profile – obrys
Recede – ustupovat
Gas – plyn
Suck – sát
Chamber – komora
Compress – stlačit
Clearance – mezera
Inlet port – vstupní otvor
Discharge port – výstupní, výtlačný otvor
Leaking – netěsnost
Cool – chladit
Supply – dodávat
Separate – oddělit
Kapitola 2: Cvičení
- Studenti zpracují na téma Liquid Ring Compressors powerpointovou prezentaci.
Kapitola 3: Kontrolní otázky
- Can you describe a liquid ring compressor?
- How does it operate?
- What are its advantages and disadvantages?
Kapitola 4: Autotest
- How are liquid ring compressors sealed?
- What is their biggest disadvantage?
- What is the usual position of the rotor in the casing?
- What do they compress?
- Why does the liquid have to be supplied during the process?
Lekce 2: Liquid ring pumps
Kapitola 1: Liquid ring pumps
A liquid ring pump, also called a liquid ring vacuum pump, is a type of a rotating positive displacement pump. These pumps are typically used as a vacuum pump or as a gas compressor.
Their function is quite similar to a rotary vane pump, but rotary vane pumps are a part of the rotor. One of the advantages of the liquid ring pumps is a very low sliding friction, which is limited only to the shaft seals.
Way of operation
Liquid ring pumps have a rotating vaned impeller and a cylindrical casing. Liquid, which usually means water, goes into the pump, where it is accelerated and this centrifugal acceleration causes that it forms a cylindrical ring against the inside of the casing. This water ring functions as a seal in the space between the impeller vanes.
Air or some other gas is drawn into the pump through the inlet valve and is trapped in the compression chambers, which were formed by the impeller vanes and the liquid ring.
Types of liquid ring pumps and their applications
Multi-stage pumps have two compression stages on a common shaft. The attainable pressure reduction is limited by the vapour pressure of the ring-liquid. As the vacuum generated approaches the vapour pressure of the ring-liquid, the increasing volume of vapor released from the ring-liquid diminishes the remaining vacuum capacity. The efficiency of the system declines as a result.
Under typical conditions (which for most manufacturers means that the pumped gas is dry air and the sealant liquid creating the ring is water of about 15°C) the single stage pumps usually produce vacuum to 35 torr, and two-stage pumps can produce vacuum to 25 torr.
Liquid ring pumps are quite simple, but highly reliable pumps and they have a wide variety of industrial applications. As an example we can mention production of molded paper pulp products, such as egg cartons and other sorts of packaging. They are also used for soil decontamination, where contaminated ground water is pumped from wells by vacuum.
Although the most typical sealant liquid found in liquid ring vacuum pumps is water (and the pumps are sometimes called “water-ring“ in this case), in fact any liquid compatible with the process can be used, if it has appropriate vapor pressure properties. Very often oil is used as well, but because it has a very low vapor pressure, pumps with this sort of sealant are usually air-cooled.
Vocabulary
Liquid ring pump, liquid ring vacuum pump – vodokružná vývěva
Positive displacement pump – objemové čerpadlo
vane – lamela
impeller – oběžné kolo
casing – obal
rotary vane pump – rotační lamelové čerpadlo
churn –vířit
chamber – komora
seal – těsnění
friction – tření
sliding friction – kluzné tření
centrifugal acceleration – odstředivé zrychlení
axis – osa
volume – objem
shaft – hřídel
vacuum – podtlak
vapour pressure – tlak páry
sealant – těsnící materiál
molded paper pulp products – výrobky z lisované papírové drtě
ground water – podzemní voda
well – studna
air-cooled – chlazený vzduchem
Kapitola 2: Cvičení
- Studenti zpracují na téma Liquid Ring Pumps powerpointovou prezentaci.
Kapitola 3: Kontrolní otázky
- Can you describe a liquid ring pump?
- How does it operate?
- Can you give some examples of their application?
Kapitola 4: Autotest
- Liquid ring pump
- The most typical liquid is
- How big is the underpressure produced by single-stage liquid-ring pumps?
- What is their typical characteristics?
- If the liquid ring is made of oil,