Properties[edit]
A tanker truck for transporting liquid vacuum at a refueling point.
A liquid vacuum is a liquid without color, taste, odor, viscosity, density, or name (the name "liquid vacuum" does not refer to liquid vacuum as such and is in fact a pseudonym). At a temperature of -300C it boils, creating an area of negative pressure above the surface (it is not recommended to cover containers with boiling liquid vacuum to avoid suction), at a pressure of 6000 GPa it crystallizes into needle-shaped blue crystals
. It has been suggested that when shaken, a liquid vacuum is prone to detonation, but none of those who conducted the relevant experiments lived to see the publication of their results in scientific journals, so science does not yet have accurate data on its detonation properties.
After a long period of keeping liquid vacuum in a “dead state” (lack of influence of factors inherent to the Earth), the substance, being in a spatially independent state, is capable of combining with vacuum in a “living state” to form a third state of vacuum, existing parallel to the first two. For a simpler distinction between vacuum states, in 2010 the Russian scientist P.S. Goncharov announced the names of three states:
- Vodkuum - liquid-dead vacuum;
- Dmokuum - vacuum-like gases;
- The living state of vacuum is Florofaukuum.
What is a vacuum?
Very often people come to us who want to buy a vacuum pump, but have little idea what a vacuum is. Let's try to figure out what it is. By definition, a vacuum is a space free of matter (from the Latin word “vacuus” - empty). There are several definitions of vacuum: technical vacuum, physical vacuum, cosmic vacuum, etc. We will consider technical vacuum, which is defined as a highly rarefied gas.
Let's look at an example of what vacuum is and how it is measured. On our planet there is an atmospheric pressure taken as one (one atmosphere). It changes depending on the weather, altitude and sea level, but we will not take this into account, since this will not in any way affect the understanding of the concept of vacuum. So, we have pressure on the surface of the earth equal to 1 atmosphere. Everything below 1 atmosphere (in a closed vessel) is called technical vacuum.
Let's take a vessel and close it with an airtight lid. The pressure in the vessel will be 1 atmosphere. If we begin to pump air out of a vessel, a vacuum will arise in it, which is called a vacuum. Let's look at an example: there are 10 circles in the left vessel. Let it be 1 and half - we get 0.5 atm, leave one - we get 0.1 atm.
Since there is only one atmosphere in the vessel, then we can get the maximum possible vacuum (theoretically) zero a - because It is almost impossible to catch all the air molecules from the vessel. Therefore, in any vessel from which air (gas) has been pumped out, some minimum amount of it always remains. This is called “residual pressure,” that is, the pressure that remains in the vessel after pumping gases out of it. There are special pumps that can reach a deep vacuum of up to 0.00001 Pa, but still not to zero. In ordinary life, a vacuum deeper than 0.5 - 10 Pa (0.00005-0.0001 atm) is rarely required.
There are several options for measuring vacuum, which depend on the choice of reference point: 1. Atmospheric pressure is taken as the unit. Everything below one is a vacuum. That is, the vacuum gauge scale is from 1 to 0 atm (1…0.9…0.8…0.7…..0.2…0.1….0). 2. Atmospheric pressure is taken as zero. That is, a vacuum - all negative numbers are less than 0 and up to -1. That is, the vacuum gauge scale is from 0 to -1 (0, -0.1...-0.2....,-0.9,...-1). Also, scales can be in kPa, mBar, but this is all similar to scales in atmospheres.
The picture shows vacuum gauges with different scales that show the same vacuum:
From all that has been said above, it is clear that the magnitude of the vacuum cannot be greater than atmospheric pressure.
People contact us almost every day who want to get a vacuum of -2, -3 atm, etc. And they are very surprised when they find out that this is impossible (by the way, every second of them says that “you yourself don’t know anything,” “but it’s like that with your neighbor,” etc., etc.)
In fact, all these people want to mold parts under vacuum, but so that the pressure on the part is more than 1 kg/cm2 (1 atmosphere). This can be achieved by covering the product with a film, pumping out the air from under it (in this case, depending on the vacuum created, the maximum pressure will be 1 kg/cm2 (1 atm=1 kg/cm2)), and then placing it all in an autoclave in which excess pressure will be created. That is, to create a pressure of 2 kg/cm2, it is enough to create an excess pressure of 1 atm in the autoclave.
Now a few words about how many clients measure vacuum at the Ampika Pumps LLC exhibition in our office: they turn on the pump, place their finger (palm) on the suction hole of the vacuum pump and immediately draw a conclusion about the vacuum value.
Usually, everyone really likes to compare the Soviet vacuum pump 2NVR-5DM and its analogue VE-2100, which we offer. After such a check, they always say the same thing - the vacuum of the 2NVR-5DM is higher (although in fact both pumps produce the same vacuum parameters).
What is the reason for this reaction? And as always - in the lack of knowledge of the laws of physics and what pressure is in general.
A little educational background: pressure “P” is a force that acts on a certain surface area, directed perpendicular to this surface (the ratio of the force “F” to the surface area “S”), that is, P = F/S. In simple terms, it is a force distributed over a surface area. From this formula it can be seen that the larger the surface area, the lower the pressure will be. And also the force that is required to lift a hand or finger from the pump inlet is directly proportional to the surface area (F=P*S). The diameter of the suction hole of the 2NVR-5DM vacuum pump is 25 mm (surface area 78.5 mm2). The suction hole diameter of the VE-2100 vacuum pump is 6 mm (surface area 18.8 mm2). That is, to lift a hand from a hole with a diameter of 25 mm, a force 4.2 times greater is required than for a hole with a diameter of 6 mm (at the same pressure). This is why, when vacuum is measured with fingers, such a paradox results. Pressure "P", in this case, is calculated as the difference between atmospheric pressure and the residual pressure in the vessel (that is, the vacuum in the pump).
How to calculate the force of pressing a part against a surface? Very simple. You can use the formula given above, but let's try to explain it more simply. For example, let’s say you need to find out with what force a part measuring 10x10 cm can be pressed when a vacuum is created under it with a VVN 1-0.75 pump.
We take the residual pressure that this vacuum pump of the BBH series creates. Specifically, for this water ring pump VVN 1-0.75 it is 0.4 atm. 1 atmosphere is equal to 1 kg/cm2. The surface area of the part is 100 cm2 (10 cm x 10 cm). That is, if you create a maximum vacuum (that is, the pressure on the part will be 1 atm), then the part will be pressed with a force of 100 kg. Since we have a vacuum of 0.4 atm, the pressure will be 0.4x100 = 40 kg. But this is in theory, under ideal conditions, if there is no air leakage, etc. In reality, you need to take this into account and the pressure will be 20...40% less depending on the type of surface, pumping speed, etc.
Now a few words about mechanical vacuum gauges. These devices indicate residual pressure in the range of 0.05...1 atm. That is, it will not show a deeper vacuum (it will always show “0”). For example, in any rotary vane vacuum pump, once its maximum vacuum is reached, the mechanical vacuum gauge will always read “0”. If a visual display of residual pressure values is required, then you need to install an electronic vacuum gauge, for example VG-64.
Often clients come to us who mold parts under vacuum (for example, parts made of composite materials: carbon fiber, fiberglass, etc.), this is necessary so that during molding gas escapes from the binder (resin) and thereby improves properties of the finished product, as well as the part was pressed to the mold with a film, from under which air was pumped out. The question arises: which vacuum pump to use - single-stage or two-stage? They usually think that since the vacuum of a two-stage is higher, the parts will be better.
The vacuum for a single-stage pump is 20 Pa, for a two-stage pump it is 2 Pa. It seems that since the difference in pressure is 10 times, the part will be pressed much stronger. But is this really so?
1 atm = 100000 Pa = 1 kg/cm2. This means that the difference in film pressure at a vacuum of 20 Pa and 2 Pa will be 0.00018 kg/cm2 (if you’re not too lazy, you can do the calculations yourself).
That is, practically, there will be no difference, because... a gain of 0.18 g in clamping force will not change the weather.
Calculation of container evacuation time
How to calculate how long it will take for a vacuum pump to pump out a vacuum chamber? Unlike liquids, gases occupy the entire available volume, and if a vacuum pump has pumped out half of the air in the vacuum chamber, the remaining air will expand again and occupy the entire volume. Below is the formula to calculate this parameter.
t = (V/S)*ln(p1/p2)*F
, Where
t is the time (in hours) required to pump out the vacuum volume from pressure p1 to pressure p2 V is the volume of the pumped out container, m3 S is the speed of the vacuum pump, m3/hour p1 is the initial pressure in the pumped out container, mbar p2 is the final pressure in the pumped out container capacity, mbar ln - natural logarithm
F - correction factor, depends on the final pressure in the tank p2: - p2 from 1000 to 250 mbar F=1 - p2 from 250 to 100 mbar F=1.5 - p2 from 100 to 50 mbar F=1.75 - p2 from 50 to 20 mbar F=2 - p2 from 20 to 5 mbar F=2.5 - p2 from 5 to 1 mbar F=3
In a nutshell, that's it. We hope that this information will help someone make the right choice of vacuum equipment and show off their knowledge over a glass of beer...
General information[edit]
Model of a liquid vacuum molecule.
As you can see in the picture on the right, this is a liquid vacuum molecule. Few people know that liquid vacuum is one of the allotropic modifications of the chemical element Vak, or more precisely, vacuum cast iron (ChuVak). Vacuum cast iron is a salt of cast iron acid. This is the least stable modification of vacuum; when heated above the temperature of absolute zero, it turns into ordinary vacuum, and another element is released - cast iron (this confirms the possibility of cold fusion, which gives hope for the creation of a perpetual motion machine in the next 54,308,428,790 203,478 762 340 052 723 346 983 453 487 023 489 987 231 275 412 390 872 348 475 years). In a free state, cast iron can only exist for 0.0000000000000000000000000000000000000000001 seconds, so it almost immediately turns into a vacuum radical, as can be seen in the figure.
Application area
- Separation of liquid mixtures of substances that differ in boiling point (less than 60 °C - with a reflux condenser, with more than 60 °C - simple distillation) and having a high boiling point. Example: separation of DMSO from a mixture of acetone (bp 56 °C)/dimethyl sulfoxide (DMSO) (bp 189 °C with decomposition at 1 atm., ~60 °C in a vacuum of a water-jet pump without decomposition).
- Separation of a high-boiling liquid substance from non-volatile impurities (solid components). Example: distillation of DMSO over calcium hydride (non-volatile).
- Separation of inseparable mixtures at atmospheric pressure. Example: separation of an ethanol/water azeotrope. Ethanol boils at 70 mm. rt. Art. at 28 °C without forming an azeotrope with water.
- Vacuum distillation is often used to purify commercial high-boiling solvents, reagents, and to purify and isolate thermolabile or high-boiling reaction products.
Receipt[edit]
In ancient times, liquid vacuum was obtained from the dried liver of a crocodile that died while attempting to rape the corpse of a virgin who had died of mad cow disease and alcoholism. To do this, dry liver, crushed in a diamond mortar and pestle from the shin bone of a negro parricide hanged on a full moon, was mixed in equal parts with “Go Away” powder and purple ink from a Lexmark ZX-25 printer; then the mixture was brought to a boil and simmered until the reality show “Dom-2” was taken off the air, after which it was drunk in one gulp by the operator of the KVU-16A cryogenic-vacuum installation (or more powerful) produced by the Kazan Optical-Mechanical Plant, which installation and produces a liquid vacuum during the operator's preparation of the infernal potion.
There are currently two known methods for producing liquid vacuum.
Complex method[edit]
Based on the property of ordinary (non-liquid) vacuum to condense when cooled to temperatures below absolute zero. Invented and first put into practice by James Maxwell in 1954 in preparation for the Cold War. This method is kept in deep secrecy.
Simple method[edit]
Soviet scientists found their own method for producing liquid vacuum on an industrial scale (described by Chomsky in his 1984 work "Introduction to Extraction"). The method is based on the ability of the storekeeper of warehouse No. 4 at the USSR Academy of Sciences to issue the required amount of liquid vacuum to the bearer of a properly completed application. How to properly fill out an application is kept a closely guarded secret.
Basic laws of GAS PHYSICS and the equation of state of an ideal gas.
Boyle-Marriott law.The Boyle-Mariotte law was established by the English physicist Robert Boyle in 1662 and independently by the French scientist Edme Mariotte in 1679 and sounds like this: For a given mass of gas at a constant temperature, the product of its pressure p for volume As an example: When the volume of a certain amount of gas gradually increases, in order to keep its temperature constant, the gas pressure must also gradually decrease. | |
Gay-Lussac's law.Law relating gas volume V and its temperature For a given mass of gas at constant pressure, the ratio of the volume of the gas to its temperature is a constant value. VT = const [ 3 ] This law is also called the LAW OF ISOBAR PROCESS. As an example: When a certain amount of gas is gradually heated, in order to keep the pressure constant, the gas must also gradually expand. | |
Charles's law.Law relating gas pressure p and its temperature For a given mass of gas in a closed, sealed volume, the gas pressure is always directly proportional to its temperature. pT = const [ 4 ] This law is also called the LAW OF ISOCHORIC PROCESS. As an example: When a certain amount of gas is gradually heated in a closed volume, its pressure will also gradually increase. | |
Equation of state of an ideal gas.The equation that allows us to generalize all three basic gas laws of thermodynamics is called the ideal gas equation of state or the Mendeleev-Clapeyron equation. It gives the relationship between the three most important macroscopic parameters that describe the state of an ideal gas: pressure p, volume V, temperature T, and has the form: [ 5 ] | |
or when written in another form: [ 6 ]
| p ∗ V = | m | ∗R∗T |
| μ |
Where:
p
– gas pressure,
Pa
(N/m2)
V
– gas volume,
m3
m
– gas mass,
kg
μ
– molar mass of gas
R = 8.31 J/mol ∗ K
– universal gas constant,
T
– gas temperature,
°K
(degrees absolute Kelvin scale).
An ideal gas is a gas whose particles are material points that do not interact at a distance and experience absolutely elastic collisions with each other and with the walls of vessels.
It is important to understand that all gas laws work for a fixed mass (amount) of gas.
These laws work well for vacuum regimes and are not acceptable at very high pressures and temperatures.
Application[edit]
The patient takes liquid vacuum. In military affairs, Liquid vacuum mixed with red mercury was previously used as a filler for vacuum bombs; Currently, the more resistant vacuum cast iron is usually used for this purpose. In aeronautics For quickly deflating balloons or assembling drogue parachutes, as well as for filling lead airships. In the confectionery industry Blue crystals formed during crystallization of liquid vacuum are included in the composition of some chewing gums. Being added to caramel, it ensures effective absorption of jam inside. Table salt, purified by liquid vacuum and used daily in food. In medicine, liquid vacuum is sometimes used to create a vacuum in medical jars. For bloating, doctors recommend taking 2-3 drops of Liquid Vacuum. In fundamental science, many scientists use liquid vacuum to blackmail state leaders in order to obtain funds for obtaining liquid vacuum to blackmail state leaders in order to obtain funds for obtaining liquid vacuum... (see Recursion) In the chemical industry, Liquid vacuum is widely used for cleaning crystals from technical impurities. In everyday life For refilling Dumbo brand vacuum cleaners.
Equipment
A typical device for vacuum distillation with a reflux condenser is shown in the figure:
- Round bottom flask with stock solution (A). The liquid should occupy no more than 1/3 of the volume of the flask to prevent boiling liquid from escaping into the receiving flask. Claisen flasks are often used for vacuum distillation ( B), already including a reflux condenser and an adapter for a thermometer and refrigerator. Important! Only use flasks with a round bottom. Look
A B
- Paw. Important! The metal foot should NOT come into contact with the glass to avoid cracking the flask during distillation. To do this, rubber gaskets are placed between the flask and the foot. Look
- Wurtz nozzle or 3-way adapter. The Wurtz nozzle is selected from option ( A ) for liquids with a boiling point of less than 120 °C and ( B ) for liquids with a temperature of more than 120 °C. Look
- Dephlegmator. The length of the reflux condenser is selected from the condition that the narrower the temperature range, the longer the reflux condenser. In terms of separating ability, one of the best reflux condensers is with a nozzle made from pieces of glass spiral. Look
- Thermometer. It is selected from the required boiling point of the liquid and is inserted into the Wurtz nozzle so that the upper part of the mercury ball coincides with the lower part of the side outlet of the nozzle. A non-ground thermometer can be used if an appropriate attachment is available. Look
- Liebig refrigerator. The Liebig refrigerator ( 1 ) is used for liquids with a boiling point up to 120 °C. Its length is greater, the lower the boiling point of the substance. Connect the refrigerator to the water so that the water flow is directed against the movement of vapor. To facilitate connection, the outer surface of the core can be moistened with water. For substances with a boiling point of more than 120 °C, an air cooler is used, or distillation is carried out without a refrigerator. In rare cases, you can use a reflux condenser ( 2 ). Look
- Allonge and receiving flasks. Allonge is selected based on the following criteria: Allonge with lateral outlet (A) – for the distillation of a single fraction. A hose is connected to the outlet and directed to the vacuum pump (through the trap). Allonge the “spider” ( B) are used to change fractions with a certain boiling point, the tap is used as in the case of allonge (A). Look
A B
- Trap. When using an oil pump, place a liquid nitrogen trap in front of the pump to prevent steam from entering the pump. Look
- Heating element. Selected based on the properties of the distilled mixture. Heaters and flame burners - for non-flammable liquids. Oil baths (boil the substance up to 200 °C) - for more precise temperature control in the distillation flask. In this case, the temperature of the bath is 20-30 °C higher than the boiling point of the liquid.
