Kapitsa Petr Leonidovich(1894- 1984) - famous Soviet physicist; Nobel Prize Laureate; student of E. Rutherford.
Kapitsa discovered the superfluidity of liquid helium and developed new industrial methods for liquefying gases. Kapitsa's work on creating super-strong magnetic fields and high-power electronic generators is of great importance.
There are many types of machines for producing liquid gases, in particular liquid air. In modern industrial installations, significant cooling is achieved by expanding the gas under thermal insulation conditions (adiabatic expansion).
Such machines are called expanders. The expanding gas does work by moving a piston (piston expanders) or rotating a turbine (turbine expanders) using its internal energy and is therefore cooled.
High-performance turboexpanders low pressure were developed by academician P. L. Kapitsa. Since the 50s, all large installations in the world for liquefying air have been operating according to the Kapitsa scheme.
Figure 6.14 shows a simplified diagram of a piston expander. Atmospheric air enters the compressor 1 , where it is compressed to a pressure of several tens of atmospheres. Air heated by compression is cooled in a heat exchanger 2 running water and enters the expander cylinder 3. Here, expanding, it does work by pushing the piston, and cools so much that it condenses into liquid. Liquefied air enters the vessel 4.
The boiling point of liquid air is very low. At atmospheric pressure it is -193 °C. Therefore, liquid air in an open vessel, when its vapor pressure is equal to atmospheric pressure, boiling. Since the surrounding bodies are much warmer, the heat flow to the liquid air, if it were stored in ordinary vessels, would be so significant that in a very short time all the liquid air would evaporate.
Storage of liquid gases
To keep air in a liquid state, it is necessary to prevent its heat exchange with environment. For this purpose, liquid air (and other liquid gases) is placed in special vessels called Dewar flasks. A Dewar flask is designed in the same way as a regular thermos. It has double glass walls, from the space between which air is pumped out (Fig. 6.15). This reduces the thermal conductivity of the vessel. The inner wall is made shiny (silvered) to reduce heating by radiation. Dewar flasks have a narrow neck, when stored in them liquefied gases they are left open so that the gas contained in the vessel has the opportunity to gradually evaporate. Due to the loss of heat through evaporation, liquefied gas remains cold all the time. In a good Dewar flask, liquid air can be stored for several weeks.
Application of liquefied gases
Liquefaction of gases has technical and scientific significance. Air liquefaction is used in technology to separate air into its component parts. The method is based on the fact that the various gases that make up the air boil at different temperatures. Helium, neon, nitrogen, and argon have the lowest boiling points. Oxygen has a slightly higher boiling point than argon. Therefore, helium, neon, nitrogen are evaporated first, and then argon and oxygen.
Liquefied gases are widely used in technology. Nitrogen is used to produce ammonia and nitrogen salts used in agriculture for fertilizing the soil. Argon, neon and other inert gases are used to fill incandescent electric lamps, as well as gas-light lamps. Most Applications has oxygen. When mixed with acetylene or hydrogen, it produces a very high temperature flame used for cutting and welding metals. Injection of oxygen (oxygen blast) accelerates metallurgical processes. Oxygen delivered from pharmacies in pillows alleviates the suffering of patients. Particularly important is the use of liquid oxygen as an oxidizer for space rocket engines. The engines of the launch vehicle that lifted the first cosmonaut Yu. A. Gagarin into space ran on liquid oxygen.
Liquid hydrogen is used as fuel in space rockets. For example, refueling the American Saturn 5 rocket requires 90 tons of liquid hydrogen.
Gases used in industry, medicine, etc. are easier to transport when they are in a liquefied state, since a larger amount of substance is contained in the same volume. This is how liquid carbon dioxide is delivered in steel cylinders to carbonated water factories.
Liquid ammonia is widely used in refrigerators - huge warehouses where perishable foods are stored. The cooling that occurs during the evaporation of liquefied gases is used in refrigerators when transporting perishable products.
TABLE OF CONTENTSPreface 3
FIRST PART
Liquefaction of gases
CHAPTER I First stages 7
Vapor pressure of liquids - Saturated and unsaturated vapors 8
Changes in the vapor pressure of various liquids depending on the properties of the latter and their temperature 10
Heat of vaporization 11
The need for cold for the existence of liquefied gases at atmospheric pressure 12
Effect of pressure on boiling point 13
Pressure reduction 13
Refrigerating machines based on the principle of evaporation 13
Pressure increase 15
Possibility of using pressure instead of cooling when producing some liquefied gases 16
The transformation of saturated vapor into liquid under the influence of pressure exceeding its elasticity 18
Reversibility of evaporation and liquefaction phenomena 20
Heat of liquefaction 21
Unsaturated steam, subjected to pressure, is compressed like a gas before becoming saturated steam 22
Deviation of unsaturated vapors from Mariotte’s law as they approach the saturation state 23
Liquefaction by simple cooling 25
Liquefaction by simple pressure 27
Faraday's experiments 28
Apparatus Tilorier 30
Some properties of solid carbon dioxide 32
Liquefaction using simultaneous compression and cooling 33
Faraday's further experiments 33
CHAPTER II Critical Point 35
New failures and their causes 35
The works of Cagnard de la Tour and the opinion of Faraday 37
Andrews experiments 38
Krisha point and its determining conditions 42
Classification of gases according to their liquefiability 43
Andrews classification 45
CHAPTER III Liquefaction of permanent gases 45
Experiments Calete 45
Pictet Experience 50
Experiments by Olszewski and Wroblewski 54
Kamerlingh Onnes experiments 56
SECOND PART
Industrial air liquefaction
CHAPTER IV Expansion and Siemens heat exchanger From Siemens to
Linda 58
Disadvantage of the multiple cycle method 58
Why does expansion produce cold? 59
Two main ways to expand 60
The need to use heat exchangers 61
About failed attempts 63
Joule and Thomson experiment 64
Gamson method and apparatus 67
The heat exchanger is not only designed to increase cooling 69
Process and apparatus Linde 71
A little about the history of my work 74
Comparison of two expansion methods 79
Expansion with external work 82
Expansion by simple expiration 83
CHAPTER V Imperfection of the gaseous state Works of Vander Waals 86
Corresponding states 94
Air compressibility at low temperatures 100
Works by Vitkovsky 100
CHAPTER VI Expansion by simple expiration 104
Calculation of efficiency 104
Expansion of an imperfect gas by simple outflow 107
The drop in temperature during expansion creates an imaginary and exaggerated idea of the cooling effect 117
Improvements made by Linde to the way it expands with internal work 117
Calculation of the cooling effect of expansion using the Linde method 121
CHAPTER VII Expansion using external work 121
Automatic lubrication Petroleum ether 125
First experiments 129
First successes 131
Disadvantages of expansion with liquefaction in a machine 132
Pressure liquefaction 135
Practical application 139
A few words about the use of expansion energy 142
End Expansion Improvement Double Expansion 143
Multiple expansion 147
Another way 148
Single expansion or double expansion when liquefying oxygen under pressure 149
Calculation of the marginal utility of expansion with external work 151
Amount of returned energy 157
supply of liquefier with oxygen 157
Other works in the field of expansion with external work 157
THE THIRD PART
Storage and properties of liquid air
CHAPTER VIII Liquid air storage 160
Difficult task 160
The first means to slow down evaporation 165
D'Arsonval method Vessels with double walls and airless space between them 166
Improvement of Dewar Vessels with double silvered walls and airless space between them 170
Transfusion apparatus Precautions required when working with liquid air 172
Degree of suitability of d'Arsonval and Dewar vessels 175
The use of low temperatures to create a perfect vacuum 177
Impossibility of storing liquid air in closed vessels 178
CHAPTER IX Physical properties and the use of liquid air 179
Color 179
Change in the boiling point of mixtures of oxygen and nitrogen depending on their composition 180
Change in boiling point or liquefaction depending on pressure 182
Densities of liquid air, liquid oxygen and liquid nitrogen 184
Heat of evaporation of liquid air: Application as a coolant 185
Heat capacity of liquid air 187
Exceptional phenomena caused by the spheroidal state 187
Harmlessness of liquid air for microbes 190
Magnetic properties of liquid air 191
Some consequences of liquid air cooling of the semi-flame Bunsen burner 192
Solidification of various bodies in liquid air 193
Skin abnormality 195
Changing the adhesion of metals 195
Freezing liquids: mercury, alcohol, etc. 197
Petroleum ether D’Arsonval’s experiments Thermometers for liquid air 198
Obtaining new gases from the atmosphere Proceedings of V Ramsay Liquefaction of helium 200
Freezing of gases Industrial production of hydrogen 202
Freezing air 202
Atmospheric air liquefaction 204
Properties of coal at liquid air temperatures. Industrial production high vacuum 205
Possible applications of the properties of cooled coal - Manufacture of incandescent lamps Metal vessels for liquid air 209
Production of liquid oxygen near waterfalls 210
Application of the absorption properties of coal in the manufacture of neon tubes 212
Absorption of various gases by coal Hydrogen anomaly 213
Application of cooled coal for separation of noble gases 215
Heat capacity of bodies at low temperatures 216
Electrical resistance of metals at low temperatures 216
Works by Kammerling-Onnes One degree from absolute zero 217
Magnetic properties of metals at low temperatures 219
Color changes Phosphorescence 219
Experiments by J. Becquerel, P. Lebeau and others 220
The use of liquid air when fitting metal rings, etc. 220
Application of liquid air as a driving force 221
Decrease in chemical affinity at low temperatures 223
CHAPTER X Properties and applications of liquid oxygen 224
Combustion in liquid oxygen 225
Explosiveness 227
Explosives with liquid oxygen 228
The current state of the issue of the use of liquid oxygen as an explosive 233
Other applications of liquid oxygen 235
Rescue apparatus Application of liquid oxygen in medicine 235
Respirators for aviators 239
Conversion of oxygen into ozone at low temperatures 240
FOURTH PART
Separation of air into its constituent elements
CHAPTER XI General considerations Various ways 241
The significance of this problem 241
The separation of air into elements requires energy 242
Various methods for oxygen from air 246
CHAPTER XII Some features of the evaporation of liquid air
Parkinson's idea 247
Features of liquid air evaporation 248
Bailey's experiments 251
CHAPTER XIII Cold recovery 253
Simultaneous evaporation and liquefaction 254
The need to compress liquefied air 258
Need for additional cold 259
Level indicators for liquid air 261
CHAPTER XIV Various methods of successive evaporation 263
Linde's first apparatus (1895) 263
Gamson's apparatus (1896) 265
Apparatus Troupe 266
Pictet method (1899) 267
CHAPTER XV Oxygen of the air is the first to liquefy 268
CHAPTER XVI Some considerations regarding the liquefaction of gas mixtures 272
Liquefaction of gas mixtures at constant temperature 274
Duhem's graphic method and its application to determine the corresponding contents 281
CHAPTER XVII Application of preliminary liquefaction of atmospheric oxygen 284
Pre-reflux (1902) 291
CHAPTER XVIII Rectification 297
Linde apparatus (1902) 298
Apparatus of Levi and Gelbronner (1902), Pictet (1903) 300
Apparatus J. Claude 300
Liquid supply quantity indicators 301
Producing two different liquids in a single liquid bath 301
Conditions necessary for correct rectification 303
Improvements in lean fluid production 304
Practical application of pre-refluxation Apparatus with a “single cycle” 306
Heat exchangers with two compartments 309
Thermodynamic efficiency when separating air elements by liquefaction 309
Other methods - Re-liquefaction (Levi, Gelbronner) 312
Various methods of partial separation of oxygen and nitrogen during air liquefaction - The principle of increasing self-purification of nitrogen - Method R Levy (1903) 313
Production of 4hctocq nitrogen, Linde method 316
Linde's new device
Equipment for liquid oxygen 318
Apparatus Le Rouge (Air Liquide Company) 319
Messer apparatus 321
Device Industriegas-Gesellschaft 322
Rational diagram of the apparatus for liquid oxygen 324
CHAPTER XIX Operation of apparatus 324
Air purification 324
Carbon dioxide removal 325
Cooling drying 327
Linde 327 scheme
J. Claude heat exchangers with defrosting 328
Amount of cold consumed during cooling drying 330
Starting up the O-va lAir Liquide 330 device
Expansion Energy Use 335
Accidents that occurred during the operation of devices 338
CHAPTER XX Production of noble gases 344
Helium and neon 345
Determination of neon and helium content in atmospheric air 346
Helium, ammonia and aeronautics 347
Helium in the United States and Canada 348
Argon 351
Krypton and xenon 354
PREFACE
Twenty-seven years ago I was called a utopian after each of my public appearances at which I demonstrated liquid air and its properties and tried to predict all those applications of it, except for laboratory research that subsequently came to fruition.
But Georges Claude went even further than me in his assumptions and he was right - therefore, with full faith and conviction, I could finish the preface to the book he published in 1903 with the following words: “The liquefaction of air on an industrial scale is not only a revolution in science, but also - and, moreover, mainly - the economic and social revolution." All the rich content that Claude put into his first work, a new edition of which he offers in this book, fully confirms the assumptions that I made 27 years ago.
This is not a mere exposition, it is a work of a completely original character, and in which the author is not content with the role of a historian in his field.
Over the course of many years, J. Claude tirelessly made new contributions to resolving this issue. He created these pages not as an instructive description of the air liquefaction industry, but mainly as an exposition of his work and the theories he created, which have advanced our knowledge so far not only in the field of science, but also in the field of application of scientific achievements in industry.
I tirelessly followed all of Claude's research and reported the most significant results at meetings of the Academies of Sciences. From some chapters of this book one can understand the paths along which these researches moved forward, and from them one can judge with what confidence and speed practice moves when it is guided by a clear, firmly grounded scientific theory.
Claude belongs to those brilliant researchers who combine the inquisitive observation of a laboratory scientist with the sober mind of a practitioner. No theory is complete for him.
value until he gets the opportunity to put it on the rails of practical application.
This is confirmed by many typical examples given in this book. I will indicate some of them:
1) An apparatus for producing liquid air through expansion with external work produced. The theory proves the superiority of this method of work over others, but its practical application failed, despite the fact that scientists and prominent engineers took up the implementation. “The theory is always right,” says Claude, and, not losing heart from the failure that befell his outstanding predecessors, he painstakingly analyzes what exactly in practical application does not satisfy the theory.
During this work, he discovered a method for lubricating machines operating at low temperatures with petroleum ether. After this discovery, the apparatus began to work, but produced only 0.20 liters of liquid air per horsepower/hour. “Obviously, the theory is not yet satisfied enough,” Claude decides. He carefully studies this phenomenon and, through subtle analysis, establishes beyond doubt that, indeed, the theory is not satisfied. He is convinced that at the very low temperature at which his machine operates, the air is no longer that ideal gas that is accepted in theory: “It is not yet a liquid,” he says, “but it is almost no longer a gas. He then tries to raise the temperature at which expansion occurs to satisfy the theory. He turns to pressure reduction, then compound liquefaction, then oxygen critical temperature liquefaction, etc.
The theory is satisfied and the liquid air output gradually reaches 0.66, 0.85, 0.95 liters per horsepower/hour.
Yes, the theory is always right, but... in the right hands.
2) There is a significant difference between the boiling points of the two components of air - oxygen and nitrogen. The ability of nitrogen to evaporate faster than oxygen served as the basis for a process that economically solves the problem of separating these two gases. Smallest details The evaporation process was carefully studied by Prof. Linda, worked out by Bali and others (without any disagreement). The theory of the opposite phenomenon, namely, the condensation of gaseous air, caused controversy: Dewar believed that both elements of air condensed simultaneously; Linde shared this view. Pictet went even further and believed that it was nitrogen, that is, the more volatile gas, that condensed first. It was necessary to decide which of these theories was correct, because if both gases condense at the same time, then, obviously, all the air must be liquefied completely in order to separate its elements; if one of the gases condenses before the other, then partial liquefaction will be sufficient to achieve this separation.
Claude was deeply struck by Dewar's theory, which contradicted the basic laws of physics. How general position“, he reasoned, the phenomenon of liquefaction is always the opposite of the phenomenon of evaporation, and air can behave differently only if some curious anomaly exists. Claude begins to carry out experiments and their results completely coincide with his own assumptions and with the theories of Gibbs, Van-der-Va al s'a and Duhem'a. We will find a detailed presentation of this in the chapter on the liquefaction of gas mixtures.
Thanks to an extremely skillful method, Claude was able to use this property. By liquefying a relatively small part of the air being processed, he obtained directly, without prior evaporation, a liquid very rich in oxygen, containing almost all the oxygen in the air being processed. This method involves so-called reverse flows. It makes it possible to completely separate all the oxygen contained in the air being treated by liquefying only half of it.
Claude immediately begins practical application the improvements he has achieved. The results are immediate. The production of liquid air and the decomposition of the latter into its elements (first carried out by Prof. Linde in Germany with the help of extremely skillful methods discovered by him) was greatly developed in France and other countries, thanks to Claude’s method, exploited by the NL’air Liquide Society.”
Apart from its special interest, this book gives new confirmation to the opinion, repeatedly expressed by me, that applied science can amend the weak laws established by so-called pure science. Any physical law can be considered really established only after it turns out to be acceptable on a wide industrial scale; in pure science one can make mistakes by establishing without much harmful consequences insufficiently precise laws; in a wide industry, this phenomenon is either completely impossible, or the error affects itself in a short time, leading to collapse. It was precisely these provisions that I supported when the Academy of Sciences, under my chairmanship, discussed the issue of the timeliness of opening the Industrial Section. Claude's work proved me right.
In conclusion, I consider it necessary to draw attention to one of the most interesting parts, appearing at least for the first time
in this edition, this is a chapter in which the author outlines the difficulties that he had to overcome in researching technically feasible methods for simultaneously extracting noble gases contained in it, often in microscopic doses, from the air, obtaining them as by-products in the production of nitrogen and oxygen. In addition to these extremely interesting scientific discoveries that have become reality, Claude has no doubt that he will be able to find new applications for the wonderful properties that these noble gases possess.
Dr. dArsonval.
Member of the Institute.
Nogent on the Marne.
April 16, 1925.
FIRST PART.
LIQUEFACTION OF GASES.
CHAPTER I.
First stages.
One of the most interesting departments of physics is the one that treats the liquefaction of gases, and before moving on to the consideration of issues related to the problem of liquefying air, we cannot pass over in silence those numerous works that have ended - only recently - with the complete dominance of science over the liquid and gaseous state of bodies.
In the field of gas liquefaction, theoretical conclusions have significantly outpaced their practical implementation. Physicists have observed how ordinary liquids, under the influence of heat, turn into vapors that are as mobile and light as gases; under the influence of cooling, these vapors easily returned to their original state - turning into liquid. Scientists were faced with the question: are gases - natural or chemically produced - also vapors of liquids, but special liquids, incomparably more volatile than ordinary ones, and which boil at very low temperatures.
Were these not the thoughts that occupied the famous Swift when he composed the next passage of his “Gulliver’s Travels” (Part 3, Travel to Laputa, Chapter V - Description of the Academies in Lagado
“Under the command of the great scientist there were 50 workers. Some condensed the air, making it tangible, extracting nitrogen from it and allowing fluid and watery particles to evaporate, etc.”
After all, this is a complete picture of the production of liquid air, oxygen and nitrogen - all in 1726!
After Swift, the concept of the ability of gases to liquefy is clarified by the prophetic words of Lavoisier given below. During the time when
) This curious comparison was brought to my attention by engineer. G. Steingel.
Even easily liquefied gases could not be brought into a liquid state, the famous chemist decided to say:
“If the earth suddenly fell into an environment with a very low temperature, similar, for example, to the temperature of Jupiter or Saturn, the water that now forms our rivers and seas, and probably the vast majority of the liquids known to us, would turn into mountains and solid rocks. In this case, the air, or at least part of the gases that make it up, would change their state, turning into a liquid from an invisible gas that exists due to being in an environment with a sufficiently high temperature; during this transition of air from one state to another, the formation of new, hitherto unforeseen, liquids."
Thus, starting with Lavoisier, the opinion has been affirmed that the three states of matter - solid, liquid and gaseous - represent a sequential series, with each of the states depending on the ambient temperature.
Modern science confirmed for all bodies, at least those that do not decompose when heated, the complete regularity and generality of this conclusion.
Without any other prefaces, let us now move on to studying the question of the liquefaction of gases, having first recalled all those laws that govern both the evaporation of liquids and the condensation of their vapors.
Vapor elasticity of liquids. - Vapors are saturated and unsaturated.
In Fig. 1 shows a barometric tube filled with mercury and immersed in its open end into a vessel with mercury. In this case, a void is formed in space E; It is known that atmospheric pressure is determined by the height of the mercury column AB (approximately 760 mm). Using a curved pipette, let us introduce a few drops of some liquid into the barometric tube: water, alcohol, etc. This liquid, having reached the free surface of the mercury, will evaporate in the empty space Ey and we will see that the level of mercury, under the influence of the resulting vapors, will decrease from the original level B to the new level C (Fig. 2). The height of the BC determines the elastic force or pressure of the vapor formed under the conditions under which the experiment is carried out. When performing this experiment, there are 2 options:
1) An excess amount of liquid is injected into the tube; in this case, only part of this liquid will evaporate. In barometric
space E will contain the maximum amount of vapor that it can accommodate, i.e. the vapor will be, as is commonly called, saturated. The decrease in the level of mercury in this case will be maximum and it is interesting to note that this decrease at a given temperature is a strictly defined and constant value, regardless of the amount of excess liquid introduced into the tube. We can say that the saturated vapor pressure at a certain temperature is a constant physical quantity and characterizes the liquid to the same extent as it is characterized by density or boiling point.
2) The liquid introduced into the tube evaporates completely, therefore, its quantity turned out to be insufficient to form the amount of steam that can fit into the tube. IN in this case the degree of decrease in the level of mercury will not be a specific value, as was the case in the first case, and will depend on the amount of liquid introduced. And it is absolutely clear that if a small amount of liquid was introduced, then the decrease in mercury levels will be insignificant.
Thus, the pressure of unsaturated vapor is not a definite value and can vary depending on the amount of liquid introduced within the limits of pi. 1, 2 and 3.
We must pay due attention to the essence of the concept of unsaturated vapor, because, as we later learn, gases are a phenomenon of the same order, that is, they are unsaturated vapors.
Changes in the vapor pressure of various liquids depending on the properties of the latter and their temperature.
The vapor pressure of various liquids at equal temperatures is greater, the more volatile these liquids are. So, for example, the elasticity of water vapor at 20° is 17.4 mm, i.e., in other words, at 20° the level of the mercury column (in a barometric tube) decreases by 17.4 mm when water is introduced into the tube; the elasticity of ordinary alcohol vapor at the same temperature is 44 mm, wood alcohol vapor - 95 mm and ether vapor - 442 mm; the sequence of these numbers simultaneously shows us the order of volatility of these liquids.
On the other hand, the vapor pressure of the same liquid increases rapidly with increasing temperature. Let us try to gradually warm up our barometric tube E - under the influence of the ever-increasing evaporation of the liquid, the vapor of which rises above mercury, the level of the latter will decrease with increasing speed and the elasticity of water vapor at 30° it will be equal to 31.5 mm, at 50° - 92 mm and at 75° - 288.5 mm.
Continuing to increase the temperature, we will see that the decrease in the level of mercury will accelerate even more, and at a certain moment (Fig. 3), under the influence of saturated vapor of the liquid (which is in the tube all the time in excess), the level of mercury in the barometric tube will reach to the level of mercury in vessel A (Fig. 3). Obviously, at this moment the vapor pressure will exactly balance the atmospheric pressure and will therefore be equal to 760 mm.
If we measure the temperature at this moment, we will see that it is equal to 100°, i.e., the boiling point of water at atmospheric pressure. We formulate this extremely interesting phenomenon as follows:
The boiling point of a liquid at atmospheric pressure is also the temperature at which the vapor pressure of this liquid is equal to one atmosphere.
All the laws of nature have their own deep meaning, but we so rarely have the opportunity to unravel them that each such case should be noted. Here we have this case. How very
9 To do this, use the barometric tube shown in Fig. Cover 1 - 3 and 5 - 13g with a glass coupling, and drive water or some other liquid heated to the desired temperature between the inner wall of the coupling and the outer wall of the tube.
It is well known that only then do bubbles begin to form in the liquid, usually observed during boiling, when the vapors are able to balance the atmospheric pressure acting on the liquid with their elasticity.
Until the vapor pressure reaches this value, vapor bubbles cannot form, and we observe only slow surface evaporation, but not boiling.
Heat of vaporization.
Let us consider the phenomena that occur when a liquid is heated in an open vessel. It is known that the temperature of this liquid will rise continuously until the boiling point is reached, after which the increase in temperature will immediately stop, no matter how strong the source of heating. The change in the physical state of the liquid, on the one hand, and, on the other hand, the enormous increase in its volume that occurs during vaporization overcoming the resistance of atmospheric pressure, require the expenditure of significant energy, which is obtained due to significant heat absorption. Some vague idea of the amount of heat expended during evaporation gives us that feeling of cold that everyone experiences when leaving the bath, when the water remaining on the body slowly evaporates.
Until the moment when the liquid we are heating has boiled, weak surface evaporation causes correspondingly weak heat absorption, and almost all the heat generated by the heating source is spent on gradually heating the liquid. From the moment boiling begins, the absorption of heat for the formation of vapor becomes enormous, and all the heat of the heater, regardless of its power, is spent on the process of vaporization.
The amount of heat required to convert one weight unit of boiling liquid into vapor is called the heat of evaporation. According to Regnaul t, for water at 100° it is equal to 537 calories per 1 ton. The amount is truly colossal!
But this figure means that water, already heated to 100°, without a further increase in temperature during the transition from liquid to gas of the same temperature, absorbs an amount of heat almost 5.5 times greater than that which was absorbed by water for the transition from melting temperature of ice to boiling temperature. In this respect, as in many others, water is a special liquid;
This can be seen from the table below, which shows the boiling points and heats of vaporization of various liquids.
The need for cold for the existence of liquefied gases at atmospheric pressure. Note that it is impossible to heat a liquid in a vessel above its boiling point, since by increasing the heating we can only cause a more violent boil, but not exceed the boiling point. In other words, no chemically pure liquid can, under normal conditions, exist under atmospheric pressure at a temperature exceeding the boiling point of a given liquid x).
If the conclusions of physicists who consider gases as pairs of extremely volatile liquids are correct, then these gases, even at very low temperatures, have the elasticity necessary for boiling, equal to one atmosphere, and as a result, these liquids can exist under atmospheric pressure only at very low temperatures.
Thus, we comprehend the essence of the role of cold for the liquefaction of gases, which Lavoisier predicted. We will be further convinced of how great the importance of cold is when we see that in all cases, the only circumstance sufficient in itself to achieve liquefaction in all cases is the action of cold: no gas, not even helium, can withstand sufficient cold . There is no doubt that the physicists who have studied this interesting problem would be very close to solving it if they accepted this proposition.
True, obtaining very low temperatures might seem to them one of the greatest difficulties in physics. But if they increased their efforts - and the problem posed is worthy of it - there is no doubt that, due to the great progress of physics, they would discover those amazing simple ways, which serve us now to obtain deep cold.
) The presence of foreign impurities and, in particular, dissolved salts in the liquid can significantly increase the boiling point. Sometimes a phenomenon of unstable equilibrium occurs, called “overheating” of the liquid.
Effect of pressure on boiling point.
a) Decrease in pressure. We have just seen that when any liquid is heated under atmospheric pressure, boiling begins at the moment when the gradually increasing vapor pressure reaches a value that balances the atmospheric pressure.
Let us reduce the pressure acting on the liquid by placing it in a closed vessel from which the air has been partially pumped out; it is clear that the lower vapor pressure at a lower temperature will be able to overcome the existing reduced pressure and thereby cause boiling: the boiling point under these conditions will be lower
normal, and the more perfect the emptiness in the vessel containing our liquid, the correspondingly lower the boiling point.
Nature itself in some cases confirms the correctness of the above. At the tops of mountains, for example, we have pressure below atmospheric pressure, and the decrease in pressure is equal to the pressure of the air column from the base of the mountain to its top. While climbing Mont Blanc, the famous climber was struck by the fact that on the icy peak of the Alpine colossus, he could hardly boil hard-boiled eggs in boiling water - the boiling point of the water there was so low.
Here is another, even more striking example!
When an air pump gradually increases the vacuum in a container of water, the boiling point of water can drop below freezing point: under such conditions, hard-boiled eggs actually become a myth! But for a good air pump it is not particularly difficult to maintain a pressure of 1-2 mm above a liquid enclosed in a closed vessel, and since at 0° the vapor pressure of water is 4.6 lsh, then, obviously, water at this temperature and at the specified pressure it should boil, since the elasticity of water vapor under these conditions significantly exceeds the pressure existing in the vessel.
Refrigerating machines built on the principle of evaporation. From the above it is obvious that evaporation occurring under the described conditions can serve as a source of very significant cooling.
If, for example, you connect a vessel filled with water to a vacuum pump of sufficient power and force the latter to work, then after some time the water will boil violently, since the moment will come when, at the temperature at which the water is located, the elasticity of its vapor exceeds reduced pressure, which is maintained by the action of the pump. Since in this case the heat absorbed by evaporation (p. 11) and leaving along with the vapor is not supplied by any extraneous source, but is borrowed from the liquid itself, the latter cools quite quickly; due to the fact that the pressure is maintained by a continuously operating pump below the vapor elasticity, despite the latter decreasing as the temperature of the liquid decreases, boiling will continue, cooling will increase, and due to this, at a certain moment the liquid will turn into a solid.
This beautiful experience served as the basis for the design of ice-making plants. cars For example, the Carré ice-making machine is based on the principle of absorbing water vapor with sulfuric acid (the greed with which water combines with sulfuric acid is well known). The same principle is embedded in an exceptional car, a true fighter for common sense, the famous engineer Leblanc, in which the work of freezing water was entrusted... to a jet of steam. This jet of steam, through the injector Zhiffar, created a vacuum of air and worked splendidly in models built by the Westinghouse company, economically freezing tens of centners per hour!
Thus we see that if a certain vacuum is maintained above the liquid by means of an air pump, the latter quickly reaches a temperature at which the vapor pressure is approximately equal to the reduced pressure maintained by the air pump, and while the vapor elasticity exceeds the pressure, the liquid boils and at the same time continues to cool. If the liquid is very volatile, that is, if its vapors have sufficient elasticity to the lowest temperatures, then these low temperatures can be obtained by simply evaporating such a liquid in a vacuum.
So, for example, sulfuric ether, the vapor pressure of which at -40° still exceeds 5 mm, can be cooled below this temperature by simple evaporation under a pressure of 5 mm 1).
But instead of obtaining a very low temperature in a very rarefied atmosphere by evaporating a very volatile liquid, it often makes sense to obtain a not so low temperature, using for this purpose a not too strong rarefaction. Let us take for example the same sulfuric ether, the vapor pressure of which at -10° is 111 mm; this rather low temperature can be easily achieved by evaporation of the liquid at a relatively slight vacuum, which can be easily created by air pumps much less powerful and less complex than those that would be needed for water.
It can easily be imagined that in order to rarefy steam to a pressure of, for example, 2 mm of mercury, considerable work will have to be expended, and pumps of enormous volumes will be required to obtain positive results.
The evaporation of volatile liquids has now become the most common method used for producing cold, and this principle is used on a very wide scale in the practice of refrigeration in thousands of machines: as, for example, in machines with methyl chloride, sulfur dioxide, ammonia, carbon dioxide, etc. .
b) The action of increasing pressure. We have already seen that as the pressure under which a liquid is located decreases, its boiling point decreases. On the contrary, we will increase the pressure: we will see that in order to give the vapors of this liquid elasticity that overcomes this pressure, we will have to heat the liquid above the temperature than would be needed under normal conditions. And the greater the pressure, the higher the boiling point will be.
That's why in steam boilers water at a pressure of 15 atmospheres boils only at 199°, and in the boiler of Serpollet cars, where the pressure often reaches 50 atmospheres, the boiling point rises to 265°. Apparently, with a little knowledge of some laws of nature, you can melt not only tin, but also lead in water!
Note that the increased pressure that should be applied to the heated liquid in order to increase its boiling point is generated by the liquid itself, if only the latter is enclosed in a closed vessel. Obviously, in this case, a pressure is automatically established above the surface of the liquid, equal at any given moment to the elasticity of the vapors accumulating above the liquid.
It should be noted that under these conditions, which are similar to those that exist in a steam boiler when steam is diluted, boiling of the water cannot begin until some of the steam is released. The elasticity of vapor in this case corresponds to the pressure experienced by the liquid, and the latter, as a result, cannot be overcome. While the heat supplied by the firebox is not removed with the steam being consumed, it is almost entirely spent on heating the liquid; in this case, the temperature rises quite quickly, and simultaneously with the temperature of the liquid, the elasticity of its vapor increases, and as a result, the pressure. And only when the pressure has already been significantly increased, by releasing part of the steam and thereby lowering the pressure, conditions are created in which the elasticity of the steam slightly exceeds the pressure, which makes it possible for boiling to begin. Then the pressure stops increasing, since the heat delivered by the firebox is consumed along with the escaping steam.
The table below, compiled by R e g n a u 11, shows those enormous fluctuations in the boiling point of water, which depend on pressure. As a matter of fact, when compiling this table, the goal was to indicate the elasticity of water vapor at the corresponding temperatures; but we already know that these quantities (vapor elasticity and boiling point) are related to each other, and that boiling begins at the moment when the difference between the pressure experienced by the liquid and the elasticity of its vapor becomes infinitesimal.
These data are graphically depicted in Fig. 4. The same diagram shows the corresponding curves for other liquids, and it is extremely interesting to note that these curves, deviating from one another depending on temperature, attract attention by the uniformity of their character.
We will dwell on this in more detail when considering the work of Vander Waals (Chapter V).
Possibility of using pressure instead of refrigeration in the production of certain liquefied gases. We have already seen (p. 12) that the existence of any liquid in the open air is impossible at a temperature above the boiling point of the liquid; from this we concluded that gases are pairs of hypothetical liquids that can exist in the open air only in very cold conditions, and hence, obtaining extremely low temperatures could seem to us an inevitable necessity for liquefying gases.
We have already seen that increasing pressure is the means that makes it possible to raise the temperature of a liquid above - and even significantly above - its boiling point at atmospheric pressure. This position, which now seems extremely simple to us, gave scientists of the last century many successes, but at the same time was the cause of many fruitless efforts.
Rice. 4. Diagram of changes in vapor pressure depending on temperature.
I - methyl chloride, II - sulfur dioxide, III - ether, IV - water.
Let us assume that we have a hypothetical liquid corresponding to some specific gas: naturally, this liquid under atmospheric pressure exists only at a very low temperature; but if we enclose this liquid in a closed vessel, we can subject it to heat and the increased pressure will raise its boiling point. If our experiment is continued until we obtain significant, and if necessary, enormous pressures, then there is no visible reason to assume that we will not be able to raise the temperature of our liquid to ambient temperature in this way. The existence of such a liquid at ambient temperature would not be impossible if it were maintained under sufficient pressure, and from this it can be understood that, in addition to any cooling, it is sufficient to properly subject the real gas to high blood pressure to cause it to liquefy.
We will now see the meaning of this conclusion; we will see, I repeat, all the satisfaction, but also the disappointment that it brought to scientists; But. First of all, let us establish what the “proper” conditions for liquefaction are.
END OF PARAGMEHTA BOOKS
AIR LIQUEFICIATION
AIR LIQUEFICIATION, a process achieved by cooling air to a critical temperature of -147 °C, at which or below the pressure the air turns into a liquid. After repeated compression followed by ADIABATIC expansion, at this temperature, according to the JOULE-THOMPSON EFFECT, water droplets appear.
Scientific and technical encyclopedic dictionary.
See what “LIQUEFICATION OF AIR” is in other dictionaries:
It includes several stages necessary to convert the gas into a liquid state. These processes are used for scientific, industrial and commercial purposes. All gases can be brought into a liquid state by simple cooling with... ... Wikipedia
The transition of a substance from a gaseous state to a liquid state. S. g. is achieved by cooling them below the critical temperature (See Critical temperature) (Tk) and subsequent condensation as a result of removal of the heat of vaporization (condensation).... ... Great Soviet Encyclopedia
It could not be considered fully studied if Dewar had not recently obtained in liquid form the most difficult of them to condense, namely hydrogen and helium. In Art. Liquefied gases (see) the history of the issue of S. gases is given and the production has already been described... ... Encyclopedic Dictionary F.A. Brockhaus and I.A. Efron
Light blue color of liquid oxygen in a Dewar flask. Liquid oxygen (LC, English Liquid oxygen, LOX) liquid pale of blue color, which is a strong paramagnetic material. It is one of the four aggregate states of oxygen. LCD... ... Wikipedia
O (oxygenium), chemical element VIA subgroups of the periodic table of elements: O, S, Se, Te, Po member of the chalcogen family. This is the most common element in nature, its content in the Earth’s atmosphere is 21% (vol.), in the earth’s crust in ... ... Collier's Encyclopedia
Natural gas- (Natural gas) Natural gas is one of the most common energy carriers. Definition and use of gas, physical and Chemical properties natural gas Contents >>>>>>>>>>>>>>> ... Investor Encyclopedia
In the time of Lavoisier (see this name), the transition of gas into a liquid and solid state seemed very likely, since during chemical reactions a similar change in physical state often occurs (Oeuvres de Lavoisier, vol. II 804). IN early XIX… … Encyclopedic Dictionary F.A. Brockhaus and I.A. Efron
- (chem., Ozon German, Ozone French and English) gaseous body, represents so far the only case of allotropic modification of an elemental gaseous substance; This is oxygen, the particle of which has not two atoms, but three. His education from... ... Encyclopedic Dictionary F.A. Brockhaus and I.A. Efron
GASES- GASES, substances in a state characterized by the fact that the molecules of the substance are located at great distances from each other and the interaction forces between the molecules are very small. Experimental studies of matter in the gas state... ... Great Medical Encyclopedia
When it was found that liquefying gases requires cooling them below a critical temperature, researchers' efforts were aimed at developing ways to obtain low temperatures. These efforts were crowned with success, and a number of machines are now available for obtaining any and all gases in liquid form. These machines, especially air liquefaction machines, are widely used in technology.
Air liquefaction is used in technology to separate it into its component parts. Separation is achieved by evaporation of liquid air. In this case, the components of the air that have a lower boiling point evaporate first: neon, nitrogen, and then argon, oxygen. The matter occurs in exactly the same way as, for example, when separating more easily boiling alcohol from water by distillation. The resulting gases find wide application: a) nitrogen is used to produce ammonia; b) argon, neon and other inert gases are used to fill incandescent electric lamps, as well as gas-light lamps; c) oxygen serves many purposes: mixing it with acetylene (or hydrogen) and burning this mixture produces a flame that has a high temperature and is used for welding and cutting metals (Fig. 499). Oxygen blast has become of great importance to accelerate metallurgical processes; Oxygen is also used for medical purposes.
Rice. 499. Autogenous welding of metals. Burner 1 is supplied with oxygen and acetylene from cylinders through two tubes; wire 2 melts in an oxygen-acetylene flame and fills the welded seam
In addition, liquid oxygen is used in explosive technology. A mixture of liquid oxygen with sawdust, soot, naphthalene and other easily oxidized substances is an explosive of enormous power (oxyliquit). The explosion occurs because in the presence of oxygen, which is in a liquid state and therefore occupies a small volume, the combustion of these substances occurs very quickly. During combustion, strong heating occurs, the reaction products become gaseous (carbon dioxide), and instantaneous and very strong expansion occurs - an explosion. This explosive has the advantage that once the oxygen evaporates it ceases to be dangerous.
Machines for producing liquid air are various types. We will describe here the circuit of a machine, the operation of which is based on the cooling of highly compressed air during its expansion (§ 225). Air enters compressor 1 (Fig. 500); here it is compressed to a pressure of several tens of atmospheres. At the same time, it heats up. From compressor 1, air enters heat exchanger 2, where it is cooled by running water to the initial temperature and then goes to expander 3 (expander). An expander is a cylinder with a piston. In an expander, the air expands. At the same time, it pushes out the piston and does work. The internal energy of the air is spent on this work, and its temperature drops so much that it condenses into a liquid; liquefied air is collected in vessel 4.
Rice. 500. Diagram of a machine for producing liquid air
Sometimes expanders are made not in the form of a cylinder with a piston, but in the form of a turbine (P.L. Kapitsa turboexpander), in which the gas expands, producing the work of rotating the turbine. It is very important that the rotor (the rotating part of the turbine) “hangs” in the flow of expanding gas during operation of the machine, without touching the walls of the turbine. As a result, there is no need for lubrication, which is very important, since the selection of lubricants for machine parts operating at such low temperatures is extremely difficult. Conventional lubricants harden at low temperatures. In addition, the advantage of machines for liquefying gases designed by P. L. Kapitsa is their high productivity with relatively small sizes.
The boiling point of liquid air is very low. At atmospheric pressure it is equal to . Therefore, liquid air in an open vessel, when its vapor pressure is equal to atmospheric pressure, boils until its temperature drops below . Since the surrounding bodies are much warmer, the heat flow to the liquid air, if it were stored in ordinary vessels, would be so significant that in a very short time all the liquid air would evaporate. Therefore, it is stored in special vessels that create good protection from access of heat from outside. These are the same type of vessels as regular thermoses. They are glass or metal vessels with double walls (Fig. 501), from the space between which the air is carefully removed. The transfer of heat through such a space with very rarefied gas is extremely difficult. In order to protect against heating by rays, the inner walls of the cavity are made shiny (silver-plated). Such vessels for storing liquid air were proposed by Dewar. In a good Dewar flask, liquid air evaporates so slowly that it can be stored for two, three days or more.
Rice. 501. Section of a Dewar flask. The end of the tube is visible from below, through which air was pumped out from the space between the walls during the manufacture of the vessel and which was sealed off after pumping was completed
To ensure that the liquefied gas does not heat up despite the continuous, albeit slow, flow of heat, it must remain in the open container so that it can gradually evaporate. Due to the loss of heat for evaporation, liquefied gas remains cold all the time. If you clog a Dewar vessel, that is, prevent evaporation, the liquefied gas will heat up and the pressure of its vapor will increase so much that it will rupture the vessel. If the vessel were very strong, for example a steel cylinder, like the one shown in Fig. 375, then the liquefied gas would gradually heat up to a temperature above the critical one and pass into a gaseous state. Thus, the only way to preserve liquefied gas for a long time is to use open Dewar vessels.
Any gas can be turned into liquid by simple compression, as long as its temperature is below the critical temperature. Therefore, the division of substances into liquids and gases is largely arbitrary. Those substances that we are accustomed to consider as gases simply have very low critical temperatures and therefore cannot be in a liquid state at a temperature close to room temperature. On the contrary, substances that we classify as liquids have high critical temperatures.
The first gas (ammonia) was converted into liquid already in 1799. Further successes in the liquefaction of gases are associated with the name of the English physicist M. Faraday (1791-1867), who liquefied gases by simultaneously cooling and compressing them.
By the second half of the 19th century. Of all the gases known at that time, only six remained not converted into liquid: hydrogen, oxygen, nitrogen, nitrous oxide, carbon monoxide and methane - they were called permanent gases. The liquefaction of these gases was delayed for another quarter of a century because the technology for lowering the temperature was poorly developed, and they could not be cooled below the critical temperature. When physicists learned to obtain temperatures of the order of 1 K, they managed to convert all gases, including helium, not only into a liquid, but also into a solid state.
Gas liquefaction plants
There are many types of machines for producing liquid gases, in particular liquid air. In modern industrial installations, significant cooling is achieved by expanding the gas under thermal insulation conditions (adiabatic expansion).
Such machines are called expanders. The expanding gas does work by moving a piston (piston expanders) or rotating a turbine (turbine expanders) using its internal energy and is therefore cooled.
High-performance low-pressure turboexpanders were developed by Academician P. L. Kapitsa. Since the 50s, all large installations in the world for liquefying air have been operating according to the Kapitsa scheme.
Kapitsa Petr Leonidovich (1894-1984) - famous Soviet physicist; Nobel Prize Laureate; student of E. Rutherford.
Kapitsa discovered the superfluidity of liquid helium and developed new industrial methods for liquefying gases. Kapitsa's work on creating super-strong magnetic fields and high-power electronic generators is of great importance.
Figure 6.14 shows a simplified diagram of a piston expander. Atmospheric air enters compressor 1, where it is compressed to a pressure of several tens of atmospheres. The air heated during compression is cooled in heat exchanger 2 running water and enters the expander cylinder 3. Here, expanding, it does work by pushing the piston, and cools so much that it condenses into liquid. Liquefied air enters vessel 4.
Air
The boiling point of liquid air is very low. At atmospheric pressure it is -193 °C. Therefore, liquid air in an open vessel, when its vapor pressure is equal to atmospheric pressure, boils. Since the surrounding bodies are much warmer, the heat flow to the liquid air, if it were stored in ordinary vessels, would be so significant that in a very short time all the liquid air would evaporate.
Storage of liquid gases
Rice. 6.15
To keep air in a liquid state, it is necessary to prevent its heat exchange with the environment. For this purpose, liquid air (and other liquid gases) is placed in special vessels called Dewar flasks. A Dewar flask is designed in the same way as a regular thermos. It has double glass walls, from the space between which air is pumped out (Fig. 6.15). This reduces the thermal conductivity of the vessel. The inner wall is made shiny (silvered) to reduce heating by radiation. Dewar vessels have a narrow neck; when liquefied gases are stored in them, they are left open so that the gas contained in the vessel has the opportunity to gradually evaporate. Due to the loss of heat through evaporation, liquefied gas remains cold all the time. In a good Dewar flask, liquid air can be stored for several weeks.
Application of liquefied gases
Liquefaction of gases has technical and scientific significance. Air liquefaction is used in technology to separate air into its component parts. The method is based on the fact that the various gases that make up the air boil at different temperatures. Helium, neon, nitrogen, and argon have the lowest boiling points. Oxygen has a slightly higher boiling point than argon. Therefore, helium, neon, nitrogen are evaporated first, and then argon and oxygen.
Liquefied gases are widely used in technology. Nitrogen is used to produce ammonia and nitrogen salts used in agriculture to fertilize the soil. Argon, neon and other inert gases are used to fill incandescent electric lamps, as well as gas-light lamps. Oxygen has the greatest use. When mixed with acetylene or hydrogen, it produces a very high temperature flame used for cutting and welding metals. Injection of oxygen (oxygen blast) accelerates metallurgical processes. Oxygen delivered from pharmacies in pillows alleviates the suffering of patients. Particularly important is the use of liquid oxygen as an oxidizer for space rocket engines. The engines of the launch vehicle that lifted the first cosmonaut Yu. A. Gagarin into space ran on liquid oxygen.
Liquid hydrogen is used as fuel in space rockets. For example, refueling the American Saturn 5 rocket requires 90 tons of liquid hydrogen. Gases used in industry, medicine, etc. are easier to transport when they are in a liquefied state, since a larger amount of substance is contained in the same volume. This is how liquid carbon dioxide is delivered in steel cylinders to carbonated water factories.
Liquid ammonia is widely used in refrigerators - huge warehouses where perishable foods are stored. The cooling that occurs during the evaporation of liquefied gases is used in refrigerators when transporting perishable products.
Importance of gas liquefaction for scientific research
The transformation of all gases into a liquid state once again confirmed the unity in the structure of substances. It showed that the state of a substance depends on its temperature and pressure, and is not determined once and for all for a given body.
On the other hand, the low temperatures achieved during the liquefaction of gases have widely expanded the boundaries of scientific research and made it possible to detect changes in many properties of substances at ultra-low temperatures. Elastic bodies made of rubber become brittle at these temperatures, like glass. A piece of rubber, after cooling in liquid air, breaks easily, and a rubber ball shatters upon impact. Mercury and zinc become malleable at low temperatures, and lead, a plastic metal, becomes elastic, like steel. A bell made of lead rings. Many substances (alcohol, eggshells, etc.), after illuminating them with white light, create their own radiation of various colors (mainly green-yellow).
At low temperatures, the intensity of thermal motion decreases sharply, so it becomes possible to observe a number of phenomena that are hidden at higher temperatures. high temperatures thermal movement of molecules.
At temperatures close to absolute zero, they change greatly electrical properties some metals and alloys: their resistance electric current becomes equal to zero. This phenomenon, called superconductivity, was discovered by G. Kamerlingh Onnes in 1911. At a temperature of 2.2 K, viscosity disappears in liquid helium, i.e. it acquires the property of superfluidity. Superfluidity was discovered by P. JI. Kapitsa in 1938
Gases such as nitrogen, oxygen, hydrogen, helium can only be in a liquid state at very low temperatures. At such temperatures, special properties of substances are revealed that are masked in normal conditions thermal movement of molecules. These properties are used in both science and technology.
