Liquid Nitrogen Packet
Temperature: A measure of how “hot” or “cold” something is in degrees. Also a measure of the average Kinetic energy of a substance. Temperature does not seem to have an upper limit. (Interior of sun = 27 million ˚F)
Ice is hot to objects that are colder than the ice. (below 0˚C)
Temperature Scales: There are four temperature scales used in the world.
Celsius scale: based on the melting and boiling point of water. Kelvin scale: similar to the Celsius scale adjusted so the 0 measurement is equal to absolute zero. Fahrenheit scale: original temperature scale that seems to work well for human functions like cooking or weather. Rankine scale: similar to the Fahrenheit scale adjusted so the 0 measurement equals absolute zero.
Absolute Zero: The theoretical temperature at which the atoms or molecules of a substance have the least possible energy. (Lowest possible temperature)
Equal to - 273.15 ˚C or - 459.67 ˚F
Liquid Air: A product made by greatly reducing the temperature of air until it turns to a fluid.
Nitrogen (78%) , Oxygen (21%) and Argon (1%) are the principle components of air.
Liquid air cannot be measured with an ordinary mercury or alcohol thermometer.
A platinum resistance thermometer is used which measures the effect on the electrical resistance of platinum. Platinum’s conductivity changes with temperature changes.
Making Liquid Air: The process of making liquid air is based on the fact that compressed air becomes cooler when it expands.
Procedure: 1. Compress air with a compressor. (This creates heat) 2. Remove heat produced by compressing air with a heat exchange system. 3. Send compressed air to an expansion engine (a piston that rapidly increases the volume of the gas) or a larger open area. 4. Some of the air liquefies and the remaining air is recirculated through the process until enough liquid air is collected. 5. Separate the Nitrogen from the Oxygen using their differences in boiling point. 6. You now have liquid nitrogen.
Cryogenics: The study of matter at temperatures much colder than those that occur naturally on earth
Cryogenic temperatures are those below the boiling point of methane (-285.3 ˚F or -176.1 ˚C) Some cryogenic fluids are: Oxygen (-183 ˚C), Nitrogen (-196˚C), Hydrogen (-253 ˚C), and Helium (-269˚C). Cryogenic Articles
Temperature is how hot or cold something is as measured on a particular scale. The concept of temperature is closely related to the flow of heat between two connected objects of different temperatures. Heat always flows from the hotter object to the cooler one.
Instruments that measure temperature are called thermometers. A scale marked on the thermometer indicates each level of “hotness.” The two most common temperature scales used on thermometers are Fahrenheit and Celsius. Temperatures on all scales are based on the International Practical Temperature Scale of 1968.
Scientists often speak of thermodynamic temperature, a fundamental physical quality completely independent of the properties of a substance. The unit of thermodynamic temperature is the Kelvin, indicated by K. This unit was agreed upon by scientists from many nations. All temperatures are based on their position above or below the freezing point of water (273.15 K or 0C). The triple point of water happens when water is at a temperature of 0.01 ˚C and a pressure of 0.61 kPa. At this temperature and pressure, water, ice, and water vapor all exist together in equilibrium. In common practice, a temperature is actually expressed in terms of its difference from the melting point of ice at standard pressure conditions of one atmosphere of pressure (760 mm Hg or 101.3 kPa).
Temperature does not seem to have an upper limit. Scientists believe the temperature at the center of the sun is about 15 million degrees Celsius (27 million degrees Fahrenheit). However, the interior of any star larger than the sun is probably much hotter. On the other hand, there does seem to be a lower limit to temperature. This theoretical limit, called absolute zero, has a value of – 273.15 C or – 459.67 F. At this temperature, the molecules and atoms of a substance have the least possible energy.
Absolute zero is the theoretical temperature at which the atoms and molecules of a substance have the least possible energy. This temperature, which scientists believe is the lowest attainable, equals–273.15C or -459.67F. The use of these values for absolute zero is based partly on observations of the relationship between the temperature and pressure of a gas. When the temperature of a gas confined in a fixed volume is lowered, its pressure decreases in direct proportion (as though it would become zero at –273.15C).
A temperature scale that has absolute zero for its zero point is called an absolute temperature scale. One such scale is the Kelvin scale, the international standard for scientific temperature measurement. On the Kelvin scale, absolute zero equals zero Kelvin (0 K). The word degree and the degree symbol () are generally not used with Kelvin temperature readings. For example, 20C equals 293.15 K. An absolute temperature scale related to the Fahrenheit scale is the Rankine scale. This scale is used in the United States for certain kinds of engineering work (like the aerospace industry). A Rankine temperature is obtained by adding 459.67 to a corresponding Fahrenheit temperature. For example, 68F equals 527.67R.
Physicists theorize that it is impossible to attain a temperature of precisely absolute zero. The lowest temperature recorded so far, about 0.00001 K, was reached by cooling certain metal alloys. The nuclei of these alloys were magnetized at extremely low temperatures in a magnetic field. When the magnetic field was removed, the nuclei became demagnetized and their temperature dropped to near absolute zero.
Liquid Air is a product made by greatly reducing the temperature of air until it turns into a fluid. Air becomes liquid at about -190C. Liquid air is so cold that it boils when poured over ice, which is almost 200C hotter. The liquid is bluish and looks like water. Liquid air, like the air we breathe, consists of about 78% nitrogen, 21% oxygen, and 1% argon. Scientists use liquid air in cryogenics, the study of temperatures of -100C and lower (see Cryogenics). Liquid air is considered a cryogenic fluid because of its extremely low temperature. It is a primary source of liquid forms of nitrogen, oxygen, and other gases. Scientists use liquid nitrogen in biology, chemistry, and physics research. Liquid oxygen and hydrogen are primarily used in compact, high-energy fuels for rocket engines that power spacecraft.
Properties of Liquid Air: Liquid air affects different substances in a variety of ways. For example, liquid mercury becomes as hard as steel when liquid air is poured over it. A racket ball that has been dipped in liquid air will shatter when bounced. A lead bell, which normally makes a dull sound, will temporarily produce a clear tone after being exposed to liquid air.
Scientists use liquid air to study the effects of extremely low temperatures on the strength of certain substances. Such materials as iron and plastics temporarily become brittle after being dipped into liquid air. However, copper and brass become tougher upon immersion in the fluid. Exposure to liquid air also makes metals better conductors of electricity and increases the strength of certain types of magnets.
Scientists measure the temperature of liquid air with special thermometers because mercury and alcohol thermometers cannot be used. The contents of such thermometers freeze at temperatures much higher than that of liquid air. The most accurate and widely used thermometer that measures the temperature of liquid air is the platinum resistance thermometer. This type of thermometer measures temperature by determining its effect on the electrical resistance of platinum. Platinum becomes a better or poorer conductor of electricity as its temperature changes. Another kind of special thermometer, the constant-volume gas thermometer, measures the effect of temperature on the pressure of a gas kept at a certain volume. Such gases as helium or neon are used to measure the temperature of liquid air because they turn into liquid at lower temperatures than air does.
Nitrogen and oxygen, the two major parts of air, can be separated and used in their liquid form by distilling liquid air. When liquid air is heated, the nitrogen turns into a gas before the oxygen does because the boiling point of nitrogen is lower. After the nitrogen has been removed, the remaining substance consists mostly of liquid oxygen. The high oxygen content of undistilled liquid could cause an explosion if a flammable material came into contact with it.
Making Liquid Air: The process of making liquid air is based on the fact that compressed air becomes cooler when it expands. This cooling effect was described in detail in 1853 by two British physicists, James Prescott Joule and William Thomson, and it later became known as the Joule-Thomson effect. In 1877, Louis-Paul Cailletet, a French physicist, liquefied air for the first time.
In 1895, the German chemist Carl von Linde invented a commercial process for liquid air production based on the Joule-Thomson effect. Linde’s method is still used today but with many improvements. Compressors raise the air pressure in a chamber to about 3,000 pounds per square inch (210 kilograms per square centimeter). Compression heats the air, and so water jackets on the compressor, plus a device called a heat exchanger, are used to lower the compressed air’s temperature before it is liquefied.
Air can be liquefied in one of two ways. In one method, called Joule-Thomson expansion, the compressed air flows through a series of throttling valves into increasingly larger chambers. The pressure and temperature of the air decreases in each chamber as the air expands. In the final chamber, some of the air has become cold enough to condense into a liquid. The cold vapor from this chamber is circulated around the other chambers to help cool the air that is still going through the liquefying process.
In 1902, Georges Claude, a French engineer, developed the second method of liquefying air. This method resembles the Joule-Thomson expansion but is more efficient because it makes use of work done by expanding air. In the Claude method, air enters a chamber and pushes a piston as it expands. As the piston moves, the volume of the chamber increases, which causes the air pressure and the temperature in the chamber to decrease. The air is sent through a series of these piston-equipped chambers, called expansion engines, until it becomes a liquid.
Special containers called Dewar flasks protect liquid air from heat and evaporation. A Dewar flask is a bottle made of two layers of glass. There is space between the layers of glass to insulate the contents. The flask may be coated with silver to reflect heat. Large quantities of liquid air for industrial use are stored in huge insulated tanks. Most liquid air is manufactured by the Claude process. (See Diagram) CRYOGENICS: The study of matter at motion” that is a permanent property of matter). temperatures much colder than those that occur At that point the substance would have no motion naturally on earth is called cryogenics. In the or energy left to give up. cryogenic temperature range, air becomes a liquid or even a solid and living tissue freezes instantly. The lowest possible temperature is the same for At the very lowest temperatures of the cryogenic all substances. Called absolute zero, it occurs at temperature range, matter behaves strangely- -273.16˚C, or -459.69˚F. The Kelvin and Rankine liquids run uphill and electric current never stops temperature scales use it as their zero point. flowing. Degrees on the Kelvin scale, commonly used in cryogenics, have the same range as degrees of the Since steel becomes brittle at even Arctic Celsius or centigrade scale. Degrees on the Rankine temperatures, scientists make their low- scale, used in the aerospace industry, have the same temperature equipment out of such metals as range as degrees of the Fahrenheit scale. copper or aluminum. Also, silicone rubbers replace natural rubber, which is as brittle as glass at liquid On an extremely cold Alaskan winter night, nitrogen temperatures. temperatures might drop to – 70˚F (around 252 K). The cryogenic temperature range begins at an One of the most widely applied cryogenic indefinite point much lower than this. The boiling changes is the liquefaction of gases. Liquid air has point of oxygen (90˚K) is in the high end of the been distilled to produce pure oxygen, nitrogen, range. Since even liquid hydrogen and helium are neon, and other gases. These are much easier to now produced commercially, scientists can begin transport and handle as liquids, since as gases they cryogenic experiments with liquid helium, which must be kept under great pressure. Rockets would has a boiling point of 4.2 ˚K. Temperatures below be far heavier if their hydrogen-oxygen fuel 0.001 ˚K have already been achieved. The supplies were gases rather than liquids. theoretical limit for one method is 0.0000005 ˚K. Nonreactive liquid nitrogen is one of the safest cooling agents available. It is used to control the Although such temperatures appear to be very temperature of scientific experiments and to close to absolute zero, that temperature can never preserve biological samples. In cryosurgery, liquid be reached. The third law of thermodynamics nitrogen is used to kill unhealthy tissue by freezing. states this to be impossible. Just as there is no largest number—since no matter how large a Temperature is a measure of how energetically number is written, another digit can be added to atoms are moving—traveling, rotating, vibrating. make it even larger—so too there is no smallest As a substance gains heat, its atoms move more number. No matter how low a temperature is quickly. As it loses heat, they slow down. If the reached as 0.001 ˚K shrinks to 0.0000001 ˚K and substance were cooled far enough, its atoms would below, temperatures even lower will always exist. cease to move (except for a theoretical “zero-point Reaching Supercold Temperatures:
Under natural conditions a substance is cooled within a system may be made more orderly (the by placing it next to something colder. However, if entropy may be decreased) only if energy from the substance is to be made colder than any source outside the system is applied to the system. available in nature, work must be done to remove heat, and insulation must be provided to keep the Cooling by demagnetization depends on this substance cold. relationship. A strong magnetic field provides the outside energy to line up the molecules of a Cryogenic cooling techniques use similar energy paramagnetic crystal. This also raises the transfer principles. Energy must first be introduced temperature. When the crystal cools back to the into a system (by compressing a gas, for example). starting temperature, the field is removed and the This raises the temperature of the system. The molecules swing back to a disorderly arrangement. excess heat energy flows out to the surrounding The energy they use to move comes from the heat area, which cools the system to its original energy of the crystal, so the temperature drops. temperature. Then the system is insulated and made to do work (by allowing the gas to expand, Unusual properties of helium at low for example). This step uses up some of the temperature make other cooling methods possible. remaining heat energy and cools the system below For example, at certain temperatures liquid helium the temperature of its surrounding. is more ordered (has less entropy) than solid helium, which can be formed only under pressure. Special techniques are used to reach If liquid helium is compressed at one of those temperatures around the millidegree (0.001 ˚K) temperatures, it solidifies. But, unlike normal level. These techniques make use of the substances, helium at these special temperatures relationship, described by the second law of must absorb heat (increase its entropy) causing the thermodynamics, between the amount of energy temperature to drop when it solidifies. This and the amount of disorder, or entropy, in a system. technique does not require a magnetic field, which According to the second law, disorderly atoms could interfere with some kinds of experiments.
Superfluidity and Superconductivity:
Above 2.2 ˚K liquid helium acts like a normal cryogenic fluid, but below that temperature, helium-4, the most abundant isotope, acquires superfluidity. Superfluid helium runs quickly One industrial application of cryogenics is the through tiny holes that would slow normal liquids; superconducting electromagnet. Most strong defies the laws of gravity by creeping up the sides electromagnets require far too much electricity— of a container; and conducts heat a thousand times enough to supply an entire town—to be practical. more efficiently than copper. Once started, however, a superconducting electromagnet needs no further electrical input. At varying temperatures below about 20 ˚K, Practical problems include maintaining low enough some metals and metal alloys become temperatures throughout a large installation and superconductors. When the transition temperature keeping the magnetic field from destroying the for a given metal is reached, its electrical resistance superconductivity. completely disappears. Presumably an electric current could run forever through an aluminum Superconducting computer elements are another ring cooled to a temperature of about 1 ˚K or industrial application of cryogenics. Cryotrons, the through a lead ring cooled to about 7 ˚K. The original cryogenic computer elements, consisted of transition temperatures of some alloys are even a straight core wire that had another wire coiled higher—an alloy of niobium, aluminum, and around it. Both wires were superconducting; a germanium is superconducting at 20.7 ˚K. strong current in the coiled wire set up a magnetic field that stopped current flow in the core wire. More recently developed cryogenic computer elements switch from one superconducting state to another, a faster process.