science

Liquefaction of gases

Liquefaction of gases is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Liquefaction of gases rather than just read about it. In short: Liquefaction of gases is physical conversion of a gas into a liquid state (condensation). The liquefaction of gases is a complex process that employs various compression and expansion steps to achieve high pressures and very low temperatures, for example, using turboexpanders.

Key takeaways

Liquefaction of gases belongs to science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Liquefaction of gases to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Liquefaction of gases from memory before moving on to harder problems.

Reference excerpt

Liquefaction of gases is physical conversion of a gas into a liquid state (condensation). The liquefaction of gases is a complex process that employs various compression and expansion steps to achieve high pressures and very low temperatures, for example, using turboexpanders.

Uses Liquefaction processes are used for scientific, industrial, and commercial purposes. Many gases can be put into a liquid state at normal atmospheric pressure by simple cooling; a few, such as carbon dioxide, require pressurization as well. Liquefaction is used to analyze the fundamental properties of gas molecules (intermolecular forces), to store gases (e.g., LPG), and in refrigeration and air conditioning. There, the gas is liquefied in the condenser, where the heat of vaporization is released, and evaporated in the evaporator, where the heat of vaporization is absorbed. Ammonia was the first such refrigerant, and is still in widespread use in industrial refrigeration. In residential and commercial applications, it has largely been replaced by compounds derived from petroleum and halogens. Liquid oxygen is provided to hospitals for conversion to gas for patients with breathing problems, and liquid nitrogen is used in the medical field for cryosurgery, by inseminators to freeze semen, and by field and lab scientists to preserve samples. Liquefied chlorine is transported for eventual solution in water, after which it is used for water purification, sanitation of industrial waste, sewage and swimming pools, bleaching of pulp and textiles and manufacture of carbon tetrachloride, glycol and numerous other organic compounds as well as phosgene gas. Liquefaction of helium (4He) with the precooled Hampson–Linde cycle led to a Nobel Prize for Heike Kamerlingh Onnes in 1913. At ambient pressure the boiling point of liquefied helium is 4.22 K (−268.93 °C). Below 2.17 K liquid 4He becomes a superfluid (Nobel Prize 1978, Pyotr Kapitsa) and shows characteristic properties such as heat conduction through second sound, zero viscosity and the fountain effect among others. The liquefaction of air is used to obtain nitrogen, oxygen, and argon and other atmospheric noble gases by separating the air components by fractional distillation in a cryogenic air separation unit.

History

Liquid air

Linde's process Air is liquefied by the Linde process, in which air is alternately compressed, cooled, and expanded; each expansion results in a considerable reduction in temperature. At lower temperatures, molecules move more slowly and occupy less space, so the air condenses into a liquid.

Claude's process Air can also be liquefied by Claude's process, in which the gas is allowed to expand isentropically twice in two chambers. While expanding, the gas has to do work as it is led through an expansion turbine. The gas is not yet liquid, since that would destroy the turbine. Commercial air liquefication plants bypass this problem by expanding the air at supercritical pressures. Final liquefaction takes place by isenthalpic expansion in a thermal expansion valve.

Illustrations

Worked examples

Example 1 — a first encounter with Liquefaction of gases

Start with the simplest possible case. Write down what Liquefaction of gases claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Liquefaction of gases before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Liquefaction of gases ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Liquefaction of gases

In research: Liquefaction of gases appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Liquefaction of gases in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Liquefaction of gases is common in secondary-school and first-year university syllabi. It links to neighbouring topics Gas technologies, Industrial gases, Industrial processes, so understanding it makes those chapters shorter.
In everyday life: Look for Liquefaction of gases outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Liquefaction of gases in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Liquefaction of gases means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Liquefaction of gases out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Liquefaction of gases in simple terms?

Why does Liquefaction of gases matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Liquefaction of gases?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Liquefaction of gases.