engineering

Low-temperature thermal desalination

Low-temperature thermal desalination is a engineering 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 Low-temperature thermal desalination rather than just read about it. In short: Low-temperature thermal desalination (LTTD) is a desalination technique which takes advantage of the fact that water evaporates at lower temperatures at low pressures, even as low as ambient temperature. The system uses vacuum pumps to create a low pressure, low-temperature environment in which water evaporates even at a temperature difference of 8 °C (14 °F) between two volumes of water.

Key takeaways

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

Reference excerpt

Low-temperature thermal desalination (LTTD) is a desalination technique which takes advantage of the fact that water evaporates at lower temperatures at low pressures, even as low as ambient temperature. The system uses vacuum pumps to create a low pressure, low-temperature environment in which water evaporates even at a temperature difference of 8 °C (14 °F) between two volumes of water. Cooling water is supplied from deep sea depths of as much as 600 metres (2,000 ft). This cold water is pumped through coils to condense the water vapor. The resulting condensate is purified water. It is often used in regions with limited freshwater resources and access to abundant seawater, particularly in coastal areas and island territories.

Using waste heat The LTTD process may also take advantage of the temperature gradient available at thermal power plants, where large quantities of warm cooling water are discharged from the plant, reducing the energy input needed to create a temperature gradient. This technique of making use of waste heat is a form of cogeneration. The first documented application of this concept dates back to 1992, with the start-up and successful operation of a seawater distillation plant rated at 500 m3/day (named "Low Temperature Flash", LTF) installed in Piombino power plant (Italy).

History The principle of LTTD has been known for some time, originally stemming from ocean thermal energy conversion research. Some experiments were conducted in the U.S. and Japan to test low-temperature-driven desalination technology. In Japan, a spray flash evaporation system was developed by Saga University. In the U.S. state of Hawai'i, the Natural Energy Laboratory of Hawaii Authority tested an open-cycle OTEC plant with cogeneration of fresh water and electric energy, using a temperature difference of 20 °C (36 °F) between surface water and water at a depth of around 500 metres (1,600 ft).

Research in India and pilot plants LTTD was studied by India's National Institute of Ocean Technology (NIOT) from 2004. Their first LTTD plant was opened in 2005 at Kavaratti in the Lakshadweep islands. The plant's capacity is 100,000 litres (22,000 imp gal; 26,000 US gal)/day, at a capital cost of ₹50 million (€922,000). The plant uses deep sea water at a temperature of 7 to 15 °C (45 to 59 °F). In 2007, NIOT opened an experimental floating LTTD plant off the coast of Chennai with a capacity of 1,000,000 litres (220,000 imp gal; 260,000 US gal)/day. A smaller plant was established in 2009 at the North Chennai Thermal Power Station (a coal-fired power plant) to test the concept using power plant cooling water.

References

Worked examples

Example 1 — a first encounter with Low-temperature thermal desalination

Start with the simplest possible case. Write down what Low-temperature thermal desalination claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In engineering, 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 Low-temperature thermal desalination 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 Low-temperature thermal desalination 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 Low-temperature thermal desalination

In research: Low-temperature thermal desalination appears in engineering 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 Low-temperature thermal desalination 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: Low-temperature thermal desalination is common in secondary-school and first-year university syllabi. It links to neighbouring topics Water desalination, so understanding it makes those chapters shorter.
In everyday life: Look for Low-temperature thermal desalination 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 Low-temperature thermal desalination in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Low-temperature thermal desalination 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 Low-temperature thermal desalination out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Low-temperature thermal desalination in simple terms?

Why does Low-temperature thermal desalination matter?

Because it connects several engineering 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 Low-temperature thermal desalination?

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 Low-temperature thermal desalination.