Most liquid air is manufactured by the Claude process. In this process, an <I>air compressor</I> increases the air pressure. The air, heated by compression, is cooled slightly in the <I>heat exchanger.</I> The air then enters <I>expansion engines,</I> which greatly reduce its temperature. Some of the air liquefies as it flows through the expansion valve.
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World Book diagram by Arthur Grebetz</P>
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