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<c.klasse_eins>An open cooling circuit consists of a cooling tower, </c>
<c.klasse_eins>a pump, heat exchangers and pipes. </c>

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<c.klasse_eins>The circulating cooling water is partially exposed to the ambient air </c>
<c.klasse_eins>and evaporates there as an important part of the process</c>

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<c.klasse_eins>The constant evaporation withdraws heat from the water.</c>

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<c.klasse_eins>It can now be used for cooling.</c>

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<c.klasse_eins>The evaporated water is then constantly replaced by fresh water.</c>

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<c.klasse_eins>Let's have a closer look: </c>

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<c.klasse_eins>Fresh water is never pure. </c>
<c.klasse_eins>Foreign substances are partly dissolved in water and partly mixed.  </c>

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<c.klasse_eins>These are salts, but also calcium and magnesium, for example. </c>

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<c.klasse_eins>As the water evaporates, these foreign substances remain in the residual water. </c>

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<c.klasse_eins>Thus, the proportion of foreign substances in the cooling circuit increases steadily.</c>

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<c.klasse_eins>If the concentration of foreign substances in the system becomes too high, </c>

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<c.klasse_eins>part of the cooling water must be drained and replaced by fresh water. </c>

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<c.klasse_eins>Here is an example:  </c>

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<c.klasse_eins>Suppose the cooling water contains 1000 foreign particles/litre.</c>

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<c.klasse_eins>By draining 10 percent of the water and replacing it with </c>
<c.klasse_eins>fresh water with 100 foreign particles/litre</c>

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<c.klasse_eins>...the absolute proportion of particles/litre thus drops to 910.</c>

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<c.klasse_eins>The Cycle of Concentration describes the ratio of the salt content of the cooling water to the fresh water. </c> 

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<c.klasse_eins>In our example we calculate a COC of 10. </c>

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<c.klasse_eins>The COC can be used to estimate the interval or amount of cooling water to be drained and replaced by fresh water.</c>

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