The method of cooling oil with an external heat exchanger that rejects heat to cooling water or antifreeze, as illustrated in Figure 5.19, was the earliest, widely-used concept. In warm climates cooling water could serve the heat exchanger, and this cooling water could come from a cooling tower or a closedcircuit cooler. In the closed-circuit cooler the fluid being cooled flows through pipe coils with water spraying from the top and ambient air flowing up through the sprays and coils. Some plants simply draw water from the pan of the evaporative condenser, but this practice is not recommended. In the first
place, this water is likely to collect foreign matter that could deposit on the
tubes of the heat exchanger, reducing its heat-transfer effectiveness. Also, in
cold climates the water in the evaporative condenser must sometimes be drained
to avoid freezing, and in that situation no means of oil cooling would be available.
Even with the closed-circuit cooler, in cold climates antifreeze must be circulated
to avoid freezing water.
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