Aftercoolers in compressed-air systems: primary purpose. Identify what an aftercooler accomplishes downstream of compression to prepare air for distribution/use.

Concept/Approach
An aftercooler cools compressed air, condensing water vapour (and some oil vapour), so that liquids can be separated before the air enters receivers/distribution. While it does cool the air, the key functional purpose is to condense and remove moisture and oil.

Option check
C is the most specific and accurate statement of purpose.
D is true but incomplete: cooling is the means, not the end, in air-system conditioning.

Final Answer
cause moisture and oil vapour to drop out.