Main stage flux chiller

From Memory Alpha, the free Star Trek reference

Main stage flux chiller refers to part of a starship's warp drive. The USS Enterprise after its refit of 2271 had port and starboard main stage flux chillers. (Star Trek: The Motion Picture)

The fact that there are separate port and starboard flux chillers suggests that these might be located in the engine nacelles, but there is no direct evidence for this.