An LN2 exhaust conduit was a piece of technology used on Intrepid-class vessels, used to vent exhaust from a ship.
In 2371, the USS Voyager was attacked by the Numiri in the Delta Quadrant. The ship's executive officer, Commander Chakotay, asked Lieutenant B'Elanna Torres to remember fighting a Starfleet runabout near Teluridian IV, while the two were affiliated with the Maquis. Torres, realizing Chakotay's plan, then called engineering to vent the LN2 exhaust conduits to make it look to the Numiri that Voyager was seriously damaged. The plan worked and Voyager was able to defeat the Numiri. (VOY: "Ex Post Facto")