Approximately how many gallons per minute (gpm) of LO is diverted toward the Gas Turbine LO cooler?

• A. 100 gpm
• B. 140 gpm
• C. 120 gpm
• D. 80 gpm

Answer: (C)

Lubricating oil for a gas turbine is cooled by diverting a portion of the pump flow through the oil cooler to carry away the heat produced by bearings, gears, and the turbine itself. The amount sent through the cooler is chosen to balance effective cooling with ensuring enough oil flow and pressure reach the bearings. In typical naval gas turbine installations, about 120 gpm provides sufficient cooling capacity to keep the oil within its required temperature range under normal load, without starving the bearings of lubrication.

If the flow through the cooler were only about 100 gpm or 80 gpm, the cooler would likely be undersized for the heat load, risking higher oil temperatures. If it were about 140 gpm, you’d be moving more oil through cooling than needed, which can waste pumping energy and potentially impact oil pressure elsewhere in the system. Thus, 120 gpm is the best representative approximation for this scenario.