US Patent 9267434 Heat exchanger

A gas turbine engine has a fan, a compressor section, a combustor, and a turbine section. The fan delivers a portion of air into the compressor, and into a duct, as bypass air. A bleed air system bleeds a quantity of air from the compressor into a chamber at least at low power conditions of the engine. The bleed air system has an opening which may be selectively closed to block bleed air, or opened to allow bleed flow from the compressor into the chamber. A heat exchanger is positioned such that a first surface of the heat exchanger is contacted by bypass air in the duct, and a second surface of the heat exchanger is contacted by bleed air when the bleed air system directs air from the compressor into the chamber.