Multiple stream heat exchanger

A gas turbine engine comprising:

• a fan disposed within a nacelle;
• a core engine disposed within a core cowling, wherein a bypass passage for a fan air stream is defined radially between the nacelle and the core cowl;
• a thermal management system for maintaining lubricant for components of the core engine within a defined temperature range, the thermal management system including:
• a heat exchanger mounted within the core cowling adjacent the bypass passage, the heat exchanger including a first coolant passage for a hydraulic fluid flow, a second coolant passage for a fuel flow, a first flow passage in thermal communication with the first coolant passage and a second flow passage in thermal communication with the second coolant passage all defined within a common housing;
• a first valve controlling a flow of first lubricant into at least one of the first flow passage or the second flow passage;
• a controller configured to operate the first valve to direct the flow of first lubricant into one of the first flow passage and the second flow passage for transferring thermal energy from the first lubricant into one of the hydraulic fluid flow and the fuel flow;
• and
• a secondary cooler for cooling a second lubricant for an integrated drive generator with the first lubricant cooled in the heat exchanger.

A method of managing thermal properties of a lubricant flow for a gas turbine engine, the method comprising:

• assembling a heat exchanger to include a first coolant passage for a hydraulic fluid flow, a second coolant passage for a fuel flow, a first flow passage in thermal communication with the first coolant passage and a second flow passage in thermal communication with the second coolant passage all defined within a common housing;
• measuring a temperature of the hydraulic fluid flow, the fuel flow and the lubricant flow with at least one sensor assembly and communicated the measured temperature information to a controller;
• and
• operating at least one valve to rout lubricant flow into thermal communication with one of the hydraulic fluid flow in the first coolant passage and fuel flow in the second coolant passages to maintain the lubricant flow within a predefined temperature range;
• and
• routing a portion of lubricant flow exiting the heat exchanger to a secondary cooler for cooling a second lubricant low for an integrated drive generator.