TURBOFAN WITH AIR-COOLED HEAT EXCHANGER IN THE INLET FLOW UPSTREAM OF THE FAN

A turbofan gas turbine engine comprises, in axial flow sequence, a heat exchanger module, a fan assembly, a compressor module, a turbine module, and an exhaust module. The fan assembly comprises a plurality of fan blades defining a fan diameter (D). The heat exchanger module is in fluid communication with the fan assembly by an inlet duct, and the heat exchanger module comprises a plurality of radially-extending hollow vanes arranged in a circumferential array, with a channel extending axially between each pair of adjacent hollow vanes. An airflow entering the heat exchanger module is divided between a set of vane airflows through each of the hollow vanes, and a set of channel airflows through each of the channels. Each vane airflow has a vane mass flow rate FlowVane,, and each channel air flow has a channel mass flow rate FlowChan. Each of the hollow vanes accommodates at least one heat transfer element for the transfer of heat from a first fluid contained within the or each heat transfer element to the corresponding vane airflow passing over a surface of the or each heat transfer element.Each hollow vane comprises, in axial flow sequence, an inlet portion, a heat transfer portion, and an exhaust portion, with the inlet portion comprising a diffuser element, and the heat transfer portion comprising at least one heat transfer element. The diffuser element is configured to cause the vane mass flow rate FlowVane to be lower than the channel mass flow rate FlowChan by a user-defined margin.