Cooling
An electric propulsion unit ( 102 ) for an aircraft is shown. A fan ( 202 ) produces a pressured airflow (P) by raising the pressure of an incident airflow (I). An electric machine ( 201 ) is arranged to drive the fan and is located within a casing ( 204 ). A primary cooling circuit ( 205 ) is located within the casing, and includes the electric machine and a first pass of a fluid-fluid heat exchanger ( 208 ), thereby placing the electric machine and the fluid-fluid heat exchanger in thermal communication. A secondary cooling circuit includes a second pass of the fluid-fluid heat exchanger and an air-fluid heat exchanger ( 210 ) located within the pressurised airflow produced by the fan, thereby placing the fluid-fluid heat exchanger and the air-fluid heat exchanger in thermal communication.
1. An electric propulsion unit for an aircraft, comprising:
a fan configured to produce a pressured airflow by raising the pressure of an incident airflow;
an electric machine arranged to drive the fan and which is located within a casing;
a primary cooling circuit located within the casing, and including the electric machine and a first pass of a fluid-fluid heat exchanger, thereby placing the electric machine and the fluid-fluid heat exchanger in thermal communication;
a secondary cooling circuit including a second pass of the fluid-fluid heat exchanger and an air-fluid heat exchanger located within the pressurised airflow produced by the fan, thereby placing the fluid-fluid heat exchanger and the air-fluid heat exchanger in thermal communication.
2. The electric propulsion unit of claim 1 , in which the fan is a ducted fan, and the electric propulsion unit comprises a nacelle defining a duct in which said fan is located.
3. The electric propulsion unit of claim 2 , in which the air-fluid heat exchanger is mounted proximal to an outer periphery of the duct.
4. The electric propulsion unit of claim 2 , in which the air-fluid heat exchanger is mounted proximal to an inner periphery of the duct.
5. The electric propulsion unit of claim 1 , in which the fan is an open propeller.
6. The electric propulsion unit of claim 5 , in which the air-fluid heat exchanger is mounted on the outside of the casing.
7. The electric propulsion unit of claim 1 , in which the air-fluid heat exchanger is substantially annular.
8. The electric propulsion unit of claim 1 , in which the electric propulsion unit further comprises one or more auxiliary cooling circuits each having respective air-fluid heat exchangers, such that the electric propulsion unit has a plurality of air-fluid heat exchangers located within the pressurised airflow produced by the fan.
9. The electric propulsion unit of claim 1 , in which each one of said plurality of air-fluid heat exchangers forms a respective sector of the same annulus.
10. The electric propulsion unit of claim 1 , in which the fluid-fluid heat exchanger is a first fluid-fluid heat exchanger, and the primary cooling circuit further includes a first pass of a second fluid-fluid heat exchanger; and
the secondary cooling circuit is a first secondary cooling circuit, and the electric propulsion unit further comprises a second secondary cooling circuit including a second pass of the second fluid-fluid heat exchanger and a second air-fluid heat exchanger located within the pressurised airflow produced by the fan, thereby placing the second fluid-fluid heat exchanger in thermal communication with the second air-fluid heat exchanger.
11. An aircraft including one or more electric propulsors according to claim 1 .