Energy conversion apparatus (10, 101, 102, 103, 104) comprising: an electrical machine including a rotor arranged to rotate about an axis, the rotor defining a first cavity therein; power electronic circuitry arranged at least partially around the axis and defining a second cavity therein, the power electronic circuitry being positioned axially adjacent to the electrical machine a heat pipe positioned within the first cavity of the rotor and within the second cavity defined by the power electronic circuitry, the heat pipe being arranged to receive thermal energy from the rotor; and a cooling arrangement (18, 181, 182, 183, 184) positioned at least partially within the second cavity and axially overlapping the power electronic circuitry, the cooling arrangement (18, 181, 182, 183, 184) being arranged to receive thermal energy from the power electronic circuitry and from the heat pipe, wherein the cooling arrangement (18, 181, 182, 183, 184) comprises: an inlet to receive a cooling fluid; and an outlet to output the cooling fluid, the second cavity being arranged to receive the cooling fluid from the inlet and to provide the cooling fluid to the outlet, the cooling arrangement (18, 181, 182, 183, 184) further comprising a plurality of first fins extending from the heat pipe into the second cavity wherein at least a subset of the plurality of first fins are oriented at a non-perpendicular angle relative to the axis to cause the cooling fluid to flow from the inlet to the outlet during operation of the rotor and wherein the cooling arrangement further comprises a structural support and coolant guide that defines a first channel comprising a plurality of second fins and a second channel comprising the plurality of first fins for the flow of coolant. an electrical machine including a rotor arranged to rotate about an axis, the rotor defining a first cavity therein; power electronic circuitry arranged at least partially around the axis and defining a second cavity therein, the power electronic circuitry being positioned axially adjacent to the electrical machine a heat pipe positioned within the first cavity of the rotor and within the second cavity defined by the power electronic circuitry, the heat pipe being arranged to receive thermal energy from the rotor; and a cooling arrangement (18, 181, 182, 183, 184) positioned at least partially within the second cavity and axially overlapping the power electronic circuitry, the cooling arrangement (18, 181, 182, 183, 184) being arranged to receive thermal energy from the power electronic circuitry and from the heat pipe, wherein the cooling arrangement (18, 181, 182, 183, 184) comprises: an inlet to receive a cooling fluid; and an outlet to output the cooling fluid, the second cavity being arranged to receive the cooling fluid from the inlet and to provide the cooling fluid to the outlet, the cooling arrangement (18, 181, 182, 183, 184) further comprising a plurality of first fins extending from the heat pipe into the second cavity wherein at least a subset of the plurality of first fins are oriented at a non-perpendicular angle relative to the axis to cause the cooling fluid to flow from the inlet to the outlet during operation of the rotor and wherein the cooling arrangement further comprises a structural support and coolant guide that defines a first channel comprising a plurality of second fins and a second channel comprising the plurality of first fins for the flow of coolant.