Final Grade: 5/5

Abstract:

Electric aircraft require effective cooling systems to maintain motor temperatures at viable levels. High altitudes present a complication; outside-air-temperature (OAT) and air density decrease. These variables conversely influence the coolant system's ability to dissipate heat from the motor. Air density decrease reduces heat transfer, while OAT decrease augments heat transfer.

The purpose of this thesis is to evaluate the relative impacts of these variables on the air-side heat transfer of liquid cooling radiators, and the coolant outlet temperatures of axial flux permanent magnet synchronous motors (AFPMSM). The Pipistrel Velis Electro aircraft is used as a case study.

Reduced-order approximation methods for coolant inlet temperatures and radiator conductance are developed using a combination of convective heat-transfer equations, airspeed relationships and the Dittus-Boelter correlation. A MATLAB/Simulink model is developed to simulate the climb of a Velis Electro through International Standard Atmosphere conditions to its service ceiling of 3660m. The model incorporates both quasi-steady state and transient calculations methods, with the latter mainly serving as a consistency check.

The developed model suggests that the impact of OAT decrease substantially outweighs the impact of reduced air density. Reduced air density increases coolant outlet temperatures by 0.7904-3.1616K, depending on assumed sea level reference temperature. Meanwhile, reduced OAT decreases coolant outlet temperature by 23.7880K. The quasi-steady state and transient calculation methods are consistent with one another. The coolant's temperature decrease produces more favourable cooling conditions for the AFPMSM, but its influence is not quantified due to insufficient thermal motor data.