Thermal control of the avionics box for a commercial supersonic aircraft through Reverse Bootstrap cycle

The work carried out in this thesis aims to contribute to the solution of the sustainability problems of new aircraft, dealing with the thermal control of the avionics that govern the operation of important on-board systems. Although the new electronic components tolerate operating temperatures that are decidedly higher than traditional ones, which, even using advanced design and production technologies, do not tolerate temperatures above 80°C, it is still necessary to dispose of quantities of heat in the order of 1000 – 2000 W to operate safely and reliably. The design of the thermal control system was therefore carried out, choosing what could be the most suitable solution, meeting various requirements: minimum power necessary for its operation, small size and weight, high reliability. The components can be designed and produced using advanced but already available technologies, although, hopefully, they will be able to benefit from the possible use of even more performing future technologies. This feasibility study of the system and its components was carried out with software specifically produced for this purpose, without using commercial programs: this allows to have total mastery of the calculation processes adopted and awareness of the simplifications that are necessary in representing physical laws by circumventing difficulties without damaging the reliability of the results. The thermal control system chosen is a Reverse Bootstrap air cycle, the use of which is already well known in the "pods" of military fighter aircraft. However, in the application covered by this thesis, the environment is quite different and the duration of the mission is decidedly longer, which has been hypothesized to be three to four hours, corresponding to a flight from a European city to one in the United States or one in the the Far East. Obviously, the most demanding mission does not allow compromises in terms of safety and reliability. The Reverse Bootstrap works without any air leakage from the aircraft's engines and therefore its energy cost is zero because it uses the shock wave generated by flying supersonic as an energy source; the overpressure that is generated downstream of the wave is used to power a turbine that drives a compressor. This overpressure would however be insufficient to cool the air temperature to values suitable for thermal control of the electronics. For this reason the expansion ratio of the turbine is increased by creating a depression at the exhaust through the suction of the compressor which finally rejects the air into the external environment. The cooled air is introduced into the avionics box which is thus thermally controlled, safeguarding the functionality and reliability of the electronics. The particular mechanical design of the avionics box, which will be described in detail, guarantees non-contamination of the avionics components and certainly protects them from contact with water that could come from the turbine exhaust due to condensation of humidity. With the boundary conditions fixed, the designed system, even in the preliminary phase, should have a mass not exceeding 7 kg (excluding the avionics box) and be contained in a space of 0.8 m x 0.3 m x 0.2 m, also including the avionics box.