Assessment of the integration of an organic Rankine cycle for waste heat recovery from bleed air for implementation on board an aircraft

Abstract

This project assesses the possibility of putting an organic Rankine cycle on board an aircraft for waste heat recovery using bleed air coming from the engine’s compressor as a heat source. Into this task the main subject taken into account was the weight of the system, since this will mean a trade-off between the power generated and the extra weight that is necessary to add.
In recent years, little research on waste heat recovery on aircraft has been done. The main source of heat for these systems comes from the engine and not from the bleed air as in this project but in all cases penalties like changes in engine design, excessive weight from the heat exchangers and a loss in thrust were faced. On the other side, some of these penalties were surpassed by the amount of power that the organic Rankine cycles provided.
To develop this project a model was designed on MATLAB varying the mass flow of the organic fluid to find out for the best arrangement that gives the most power output with the less weight. The model was performed under cruise conditions from an Airbus A320, a single aisle aircraft. The ORC was assessed in two locations; before the entrance of the precooler, a system that cools down the air before going into the pneumatic system, and before the air conditioning (AC) packs. The results show that heat recovery is possible only when the ORC is placed before the precooler but certain conditions need to be met so the energy balances result in positive outcomes. Current techniques were used to estimate the weight of the heat exchangers but improvements of these or availability of new materials in the future will increase the amount of energy that could be saved. The implementation of an ORC using the bleed system gives an option to recover wasted energy from aircraft since the conditions available are suitable for the system.