Numerical Investigation of an Aircraft Thermal Management System
Aircraft Thermal Management System , Fuel Thermal Management System
Thermal management requirements in modern aircraft have been increasing over time, driven by the increase in the thermal loads generated by a variety of electronic components and hydraulic systems. A literature review has suggested that using the fuel, which is meant for propulsion, to collect the heat generated and reject part of it to the ambient is the most effective method to achieve thermal management in the current generation of aircraft. The analysis presented in this thesis thus focused on the performance of fuel thermal management systems (FTMS) for managing the various thermal loads in an aircraft. The FTMS model consisted of four major components including a fuel storage tank, high-temperature and low-temperature heat exchangers and bypass-loop with proportioning valve. To facilitate the analysis, the FTMS was numerically modelled using a “systems” approach based on the principles of conservation of mass and energy. From this theoretical model, a numerical model of the FTMS was developed in the MATLAB/Simulink programming environment. For the model, the system’s heat exchangers were simulated using a logarithmic-mean temperature-difference (LMTD) approach. The model also considered variation in air and fuel properties with temperature and altitude conditions. The numerical model was compared against values published in the literature and then used to perform parametric studies for both uniform (i.e., constant altitude and cruise speed) and non-uniform (i.e., variable altitude and cruise speed) flight conditions. The research considered three primary operational conditions for the FTMS, namely: (1) a specified operating temperature for heat-dissipating elements, (2) a specified heat removal rate, and (3) a specified fuel temperature. The performance of the FTMS was evaluated for these three operational modes during both uniform and non-uniform flight conditions. In each case, the variations in the heat transfer rates and temperatures at critical point in the FTMS were calculated for a variety of flight conditions. These conditions included variations iii in altitudes, cruise speeds, fuel burn rates, high-temperature and low-temperature heat exchanger capacities, fuel tank heat-losses and fuel recirculation rates. The results of this analysis indicated that when the heat source temperature was maintained at a constant value, the heated fuel temperature increased, and the heat removal capacity degraded over the duration of flight. Conversely, for a prescribed heat removal capacity, both the heat source temperature and heated fuel temperature increased during the flight. Lastly, when the desired heated fuel temperature was specified, it was observed that the heat source temperature and the heat removal rate both decreased over time. It was concluded that the optimum fuel recirculation rate was a complex function of variables, thus highlighting the need for a dynamic control strategy.