The potential of utilizing the rejected heat of a fuel cell system to improve the aircraft propulsive efficiency is discussed for various flight conditions. The thermodynamic background of the process and the connection of power consumption in the fan of the ducted propulsor and fuel cell heat are given, and a link between these two components is presented. A concept that goes beyond the known ram heat exchanger is discussed, which outlines the potential benefits of integrating a fan upstream of the heat exchanger. The influence of the fan pressure ratio, flight speed, and altitude, as well as the temperature level of the available fuel cell heat on the propulsive efficiency, is presented. A correlation between the fan pressure ratio, flight speed, and exchangeable fuel cell heat is established, providing a simplified computational approach for evaluating feasible operating conditions within this process. This paper identifies the challenges of heat exchanger integration at International Standard Atmosphere sea level conditions and its benefits for cruise flight conditions. The results show that for a flight Mach number of 0.8 and a fan pressure ratio of 1.5 at a cruising altitude of 11,000 m, the propulsion efficiency increases by approximately 8 percentage points compared to a ducted propulsor without heat utilization. Under sea-level conditions, the concept does not offer any performance advantages over a ducted propulsor. Instead, it exhibits either comparable or reduced propulsive efficiency.

Propulsion systems in aircraft using reciprocating engines often face the challenge of managing thermal loads effectively. This problem is similar to the utilisation of polymer electrolyte membrane fuel cell systems, which, despite their high efficiency, emit a high proportion of heat when converting chemical energy into electrical energy. Transfer of the rejected heat to the air is efficiently performed by heat exchangers. Since convective heat transfer is physically linked to fluid friction at the heat exchanger walls, a pressure loss occurs. In a high-speed flow regime of the aircraft during cruise the integration of heat exchangers combined with a fan stage inside a nacelle (thus forming an impeller configuration) represents a promising approach for the dual benefit of dissipating excess heat and harnessing it for additional thrust generation through the ram jet effect. Striving for enhanced thrust performance of hydrogen electric commercial aircraft, this paper presents the results of a parameter study based on a 1D-modelling approach. The focus is placed on the influence of design and operating parameters (ambient conditions, fan pressure ratio, diffusion ratio, airside temperature difference) on performance and sizing of the proposed propulsion system. It is shown that the proposed system performs best at an altitude of 11 km and with increasing freestream Mach number. Furthermore, the main challenges related to the combination of a thrust generation system with a heat exchanger in terms of sizing, in particularly the required heat exchanger dimensions, under different operating conditions are discussed.

Concentrated solar power (CSP) systems impose high demands on individual components such as receivers, optical elements, etc. due to high solar flux. Characterisation of these components often requires measurements under defined, constant conditions, which can be challenging or even impossible in real-world applications due to changes in irradiance, weather conditions, accessibility, tracking inaccuracies, etc. . Solar simulators are used for this purpose, with the challenge of providing sun-like, uniformly distributed and highly concentrated light. This paper presents an approach to automatically investigate the irradiance distribution of concentrated light in a solar simulator. A water-cooled flux meter (thermopile) is used in combination with an XY table to scan the area of interest, resulting in a high-resolution image of the irradiance distribution in the target area. The results are presented and discussed based on measurement data recorded in a real solar simulator. Issues such as sensor area i.e. spatial resolution, light spectrum dependence, temperature influence, and measurement speed are addressed.