Evaluation of a Thermal Management System With Energy Storage for an Airborne Laser Power System

Abstract

In order to determine the impact of thermal management related conceptual improvements on the overall performance of an aircraft based high-energy laser power system, a general thermodynamic analytical investigation was conducted for several power system architectural variations. The Thermal Management System (TMS) is one of six primary components of the Aircraft Electrical Laser (AEL) power system that is mounted on a cargo aircraft and operated at a fixed altitude. Air properties at this altitude and a designated aircraft speed were used in the thermal management of the various components of the power system architectures. Data for a layered plate-fin type of heat exchanger configuration was generated based on liquid-air heat transfer with the liquid providing the bulk of the heat absorption from each component by single-phase forced convection. Thermal energy storage was also involved in the TMS design and analysis depending on the ambient conditions for any given architectural variation. When there is a restriction on the payload mass and volume in an aircraft at a high altitude, it becomes imperative to look for a TMS that would suitably accommodate a wide spectrum of heat loads. A closed-loop cooling scheme was selected with water as the coolant that carries the heat loads from the various components and either dissipates it to the ambient conditions through a ram air heat exchanger (RAHX) or stores it in a thermal energy storage (TES) cell. The impacts of varying technologies, diode operational parameters, duty cycles and environmental conditions on the size of the TMS were evaluated based on a laser system output of 100 kW with a corresponding total heat load of 787 kWt in the near-term. The introduction of advanced technologies for the far-term architectural evaluations resulted in a decrease of the TMS mass from 1870 kg for the near-term architecture to 1190 kg While the TMS system mass came down by 200 kg when the diode operating temperature was increased from 298 K to 318 K, there was a negligible decrease in mass at higher temperatures. Increasing the temperature gradient in the diode did not yield any significant changes in TMS mass. Environmental conditions resulted in a 50% increase in TMS mass going from the coldest day to the hottest day.