Thermal Management Challenges For Future Military Aircraft Power Systems

General thermodynamic analytical investigations on the primary components of aircraft power systems, as well as vehicle integration and mission considerations, have revealed that thermal management plays a key role in limiting payload size and performance. All power system components such as batteries, capacitors, power semiconductors, generators, pulsed power sources and beam conditioners have thermal design issues when their performance is pushed to deliver higher powers. Several technology driven thermal challenges need to be addressed in the development of these envisioned aircraft based weapon power systems. High power and high heat flux cooling requirements, coupled with a limited payload capacity, is one of the primary design challenges tackled in the development of this type of power system. Partial solutions have been sought by way of increased heat transfer through the use of spray cooling, microchannel and subcooled boiling, loop heat pipes, capillary pumped loops, energy storage and spray cooling arrays. Of course complexities abound in an aircraft environment, and since payloads are severely limited, it is therefore very important to recognize these thermal challenges and approach the design and development of large power systems with cautious optimism. Power and thermal management systems will likely be optimized for specific applications and aircraft platforms, so two typical applications have been investigated: an airborne solid-state laser and a pulsed power directed energy application. Three different thermal management approaches were considered for a typical airborne solid-state laser based power system with a laser output power of 100 kW. Some of the consequences of using advanced thermal management concepts on the tactical mission legs are presented from a time-constraint and mass-constraint points of view. Several thermal management approaches were also evaluated for a pulsed power system with a directed energy application. Both open and closed aircraft level thermal management configurations were investigated. Typically an open cycle system will be considerably lighter than a closed cycle system, except when run times are lengthy. Coolant requirements for an open thermal management system, for a pulsed power source with a 30% duty cycle with an average heat load of 2.9 MW, ranged from 2007 kg of ammonia or 1127 kg of water.