Two recent studies highlight the unique cooling requirements of Directed Energy Weapons (DEW) and identify methods to address these requirements. Both systems generate substantial heat loads, one requiring more than 1 MW of cooling. Furthermore, much of the heat is generated within a small volume, resulting in a high heat flux. Both spray cooling with ammonia and microchannel heat exchangers with de-ionized water or ammonia were considered. In each case it was determined that the ultimate heat sink would be the ambient air. In one study the heat transfer process was more challenging due to a relatively narrow allowable temperature range and a maximum allowable temperature near the ambient air temperature. Heat transfer options considered the use of a liquid loop with either direct ram air cooling, an air cycle cooling system, and a vapor cycle cooling system. The latter options provided greater differential temperatures between the working fluid and ambient air, resulting in smaller and lighter systems at the expense of increased cooling system power requirements.
Since neither of the systems studied operates continuously, the size and weight of some of the heat transfer components could be reduced by incorporating thermal storage capacity in the systems. For the duty cycles studied, the savings in overall system weight, size, drag, and power required was substantial. A thermal storage unit utilizing a paraffin-based phase-change material was developed and tested. Test results validated the performance models.
Methods of power generation for DEW systems are also considered. Approaches include the use of existing power generation systems combined with batteries, high-power engine-mounted generators, bleed-air-driven generators, a novel bleed and burn concept, propellant power systems, ram air turbines, and generators driven by an auxiliary gas turbine engine.