Directed Energy Weapons are designed to damage targets at long distances with concentrated energy including lasers, microwaves and particle beams. The concentration of this energy leads to large heat loss. The overall reliability of the system relies on keeping the energy source at safe operating temperature. In many applications, the effectiveness of the laser can be negatively impacted by poor thermal management. In addition to power and thermal performance, these systems must be contained in extremely size and weight friendly packages.
Currently, in directed energy systems, the power levels are too high to safely operate with traditional air-cooling options. Instead, the laser side of the system is cooled with an active pumped liquid system. The fluid loop must then transfer the heat to a location in the system for rejection; typically a large vehicle radiator. There are a couple of unique thermal challenges that are paving a path for some emerging technologies in the Directed Energy industry.
- The need to incorporate high quantities of laser diodes to concentrate/combine outputs to improve laser functionality. The success of the system hinges on these diodes operating at similar temperatures throughout the array. Therefore, the thermal management system must provide temperature uniformity over long distances.
- Thermal Technology Option: Pumped Two Phase (P2P)
- Pulsed operation (on when firing, off the remainder of time). This leads to opportunity to dampen the overall heat load with a thermal storage medium. If successful, all downstream components can be sized for average heat load instead of peak heat load.
- Thermal Technology Option: Phase Change Material (PCM) Heat Exchanger (HX)
In scenario 1, the change from pumped single phase to a pumped two phase (P2P) allows for much better isothermality along the cold plate that interfaces with the laser diodes. In a P2P system, the fluid leverages the high latent heat of vaporization to create an extremely high internal heat transfer coefficient. As the fluid is pumped and vaporizes across the heat sources, it adjusts quality (percentage of vapor to liquid) of the fluid while maintaining uniform temperature. As the cold plates contacting the laser systems grow in physical size or power densities, a single phase system will have large temperature gradients which can affect the system performance. P2P is a strong option to create highly uniform cold plates that are capable of moving high heat flux and higher overall power. Check out this video to see a visual demonstration and performance of a P2P system.
In scenario 2, a PCM HX is introduced to exchange heat between the primary coolant loop (that contacts the laser system) and the secondary cooling loop (that transports heat to the radiator). This PCM HX can be used to dampen the pulsed load so that the secondary loop can be sized for average instead of maximum heat load. This can mean significant packaging advantages and lower weight for the system integrator. Check out this video for more information.
ACT works with customers to design and develop system level thermal solutions for DEW programs. The technologies outlined above are two key components, but the overarching system required pumps, heat exchangers, controls, and many other components. At ACT we make sure we understand our customers’ and end user needs to strategically implement a thermal management solution that will meet stringent thermal, mechanical and environmental requirements.