ACT would like to thank the DSI Group for organizing the Annual Directed Energy Day in Alexandria, VA. This was ACT’s first time attending and it was a truly great experience to see the leaders of the Directed Energy Community share ideas and insights to a growing market segment. If you are interested in learning about future industry needs, plan to attend future events!
From a thermal technology perspective, the message is clear- solutions must be able to meet very stringent, high power demands in extremely size and weight friendly packages (in addition to the DOD “must haves”; high reliability, durability, etc).
Currently, in directed energy systems, the power levels exceed passive, air cooled options. Instead, the laser side of the system is typically 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. These systems can get very complex and the Directed Energy Day pointed out the importance of cooling; the acronym SWAP-C2 was used as an important system level decision making factor. Size, Weight and Power (SWAP) and Cost have been staples of decision making in the military field, but he second C is dedicated to cooling! There are a couple of unique thermal challenges that are paving a path for some emerging technologies in the Directed Energy industry.
- The use of a high quantity of laser diodes to concentrate/combine outputs to improve laser functionality.
- Need: Creates the need to control temperature over large arrays of laser diodes
- Technology Option: Pumped Two-Phase (P2P)
- Pulsed operation (on when firing, off the remainder of time)
- Need: Thermal dampening device to package system more efficiently
- Technology Option: Phase Change Material (PCM) Heat Exchanger (HX)
In scenario 1, the change here is from pumped single phase to a pumped two-phase on the cold plates contacting 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 of the fluid but can maintain fairly 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 is excited to continue our participation in Directed Energy Technology. We'll exhibit for the first time at next year's "Directed Energy to DC" event hosted by the Directed Energy Professional Society, to be held in late April at the Pentagon.
Check out ACT's case study on Thermal Storage for Military Application to read how we helped provide efficient, lightweight, compact thermal storage and management subsystem for the Navy's GBAD program.