Many DEW systems are designed to disable enemy drones that are extremely far away and moving fast. Needless to say, it requires a tremendous amount of engineering to hit a small, moving target with a laser! Thermal management is a key enabling technology to allow these systems to operate successfully. There are several criteria that ACT engineers believe to be critical to successful DEW thermal management; achieving temperature uniformity, managing short (and intense) temperature spikes, and meeting packaging size limitations.
Leading engineering companies in the defense industry have significantly advanced laser technology by using novel approaches to combine the output of multiple arrays of laser diodes. This can move the boundaries of what’s possible, expanding the usable distance and impact capabilities. However, this will likely lead to additional waste heat dissipation requirements as the effectiveness and accuracy of the laser are influenced by the thermal management. Pumped Two Phase (P2P) technology may provide a technology breakthrough for successful DEW applications, as its ability to provide temperature uniformity and thermal responsiveness far exceeds current thermal solutions, without sacrificing valuable packaging space.
It is desirable to maintain a uniform temperature across the diodes of a DEW system, leading to requirements for designs that have the hottest diode to coldest diode with less than a +/- 2 degree C difference. In high power systems, this is not possible with traditional single-phase cooling because heat enters the fluid and raises the fluid temperature. Each diode dumps additional heat into the liquid flow, further raising its temperature. By the time the fluid flows to the final diode in the given flow channel, it’s much hotter than near the inlet. The only option to reduce the temperature gradient in single-phase systems is to increase the flow velocity which requires very large pumps and decreases system reliability. In many cases, even the highest flow rates achievable cannot meet the performance requirements of DEW systems. P2P technology, on the other hand, absorbs the waste heat in the form of latent heat. By doing so, the fluid adjusts quality (percentage of vapor to liquid) more so than temperature as it progresses through the system, allowing a very uniform temperature profile. By leveraging manifolds and parallel flow within cold plates, P2P technology can be scaled to maintain temperature uniformity across multiple cold plate surfaces, each with dozens of laser diodes.
Another unique aspect of a DEW system is the frequency of use. In many cases, the diodes only output high concentrations of heat when the laser fires, and the waste heat during “off” or “standby” mode is much lower. This requires the thermal system to be responsive, in order to avoid short term temperature spikes that can harm laser performance. P2P is capable of cooling axillary/standby electronics in single-phase and transitioning to two-phase boiling once the lasers are activated. The two-phase heat transfer at the laser diode interface allows for temperature stability to be realized very quickly, making this an ideal candidate for modern DEW designs.
As these systems are being integrated onto ground, air and shipboard platforms, space claim is also an extremely important aspect of thermal design. The enhanced thermal performance from P2P can be achieved in smaller packages due to the lower required flow rates (smaller pumps). Additionally, it is a modular and scalable technology that benefits designers as they scale various laser systems.
As temperature uniformity and heat flux continue to drive thermal design considerations, P2P should be a considered technology. Contact ACT for additional information on what can be achieved with active two-phase cooling.
ACT’s related resources can be found on our Directed Energy Weapons page, and more background on the technology, on the Pumped Two Phase page.