Vapor Compression System with PCM HX for Cooling High Power Lasers

Directed energy weapons (DEWS) are being developed to compliment conventional weaponry and offer advantages that include: faster speeds, longer ranges, and higher precision at less cost.  Some systems such as the Active Denial System involve microwave emission while other systems are laser-based.  Common to these high-energy systems is the need to effectively handle transient, high heat loads with minimal Size, Weight, Power and Cost (SWaP-C) dependent on platform.

Thermal Management of DEWS

Thermal management is a critical component in DEWS.  Further, it is often impractical (due to large SWaP) to efficiently dissipate the high heat loads in real-time in mobile and lightweight airborne platforms.  The SWaP of the cooling system can however be substantially reduced with a cooling system having thermal energy storage, which is especially attractive for systems with a short duty cycle.   ACT has developed several custom cooling systems with thermal storage for DEWS that were 40-60% lighter than the systems otherwise needed to continuously handle the peak heat load.  The ultimate heat sink in these systems was ambient air, which could be hot depending on local conditions.

How ACT’s System Works

Our system is based on a compact vapor compression system (VCS) integrated with a thermal storage unit.  The thermal energy generated is stored at a high rate when the DEWS is on and dissipated to a heat sink (typically ambient air) during the remainder of the duty cycle.   For thermal storage, Phase Change Materials (PCMs) and metal hydrides have been used.  In effect, the thermal energy storage unit stores the heat and effectively “dampens” the heat load such that the time-averaged heat load, rather than peak heat load, needs to be handled by the cooling system.  This enables the SWaP of the vapor compression system to be reduced compared to that otherwise needed to handle very high peak heat loads.

Figure 1:  (Left) A schematic of a vapor compression system with integrated thermal energy storage; (Right) A representative transient thermal energy profile showing that the use of thermal energy storage dampens the heat loads that need to be managed by the vapor compression system.Figure 1: (Left) A schematic of a vapor compression system with integrated thermal energy storage; (Right) A representative transient thermal energy profile showing that the use of thermal energy storage dampens the heat loads that need to be managed by the vapor compression system.

Systems Developed at ACT

ACT has developed several cooling systems for DEWS including work done for MDA, the Navy Vehicle Stopper program, and the Navy Ground-Based Air Defense (GBAD) system (featured below).  The GBAD program, for example, has been a 5-year development effort that employs an advanced laser (30kW nominal power), lightweight beam director, on-board battery power storage and ACT’s DEWS cooling system, all packaged on a tactical vehicle platform.

Complimentary work

ACT has also developed advanced, compact, large nearly-isothermal heat exchangers that have been integrated with DEWS developed by military primes.  Some of these systems were proof-of-concept while others are being validated through field testing.

 

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