Increased Capacity for Thermal Energy Storage by Combining Latent and Bonding Reaction Heat Storage

Avionic systems which feature low duty cycle heat loads, such as high-powered microwave (HPM) or high-energy lasers (HEL) require thermal energy storage (TES) to minimize the volume/mass of the thermal management system. The Air Force currently seeks a TES with system-based heat capacities of 68 kJ/kg and 120 MJ/m3 while allowing for a charge/discharge rate of 2 kW/kg. Currently state-of-the-art paraffin-, metal-hydride-, and ammonia-based reversible systems have volume based system heat capacities that do not exceed 90 MJ/m3. Mainstreams approach which combines both latent- and bond-reaction thermal storage is capable of>450 MJ/m3 by employing an open-loop concept that allows for recharging during ground-operations. This approach can easily be tailored for either HPM, 70 aC, or HEL, 20 aC, DEW. For the Phase I effort, Mainstream will experimentally demonstrate the heat capacity and heat input rate. The Phase II effort will focus on the integration of the TES with an avionic TMS. BENEFIT: Solid-state lasers for direct energy weapons (DEW) require a minimum capacity of 100 kW of optical power. However, existing efficiencies of the DEW are<10%, yielding a thermal load of>1 MW. However, DEWs are also characterized by low duty cycles allowing for thermal energy storage (TES) to significantly reduce the size of the thermal management system (TMS). Even if a reversible system could be designed to yield 120 MJ/m3 (current state of the art is<90 MJ/m3), the TES would require 12.6 m3 (assuming ATLS mission profile). However, if a mission profile can be designated pre-flight, the total energy storage would be defined allowing for an open-loop system that can be recharged during ground-operations between missions. Mainstreams open-loop system provides for a 5x increase over the SBIR solicitation in both mass- and volume-specific heat capacity without the obstacles faced with common open-loop systems such as water vaporization (inadequate operating temperatures and high vacuum requirement) and ammonia vaporization (hazardous material storage and venting). The proposed design would allow for optimization of TMS/TES for finite mission/life cycle systems such as single-flight UAVs, missiles, and DEWs.