Modified Ionic Liquid-Based Phase Change Materials as Effective Heat Exchangers

Future manned mission venturing into deep space will require sophisticated thermal control systems to protect against extreme environments ranging from direct illumination by solar radiation to complete darkness. To manage these extremes, heat exchangers composed of phase change materials that can expand and contract without causing structural damage, will be essential. This project will further-engineer ionic liquid-based phase change materials (PCMs) to: (1) tune the melting point for ORION platform heat exchanger applications, (2) further-elevate thermal conductivity for both solid and liquid, and (3) evenly-regulate heat transfer among components. In Phase I, InnoSense LLC (ISL) developed effective PCM formulations and tested their thermal properties. These materials exhibited high heat of fusion (254-272 kJ/kg) with low volume expansion (4-6%) compared with the current standard, pentadecane (~6-7%). We demonstrated IonoTherm to have higher thermal conductivity, heat storage, thermal diffusivity and thermal inertia over pentadecane. Further, tests indicated that IonoTherm did not corrode metallic substrates, phase-separate or degrade. In Phase II, ISL will fine-tune the PCM formulation and evaluate it in a flight level prototype heat exchanger. A NASA prime contractor has teamed with ISL to transition ISL's IonoTherm, and perform independent testing during Phase II and beyond under simulated field conditions.

Future missions will require manned spacecraft to travel further from the earth more than ever before. A major requirement for these spacecrafts is to maintain comfortable living conditions for the crew members. External temperatures and operating environments vary widely as the craft travels through space. In order to successfully-regulate cabin temperatures, heat exchangers requiring minimal volume and weight must be employed. ISL's phase change material will provide a nontoxic system that will operate effectively in a wide temperature range to maintain cabin temperatures. ISL will tailor IonoTherm for insertion into a heat exchanger that will offer excellent thermal behavior with low volume expansion. By reducing heat exchanger bulk, working space will be maximized. ISL's IonoTherm shows promise for long-term reliability, which will ensure its effectiveness for long duration space missions.

The proposed heat transfer fluids will find a wide variety of commercial applications. They include the temperature regulation for polar shelters and vehicles. The wide operating range and high heat capacity will aid in the size and weight reduction of existing heat exchangers. Therefore, it will be possible to optimize workable space. Other applications can include the use of the fluid for high powered telescopes, cryogenic fuel utilization sources, and energy generation applications.

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