Active Electrochromic Thermal Control Devices, 14-R9878

Principal Investigator
Jeffrey L. Boehme

Inclusive Dates:  10/01/08 – 03/31/10

Background - Thermal management is critical for optimum functionality of many systems. These systems can include sensitive electronics with high-power processors or billion dollar spacecraft orbiting Earth. In general, there are two types of thermal control systems: active and passive. An active system is typically used in addition to the passive system when the passive system is not adequate. Examples of active thermal control systems include heat pipes, heat exchangers, evaporators and louvers.

SwRI researchers developed novel active thermal control devices based on solid-state, thin-film electrochromic (EC) materials. By proper choice of the electrochromic material, the reflectance [or equivalently, the emissivity (ε)] of the device in the infrared is modulated by applying an external electrical potential. The emissivity is reversed by changing the polarity of the applied potential.

Approach - The primary objective of this project was to demonstrate the feasibility of fabricating novel active thermal control devices based on thin-film electrochromic materials. The following specific objectives were achieved during the project to meet the primary objective.

• Developed thin-film electrochromic devices capable of modulating their reflectance in the long-wavelength infrared (8 to 12 μm)

• Developed outer IR transparent window and current collector capable of transmitting >80 percent of IR radiation

• Demonstrated device performance at temperatures ranging from -30 to 90 °C

• Developed preliminary system design including application schemes, electrical traces, and device sealing methods

• Assembled devices for client demonstration purposes

Accomplishments - During this project, SwRI fully characterized numerous organic and inorganic electrochromic materials. Furthermore, techniques were developed for fabricating electrochromic devices that operate in the longwave infrared (8 to 12 microns). The final demonstrator device used a novel current collector configuration resulting in a unique device design. The final device demonstrated an emissivity modulation from a high emissivity state (ε~0.8) to a low emissivity state (ε~0.5) by applying a small voltage. Lastly, the devices demonstrated emissivity modulation over 10,000 cycles at high (90 °C) and low (-30 °C) temperatures.

 

Figure 1. Thermal infrared image of an electrochromic thermal control device in its high emissivity state (left) and low emissivity state (right).

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