UCLA

Cooling is a basic need for human beings. Vapor compression cooling is the technology behind almost all of the applications. However, limited by its mechanism, the vapor compression refrigeration is not suitable for modern technologies such as mobile devices and personal cooling. Besides, it relies on refrigerants like Freon and hydrofluorinecarbons, which pose serious environmental problems. Therefore, it is urgent and over-due to develop new cooling technologies that are efficient and environmentally friendly.

As a solid-state cooling technology, electrocaloric cooling offers several advantages over traditional cooling systems, but few devices offer high specific cooling power and a high coefficient of performance (COP). To develop electrocaloric cooling technology towards commercialization, we attacked the project through both material and device directions.

We developed a solution process fabrication method for large area EC film fabrication. Various material characterizations were conducted to study and optimize the performance of the EC film. The as-fabricated EC film has an active area of 10 cm2 and a cycling test was conducted to prove its reliability under repeating high voltage. Another material’s effort is to chemically modify the EC polymer for features like better mechanical strength, reliability, and high dielectric constant. Poly(vinylidene fluoride-trifluoroethylene-chlororfluoroethylene) was used as the starting material. It is a dehydrochlorination reaction catalyzed by triethylamine. The organic base attacks the hydrogen close to the Cl atoms, and the reaction introduces unsaturated double bond in the polymer chain. The unsaturated sites can be used as active sites for functional group introduction to modify the polymer further. In particular, we used this double-bonding containing polymer as the precursor to prepare crosslinked thin films and demonstrated improved capacitive energy storage.

We presented a cooling device with high intrinsic thermodynamic efficiency using a flexible electrocaloric (EC) polymer film and an electrostatic actuation mechanism to transfer heat between a heat source and a heat sink. Reversible electrostatic forces reduce parasitic power consumption and allow efficient heat transfer through excellent thermal contact with the heat source or sink. The EC device produced a specific cooling power of 2.8 W/g and a relative COP of 13. Our cooling device is more efficient and compact than existing solid-state cooling technologies, showing a path towards using the technology for a variety of practical applications.