Guangfa Wang,Peijia Bai,Shaoheng Yuan,Yiwen Bo,Zhengxue Zhou,Ding Zhang,Rujun Ma
Electro-phase change materials (electro-PCM), based on the electrocaloric effect, have attracted significant attention and achieved rapid development in the field of cooling technology owing to their environmental protection, low energy consumption, and miniaturization. However, due to their limited isothermal entropy change and thermal conductivity, the cooling capacity of the electro-PCM devices has severely limited their cooling effect on electronic devices. Here, with the synergistic electro-thermal phase changes, the entropy change and thermal conductivity of electro-PCM are significantly improved by stacking it with thermo-phase change materials (thermo-PCM). Compared with that of the electro-PCM, the entropy change and thermal conductivity of electro-thermal phase change materials (ETPCM) stack can be up to 4.68-fold (from 28.31 to 132.35 J kg −1 K −1 at electric field of 100 MV m −1 ) and 2.39-fold (from 0.18 to 0.43 W m −1 ·K −1 ), respectively. The practicality of this strategy has also been fully validated by cooling a simulated electronic chip (1.75 W cm −2 ) with a temperature drop of 49.32 K after constructing ETPCM stack-based cooling device using the electrostatic actuation prototype. The synergistic enhancement of entropy change and thermal conductivity paves the way for the future direction of electrocaloric cooling toward interdisciplinary fusion.
Enhanced boiling heat transfer via surface engineering is a topic of general interest for its great demand in industrial fields. However, as a dynamic interfacial phenomenon, a deep understanding of its process and mechanism, including liquid re-wetting and vapor departure, is still challenging. Herein, a micro-/nanostructured Cu surface containing a periodic microgroove/pyramid array with rich nanowrinkles is designed, where superspreading (<134.1 ms) of organic cooling agents highly boosts the liquid re-wetting process, causing a discontinuous solid–liquid–vapor three-phase contact line and ultralow under-liquid bubble adhesion force (≈1.3 µN). Therefore, a characteristic, ultrafast jet-flow boiling (bubbles rapidly ejected in multiple strips) is obtained on this surface, giving a priority to nucleation (superheat ≈ 1.5 °C) and simultaneously enhancing the critical heat flux and heat-transfer coefficient by up to 80% and 608%, respectively, compared with a flat surface. In situ observation and analysis of the nucleation, growth, and departure of micro-sized jet-flow bubbles reflects that microgrooves/pyramids with nanowrinkles promote the latent heat exchange process by superspreading-induced ultrafast liquid re-wetting and constant vapor film coalescing. Based on the designed structures, high-performance phase-change cooling for central processing unit heat management in supercomputer centers is accomplished with an ultralow power usage effectiveness (PUE < 1.04).
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