Hydrophobic Porous Polymeric Surface to Enhance Nucleation Boiling Heat Transfer: A Road to Achieve 1000 kW/m2 Heat Removal from Microelectronics

The study illustrates a simple yet cost-effective measure to enhance boiling heat transfer characteristics of de-ionized (DI) water by employing a polymeric nanofibrous texture on a superheated substrate mimicking high-performance microelectronics. The nanofibers were coated on the copper substrate as a base, using a novel method, namely supersonic solution by blowing for 90 s. The results revealed that the onset of nucleate boiling (ONB) for the nanotextured surface was 3.23 °C, whereas for bare copper surface it was 9.07 °C. Additionally, the maximum heat flux in the nucleate boiling region on the nanotextured surfaces (1265 kW/m2) was enhanced by 143% compared to the bare copper surface (517.1 kW/m2). Moreover, the boiling heat transfer coefficient (BHTC) for the coated surface was approximately 5.1 times better than the bare surface. With introduction of the nanofluid (a suspension of CNT in water), an early ONB (3.2 °C) on the bare surface was seen, mostly due to thin fouling layer. With nanotextured and nanofluid combination, the maximum heat flux was 106% better than bare and water combination. This is to be noted that all the experiments were tested between a supply voltage of 40–140 V. The nanofiber coated sample exhibited hydrophobic behavior with contact angle of 137.7°. The higher contact angle on the coated surface facilitated earlier ONB. The presence of ultrafine nanofibers on the copper surface increased the bubble departure frequency due to cage-like structure, which chopped the growing bubbles into smaller bubbles. The nanofibers also overheated the surrounding fluid of vapor bubbles, which impeded the growth and kept the bubbles smaller. Both phenomena, aided by the higher contact angle of fibrous network improved the overall nucleation boiling heat transfer.