Study Of MEMS-based Chip-integrated Microstructures For Efficient Boiling Heat Transfer

With the increase of chip integration and electronic packaging density,the heat of electronic devices keeps increasing.Heat dissipation has become a technical bottleneck in the development of electronic devices The development of new efficient cooling technologies becomes an urgent task.Enhanced boiling cooling technology,as a type of efficient two-phase flow liquid cooling technologies,has been getting more attention.Recent years,it has become one of the research hotspots in this field to enhance heat transfer performance by introducing micro-structures to increase bubble nucleation sites,optimize gas-liquid interface behavior and expand heat transfer area.Several chip-integrated microstructures for efficient boiling heat transfer were designed,fabricated and tested,improving heat transfer by enhancing bubble dynamic behaviors and increasing nucleation sites.Firstly,an improved microstructure consisting of two layers of crossing strip Cu arrays was proposed.The bubble dynamic behaviors and the heat transfer performances were numerically studied under Cahn-Hilliard phase-field model in COMSOL.Besides providing extra heat transfer area and nucleation cites,the designed microstructure forms suspended platforms that become extra surfaces for the bubbles'coalescing and departure.While more solid-liquid contact area is released,the existence of micro-liquid layer at the bottom of bubbles is ensured.The liquid consumed by evaporation in the micro-area is supplied in time to keep the stability of boiling state,avoiding the occurrence of drying out.The micro-fabrication process based on electroplating and sacrificial layer technology was designed and implemented.Testing samples with the microstructures for enhanced boiling were fabricated.Layered resistance wire was utilized to provide stable heat input as a simulated chip heating source.Based on the testing samples,a real time testing system was designed and established to assess the visualized bubble dynamic behaviors and heat transfer performance during pool boiling.Verification of enhanced heat transfer performance on the designed surface was reached:the heat flux dissipated by this improved microstructure surface in DI water was 4 times of that on a bare flat surface,and the heat transfer coefficient reached 50,000 W/(m~2K)at the superheat of 20?.It is proved that the bubbles suspended coalescing and departure dynamic behaviors have a significant contribution to enhance the cooling efficiency.Furthermore,the enhancement of boiling heat transfer on AlN substrate with high granularity surface was discussed.The heat transfer performances of AlN substrate and smooth silicon oxide substrate were compared with experiments.The heat transfer coefficient reached 40 000 W/(m~2K)at the superheat of 15?.Moreover,aiming at the deterioration of heat transfer caused by the large coverage of bubbles stacked on the heating surface at low heat flux input during subcooled boiling,a three-dimensional hollow cavity structure was designed.Its barrier effect on bubbles and the enhancement of thermal performance during subcooled boiling were confirmed by experiments.The low-cost manufacture route compatible with the regular IC manufacture established in this work provides potential for chip cooling enhancement in industrial applications.