Session: 04-04: Nano/Microscale Boiling and Condensation Heat Transfer

Paper Number: 132060

132060 - Micro/nanostructuring of Additively Manufactured 316l Stainless Steel for Enhanced Pool Boiling Heat Transfer 

Abstract: 

Recent advances in scalable surface micro- and nano-structuring techniques for metallic surfaces have opened new opportunities to augment two-phase cooling of high-heat-flux components. These include high-performance electronics, high-energy-density batteries, and high-power lasers. While appropriately designed surface structures have the potential to significantly enhance pool boiling heat transfer coefficient and critical heat flux by increasing bubble nucleation site density and liquid capillarity, many of these micro/nanoengineered surfaces are limited to conventionally manufactured copper and aluminium alloys. However, stainless steel, a material commonly used in thermal management devices due to its remarkable corrosion resistance and high strength, has limited structuring techniques which can enhance boiling. Interestingly, its resilience to chemical treatment and oxidation is what makes stainless steel difficult to structure in the first place.

The challenge of optimizing structure morphology on stainless steel for enhanced boiling is further exacerbated with the recent proliferation of metal additive manufacturing (AM). Laser powder bed fusion is an AM technology that utilizes laser sources to melt and fuse base metallic powder layer-by-layer to form a three-dimensional part. Due to the wide design freedom offered by AM to produce highly complex and quality parts, there has been an increasing adoption of AM in a plethora of industries. However, the high melting and solidification rates of molten stainless steel during the AM process have resulted in vastly different surface chemistry, material composition and grain boundaries as compared to conventionally cast or stamped stainless steel parts, rendering significant challenges to the structuring of stainless steel parts made using AM.

In this work, we develop a highly scalable structuring technique to generate and tailor the surface micro and nanostructure morphology of additively manufactured 316 stainless steel. We show that structuring has the ability to enhance the pool boiling performance of dielectric fluid HFE7100. The fabrication technique utilizes electrochemical etching with oxalic acid as the electrolyte. By systematically varying the magnitude of the supplied current and reaction time, pyramidal micro/nanostructures with length scales ranging from 0.5 µm to 2 µm with exceptional superhydrophilicity are obtained. Wicking experiments are performed to identify the AM micro/nanostructured specimen with the best wickability. The optimum specimen is then characterized for its pool boiling performance with HFE7100, a commonly used liquid in two-phase immersion cooling applications. Our results show that our optimal micro/nanostructured AM surfaces enhance the heat transfer coefficient by more than 4X as compared to conventionally cast plain stainless steel surfaces. While the plain stainless steel surface attained critical heat fluxes of only 10 W/cm², no critical heat flux was recorded on the micro/nanostructured AM surface at high fluxes as high as 13 W/cm². Our work not only reports the first scalable structuring technique for additively manufactured 316 stainless steel with significant boiling enhancements, but it also develops a surface structuring optimization methodology that can be adopted for other AM alloys.

Presenting Author: Jin Yao Ho Nanyang Technological University

Presenting Author Biography: Jin Yao Ho joined the School of Mechanical and Aerospace Engineering on December 2021 as Assistant Professor, under the ThermoFluids & Marine Engineering Cluster. He obtained his Bachelor of Engineering, Master of Engineering and Doctor of Philosophy in Mechanical Engineering in 2010, 2014 and 2019 respectively, from Nanyang Technological University (NTU). Between March 2020 and December 2021, he undertook his postdoctoral training in the Energy Transport Research Laboratory at University of Illinois at Urbana-Champaign (UIUC). His research focuses on the development of advanced thermal devices using additive manufactured designs to enhance condensation; boiling and phase change heat transfer; and the development of micro/nanostructured metal additively manufactured materials to promote interfacial transport of heat and mass.

Authors:

Leymus Yong Xiang Lum Nanyang Technological University
Xinrui Wang Nanyang Technological University
Kazi Fazle Rabbi University of Illinois at Urbana-Champaign
Nenad Miljkovic University of Illinois at Urbana-Champaign
Jin Yao Ho Nanyang Technological University