Pool boiling heat transfer of low surface tension fluids on micro/nanostructured metal additively manufactured materials

• Main Author: Muhammad Syukran Bin Ibrahim
• Other Authors: Ho Jin Yao
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2024
• Subjects: Engineering
• Online Access: https://hdl.handle.net/10356/181548
• Institution: Nanyang Technological University

This project investigates and characterises the pool boiling heat transfer performance of micro/nanostructured stainless steel surfaces in dielectric fluid, HFE 7100. The stainless steel surfaces investigated in this study were conventionally manufactured SS304 and metal additively manufactured (AM) AM-SS316L. Selective laser melting (SLM), an AM technique, was employed for the fabrication of pristine AM-SS316L. The micro/nanostructures formed on the SS304 surfaces were achieved using chemical etching by submerging the surfaces in 45% weight concentration solutions of ferric chloride at time intervals of 2, 4, 6, 8 and 10 hours, while the structures formed on the AM-SS316L surfaces were achieved using anodic etching at different current densities of 9, 18, 27 and 45 mA/cm2 for 30 minutes. Additionally, the non-structured plain surfaces of SS304 and AM-SS316L were also investigated to serve as a baseline for pool boiling performance comparison. To characterise the pool boiling performance of the various surfaces, experiments were conducted in a two-phase thermosyphon at atmospheric pressure and near saturated temperature of HFE 7100. To further delineate the different surface performances, studies were carried out to analyse the surface characteristics of the test specimens. As surface characteristics affect pool boiling performance metrics such as critical heat flux (CHF) and heat transfer coefficient (HTC), this study analysed characteristics such as surface wettability, wicking speed, surface roughness and surface morphology. Video recordings were captured under pseudo-steady state conditions throughout the experiments to capture the boiling characteristics of the surfaces. The experimental results showed that AM-SS316L surfaces performed better than its conventional SS304 counterparts. The plain AM-SS316L achieved 4.08% HTC enhancement as compared to plain SS304, and the anodic etched AM-A(27,30) achieved 89.8% HTC enhancement as compared to etched conventional 304-E(8). Furthermore, the micro/nanostructured surfaces performed better than their plain counterpart, with 304-E(8) achieved 20.4% HTC enhancement as compared to plain SS304, and AM-A(27,30) achieved 119.605 HTC enhancement as compared to plain AM-SS316L. The etched conventional 304-E(8) was also noted to perform better than the plain AM-SS316L, i.e. 304-E(8) achieved HTC enhancement of 15.7% over the AM-SS316L.