Investigation of quenching heat transfer characteristics of stainless steel 304l in AI₂O₃ and SiO2 nanofluids / Hazman Bin Zeol

Faculty of Mechanical and Automotive Engineering Technology

Thesis (Master of Science) -- Universiti Malaysia Pahang - 2025

Includes bibliographical references

Conventional quenching fluids such as water and oils, commonly used in thermal management systems and emergency core cooling systems (ECCS), exhibit limited heat transfer performance and often result in inconsistent surface quality. This study aims to investigate the quenching heat transfer performance of stainless-steel rods in water-based nanofluids, with particular emphasis on nanoparticle type (Al₂O₃ and SiO₂), concentration, subcooling conditions, and repeated quenching cycles. Quenching experiments were conducted using both single and repeated (7 times) processes in nanofluids containing Al₂O₃ and SiO₂ nanoparticles at concentrations of 0.001, 0.01, and 0.025 vol% under saturated and subcooled conditions (ΔTsub = 10–40 °C). Surface morphology was analyzed post-quenching to investigate the influence of nanoparticles on surface roughness and thermal response. Al₂O₃ nanofluids demonstrated superior quenching performance at low concentrations (0.001 vol%), achieving a 23% improvement over distilled water and reaching the maximum heat flux (MHF) at 360.8 °C in 69 seconds. SiO₂ nanofluids showed minimal improvement at low concentration but the highest enhancement at 0.025 vol%, with an MHF temperature approximately 30% higher than that of distilled water. Al₂O₃ nanofluids consistently produced smoother surfaces (roughness 0.033–0.046 μm), while SiO₂ resulted in increased roughness, especially at higher concentrations. In repeated quenching, SiO₂’s initial effectiveness declined due to surface degradation. Under varying subcooling conditions (ΔTsub = 10–40 °C), distilled water showed optimal quenching performance at moderate subcooling levels (ΔTsub = 10–20 °C), where the minimum heat flux (MHF) point was clearly observed reaching 477.27 °C in 26 seconds at ΔTsub = 20 °C. At higher subcooling (ΔTsub = 30–40 °C), stable film boiling was suppressed, and the cooling rate peaked at 33.99 °C/s (ΔTsub = 40 °C), indicating rapid vapour collapse. In nanofluids, the influence of nanoparticle concentration diminished under strong subcooling. For example, SiO₂ nanofluids at 0.025 vol% under ΔTsub = 10 °C raised the MHF temperature to 440 °C in 36 seconds, while Al₂O₃ nanofluids maintained consistent MHF values (~330–380 °C) across concentrations. These results confirm that subcooling, more than nanoparticle concentration, governs both heat transfer efficiency and surface behavior during quenching. The study confirms that nanoparticle type, concentration, subcooling level, and surface morphology significantly affect quenching heat transfer. Nanofluids, particularly those with optimized Al₂O₃ and SiO₂ compositions, offer promising potential for enhancing heat transfer performance and surface quality in thermal management and industrial cooling applications.