International Journal of Thermal Sciences 147 (2020) 106131 Available online 14 October 2019 1290-0729/© 2019 Elsevier Masson SAS. All rights reserved. Pool boiling heat transfer characteristics of iron oxide nano-suspension under constant magnetic feld M.M. Sarafraz a, * , O. Pourmehran a , B. Yang a , M. Arjomandi a , R. Ellahi b, c a School of Mechanical Engineering, The University of Adelaide, South Australia, Australia b Department of Mathematics & Statistics, FBAS, IIUI, Islamabad, Pakistan c Fulbright Fellow, Department of Mechanical Engineering, University of California Riverside, USA A R T I C L E INFO Keywords: Pool boiling Magnetic feld Critical heat fux Fouling mitigation Bubble formation ABSTRACT In this paper, we quantifed the heat transfer coeffcient (HTC) of Fe 3 O 4 aqueous nano-suspension at various mass concentrations of 0.05% 0.2%. The potential role of operating parameters including heat fux perpendicular to the surface (HF), concentration of the nanoparticle (NP), strength of magnetic feld (MF), zeta potential and concentration of a specifc surfactant on HTC, critical heat fux (CHF) and transient fouling resistance of the surface was identifed. Results showed that MF can lower the fouling resistance providing that the nano- suspension is stable. It was shown that in this case, the HTC value was also promoted. However, the enhance- ment of HTC strongly depended on the zeta potential value. Likewise, by increasing the NP concentration, the CHF value was augmented, while the HTC was promoted u to wt. % ¼ 0.15 and then decreased at wt. % ¼ 0.2. This behavior was attributed to the existence of a thermal resistance on the surface. Notably, the bubble for- mation on the surface was intensifed due to the MF, which was attributed to the formation of irregularities and micro-cavities due to the deposition of the NPs. 1. Introduction Boiling is one of the most effcient mechanism of heat transfer for cooling and heating applications at high heat fux conditions. This plausible feature is attributed to the formation of the bubbles which creates a two-phase heat transfer mechanism. The presence of the bubbles can renew the thermal and fuid boundary layer, which in turn promotes the heat transfer coeffcient (HTC) of the system. There are extensive studies in the literature towards the lack of understanding of the governing mechanisms and exact behavior of fuids in a two-phase boiling regime. Nano-suspensions are the promising working fuids for the future of the advanced thermal engineering and have been assessed for various applications. When the boiling heat transfer comes to the nano-suspensions, understanding the mechanism of heat transfer be- comes challenging as bubble-bubble, bubble-surface and bubble-liquid interactions affect the heat transfer rate. Moreover, deposition of the nanoparticle (NP) is another challenge affecting the properties of the surface, which in turn can suppress or promote the performance of the system. It is worth saying that, in boiling of nano-suspensions, the sta- bility of the nano-suspension can be altered due to the evaporation of the base fuid, which can intensify the rate of deposition and surface change. Thus, boiling heat transfer of nano-suspensions requires further investigation. Critical Heat Flux referred to as CHF point is a heat fux (HF), in which the HTC of the system is maximum and thereby, the rate of bubble formation is superior such that the bubbles surround the boiling surface. By increasing the population density of the bubbles over the surface, bubble coalescence occurs, which in turn creates a large-size bubbles and blanket of vapor on the surface. Such large blankets can insulate the surface and reduce the heat transfer. Overall, the HTC value decreases and performance of the system is suppressed. This can lead to the system failure. There are extensive studies conducted on heat transfer mecha- nisms involved in boiling heat transfer. Hence, the studies can be cate- gorized into three different groups. The frst group of study shows that the boiling heat transfer is suppressed once NPs are added to the system, while there is a second group demonstrating that the boiling heat transfer can be promoted due to the presence of the NPs. These two groups of study have one point in common that the deposition of the NPs on the surface can improve the CHF value. Therefore, a vision was created to use passive and active methods with the aim to prevent or regulate the deposition of the NPs such that the HTC remains untouched or be promoted. The utilization of magnetic feld (MF) is one plausible * Corresponding author. E-mail address: mohammadmohsen.sarafraz@adelaide.edu.au (M.M. Sarafraz). Contents lists available at ScienceDirect International Journal of Thermal Sciences journal homepage: http://www.elsevier.com/locate/ijts https://doi.org/10.1016/j.ijthermalsci.2019.106131 Received 23 May 2018; Received in revised form 3 October 2019; Accepted 5 October 2019