Magnetic-field induced flattening of evaporating ferro-nanofluid meniscus for enhanced cooling.

• Thickness profile investigation using reflectometry for a ferro-nanofluid thin film meniscus under the influence of magnetic field. • Significant thinning of the adsorbed layer and elongating of the transition region (flattening effects) reported on the meniscus shape. • The derived curvature and pressure profiles exhibit dominating effect of disjoining pressure in pulling liquid towards the transition region. • Evaporative overall mass flux enhanced up to 156% while the average heat flux increased to 101% on subjecting to magnetic field. This work envisages applying magnetic fields to flatten thin ferro-nanofluid film meniscus for enhanced heat transfer during evaporative cooling process. Experiments are conducted to examine the shape of the evaporating extended meniscus of ferro-nanofluid (Fe 3 0 4 nanoparticles in water suspension 0.01% v/v) under axisymmetric vertical magnetic fields (∼ 10 − 2 T) generated by solenoid placed below the heated substrate. The study includes measuring the thickness profile of the meniscus evaporating region using high nano-scale resolution reflectometry and theoretically interpreting meniscus shape in terms of flow and film heat transfer. Profile measurements reveal an increasing influence of magnetic fields in thinning of the adsorbed region and stretching of the transition region, which effectively reduce the thermal resistance across meniscus width. Data reduction based on thickness as well as the derived curvature profiles yields a high-pressure gradient driving flow along the evaporating thin film region. The results imply additional suction induced by disjoining pressure of thinner adsorbed layer which sustains replenishment of lost evaporative mass across a longer transition region interface. Subsequent heat transfer analysis reveals up to 156 % enhancement in overall heat flux and 101 % in average heat transfer with increasing magnetic field intensity. The findings establish proof of concept of applying magnetic field to augment film-based cooling. [ABSTRACT FROM AUTHOR]