On saturated flow boiling heat transfer of deionized water/ferrofluid on structured surfaces with or without external magnetic field

Flow boiling is one of the most effective methods for achieving high heat dissipation rates. The manipulation of magnetic fluids (ferrofluid) is one of the popular approaches for heat transfer enhancement. This study aims to experimentally investigate the effect of magnetic nanoparticles on saturated flow boiling heat transfer (FBHT) on microstructured silicon surfaces. The FBHT performance was assessed in the absence and presence of an external magnetic field with bubble force analysis by considering a single bubble under flow boiling conditions. The experimental setup consisted of a rectangular minichannel with two heating blocks on the bottom and top sides. Two different structures, including square and circular cavities, were tested. SPIONs (superparamagnetic iron oxide nanoparticles) were employed as magnetic nanoparticles. Two different types of working fluid were utilized, including deionized water (DW) and ferrofluid (FF), which contained diluted SPIONs in water. Helmholtz coils were utilized to generate an external magnetic field. Visualization with a high-speed camera enabled the study of boiling heat transfer (BHT) and bubble dynamics characteristics along with parametric effects. Experimental tests were conducted under three conditions: tests with DW, tests with FF, and ferrofluid in the presence of a magnetic field (FF/MF). These tests were carried out at two mass fluxes (300 and 400 kg/m2s) and over a heat flux range of 26.28 - 142.8 W/cm2. Adding nanoparticles further enhanced heat transfer and resulted in an increase in heat transfer coefficient (HTC) by up to 21% (from 32 to 38.7 kW/m2K). Moreover, application of an external magnetic field to the ferrofluid resulted in a reduction in the bubble departure size and an increase in HTC on the top surface, especially at high heat fluxes. The maximum HTC enhancement in the presence of the magnetic field was 25% (from 31.7 to 39.7 kW/m2K). These findings demonstrate the potential benefits of the use of magnetic nanoparticles and external magnetic fields to enhance flow boiling heat transfer on microstructured surfaces.