Numerical simulation and study of flow and heat transfer performance of direct contact heat exchanger based on sinusoidal alternating magnetic field

• Direct contact heat exchanger is simulated using VOF and MHD models. • Heat transfer is enhanced by sinusoidal alternating magnetic field. • Vortices are identified using Ω-vortex method in direct contact heat exchanger. • Volumetric heat transfer coefficient is predicted by regression model. Alternating magnetic fields of various frequencies and intensities were employed in this investigation to enhance the efficiency of the direct contact heat exchanger (DCHE). To explore how magnetic field intensity and frequency affect flow behavior and heat transfer performance, the volume of fluid method combined with the MHD model was used. During heat transfer, the effects of various magnetic fields on the vortex structure, turbulent kinetic energy, and volume heat transfer coefficient (VHTC) were analyzed. Results indicate that low-frequency magnetic fields promote the formation of small-scale vortices, enhancing local turbulence and heat transfer efficiency. In contrast, high-frequency fields tend to generate large-scale vortices, but excessive field intensity may suppress local mixing. Both vortex formation and turbulence enhancement significantly improve heat transfer, leading to notable increases in VHTC. A multivariate regression model was developed to describe the relationship between VHTC, magnetic field intensity, and frequency, with variance analysis confirming its predictive reliability. Under Case VII conditions (1T, 10 Hz), the heat exchanger achieved optimal performance, with turbulent kinetic energy increasing by 57.3 %, outlet temperature rising by 3.76°C, and VHTC improving by 5.779 W/m 3 ·K, relative to the case without magnetic field application.