# Quasistatic magnetoconvection: Heat transport enhancement and boundary layer crossing

## TL;DR

This study numerically investigates quasistatic magnetoconvection in a cubic cell, revealing a novel heat transport enhancement due to the Lorentz force, linked to boundary layer crossing and thermal plume coherence.

## Contribution

First demonstration of heat transfer enhancement by Lorentz force in quasistatic magnetoconvection, linking boundary layer crossing to optimal heat transport.

## Key findings

- Heat transport is enhanced at moderate Hartmann numbers.
- Maximum heat transfer occurs at an optimal Hartmann number.
- Boundary layer crossing correlates with maximum temperature fluctuations.

## Abstract

We present a numerical study of quasistatic magnetoconvection in a cubic Rayleigh-B\'enard (RB) convection cell subjected to a vertical external magnetic field. For moderate values of the Hartmann number Ha, we find an enhancement of heat transport. Furthermore, a maximum heat transport enhancement is observed at certain optimal $Ha_{opt}$. The enhanced heat transport may be understood as a result of the increased coherency of the thermal plumes, which are elementary heat carriers of the system. To our knowledge this is the first time that a heat transfer enhancement by the stabilising Lorentz force in quasistatic magnetoconvection has been observed. We further found that the optimal enhancement may be understood in terms of the crossing between the thermal and the momentum boundary layers (BL) and the fact that temperature fluctuations are maximum near the position where the BLs cross. These findings demonstrate that the heat transport enhancement phenomenon in the quasistatic magnetoconvection system belongs to the same universality class of stabilising$-$destabilising ($S$-$D$) turbulent flows as the systems of confined Rayleigh-B\'enard (CRB), rotating Rayleigh-B\'enard (RRB) and double-diffusive convection (DDC). This is further supported by the findings that the heat transport, boundary layer ratio and the temperature fluctuations in magnetoconvection at the boundary layer crossing point are similar to the other three cases.