Heat and mass transfer modeling and performance analysis of a multi-stage coaxial solar-magnetic hybrid distiller based on global energy balance

Dissipation of condensation latent heat constrains the energy utilization, and multi-stage latent heat recovery is a promising strategy to overcome the efficiency limitation of solar-driven interfacial evaporation. Here, we design and demonstrate a multi-stage coaxial solar-magnetothermal distiller (MSCSMD) employing a three dimensional magnetic porous carbon scaffold for heat generation, enabling efficient freshwater production under photothermal and magnetothermal heating. To elucidate the coupled heat and mass transfer within MSCSMD and predict the evaporation performance, a radial heat and mass transfer model is developed based on global energy balance and solved using a backward iteration scheme. Firstly, experimental validation confirms good agreement between predictions and measurements, with relative deviations of 2–7% in outer wall temperature and water yield. Benefiting from stage wise recovery of condensation latent heat in coaxially nested units, the 16-stage MSCSMD achieves a recoverable efficiency of 581.42% and a nominal evaporation rate of 65.99 kg·m⁻²·h⁻¹ . Based on parameter sensitivity analysis, the gap width should be constrained to δ gap < 5 mm to ensure efficient heat transfer and to mitigate the rapid escalation of sidewall losses and vapor diffusion resistance. Moreover, a longer axial length strengthens heat recovery and diminishes sidewall losses, increasing the total efficiency of the 16-stage device to 779.77%, corresponding to a GOR of 7.80, confirming the advantage of high aspect-ratio designs in retaining heat. Increasing ambient temperature or reducing external heat transfer coefficient suppresses convective and radiative losses, shifts operation to a higher temperature condition and enhances water production. Finally, economic analysis reveals a marginal electricity cost of 0.043 RMB·L⁻¹ for freshwater production in the solar-magnetothermal mode. This work provides mechanistic insights into heat and mass transport in coaxial multi-stage distillers, and offers a novel model for the design and performance prediction of compact, high efficiency distillation systems.