Layer melt crystallization (LMC) is an eco-friendly, efficient separation process crucial for sustainable chemical production. Axial temperature gradients represent a challenge in industrial LMC, reducing separation efficiency through complex thermal-hydrodynamic-mass transfer coupling mechanisms that remain poorly quantified. This study proposes an operational optimization strategy: regulating coolant flow direction from conventional bottom-up to top-down configuration within existing heat transfer constraints. Through systematic experiments in a 2.4 m industrial-scale crystallizer and validated CFD simulations, we show that closed-loop top-down flow effectively suppresses axial melt temperature fluctuations, enhances solid–liquid (S-L) interface mass transfer, and yields high-purity, low-impurity-inclusion crystal layers. Under the conditions of a liquid level of 2.4 m and an axial inlet–outlet coolant temperature gradient of 0.675 K/m, the purity of the target substance is increased by 0.2% to 0.4% when the coolant adopts the top-down flow mode compared with the bottom-up flow mode. CFD analysis reveals a multiscale framework connecting coolant flow direction, axial temperature distribution, natural convection structure, interfacial mass transfer, and crystal purity. Notably, the operational window of this strategy is identified at low coolant flow rates (<50 L/h) and moderate feed concentrations (85% to 95%). These findings provide fundamental insights and practical guidance for optimizing heat transfer-constrained LMC processes.
Li et al. (Mon,) studied this question.