Membrane scaling is a barrier to membrane distillation (MD). In this study, 3D-printed carbon nanotube (CNT) spacer was used to investigate its capability for mitigating membrane scaling during MD and to elucidate the scaling mechanism experimentally and theoretically. CNT spacer was tested under temperature-dependent calcium sulfate scaling conditions, and optical coherence tomography (OCT) and scanning electron microscopy (SEM) were used to measure scaling quantitatively. CNT spacer exhibited unique membrane scaling mechanism, where only a 37% reduction (29 Lm⁻²h⁻¹) in the initial flux was achieved, even above a volume concentration factor (VCF) of 4. On the other hand, the membrane with a polylactic acid (PLA) spacer (controls) entirely lost flux before reaching a VCF of 3.5. Interestingly, bubble formation was observed in CNT spacer, which could be attributed to the enhanced flux and vaporization rate on membrane surface in the presence of rough-surfaced CNT spacer. Bubbly flow along the membrane channel with CNT spacer can potentially reduce surface scaling on membrane during MD. Moreover, due to the surface roughness of CNT spacer, the initial nuclei might be detached more easily from CNT spacer surface than from smooth PLA surface and grow further into larger crystals in the bulk, resulting in reduced dissolved solutes in the solution. This phenomenon was indirectly corroborated by comparing the experimentally measured fluxes and theoretically computed values from our mechanistic model of MD-crystallization developed in this study. Therefore, this study revealed that CNT spacer with rough surfaces can potentially have benefit of mitigating membrane scaling during MD.

膜结垢是膜蒸馏 (MD) 的一个障碍。在这项研究中，使用 3D 打印的碳纳米管 (CNT) 间隔物来研究其在 MD 过程中减轻膜结垢的能力，并从实验和理论上阐明结垢机制。在依赖于温度的硫酸钙结垢条件下测试了CNT间隔物，并使用光学相干断层扫描（OCT）和扫描电子显微镜（SEM）来定量测量结垢。CNT间隔物表现出独特的膜结垢机制，即使在体积浓度因子（VCF）为4以上的情况下，初始通量也仅降低了37％（29 Lm ^-2 h ^-1）。另一方面，具有聚乳酸 (PLA) 间隔物（对照）在 VCF 达到 3.5 之前完全失去通量。有趣的是，在 CNT 间隔物中观察到气泡形成，这可能归因于粗糙表面 CNT 间隔物存在下膜表面通量和蒸发速率的增强。沿着带有 CNT 间隔物的膜通道的气泡流可以潜在地减少 MD 过程中膜上的表面结垢。此外，由于 CNT 间隔物的表面粗糙度，初始核可能比光滑的 PLA 表面更容易从 CNT 间隔物表面分离，并进一步生长成块体中更大的晶体，导致溶液中溶解的溶质减少。通过比较实验测量的通量和本研究中开发的 MD 结晶机械模型的理论计算值，间接证实了这种现象。因此，这项研究表明，具有粗糙表面的 CNT 间隔物可能有利于减轻 MD 过程中的膜结垢。