Suitable methods to realize a multi-dimensional fractionation of microparticles smaller than \({10}\,\upmu \mathrm{{m}}\) diameter are still rare. In the present study, size and density fractionation is investigated for \(3.55\,\upmu \mathrm{{m}}\) and \({9.87}\,\upmu \mathrm{{m}}\) particles in a sharp-corner serpentine microchannel of cross-sectional aspect ratio \(h/w = 0.25\). Experimental results are obtained through Astigmatism Particle Tracking Velocimetry (APTV) measurements, from which three-dimensional particle distributions are reconstructed for Reynolds numbers between 100 and 150. The 3D reconstruction shows for the first time that equilibrium trajectories do not only develop over the channel width, i.e. in-plane equilibrium positions but also over the channel height at different out-of-plane positions. With increasing Reynolds number, \(9.87\,\upmu \mathrm{{m}}\) polystyrene \(\left( \rho _{\mathrm{{PS}}} = 1.05\,\mathrm{{g}}\;\mathrm{{cm}}^{-3} \right)\) and melamine \(\left( \rho _\mathrm{{MF}} = 1.51\,\mathrm{{g}}\;\mathrm{{cm}}^{-3} \right)\) particles focus on two trajectories near the channel bisector. In contrast to this, it is shown that \(3.55\,\upmu \mathrm{{m}}\) polystyrene particles develop four equilibrium trajectories at different in-plane and out-of-plane positions up to a critical Reynolds number. Beyond this critical Reynolds number, also these particles merge to two trajectories at different channel heights. While the rearrangement of \(3.55\,\upmu \mathrm{{m}}\) polystyrene particles just starts beyond \(\mathrm{{Re}}>140\), \(9.87\,\upmu \mathrm{{m}}\) polystyrene particles undergo this rearrangement already at \(Re=100\). As the equilibrium trajectories of these two particle groups are located at similar out-of-plane positions, outlet geometries that aim to separate particles along the channel width turn out to be a good choice for size fractionation. Indeed, polystyrene particles of different size assume laterally well-separated equilibrium trajectories such that a size fractionation of nearly 100% at \(Re=110\) can be achieved.

实现小于\（{10} \，\ upmu \ mathrm {{m}} \）直径的微粒的多维分离的合适方法仍然很少。在本研究中，研究了颗粒中的\（3.55 \，\ upmu \ mathrm {{m}} \）和\（{9.87} \，\ upmu \ mathrm {{m}} \）颗粒的大小和密度分级截面长宽比\（h / w = 0.25 \）的尖角蛇形微通道。通过散光粒子跟踪测速（APTV）测量获得了实验结果，从中重建了雷诺数在100到150之间的三维粒子分布。3D重建首次表明平衡轨迹不仅在通道宽度上发展，即平面内的平衡位置，但在不同平面外位置的通道高度上也是如此。随着雷诺数的增加，\（9.87 \，\ upmu \ mathrm {{m}} \）聚苯乙烯\（\ left（\ rho _ {\ mathrm {{PS}}} = 1.05 \，\ mathrm {{g}} \; \ mathrm {{cm}} ^ {-3} \ right）\）和三聚氰胺\（\ left（\ rho _ \ mathrm {{MF}} = 1.51 \，\ mathrm {{g}} \; \\\ mathrm {{cm}} ^ {-3} \ right）\）粒子集中在通道等分线附近的两个轨迹上。与此相反，表明\（3.55 \，\ upmu \ mathrm {{m}} \）聚苯乙烯颗粒在不同的面内和面外位置发展了四个平衡轨迹，直至达到雷诺数临界值。除了这个关键的雷诺数之外，这些粒子还在不同的通道高度处合并为两条轨迹。虽然\（3.55 \，\ upmu \ mathrm {{m}} \）聚苯乙烯颗粒的重排刚好超出\（\ mathrm {{Re}}> 140 \），\（9.87 \，\ upmu \ mathrm {{ m}} \）聚苯乙烯颗粒已经在\（Re = 100 \）处经历了这种重排。由于这两个粒子组的平衡轨迹位于相似的平面外位置，因此旨在沿通道宽度分离粒子的出口几何形状成为尺寸分级的理想选择。实际上，不同尺寸的聚苯乙烯颗粒具有横向分离良好的平衡轨迹，从而可以实现在（Re = 110 \）时接近100％的尺寸分数。