Abstract Nano-aerosols, less than 100 nm, are present in high concentration in air in the millions per cubic meter both indoor and outdoor. By virtue of their small size, they are easily inhaled into our body and can lead to chronic diseases. Nanofiber filter is effective in capturing these nano-aerosols suspended in air. Understanding the pressure drop behavior during aerosol loading of nanofiber filter is important for the operation of these filters. Given these filters are highly efficient for capturing nano-aerosols, over aerosol loading they can change from depth filtration, for which aerosols are captured inside the filter, to surface filtration, for which a cake forms on the filter surface that ultimately becomes the effective filter media. This transition, which is important in operation of nanofiber filters, is largely not understood. This study fulfills such unmet needs by investigating experimentally and theoretically the transition from depth- to surface-filtration of nanofiber filter challenged by nano-aerosols. Initially, filtration occurs across the filter that quickly leads to most filtration taking place in the upstream thin skin layer facing the incoming flow. As flowable pores in the skin layer get blocked, aerosols “bridge” across the pore openings and subsequently build-up above the filter surface. A new bridging model is developed that characterize this behavior. The bridge of aerosols among adjacent pores starts to interact at the filter surface that eventually leads to a continuous aerosol cake layer forming across the filter. Experiments are conducted using 50–400 nm sodium chloride aerosols challenging high-efficiency nanofiber filters (>50% for 300 nm sodium chloride challenging aerosol) that exhibit transition change from depth- to surface-filtration under accelerated loading condition. The new model not only matches well the test data in the depth-surface transition regime, it also predicts correctly the concave downward behavior of the pressure-drop test data. It also provides a smooth transition to the cake filtration for which the pressure drop varies linearly with deposited aerosol mass.

中文翻译：

---

在连续纳米气溶胶负载下从深层过滤到表面过滤的过渡，以获得高效、高趋肤效应的纳米纤维过滤器

摘要 小于 100 nm 的纳米气溶胶在室内和室外空气中以每立方米数百万计的高浓度存在。由于它们的体积小，它们很容易被吸入我们的身体，并可能导致慢性疾病。纳米纤维过滤器可有效捕获这些悬浮在空气中的纳米气溶胶。了解纳米纤维过滤器气溶胶加载过程中的压降行为对于这些过滤器的运行非常重要。鉴于这些过滤器对于捕获纳米气溶胶非常有效，在气溶胶负载上，它们可以从深层过滤（气溶胶被捕获在过滤器内部）转变为表面过滤（在过滤器表面形成滤饼，最终成为有效过滤器）媒体。这种转变对纳米纤维过滤器的操作很重要，但在很大程度上尚未被理解。本研究通过从实验和理论上研究纳米纤维过滤器受到纳米气溶胶挑战的从深层过滤到表面过滤的转变，满足了这种未满足的需求。最初，过滤发生在过滤器上，这很快导致大部分过滤发生在面向流入流的上游薄表层中。由于表层中的可流动孔被阻塞，气溶胶“桥接”穿过孔开口，随后在过滤器表面上方积聚。开发了一种新的桥接模型来表征这种行为。相邻孔隙之间的气溶胶桥开始在过滤器表面相互作用，最终导致在整个过滤器上形成连续的气溶胶饼层。使用 50–400 nm 氯化钠气溶胶进行实验，挑战高效纳米纤维过滤器 (> 50% 的 300 nm 氯化钠具有挑战性的气溶胶）在加速加载条件下表现出从深度过滤到表面过滤的转变。新模型不仅能很好地匹配深度-表面过渡区的测试数据，还正确预测了压降测试数据的下凹行为。它还提供了到滤饼过滤的平滑过渡，压降随沉积的气溶胶质量线性变化。