水流经管道时颗粒能否被吸入？Water Scaler喷水时细菌流入原理问询

Absolutely—whether particles get sucked into a pipe depends on a few key factors, and it’s super common in real-world scenarios:

• Pressure differences are the main driver: If there’s a region inside or at the entrance of the pipe with lower pressure than the surrounding environment (like when water flows quickly through a narrow section, thanks to Bernoulli’s principle), atmospheric pressure will push nearby particles toward the low-pressure zone and into the pipe. For example, think about how a vacuum cleaner works—fast-moving air creates low pressure that sucks in dirt.
• Particle size and weight: Small, light particles (like dust, bacteria, or fine sediment) are way easier to pull in than large, heavy ones. If the pressure difference is strong enough, even slightly heavier particles can get caught in the incoming flow.
• Flow dynamics: Turbulent flow (chaotic, swirling water) can create eddies that pull particles from the surrounding area into the pipe, even if the overall pressure difference is small. Laminar flow (smooth, straight flow) is less likely to entrain particles unless the pressure gradient is significant.

So in short: Yes, particles can absolutely be sucked into a pipe when water’s flowing—just depends on the pressure setup, particle properties, and flow type.

Great question—this is a tricky one because we’re combining macro-scale flow (the water jet) with micro-scale capillary effects, which are easy to mix up. Let’s break it down step by step:

First, let’s recap what capillary forces are: They’re the result of surface tension and adhesion between a liquid and a solid surface. In trees, it’s the continuous network of tiny xylem tubes where adhesion to the tube walls and cohesion between water molecules pull water upward against gravity. In your water scaler, the mechanism is similar but happens in reverse, and it’s interacting with the outgoing water jet.

Here’s the play-by-play for the scaler’s elbow hole:

• The hole is extremely small (micro-scale), which amplifies capillary forces (capillary action gets stronger as tube diameter decreases). The inner walls of the hole are probably made of a material that water adheres to well (like stainless steel or plastic), so a thin film of water sticks to the walls even when the main jet is flowing out.
• When the water jet is actively spraying, the main flow is moving outward, but the micro-scale liquid film on the hole’s walls is subject to capillary forces. Because the surrounding area (mouth cavity) has water mixed with bacteria, the capillary forces can pull this external liquid into the thin film on the hole’s inner walls—even against the direction of the main outgoing jet.
• Unlike the tree example (where capillary action moves a continuous column), here it’s about the micro-channel (the hole’s wall-film interface) acting like a tiny "capillary tube" that siphons nearby liquid in. The main jet doesn’t completely disrupt this film because the hole’s diameter is so small—capillary forces are strong enough to hold the film in place and pull external fluid into it, which then gets carried back into the device’s internal lines over time.

Your guess about no-slip condition and turbulence isn’t off-base either! The no-slip condition means the water right at the hole’s walls doesn’t move (or moves very slowly) relative to the wall, which lets the capillary film stay intact. Turbulence in the main jet might actually create small pressure fluctuations near the hole’s entrance, which can help "pull" the capillary film (and bacteria) inward more easily, but the core driver is the capillary force acting on that micro-scale liquid layer.

So to sum it up: The tiny hole’s micro-scale size makes capillary forces dominant at the wall interface, allowing bacteria-laden water from the mouth to be pulled into the device through the thin liquid film on the hole’s inner walls—even while the main water jet is spraying outward.

内容的提问来源于stack exchange，提问作者Stewie Griffin