3 ms·

How does the nozzle diffuse?

by anotheryou 8y ago

jstanley 8y ago
I would guess it's just a fine mesh that the liquid is forced through.
- masklinn 8y ago
  I wouldn't think so, that's how you go from spray to foam (e.g. some household detergents around here have a small mesh screen you can clip over the spray nozzle to get a detergent foam instead of the liquid droplets of a regular spray bottle).
- steve_adams_86 8y ago
  I think it's actually that the particles are forced to collide at relatively high speed due to the pressure behind the small opening. A mesh could eventually get clogged with minerals or debris, but this approach leaves less room for failure. Basically you're just ripping the fluid into mist with high pressure.
- deltron3030 8y ago
  It's just a hole. If you take a hot needle you can widen the hole of spray caps and increase the throughput (and size of the throw if you also increase the distance to the object). Another trick for spraypaint bottles is to stomp them vertically if you run out of spraypaint, it won't hurt the system that takes your cap, and gives you little bit more paint.
masklinn 8y ago
Thank you, I was also expecting that information, not an essay on small-scale ball check valves.
btrettel 8y ago
Fluid dynamicist here who works on the breakup of larger water jets. How the jet breaks up depends on the design of the system. (I assume you mean break up, not diffuse. Diffusion is a different physical process which occurs independent of breakup.) A low speeds (laminar flow), Rayleigh's analysis shows that a simple liquid jet breaks up due to surface tension effects. https://en.wikipedia.org/wiki/Plateau%E2%80%93Rayleigh_instability https://en.wikipedia.org/wiki/Plateau%E2%80%93Rayleigh_insta... At higher speeds (e.g., transitional or turbulent flows), the mechanisms change. For your typical spray bottle (without a swirl chamber) I'd say turbulence is the primary cause of breakup. Aerodynamic influence won't factor in at typical air densities and cavitation isn't happening as it probably would break the nozzle. Here's a conference paper I wrote on turbulent breakup theory, which hopefully is readable for anyone with an understanding of probability theory and basic turbulence theory: https://engrxiv.org/35u7g/ https://engrxiv.org/35u7g/ (RMS velocity is just the standard deviation of the velocity. Turbulent kinetic energy is an energy formed from the RMS velocity. Kolmogorov's 5/3 theory is used a bit, but you can just view it as power law distribution. Etc.) I also have some small spray bottles with swirl chambers, which makes the bulk fluid spin, destabilizing the interface, leading to droplet formation. The spray angle for these is large compared against the simple pressure atomizer described previously.
- cantrevealname 8y ago
  > Fluid dynamicist here who works on the breakup of larger water jets One of the reasons I freaking love HN. No matter the topic, there are actual experts reading it and willing to comment.

How does the nozzle diffuse?

jstanley 8y ago

I would guess it's just a fine mesh that the liquid is forced through.

masklinn 8y ago
I wouldn't think so, that's how you go from spray to foam (e.g. some household detergents around here have a small mesh screen you can clip over the spray nozzle to get a detergent foam instead of the liquid droplets of a regular spray bottle).
steve_adams_86 8y ago
I think it's actually that the particles are forced to collide at relatively high speed due to the pressure behind the small opening. A mesh could eventually get clogged with minerals or debris, but this approach leaves less room for failure. Basically you're just ripping the fluid into mist with high pressure.
deltron3030 8y ago
It's just a hole. If you take a hot needle you can widen the hole of spray caps and increase the throughput (and size of the throw if you also increase the distance to the object). Another trick for spraypaint bottles is to stomp them vertically if you run out of spraypaint, it won't hurt the system that takes your cap, and gives you little bit more paint.

masklinn 8y ago

Thank you, I was also expecting that information, not an essay on small-scale ball check valves.

btrettel 8y ago

Fluid dynamicist here who works on the breakup of larger water jets. How the jet breaks up depends on the design of the system. (I assume you mean break up, not diffuse. Diffusion is a different physical process which occurs independent of breakup.) A low speeds (laminar flow), Rayleigh's analysis shows that a simple liquid jet breaks up due to surface tension effects. https://en.wikipedia.org/wiki/Plateau%E2%80%93Rayleigh_instability https://en.wikipedia.org/wiki/Plateau%E2%80%93Rayleigh_insta... At higher speeds (e.g., transitional or turbulent flows), the mechanisms change. For your typical spray bottle (without a swirl chamber) I'd say turbulence is the primary cause of breakup. Aerodynamic influence won't factor in at typical air densities and cavitation isn't happening as it probably would break the nozzle. Here's a conference paper I wrote on turbulent breakup theory, which hopefully is readable for anyone with an understanding of probability theory and basic turbulence theory: https://engrxiv.org/35u7g/ https://engrxiv.org/35u7g/ (RMS velocity is just the standard deviation of the velocity. Turbulent kinetic energy is an energy formed from the RMS velocity. Kolmogorov's 5/3 theory is used a bit, but you can just view it as power law distribution. Etc.) I also have some small spray bottles with swirl chambers, which makes the bulk fluid spin, destabilizing the interface, leading to droplet formation. The spray angle for these is large compared against the simple pressure atomizer described previously.

cantrevealname 8y ago
> Fluid dynamicist here who works on the breakup of larger water jets One of the reasons I freaking love HN. No matter the topic, there are actual experts reading it and willing to comment.