# Viscosity & Pressure: Can Hydraulic Resistance Prevent Boiling?

• Samson4
In summary, the tube connecting the fluid to the vacuum chamber might prevent boiling until it reaches the nozzle. If the tube were too resistant, the liquid would flow out more slowly and eventually boil.
Samson4
I made a simple diagram. My question is, in the picture, can the hydraulic resistance of the tube connecting the fluid to the vacuum chamber prevent boiling of the fluid until it reaches the nozzle?

So you're asking if the tube can keep the fluid from flowing/boiling away?

I'd say any vapor pressure of the fluid would be enough to evaporate it all against a vacuum, over time.

If the resistance were too high, it would just flow out more slowly, no?

I assume here that your fluid must be a liquid since it is boiling (make sure you are careful with the term fluid; gases and plasmas are fluids, too). That said, if your fluid from the tank stretches all the way up to the nozzle already such that the only surface exposed to vacuum is the nozzle and that condition was maintained, then I don't see why you would observe boiling all the way back in the tank. You would probably observe boiling only as deep as it takes before hydrostatic pressure is greater than the vapor pressure. I don't see fluid resistance as being relative here. If the fluid is just sitting in the tank with vacuum in that entire tube before it, then yes, I would imagine the tank liquid would boil.

What you are describing is one of the 4 elements required in a heat pump or air conditioner--the expansion valve. "Expansion valve" misnamed. It's a restriction in the circuit as you've depicted in your drawing. The low pressure side is not a good vacuum, but it's fairly close to your schematic.

Samson4
The fluid is viscous and through heating and the establishment of a vacuum, it finally reaches the nozzle. I am trying to understand if I can prevent boiling with hydraulic resistance until it reaches the chamber? More importantly could atomization occur with ideal temperatures even though the fluid is moving slowly?

So its an expanding liquid?

Expanding because of heating and because of the vacuum pump

I understand -- which liquid expands significantly?

Hint: The fluid you are imagining is probably more like a gas.

I'm imagining paraffin. It is both viscous and high boiling temps.

And the question is then whether paraffin oil can expand significantly up that column you drew, without going into gas phase. No (at least I doubt it, given the definition of a liquid). Basically the oil will sit in the tank, giving off fumes that you vacuum away. It will continue to do so since you keep heating it. Considering you have a vacuum it will boil as well, so long as you are not so deep in the oil that the static pressure overwhelms the vapor pressure, as aformentioned.

Feel free to correct me if you see an error in my reasoning!

## 1. What is viscosity?

Viscosity is a measure of a fluid's resistance to flow. It is determined by the internal friction between molecules in the fluid and is often referred to as "thickness."

## 2. How does viscosity affect hydraulic resistance?

The higher the viscosity of a fluid, the more resistant it is to flow. As a result, fluids with higher viscosities will experience greater hydraulic resistance, making it more difficult for them to flow through pipes or other channels.

## 3. Can hydraulic resistance prevent boiling?

Yes, hydraulic resistance can prevent boiling. When fluids are subject to high pressure, their boiling point increases. This means that it takes more energy for the fluid to reach its boiling point, and it may not boil at all if the pressure is high enough.

## 4. How does hydraulic resistance affect the boiling point of a fluid?

Hydraulic resistance increases the boiling point of a fluid by increasing the pressure exerted on the fluid. This is because the molecules in the fluid are more tightly packed together, making it more difficult for them to break free and form a gas (boil).

## 5. Can the use of hydraulic resistance be dangerous in certain situations?

Yes, the use of hydraulic resistance can be dangerous in certain situations. If the pressure in a hydraulic system becomes too high, it can cause pipes or other components to burst, potentially causing injuries or damage. It is important to carefully monitor and regulate hydraulic systems to prevent dangerous pressure levels.

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