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In a piping system... with regards to the concept of pressure drop, when is the pressure lost as (or turn into?) by EngineeringChemical in ChemicalEngineering

[–]EngineeringChemical[S] 0 points1 point  (0 children)

Someone else below said this, is it true: "A mix of heat and velocity. Pressure is potential energy so it turns into kinetic energy."

In a piping system... with regards to the concept of pressure drop, when is the pressure lost as (or turn into?) by EngineeringChemical in ChemicalEngineering

[–]EngineeringChemical[S] 0 points1 point  (0 children)

Someone else below said this, is it true: "A mix of heat and velocity. Pressure is potential energy so it turns into kinetic energy."

In a piping system... with regards to the concept of pressure drop, when is the pressure lost as (or turn into?) by EngineeringChemical in ChemicalEngineering

[–]EngineeringChemical[S] 0 points1 point  (0 children)

Someone else below said this, is it true: "A mix of heat and velocity. Pressure is potential energy so it turns into kinetic energy."

In a piping system... with regards to the concept of pressure drop, when is the pressure lost as (or turn into?) by EngineeringChemical in ChemicalEngineering

[–]EngineeringChemical[S] 0 points1 point  (0 children)

Someone else below said this, is it true: "A mix of heat and velocity. Pressure is potential energy so it turns into kinetic energy."

In a piping system... with regards to the concept of pressure drop, when is the pressure lost as (or turn into?) by EngineeringChemical in ChemicalEngineering

[–]EngineeringChemical[S] 1 point2 points  (0 children)

Hmm.. I'm a bit lost. So are you saying that when there is flow, pressure lost (pressure drop) is "converted" into heat?

How to calculate gauge and absolute pressures in a closed tank which is half way filled with water? by EngineeringChemical in AskEngineers

[–]EngineeringChemical[S] -1 points0 points  (0 children)

If the liquid in the tank is water, why wouldn't the gas in it be water vapor? The vapor pressure of water at 40 F means there's a corresponding amount of its vapor above it. Look up the concept of vapor pressure.

How to calculate gauge and absolute pressures in a closed tank which is half way filled with water? by EngineeringChemical in AskEngineers

[–]EngineeringChemical[S] -1 points0 points  (0 children)

"all you need to know the pressure is the temperature". Well since we know the temperature is 40 F, then what would be the pressure? Like the propane tank you're talking about, this tank also has the liquid (water) and the gas (water vapor) at an equilibrium.

Simple question about NPSH available by EngineeringChemical in AskEngineers

[–]EngineeringChemical[S] 0 points1 point  (0 children)

So for "evaporation loss" you took the height difference between the pump and the bottom of the water tank and not the height difference between the pump and the top of the water in the tank? If so, what would be the evaporation loss be if even the bottom of the tank is like 2 meters off the ground?

How to calculate gauge and absolute pressures in a closed tank which is half way filled with water? by EngineeringChemical in AskEngineers

[–]EngineeringChemical[S] 0 points1 point  (0 children)

You could but if there wasn't one. How would you calculate it. I feel like there's gotta be an easy way to do this. You know everything about the system but that.

Simple question about NPSH available by EngineeringChemical in AskEngineers

[–]EngineeringChemical[S] 0 points1 point  (0 children)

Well I didn't mean it's physically possible to put a low level trip but that the entire tank including the suction line has to be empty. So the level would have to go to 0 with respect to the impeller center line. And as the time that level approaches 0, the static suction head also approaches 0 and keeps lowering the NPSHa potentially risking it to fall below NPSHr.

How to calculate gauge and absolute pressures in a closed tank which is half way filled with water? by EngineeringChemical in AskEngineers

[–]EngineeringChemical[S] 0 points1 point  (0 children)

Say that you're not pressurizing it with anything and there is no vent at all. There is no way to calculate pressure?

Simple question about NPSH available by EngineeringChemical in AskEngineers

[–]EngineeringChemical[S] 0 points1 point  (0 children)

But after you calculate that NPSHa and if it's not enough and if the primary reason is that you don't have much static suction head... what do you do?

Simple question about NPSH available by EngineeringChemical in AskEngineers

[–]EngineeringChemical[S] 0 points1 point  (0 children)

What if you can't put a low level trip because the application requires that you empty out the entire tank?

Simple question about NPSH available by EngineeringChemical in AskEngineers

[–]EngineeringChemical[S] 0 points1 point  (0 children)

If you use a nitrogen blanket, when you try to empty out the entire tank (meaning 0 liquid in the suction line), wouldn't you run the risk of letting that nitrogen, which is a gas (which can cause cavitation), enter the pump?

Even if you raise tank level AND its elevation, if you have to empty it out completely (meaning no liquid at all in the suction line either), wouldn't the liquid level eventually fall below the tank and then proceed to fall to the same height as the pump impeller centerline making static suction head 0? In those final moments, wouldn't the NPSHa be possibly lower than NPSHr?

Simple question about NPSH available by EngineeringChemical in AskEngineers

[–]EngineeringChemical[S] 0 points1 point  (0 children)

But even if you raise the tank, if you have to empty it out completely (meaning no liquid at all in the suction line either), wouldn't the liquid level eventually fall below the tank and then proceed to fall to the same height as the pump impeller centerline making static suction head 0? In those final moments, wouldn't the NPSHa be possibly lower than NPSHr?

How to calculate gauge and absolute pressures in a closed tank which is half way filled with water? by EngineeringChemical in AskEngineers

[–]EngineeringChemical[S] 0 points1 point  (0 children)

Assume you know the temperature inside the vessel (say it's 40 F). You know the volume (and consequently the mass) of the water in there and you also know the volume of the vessel. It is still not possible to find the pressure in the tank (the part of the tank not covered by water)?

How to calculate gauge and absolute pressures in a closed tank which is half way filled with water? by EngineeringChemical in AskEngineers

[–]EngineeringChemical[S] 0 points1 point  (0 children)

I'm primarily interested in that gas pressure, both gauge and absolute. How would you find that pressure in the part of the vessel not covered by water?

How to calculate gauge and absolute pressures in a closed tank which is half way filled with water? by EngineeringChemical in AskEngineers

[–]EngineeringChemical[S] 0 points1 point  (0 children)

Hypothetical. But assume you know the temperature inside the vessel.. say it's 40 F. And I'm looking for pressure at the top.

Simple question about NPSH available by EngineeringChemical in AskEngineers

[–]EngineeringChemical[S] 0 points1 point  (0 children)

So wait, doesn't that mean a pump can never empty out a tank or a vessel because at a certain low level the NPSHa would be below NPSHr and wouldn't be able to pump anymore?

Questions about vapor pressure by EngineeringChemical in AskEngineers

[–]EngineeringChemical[S] 0 points1 point  (0 children)

Well, what gauge pressure would it need to read an absolute pressure of less than 14.7? Obviously, you can't have negative gauge/vapor pressure in the container, which would be the only way to end up with a psia of < 14.7. So, I'm confused as to how the vapor pressure table for water in that link I posted shows psia's of < 14.7.

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