Is vacuum = pressure for same material?

[v8landy]

In transfering material along a pipe would the pressure required to move this material be equal to the vacuum required to move the same material anlong the same pipe?

 

[Artisi]

The pressure to move something thru a pipe whether it is from a mechanical source or from atmospheric pressure is the same - pressure is pressure - however, remember it's not the vacuum "sucking" the product but atmospheric pressure forcing it thru the pipe, also bear-in-mind the maximum pressure differential can only be atmospheric pressure at the source less the reduced pressure from the vacuum source.

 

[Unotec]

Are push and pull the same? According to Newton, they are

 

[v8landy]

thanks Unotec for the staight answer.

 

[Unotec]

Sorry for the tone of the answer. Just having a bad morning with EH&S. I should have said: push and pull are the same according to Newton and the laws of physics. Pumping follows these same principles as it involves the same vectors and forces. However, it is typically easier to generate a higher pressure than a lower vaccumm.

 

[Compositepro]

Differential pressure is is the main force that moves things in a a pipe and it always "pushes". Vacuum does not create a pulling force. The way to avoid confusing yourself is to think in terms of "absolute pressure" rather than gage pressure and vacuum. In the language of Physics only absolute pressure matters.

That said, absolute pressure strongly affects the density of gasses so when it comes to blowers it can make a big difference as to whether you are "pushing" or "pulling".
If you keep the pipe size the same, the velocity in the suction to a blower is greater than at the discharge even though the mass flow rate is the same.

 

[v8landy]

I am happy with all of your answers. Thanks

 

[quark]

Yes and no. First of all, you should keep in mind that liquids can't be towed. As Artisi explained, it is the atmospheric pressure that pushes against a negative pressure.

Secondly, for this condition to be true, the pressure drop in the pipe shouldn't exceed the atmospheric pressure at your location minus the vacuum pump losses.

 

[v8landy]

I am now a bit stuck!

I have calculated that as a "pressure" it would require 1.95 Bar, to move my fluid along a pipe.

BUT, our vacuum is only capable upto 0.2 Bar or 200 Mbar.

Have I got somthing wrong?

 

[v8landy]

I have re-adjusted some of my figures, and now have a theoretical requiremnt of 0.83 Bar !!!

Will go ahead and hope for best on pipe!

 

[Artisi]

Re-adjust the input to suit the outcome required - it works everytime.

 

[v8landy]

I am learing fast ;-)

In fact by further "adjustment" I now have it down to 0.21 Bar.

 

[quark]

In fact by further "adjustment" I now have it down to 0.21 Bar.

I think it just about right time to stop further learning on this issue

 

[Artisi]

With more adjustment the losses might get down to zero.

 

[v8landy]

THis is just theory though!!!.

Just wait until after I have intalled the pipeline and it blocks, I will end up being used as a "pig" to clear the line!

 

[IFRs]

I think there is a difference between pulling and pushing if the vacuum created exceeds the partial vapor pressure of a component of the liquid. In effect you will be separating the liquid and vapor phases of the liquid surface. You may even induce what might be called "boiling". Given the right circumstances you might experience a blast of a more flammable or even explosive vapor mixture in front of the liquid slug. I may be all wet in this thought and would appreciate any more informed opinions to learn from.

 

[Artisi]

Well first up there is no pulling by applying a vacuum, if you lower the pressure on one side, any positive pressure on the other side will push the product towards the low pressure area.

As to your comment re exceeding the vapour pressure, yes you could vapourise the liquid by applying vacuum, it therefore follows that you can only use vacuum to transport a liquid so long as the vacuum equipment can handle the vapour being produced and maintain a lower pressure than on the supply side.