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Tank pressure

  • Thread starter jderulo
  • Start date
  • #26
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0
No. That is not the pressure at the bottom of the tank.

I told you to forget about the tank, and to focus on the column of liquid on the left. The ideal gas law will not be part of the solution to this problem. Looking at the column of liquid on the left in your figure, did you notice that little triangular "symbol thingie" at the top of the left column. The left column is full of liquid all the way up to that triangular "symbol thingie." Above that point there is air at atmospheric pressure, but below that point there is liquid. Were you aware of that?

Chet
No I wasn't - I had incorrectly assumed the liquid level in the column was the same as in the tank. Thought the triangle symbol was maybe a smudge of a scan. The head is 6.7m?

I am guessing at this point to move onto the tank? If so, a 6.7m head factored into my rho * g * h equation then gives me the pressure at the interface inside the tank?
 
  • #27
20,236
4,265
No I wasn't - I had incorrectly assumed the liquid level in the column was the same as in the tank. Thought the triangle symbol was maybe a smudge of a scan. The head is 6.7m?

I am guessing at this point to move onto the tank? If so, a 6.7m head factored into my rho * g * h equation then gives me the pressure at the interface inside the tank?
No. You went downward 6.7 m from the top water surface in the column. This puts you at the bottom of the tank. Now you've got to go back up 1.7 m to get to the water surface in the tank.

Chet
 
  • #28
34
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No. You went downward 6.7 m from the top water surface in the column. This puts you at the bottom of the tank. Now you've got to go back up 1.7 m to get to the water surface in the tank.

Chet
OK - so 9.4m. That makes sense. I didn't realise we added the head backupwards.

I am right in thinking the answer is 110657N.m^-2 ?
 
  • #29
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4,265
OK - so 9.4m. That makes sense. I didn't realise we added the head backupwards.

I am right in thinking the answer is 110657N.m^-2 ?
No. If you go back upwards, you have got to subtract, not add.
 
  • #30
34
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No. If you go back upwards, you have got to subtract, not add.
58860N.m^-2 ? Assuming a head of 5m?
 
  • #31
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58860N.m^-2 ? Assuming a head of 5m?
Yes. That's the air pressure in the tank headspace (over and above atmospheric pressure).

Chet
 
  • #32
34
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Thanks Chet - I had that value earlier, was you trying to see if I understood it?

The y value, the 1.7m - seems odd that I do not include that. I always thought we had to use all the data in chem eng problems. At least I have in the past!
 
  • #33
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Thanks Chet - I had that value earlier, was you trying to see if I understood it?

The y value, the 1.7m - seems odd that I do not include that. I always thought we had to use all the data in chem eng problems. At least I have in the past!
Why do you think they put the y into the problem description?
 
  • #34
34
0
Why do you think they put the y into the problem description?
Not really sure can only assume it would make the solution glaringly obvious if it wasn't there.....?
 
  • #35
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4,265
Not really sure can only assume it would make the solution glaringly obvious if it wasn't there.....?
Exactly.
 

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