The document provides calculations to determine the pressure of nitrogen in a tank and the minimum required wall thickness. It uses the ideal gas law to calculate the pressure as 3520 lbf/in2. It then sets up a force balance equation considering one hemisphere of the tank to determine the minimum wall thickness is 0.880 inches.
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Problem 3.1
1. Problem 3.1 [Difficulty: 2]
Given: Data on nitrogen tank
Find: Pressure of nitrogen; minimum required wall thickness
Assumption: Ideal gas behavior
Solution:
Ideal gas equation of state: p V M R T=
where, from Table A.6, for nitrogen R 55.16
ft lbf
lbm R
=
Then the pressure of nitrogen is p
M R T
V
= M R T
6
D
3
=
p 140 lbm 55.16
ft lbf
lbm R
77 460+( ) R
6
2.5 ft( )
3
。
「
」
、
・
ヲ
ft
12 in
2
=
p 3520
lbf
in
2
=
cDt
pD2
/4
To determine wall thickness, consider a free body diagram for one hemisphere:
裡F 0= p
D
2
4
c D t=
where c is the circumferential stress in the container
Then t
p D
2
4 D c
=
p D
4 c
=
t 3520
lbf
in
2
2.5 ft
4
in
2
30 10
3
lbf
=
t 0.0733 ft= t 0.880 in=