Question

2-48. The pressure in a natural gas pipeline is measured by the manometer shown in Fig. P2-48 with one of the arms open to the atmosphere where the local atmospheric pressure is 98 kPa. Determine the absolute pressure in the pipeline.

Repeat Prob. 2-48 by replacing air by oil with a specific gravity of 0.69.

Answer 1

Answer:

Explanation:

the pressure in a natural gas pipeline is measured by the manometer shown in Fig. P1–69E with one of the arms open to the atmosphere where the local atmospheric pressure is 14.2 psia. Determine the absolute pressure in the pipeline.

 

     

 

Step-by-step solution

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Step 1 of 4

Calculate the density of mercury  in the U tube manometer.

…… (1)

Here, specific gravity of mercury is  and density of water is .

From appendix Table A-3, “the properties of common liquids, solids and foods table”, select the density of water as .

Answer 2

Given:

The atmospheric pressure = 98 kPa

The specific gravity of Hg = 13.6

To Find:

The absolute pressure in the pipeline

Solution:

From the diagram,

The height difference for water (hw) = 65 + 5 =70cm

The height difference for mercury (hm) = 15 cm

The height difference for air (ha) = 65 - 25 = 40cm

We know that absolute pressure P = Po + hρg

Accoding to the question,

P gas = P atm + g [ (ρw X hw) + (ρm X hm) - (ρa X ha)]

Taking g = 10 and substituting the values,

P gas = 98000 Pa + 9.8 X 10 [ 70 + 204 - 0.0012 X 40]

or P gas = 98000 + 26852 (approximated)

= 124 kPa

If we replace air bu oil (ρo = 0.69) then,

P gas = 98000 Pa + 9.8 X 10 [ 70 + 204 - 0.69 X 40]

= 98000 + 24147.2

= 122 kPa

Hence, the absolute pressure in the case of air and oil is 124 kPa and 122 kPa respectively.