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Consider the system shown in Fig. P3–52. If a change of
Chapter 3, Problem 48P(choose chapter or problem)
Problem 48P
Consider the system shown in Fig. P3–52. If a change of 0.7 kPa in the pressure of air causes the brine–mercury interface in the right column to drop by 5 mm in the brine level in the right column while the pressure in the brine pipe remains constant, determine the ratio of A2/A1.
Questions & Answers
QUESTION:
Problem 48P
Consider the system shown in Fig. P3–52. If a change of 0.7 kPa in the pressure of air causes the brine–mercury interface in the right column to drop by 5 mm in the brine level in the right column while the pressure in the brine pipe remains constant, determine the ratio of A2/A1.
ANSWER:
Solution
Step 1
We need to find the ratio of brine level change. The liquids in this U-tube can’t be incompressible were in the brine pressure remains constant and it is traped in space.
We know that SGme=13.6, SGbr=1.1,
The pressure of brine is much higher than air when it drops by 0.7 kpa. The pressure difference between the brine and air space increases by the same amount. The air pressure at point A moves along the tube by adding and by subtracting to reach brine to point B.