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Question

Difficulty: MediumProperties of Fluids

A hydraulic accumulator is a sealed, rigid tank that contains both hydraulic fluid (a liquid) and pressurized nitrogen (a gas). When a pump forces additional hydraulic fluid into the tank and significantly raises the internal pressure, which of the following best describes the volumetric changes of the original contents?

  1. A
    Both the original hydraulic fluid and the nitrogen gas compress by an equal percentage to absorb the increased pressure.
  2. The volume of the nitrogen gas decreases significantly, while the volume of the original hydraulic fluid remains virtually unchanged.Answer
  3. C
    The original hydraulic fluid compresses substantially to make room, while the nitrogen gas volume remains constant.
  4. D
    The nitrogen gas expands to increase the pressure, while the hydraulic fluid decreases in density.

Answer

The volume of the nitrogen gas decreases significantly, while the volume of the original hydraulic fluid remains virtually unchanged.
Liquids, such as hydraulic fluid, are practically incompressible, meaning their volume does not significantly change when subjected to high pressure. Gases, such as nitrogen, are highly compressible. When the pump forces more liquid into the rigid tank, the internal pressure rises. The gas acts like a spring, compressing into a smaller volume to accommodate the new liquid, while the original liquid retains its volume.

Step-by-Step Solution

1
Identify the states of matter of the materials inside the accumulator.
The nitrogen is a gas, and the hydraulic fluid is a liquid.
Different states of matter respond differently to applied pressure.
2
Recall the compressibility property of liquids.
Liquids are practically incompressible.
This means adding pressure will not noticeably change the volume of the original hydraulic fluid.
3
Recall the compressibility property of gases.
Gases are highly compressible.
This means the nitrogen gas will be forced into a smaller volume as the pressure inside the rigid tank increases.
4
Combine these principles to determine the outcome.
The added fluid forces the gas to compress into a smaller space, while the original liquid maintains its volume.
This allows the rigid tank to accommodate the additional hydraulic fluid.

Key Concept

Compressibility of Liquids vs. Gases
Estimated Time:1m 0s
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Topics

Properties of Fluids

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