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Difficulty: MediumThermal Expansion and Contraction

A technician completely fills a rigid metal container with hydraulic fluid, seals it tightly, and leaves no air space inside while working in a cold environment. If this sealed container is later moved into a very hot boiler room, what is the most likely mechanical consequence?

  1. A
    The container will tend to collapse inward because the heat causes the fluid to contract and create a vacuum.
  2. B
    The internal pressure will remain constant because the heat capacity of the fluid matches the expansion of the metal.
  3. The internal pressure will rise significantly because the fluid expands at a greater rate than the metal container.Answer
  4. D
    The internal pressure will decrease because the metal container expands much more than the liquid fluid.

Answer

The internal pressure will rise significantly because the fluid expands at a greater rate than the metal container.
When heated, almost all substances expand. However, liquids generally expand at a significantly greater volumetric rate than solid metals. Because the sealed container has no air gap to absorb this difference in expansion, the expanding fluid is forced against the walls of the slower-expanding rigid container. This results in a severe increase in internal pressure, which can potentially rupture the container.

Step-by-Step Solution

1
Analyze the initial conditions of the mechanical system.
The system is a sealed, rigid metal container completely full of hydraulic fluid at a low temperature, with no compressible air gaps inside.
Understanding that there is no compressible air space is crucial for determining how temperature-induced volume changes will affect internal pressure.
2
Determine the physical effect of a significant temperature increase on the materials.
Both the metal container and the hydraulic fluid will undergo thermal expansion as they absorb heat in the boiler room.
Thermal expansion is a fundamental thermodynamic property where an increase in temperature causes an increase in volume for most materials.
3
Compare the relative rates of volumetric thermal expansion for the liquid versus the solid metal.
Liquids (like hydraulic fluid) have a significantly higher coefficient of volume expansion than solid metals.
Because the nearly incompressible liquid expands more than the container's internal capacity grows, the fluid will exert immense outward force, sharply increasing the internal hydrostatic pressure.

Key Concept

Differences in volumetric thermal expansion between liquids and solids in closed systems.
Estimated Time:1m 0s
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Topics

Thermal Expansion and Contraction

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