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Difficulty: MediumHeat Engines and Refrigeration Principles

In a standard vapor-compression refrigeration cycle, the compressor significantly increases the pressure of the refrigerant vapor before it enters the condenser. What is the primary thermodynamic purpose of this pressure increase?

  1. It raises the condensation temperature of the vapor, allowing the refrigerant to release heat to the surrounding environment.Answer
  2. B
    It acts as a hydraulic pump to force the incompressible liquid refrigerant through the restrictive condenser coils.
  3. C
    It squeezes the refrigerant into a smaller volume, which directly causes its internal temperature to drop rapidly.
  4. D
    It provides the energy required to continuously raise the refrigerant's temperature while it changes from a gas to a liquid.

Answer

It raises the condensation temperature of the vapor, allowing the refrigerant to release heat to the surrounding environment.
The primary purpose of the compressor is to elevate the pressure and temperature of the refrigerant vapor. Because heat naturally transfers only from a warmer area to a cooler area, the refrigerant must be made hotter than the outside ambient air. By compressing the gas, its saturation temperature is raised, which allows the refrigerant to successfully reject absorbed heat into the surrounding environment when it passes through the condenser.

Step-by-Step Solution

1
Analyze the physical state of the refrigerant as it enters and leaves the compressor.
The refrigerant enters the compressor as a low-pressure gas and leaves as a high-pressure, high-temperature gas.
Understanding the state changes across the component is the first step in identifying its functional purpose in the cycle.
2
Evaluate the conditions required for heat transfer to occur in the condenser.
Heat must flow from the refrigerant to the ambient environment. This requires the refrigerant to be at a higher temperature than its surroundings.
The second law of thermodynamics dictates that heat flows naturally from hotter regions to colder regions.
3
Connect the compressor's function to the condenser's thermodynamic requirement.
By increasing the pressure, the compressor raises the saturation (condensation) temperature of the gas, ensuring it is hot enough to reject heat to the outside air.
The pressure and temperature of a gas are directly proportional during the compression phase.

Key Concept

Thermodynamics of Vapor-Compression Refrigeration
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Topics

Heat Engines and Refrigeration Principles

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