Question

Difficulty: MediumThermodynamics and Heat

Household refrigerators transfer thermal energy from a cooler interior to a warmer room through a continuous closed-loop thermodynamic cycle. Starting with the stage where low-pressure refrigerant vapor enters the compressor, what is the correct sequential order of these stages in the refrigeration cycle?

  1. 1The compressor pressurizes and heats the low-pressure refrigerant vapor.
  2. 2The hot refrigerant releases heat to the surrounding air and condenses into a high-pressure liquid inside the condenser coils.
  3. 3The high-pressure liquid passes through an expansion valve, rapidly dropping in pressure and temperature.
  4. 4The cold refrigerant absorbs heat from the refrigerator compartment and evaporates into a low-pressure gas inside the evaporator coils.

Answer

The compressor pressurizes and heats the vapor, followed by the condenser releasing heat to turn the vapor into liquid, then the expansion valve lowering the pressure and temperature, and finally the evaporator absorbing heat from the interior compartment as the liquid vaporizes.
The correct sequence follows the standard vapor-compression cycle: compression raises the temperature and pressure of the vapor, condensation expels heat to the environment to form a liquid, expansion drops the pressure and chills the liquid, and evaporation absorbs heat from the cold space to turn the fluid back into vapor.

Step-by-Step Solution

1
Identify the initial compression stage.
The compressor does mechanical work to compress the low-pressure vapor into a high-pressure, high-temperature gas.
Raising the pressure and temperature ensures the refrigerant is hotter than the ambient room air.
2
Follow the refrigerant into the exterior condenser coils.
Heat transfers from the hot refrigerant to the surrounding room, causing the refrigerant to condense into a high-pressure liquid.
Thermal energy naturally transfers from the hotter gas to the cooler room air.
3
Track the fluid through the expansion valve.
The high-pressure liquid passes through an expansion valve, where pressure suddenly drops, causing a steep decline in temperature.
Rapid fluid expansion and pressure reduction dramatically lower the boiling point and temperature of the refrigerant.
4
Analyze heat absorption in the interior evaporator coils.
The cold refrigerant absorbs thermal energy from the refrigerator interior and boils into a low-pressure gas.
Because the refrigerant is now colder than the interior air, heat transfers into the fluid, cooling the compartment.

Key Concept

Thermodynamic refrigeration cycle, phase transitions, and forced heat transfer
Estimated Time:1m 0s
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