GRE Reading Comprehension

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Source: XDF

Heat pumps circulate a fluid refrigerant that cycles alternatively from its liquid phase to its vapor phase in a closed loop. The refrigerant, starting as a low-temperature, low-pressure vapor, enters a compressor driven by an electric motor. The refrigerant leaves the compressor as a hot, dense vapor and flows through a heat exchanger called the condenser, which transfers heat from the refrigerant to a body of air. Now the refrigerant, as a high-pressure, cooled liquid, confronts a flow restriction which causes the pressure to drop. As the pressure falls, the refrigerant expands and partially vaporizes, becoming chilled. It then passes through a second heat exchanger, the evaporator, which transfers heat from the air to the refrigerant, reducing the temperature of this second body of air.

Question List: 1

According to the passage, the role of the flow restriction in a heat pump is to

  • A measure accurately the flow rate of the refrigerant mass at that point
  • B compress and heat the refrigerant vapor
  • C bring about the evaporation and cooling of refrigerant
  • D exchange heat between the refrigerant and the air at that point
  • E reverse the direction of refrigerant flow when needed

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