Mechanical engineeringLesson 2 of 2 in the course Fluid and thermal machines

Refrigeration: History, Cycles, Applications, and Emerging Methods

5 flashcards · 5 quiz questions · 5 match pairs · 4 fill-in sentences · English

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Summary

Refrigeration lowers or maintains the temperature of a space, substance, or system below the surrounding temperature. This lesson introduces the basic idea and traces the progression from natural ice to practical mechanical cooling.

Refrigeration does not make heat disappear. It transfers thermal energy from a colder region to a warmer one, opposite to the direction heat flows naturally. Modern systems use a refrigerant, a working fluid that absorbs heat from the cooled space and releases it elsewhere. A compressor or another energy source helps drive the transfer, while heat exchangers move heat into and out of the refrigerant.

All flashcards

What is refrigeration?
The artificial removal of heat to lower or maintain a space or substance below ambient temperature.
What is a refrigerant?
A working fluid that absorbs heat from a cooled region and releases it elsewhere.
What is a cold chain?
A connected system of temperature-controlled storage and transport.
How does insulation help a refrigeration system?
It reduces heat entering the cooled space, lowering the work needed to maintain its temperature.
What physical effect powers thermoelectric refrigeration?
The Peltier effect, in which electric current through dissimilar-material junctions transfers heat.

Quiz questions

  1. What happens to refrigerant as it passes through the expansion valve in a vapor-compression system?Answer: Its pressure drops, producing a colder liquid-vapor mixture.
  2. What distinguishes adsorption refrigeration from absorption refrigeration?Answer: Adsorption takes refrigerant up with a solid; absorption dissolves it in a liquid.
  3. For a refrigeration system, how is the coefficient of performance defined?Answer: Cooling capacity divided by the energy input required to operate the system.
  4. Why are reverse-Brayton air-cycle systems used in aircraft environmental-control systems?Answer: They are compact, lightweight, and reliable.
  5. How does magnetic refrigeration produce a temperature change in a solid refrigerant?Answer: Changing the magnetic field changes the material's magnetic order and entropy.

Based on the Wikipedia article Refrigeration, licensed CC BY-SA 4.0. Adapted into a summary, flashcards and quizzes.

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