Refrigerators

Summary

• A refrigerator is any kind of enclosure (like a box, cabinet, or room) whose interior temperature is kept substantially lower than the surrounding environment.
• Types of Refrigerators
  • non-mechanical
    • for example: ice box, root cellar, wine cellar
    • are not often considered true refrigerators
  • mechanical
    • vapor compression
    • vapor absorption
    • multievaporator, cascade
    • gas cycle, air cycle
    • pulse tube
    • thermoacoustic
  • electronic
    • thermoelectric
    • magnetic, magneto-calorific
• An air conditioner is a mechanical system in a room, building, or vehicle for controlling…
  • temperature (by providing cool air),
  • humidity (by providing dry air),
  • and ventilation (by providing fresh air).
• A heat pump is a device for moving heat mechanically.
  • A heat pump can move heat against the temperature gradient (from cold to hot).
  • Refrigerators and air conditioners are examples of heat pumps.
  • In common usage, the tem heat pump often refers to air conditioners that can be run…
    • "forward" to cool a building in summer by extracting heat from the building and depositing it in the environment (refrigerating the building and heating the environment) or
    • "backward" to warm a building in winter by extracting heat from the environment and depositing it in the building (refrigerating the environment and heating the building).
• Energy is conserved in the operation of a heat pump.
  • The heat extracted from the cold reservoir (Q_c) plus the work done by the system (W) is equal to the heat deposted in the hot reservoir (Q_h).
• The coefficient of performance (COP) is the ratio of the useful energy output of a system to the mechanical work required to operate it.
  • The COP is a measure of the effectiveness of a mechanical device or system at performing some task.
  • The COP of a heat pump used as…
    • an air conditioner or refrigerator is the ratio of the heat extracted to the mechanical work required to operate it.

      COP = Q_c/W

    • a heater is the ratio of the heat deposited in the room to the mechanical work required to operate it.

      COP = Q_h/W