heat sink vs immersion heater

heat sink

noun
  • A material capable of absorbing heat. 

  • An object, system or environment that absorbs and dissipates heat from objects in thermal contact (either direct or radiant) with it. 

  • A place toward which the heat moves in a system. 

immersion heater

noun
  • A device for supplying domestic hot water in which a thermostatically-controlled heating element is immersed within a tank of water 

How often have the words heat sink and immersion heater occurred in a corpus of books? (source: Google Ngram Viewer )