Combined heat transfer

Conduction and convection occur through the contact between atoms and molecules in matterThe thermal energy carried by conduction and convection is fundamentally the energy in random motion of atoms and molecules in matter. This is why conduction and convection only occur in matter. It also explains why heat moves relatively slowly in both conduction and convection. Energy must be ultimately transferred by trillions of tiny, random collisions between individual molecules. Conduction occurs in all phases of matter: solid, liquid, and gas. Convection occurs only in the liquid and gas phases in which entire collections of molecules can move as a whole in addition to their individual thermal motion. Read the text aloud
Radiation transfers heat through electromagnetic wavesRadiation is fundamentally different from conduction and convection. Electromagnetic waves are pure energy independent of matter. This is why radiation can transfer heat through the vacuum of space. Radiation also moves at the speed of light, 3 × 108 m/s, far faster than other types of heat transfer. When radiation encounters matter, some of the electromagnetic energy is transformed into molecular thermal motion—ordinary heat. Read the text aloud
Our world of matter and energy includes solids, liquids, and gases at temperatures far above absolute zero. All three forms of heat transfer act together to determine the rate at which thermal energy is exchanged. Which of the three is most important depends on the temperature and on the circumstances. Although it is uncommon for all three modes of heat transfer to be equally important in a single transformation of energy, heat transfer usually occurs in many steps. In both nature and technology, a different form of heat transfer may be most important at each different step. For example, in a solar-thermal power station, radiant energy heats a metal tube. The heat travels through the walls of the tube by conduction, where it heats water into steam, which in turn carries the heat to a turbine by convection. Read the text aloud Show Heat inside computers and electronic devices
Combined heat transfer in a solar-thermal power station
Diagram of a vacuum or Thermos® bottleA Thermos® or vacuum bottle is an insulated container that keeps food warm for many hours by reducing heat transfer from the inside to the outside. Which is the best reason why Thermos® bottles have a vacuum space (no air) between the inner and outer walls?
  1. Radiation cannot transfer heat through a vacuum.
  2. Convection cannot transfer heat through a vacuum.
  3. Vacuum has no mass and is therefore lighter than other insulators such as foam.

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