As temperature rises, the molecules increase in thermal agitation manifested in linear motion and vibration. Regions that contain higher kinetic energy transfer the energy to regions with lower kinetic energy. Simply put, heat transfer can be grouped into three broad categories: conduction, convection, and radiation.
What is heat conduction?
The image above, provided by NASA, highlights how all three heat-transfer methods conduction, convection, and radiation work in the same environment. Conduction transfers heat via direct molecular collision. An area of greater kinetic energy will transfer thermal energy to an area with lower kinetic energy.
Higher-speed particles will collide with slower speed particles. The slower-speed particles will increase in kinetic energy as a result.
The Science of Heat Transfer: What Is Conduction?
Conduction is the most common form of heat transfer and occurs via physical contact. Examples would be to place your hand against a window or place metal into an open flame. The process of heat conduction depends on the following factors: temperature gradient, cross-section of the material, length of the travel path, and physical material properties. The temperature gradient is the physical quantity that describes the direction and rate of heat travel.
Temperature flow will always occur from hottest to coldest or, as stated before, higher to lower kinetic energy. Cross-section and path of travel both play an important part in conduction. Smaller objects with small cross-sections have minimal heat loss. Physical properties determine which materials transfer heat better than others.
Specifically, the thermal conductivity coefficient dictates that a metal material will conduct heat better than cloth when it comes to conduction. The following equation calculates the rate of conduction:. A modern of use of conduction is being developed by Dr.
Gyung-Min Choi at the University of Illinois. Choi uses spin current to generate spin transfer torque.
What Is Conduction?
Spin transfer torque is the transfer of the spin angular momentum generated by the conduction electrons to the magnetization of a ferromagnet. Instead of using magnetic fields, this allows the manipulation of nanomagnets with spin currents. When a fluid, such as air or a liquid, is heated and then travels away from the source, it carries the thermal energy along. This type of heat transfer is called convection. The fluid above a hot surface expands, becomes less dense, and rises.
At the molecular level, the molecules expand upon introduction of thermal energy. As temperature of the given fluid mass increases, the volume of the fluid must increase by same factor.
This effect on the fluid causes displacement. As the immediate hot air rises, it pushes denser, colder air down. This series of events represents how convection currents are formed. The equation for convection rates is calculated as follows:. A space heater is a classic convection example.
As the space heater heats the air surrounding it near the floor, the air will increase in temperature, expand, and rise to the top of the room. Thermal energy is related to the average kinetic energy of atomic-scale particle movements within matter - the more vigorous the movement of particles, the higher the temperature.
Conduction of thermal energy takes place when local interactions between atoms and molecules and electrons pass kinetic energy from particle to particle.
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There is no net movement of particles in a flow of thermal energy or heat. Heat transfer in fluids is by random motion of atoms and molecules; in solids, heat is transferred by electrons and phonons. In general, thermal conductivity is greatest in solids, then liquids , then gases.
- Definition of Heat Conduction.
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Metals are generally good conductors of heat for the same reason they are good conductors of electricity. Their mobile electrons are excellent carriers of thermal energy.