Heat is energy transfer to or from a thermodynamic system, by mechanisms other than a transfer of matter such as conduction, radiation, and convection or thermodynamic work. Heat transfer involves the surroundings of a system, as well as the system itself. But it is not a property of the system alone, even though it contributes to change in the system’s internal energy, which is a property of the system alone.
The quantity of energy transferred as heat in a process is the amount of transferred energy. It excludes any thermodynamic work that was done. For the precise definition of heat, it must occur by a path that does not include the transfer of matter. For example, radiative heat transfer can co-occur with matter transfer.
The conventional symbol that is used to represent the amount of heat transferred in a thermodynamic process is Q or q. As an amount of energy, the SI unit of heat is the joule (J).
The particles moving fast will excite nearby particles. When heated sufficiently, the movement of particles in a solid increase and thereby overcomes the bonds that hold the particles together. The substance changes its state from a solid to a liquid. If the movement of the particles increases further in liquid, the substance changes into a gas.
Three methods of transferring heat energy.
It is the transfer of heat between any two bodies by currents of moving gas or fluid. Here air or water moves away from the heated body, as the warm air or water rises. In forced convection, air or water is forcibly moved across the body surface. It efficiently removes heat from the body. It is a very efficient way of heat transfer because it maintains a steep temperature gradient.
Conduction heat transfer
It is the transfer of heat through matter without bulk motion of the matter. It is the transfer of energy from the more energetic to less energetic particles due to interaction between the particles. Conduction heat transfer in gases and liquids. It is due to the collisions and diffusion of the molecules. Heat transfer in solids is due to the combination of lattice vibrations of the molecules, and the energy transport by free electrons. Consider an example, heat conduction can occur through the wall of a vein in the human body. The inside surface,is exposed to blood, at a higher temperature than the outside surface.
Heat Transfer by Thermal Radiation
Transfer of heat from a body with a high temperature to a body with a lower temperature. When bodies are not in direct physical contact with each other is called heat radiation. All physical substances in solid, liquid or gaseous states can emit energy via a process of electromagnetic radiation. It is because of the rotational and vibrational of their molecules and atoms. The intensity of such energy flux will depend on the temperature of the body and on the nature of its surface. The radiation occurs at all temperatures and the rate of emission increases with the temperature. Heat transfer by thermal radiation does not necessarily need a material medium for energy transfer whereas in the case of conduction and convection needs a material medium. The medium through which the radiation passes could be a vacuum, gas, or liquid in the case of radiation from a solid surface. Molecules as well as atoms of the medium can absorb, reflect, or transmit the radiation energy. If the medium is a vacuum, then the radiation energy is not attenuated since there are no molecules or atoms. Therefore, it is fully transmitted. Thus radiation heat transfer is more efficient in a vacuum. In the case of a gas, energy can be slightly absorbed or reflected by air molecules and the rest is transmitted whereas in the case of a liquid most of the radiation is absorbed in a thin layer close to the solid surface and nothing is transmitted.
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Heat energy is the result of the movement of tiny particles called atoms, molecules or ions in solids, liquids, and gases. Heat energy can be transferred from one object to another. The transfer or flow due to the difference in temperature between the two objects is called heat.
The first is conduction, which occurs in solids or fluids that are at rest, such as this metal bar. The second form of heat transfer is convection, which occurs in liquids or gases that are in motion. And the third form of heat transfer is radiation, which takes place with no material carrier.
Natural gas, propane (LP), oil, coal, wood, electricity, heat pumps, ground source heat pumps and solar energy.
The Sun is the biggest source of heat energy in our solar system.
A stovetop acts as a source of heat energy when it burns the gas
Automobile fuels are also a source of heat energy.
A hot cup of tea or coffee contains heat energy.