Heat transfer

Heat conduction, also called diffusion, is the direct microscopic exchanges of kinetic energy of particles (such as molecules) or quasiparticles (such as lattice waves) through the boundary between two systems.

Enthalpy is a thermodynamic potential, designated by the letter "H", that is the sum of the internal energy of the system (U) plus the product of pressure (P) and volume (V).

This usage has its origin in the historical interpretation of heat as a fluid (caloric) that can be transferred by various causes,[4] and that is also common in the language of laymen and everyday life.

This can be as simple as placing hot water in a bottle and heating a bed, or the movement of an iceberg in changing ocean currents.

[15] Thermal radiation is emitted by all objects at temperatures above absolute zero, due to random movements of atoms and molecules in matter.

Since these atoms and molecules are composed of charged particles (protons and electrons), their movement results in the emission of electromagnetic radiation which carries away energy.

When the objects and distances separating them are large in size and compared to the wavelength of thermal radiation, the rate of transfer of radiant energy is best described by the Stefan-Boltzmann equation.

The (on its surface) somewhat 4000 K hot sun allows to reach coarsely 3000 K (or 3000 °C, which is about 3273 K) at a small probe in the focus spot of a big concave, concentrating mirror of the Mont-Louis Solar Furnace in France.

The Mason equation explains the growth of a water droplet based on the effects of heat transport on evaporation and condensation.

At standard atmospheric pressure and low temperatures, no boiling occurs and the heat transfer rate is controlled by the usual single-phase mechanisms.

As the surface temperature is increased, local boiling occurs and vapor bubbles nucleate, grow into the surrounding cooler fluid, and collapse.

At similar standard atmospheric pressure and high temperatures, the hydrodynamically quieter regime of film boiling is reached.

The Leidenfrost Effect demonstrates how nucleate boiling slows heat transfer due to gas bubbles on the heater's surface.

[24] There are several types of condensation: Melting is a thermal process that results in the phase transition of a substance from a solid to a liquid.

[28] Climate models study the radiant heat transfer by using quantitative methods to simulate the interactions of the atmosphere, oceans, land surface, and ice.

Thermal insulators are materials specifically designed to reduce the flow of heat by limiting conduction, convection, or both.

[32][33] A thermocouple is a temperature-measuring device and a widely used type of temperature sensor for measurement and control, and can also be used to convert heat into electric power.

An alternative method is passive daytime radiative cooling, which enhances terrestrial heat flow to outer space through the infrared window (8–13 μm).

[39][40] The greenhouse effect is a process by which thermal radiation from a planetary surface is absorbed by atmospheric greenhouse gases and clouds, and is re-radiated in all directions, resulting in a reduction in the amount of thermal radiation reaching space relative to what would reach space in the absence of absorbing materials.

Clothing can be considered an insulator which provides thermal resistance to heat flow over the covered portion of the body.

The body continuously loses water by evaporation but the most significant amount of heat loss occurs during periods of increased physical activity.

In the case of the Earth-atmosphere system, it refers to the process by which long-wave (infrared) radiation is emitted to balance the absorption of short-wave (visible) energy from the Sun.

Applications include space heating, domestic or process hot water systems, or generating electricity.

[49] The phrase "temperature change" was later replaced with "heat loss", and the relationship was named Newton's law of cooling.

In the case of heat transfer by thermal radiation, Newton's law of cooling holds only for very small temperature differences.

... Silver conducted heat far the best of all other metals, next to this was copper, then gold, tin, iron, steel, Lead.During the years 1784 – 1798, the British physicist Benjamin Thompson (Count Rumford) lived in Bavaria, reorganizing the Bavarian army for the Prince-elector Charles Theodore among other official and charitable duties.

During his years in Mannheim and later in Munich, Thompson made a large number of discoveries and inventions related to heat.

It is likewise plain [why] ... inhabiting damp houses, is so very dangerous; and why the evening air is so pernicious in summer ... and why it is not so during the hard frosts of winter.Thompson concluded with some comments on the important difference between temperature and sensible heat.

In treatise VIII by William Prout, in the book on chemistry, it says:[59]This motion of heat takes place in three ways, which a common fire-place very well illustrates.

There is at present no single term in our language employed to denote this third mode of the propagation of heat; but we venture to propose for that purpose, the term convection, [in footnote: [Latin] Convectio, a carrying or conveying] which not only expresses the leading fact, but also accords very well with the two other terms.Later, in the same treatise VIII, in the book on meteorology, the concept of convection is also applied to "the process by which heat is communicated through water".