Adiabatic Cooling
|
Adiabatic cooling occurs when the pressure of a substance is decreased as it does work on its surroundings. Adiabatic cooling does not have to involve a fluid.
|
Advection
|
A transport mechanism of a substance, or a conserved property, by a fluid, due to the fluid's bulk motion in a particular direction. An example of advection is the transport of pollutants or silt in a river.
|
Bridgman Effect
|
(or internal Peltier effect) A phenomenon that occurs when an electric current passes through an anisotropic crystal - there is an absorption or liberation of heat because of the non-uniformity in current distribution
|
Capillary Evaporation
|
The transport of a liquid from within a capillary system (e.g. a block of porous material) and the subsequent evaporation from its surface.
|
By lowering temperature through latent heat of evaporation
|
Conduction (thermal)
|
The spontaneous transfer of thermal energy through matter, from a region of higher temperature to a region of lower temperature. Conduction acts to equalize temperature differences. It is also described as heat energy transferred from one material to another by direct contact.
|
Convection
|
The movement of molecules within fluids (i.e. liquids, gases) and rheids. One of the major modes of heat transfer and mass transfer. Convective heat and mass transfer take place through both diffusion (random Brownian motion) and by advection (transport by the larger-scale motion of currents). Note that a common use of the term convection refers specifically to heat transfer by convection, as opposed to convection in general.
|
Cooling
|
The act of reducing temperature.
|
Corona Discharge
|
An electrical discharge brought on by the ionization of a fluid surrounding a conductor, which occurs when the potential gradient (the strength of the electric field) exceeds a certain value, but conditions are insufficient to cause complete electrical breakdown or arcing.
|
For example, for computer processor cooling, a high electric field is generated between a cathode and anode placed at opposite ends of the CPU. The highly charged cathode ionizes the surrounding air and it causes the air to quickly move towards the anode. This results in movement of air towards the anode, cooling the processor.
|
Cryogenics
|
The behavior of materials at very low temperatures (typically below -150 °C, -238 °F or 123 K).
|
Curie Point (ferromagnetic)
|
The Curie point of a ferromagnetic material is the temperature above which it loses its characteristic ferromagnetic ability
|
The ferromagnetic 'phase change' that occurs at the Curie Point requires (or releases) energy in the form of heat.
|
Electrocaloric Effect
|
A phenomenon in which a material shows a reversible temperature change under an applied electric field. Often considered the physical inverse of the pyroelectric effect. The effect comes from the voltage raising or lowering the entropy of the system. Analogous to the magnetocaloric effect.
|
Endothermic Reaction
|
A process or reaction that absorbs energy typically (but not always) in the form of heat. The concept is frequently applied in physical sciences to e.g. chemical reactions, where thermal energy (heat) is converted to chemical bond energy.
|
Ettingshausen Effect
|
(or Second Nernst-Ettingshausen Effect) A thermoelectric (or thermomagnetic) phenomenon that affects electric current in a conductor when a magnetic field is present, resulting in a potential difference is induced normal to both the direction of the magnetic field and the current. Alternately, a temperature gradient is induced. The inverse of the Nernst Effect.
|
Evaporation
|
The change of the physical state of aggregation (or simply state) of matter from liquid phase to gaseous phase.
|
By lowering temperature through latent heat of evaporation
|
Fluidisation
|
A process similar to liquefaction whereby a granular material is converted from a static solid-like state to a dynamic fluid-like state. This process occurs when a fluid (liquid or gas) is passed up through the granular material. When fluidized, a bed of solid particles will behave as a fluid, like a liquid or gas.
|
Forced Convection
|
Heat advection by a fluid which is not due to the natural forces of buoyancy induced by heating. In forced heat convection, transfer of heat is due to movement in the fluid which results from many other forces, such as (for example) a fan or pump.
|
Free Convection
|
Movement of molecules of fluids (or gases) dues to density differences in the fluid (or gas) occurring due to temperature gradients.
|
Incandescence
|
The emission of light (visible electromagnetic radiation) from a hot body due to its temperature.
|
Infrared Radiation
|
Infrared (IR) radiation is electromagnetic radiation whose wavelength is longer than that of visible light (400-700 nm), but shorter than that of terahertz radiation (3-300 µm) and microwaves (~30,000 µm). Infrared radiation spans roughly three orders of magnitude (750 nm and 1000 µm).
|
By emission of infrared radiation
|
Joule-Thomson Effect
|
The temperature change of a gas resulting from expansion without production of work or the transfer of heat. For example, when a gas or liquid is forced through a valve or porous plug while kept insulated.
|
Indirectly through the heating of a gas by the Joule-Thompson Effect
|
Latent Heat
|
Energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process. An example is a state of matter change, meaning a phase transition, such as ice melting or water boiling.
|
Leidenfrost Effect
|
A phenomenon in which a liquid, in near contact with a mass significantly hotter than its boiling point, produces an insulating vapour layer which keeps that liquid from boiling rapidly. Due to this repulsive force, the droplet hovers over the surface rather than making physical contact with it. Commonly seen in the case of droplets of water skittering across a very hot metal surface.
|
Magnetocaloric Effect
|
(or Magnetothermal Effect) A magneto-thermodynamic phenomenon in which a reversible change in temperature of a suitable material is caused by exposing the material to a changing magnetic field. Also known as adiabatic demagnetisation. Can be used to attain extremely low temperatures (well below 1 K), as well as the ranges used in common refrigerators.
|
Melting
|
A process that results in the phase change of a substance from a solid to a liquid. The internal energy of a solid substance is increased (typically by the absorbtion of heat) to a specific temperature (called the melting point) at which it changes to the liquid phase.
|
Mixed Convection
|
Movement of fluids or gases (or particles carried by fluids or gasses) by a combination of Free and Forced Convection
|
Peltier Effect
|
Heat is evolved or absorbed at the junction of two dissimilar metals carrying a small current, depending upon the direction of the current. One of a number of thermoelectric effects (See Seebeck Effect and Thompson Effect).
|
Phase Change
|
The transformation of a thermodynamic system from one phase to another. Most commonly used to describe transitions between solid, liquid and gaseous states of matter, in rare cases including plasma.
|
Evaporation (liquid to gas) or melting (solid to liquid) are endothermic phase changes
|
Porosity
|
The quality of being porous - i.e. having voids or spaces within a solid substance within or through which fluids can be present.
|
By passing a cooling liquid or gas through the porous solid.
|
Radiation
|
A process in which energetic particles or waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing.
|
Through loss of energy by radiation.
|
Rayleigh-Bénard Convection
|
Convection cells that appear spontaneously in a liquid layer when heat is applied from below.
|
Reflection
|
The change in direction of a wavefront at an interface between two different media so that the wavefront returns into the medium from which it originated. Common examples include the reflection of light, sound and water waves.
|
By reflection of incident radiation.
|
Righi-Leduc Effect
|
A magnetic field applied at right angles to the the direction of a temperature gradient in an electrical conductor will produce a temperature difference at right angles to the direction of both the temperature gradient and the magnetic field.
|
Second Sound
|
A quantum mechanical phenomenon in which heat transfer occurs by wave-like motion, rather than by the more usual mechanism of diffusion. Heat takes the place of pressure in normal sound waves. This leads to a very high thermal conductivity. It is known as 'second sound' because the wave motion of heat is similar to the propagation of sound in air.
|
Solvation
|
(commonly called dissolution) The process of attraction and association of molecules of a solvent with molecules or ions of a solute. As ions dissolve in a solvent they spread out and become surrounded by solvent molecules. The bigger the ion, the more solvent molecules are able to surround it and the more it becomes solvated.
|
Solvation can be endothermic
|
Sublimation
|
The change of the physical state of aggregation (or simply state) of matter directly from solid phase to gaseous phase without passing through an intermediate liquid phase.
|
By latent heat of sublimation.
|
Supercritical Fluid
|
Any substance at a temperature and pressure above its critical point. It can diffuse through solids like a gas, and dissolve materials like a liquid. Additionally, close to the critical point, small changes in pressure or temperature result in large changes in density, allowing many properties to be 'tuned'.
|
Supercritical carbon dioxide is also an important emerging refrigerant, being used in new, low-carbon solutions for domestic heat pumps
|
Suspension
|
A heterogeneous fluid containing solid particles that are sufficiently large for sedimentation. Usually they must be larger than 1 micrometer. The internal phase (solid) is dispersed throughout the external phase (fluid - which may be liquid or gas) through mechanical agitation, with the use of certain excipients or suspending agents.
|
Thermal Expansion
|
The tendency of matter to change in volume in response to a change in temperature or when a substance is heated.
|
Thermal Expansion is endothermic
|
Thermal Hall Effect
|
The thermal analog of the Hall effect, i.e. a thermal gradient is produced across a solid instead of an electric field. When a magnetic field is applied, an orthogonal temperature gradient develops. For conductors, a significant portion of the thermal current is carried by the electrons. In particular, the Righi-Leduc Effect describes the heat flow resulting from a perpendicular temperature gradient and vice versa, and the Maggi-Righi-Leduc effect describes changes in thermal conductivity when placing a conductor in a magnetic field.
|
Thermal Radiation
|
Electromagnetic radiation emitted from the surface of an object due to the object's temperature.
|
A hot solid (e.g. red-hot or white-hot metal) cools as a result of the loss of energy required to generate the thermal radiation.
|
Thermionic Emission
|
Emission of electrons or ions caused by thermal vibrational energy . Also known as the Edison Effect.
|
Thermoacoustic Effect
|
Acoustic waves can be used for heat transfer. The pressure variations in the acoustic wave are accompanied by temperature variations due to compressions and expansions of the gas which, being inherantly associated with a displacement, results in a net transfer of heat. Direction of heat flow can be fixed by, for example, a standing wave pattern generated by an acoustic resonator.
|
Thermoacoustics
|
The interaction between thermodynamic and acoustic phenomena, for example the relation between pressure changes, and temperature changes. A dynamic pressure would cause a dynamic temperature and vice versa.
|
Thermolysis
|
(or Thermal decomposition) A chemical decomposition caused by heat. The reaction is usually endothermic as heat is required to break chemical bonds in the compound undergoing decomposition. If decomposition is sufficiently exothermic, a positive feedback loop is created producing thermal runaway and possibly an explosion.
|
Thermolysis is usually endothermic.
|
Thompson Effect
|
The heating or cooling of a current-carrying conductor with a temperature gradient Depending on the material it may cause heating or cooling. One of a number of thermoelectirc effects (see Seebeck effect and Peltier Effect).
|
Transpiration
|
The loss of water vapour from parts of plants (similar to sweating), especially in leaves but also in stems, flowers and roots. Leaf surfaces are dotted with openings called, collectively, stomata. Leaf transpiration occurs through stomata, and can be thought of as a necessary 'cost' associated with the opening of the stomata to allow the diffusion of carbon dioxide gas from the air for photosynthesis. Transpiration also cools plants and enables mass flow of mineral nutrients and water from roots to shoots.
|
