Adiabatic Cooling
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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.
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Advection
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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.
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Bubble
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A globule of one substance in another, usually gas in a liquid. Due to the Marangoni effect, bubbles may remain intact when they reach the surface of the immersive substance.
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Capillary Evaporation
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The transport of a liquid from within a capillary system (e.g. a block of porous material) and the subsequent evaporation from its surface.
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By lowering temperature through latent heat of evaporation
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Conduction (thermal)
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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.
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Convection
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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.
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Cooling
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The act of reducing temperature.
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Cryogenics
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The behavior of materials at very low temperatures (typically below -150 °C, -238 °F or 123 K).
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Curie Point (ferromagnetic)
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The Curie point of a ferromagnetic material is the temperature above which it loses its characteristic ferromagnetic ability
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The ferromagnetic 'phase change' that occurs at the Curie Point requires (or releases) energy in the form of heat.
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Depressurisation
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Reduction in pressure. Rapid depressurisation can be used to create pressure differences.
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Dufour Effect
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The development of a temperature gradient due to diffusion. Can be thought of as inverse thermophoresis.
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Electrocaloric Effect
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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.
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Endothermic Reaction
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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.
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Ettingshausen Effect
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(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.
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Evaporation
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The change of the physical state of aggregation (or simply state) of matter from liquid phase to gaseous phase.
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By lowering temperature through latent heat of evaporation
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Forced Convection
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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.
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Free Convection
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Movement of molecules of fluids (or gases) dues to density differences in the fluid (or gas) occurring due to temperature gradients.
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Incandescence
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The emission of light (visible electromagnetic radiation) from a hot body due to its temperature.
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Infrared Radiation
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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).
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By emission of infrared radiation
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Joule-Thomson Effect
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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.
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At ordinary temperatures and pressures, all real gases except hydrogen and helium and neon are cooled by the Joule-Thompson effect.
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Latent Heat
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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.
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Magnetocaloric Effect
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(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.
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Mechanocaloric Effect
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An effect resulting from the fact that a temperature gradient in helium II is invariably accompanied by a pressure gradient, and conversely; examples are the fountain effect, and the heating of liquid helium left behind in a container when part of it leaks out through a small orifice.
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Melting
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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.
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Mixed Convection
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Movement of fluids or gases (or particles carried by fluids or gasses) by a combination of Free and Forced Convection
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Peltier Effect
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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).
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Phase Change
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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.
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Evaporation (liquid to gas) or melting (solid to liquid) are endothermic phase changes
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Porosity
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The quality of being porous - i.e. having voids or spaces within a solid substance within or through which fluids can be present.
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By passing the gas though a colder porous solid.
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Radiation
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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.
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Through loss of energy by radiation.
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Ranque-Hilsch Effect
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The Ranque-Hilsch vortex tube (or vortex tube), is a mechanical device that separates a compressed gas into hot and cold streams. It has no moving parts. Pressurised gas is injected tangentially into a swirl chamber and accelerates to a high rate of rotation. Due to the conical nozzle at the end of the tube, only the outer shell of the compressed gas is allowed to escape at that end. The remainder of the gas is forced to return in an inner vortex of reduced diameter within the outer vortex.
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Rarefaction
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(also called rarefraction) The reduction of a medium's density, or the opposite of compression. Has a variety of causes, such as the passage of a sound wave through a gas, of the diminishing effect of the earth's gravity on the atmosphere with altitude.
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Rayleigh-Bénard Convection
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Convection cells that appear spontaneously in a liquid layer when heat is applied from below.
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Reflection
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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.
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By reflection of incident radiation.
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Second Sound
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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.
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Solvation
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(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.
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Solvation can be endothermic
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Supercooling
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(also known as undercooling) The process of lowering the temperature of a liquid or a gas below its freezing point, without it becoming a solid. A liquid below its standard freezing point will crystallize in the presence of a seed crystal or nucleus around which a crystal structure can form. Without any such nucleus, the liquid phase can be maintained all the way down to the temperature at which crystal homogeneous nucleation occurs.
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Supercritical Fluid
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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'.
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Supercritical carbon dioxide is an important emerging refrigerant, being used in new, low-carbon solutions for domestic heat pumps
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Suspension
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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.
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Thermal Expansion
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The tendency of matter to change in volume in response to a change in temperature or when a substance is heated.
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Thermal Radiation
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Electromagnetic radiation emitted from the surface of an object due to the object's temperature.
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A hot gas cools as a result of the loss of energy required to generate the thermal radiation.
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Thermoacoustic Effect
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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.
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Thermoacoustics
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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.
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Thermolysis
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(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.
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Thermolysis is usually endothermic.
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Thompson Effect
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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).
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Indirectly: Thompson effect could be used to cool a metal, which would function as a heat sink
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