Latent heat

Latent heat is thermal energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process — usually a first-order phase transition.

Latent heat can be understood as heat energy in hidden form which is supplied or extracted to change the state of a substance without changing its temperature. Examples are latent heat of fusion and latent heat of vaporization involved in phase changes, i.e. a substance condensing or vaporizing at a specified temperature and pressure.[1][2]

The term was introduced around 1762 by British chemist Joseph Black. It is derived from the Latin latere (to lie hidden). Black used the term in the context of calorimetry where a heat transfer caused a volume change in a body while its temperature was constant.

In contrast to latent heat, sensible heat is a heat transfer that results in a temperature change in a body.

Usage

The terms ″sensible heat″ and ″latent heat″ refer to types of heat transfer between a body and its surroundings; they depend on the properties of the body. ″Sensible heat″ is ″sensed″ or felt in a process as a change in the body's temperature. ″Latent heat″ is heat transferred in a process without change of the body's temperature, for example, in a phase change ( solid / liquid / gas ).

Both sensible and latent heats are observed in many processes of transfer of energy in nature. Latent heat is associated with the change of phase of atmospheric or ocean water, vaporization, condensation, freezing or melting, whereas sensible heat is energy transferred that is evident in change of the temperature of the atmosphere or ocean, or ice, without those phase changes, though it is associated with changes of pressure and volume.

The original usage of the term, as introduced by Black, was applied to systems that were intentionally held at constant temperature. Such usage referred to latent heat of expansion and several other related latent heats. These latent heats are defined independently of the conceptual framework of thermodynamics.[3]

When a body is heated at constant temperature by thermal radiation in a microwave field for example, it may expand by an amount described by its latent heat with respect to volume or latent heat of expansion, or increase its pressure by an amount described by its latent heat with respect to pressure.[4] Latent heat is energy released or absorbed, by a body or a thermodynamic system, during a constant-temperature process. Two common forms of latent heat are latent heat of fusion (melting) and latent heat of vaporization (boiling). These names describe the direction of energy flow when changing from one phase to the next: from solid to liquid, and liquid to gas.

In both cases the change is endothermic, meaning that the system absorbs energy. For example, when water evaporates, energy is required for the water molecules to overcome the forces of attraction between them, the transition from water to vapor requires an input of energy.

If the vapor then condenses to a liquid on a surface, then the vapor's latent energy absorbed during evaporation is released as the liquid's sensible heat onto the surface.

The large value of the enthalpy of condensation of water vapor is the reason that steam is a far more effective heating medium than boiling water, and is more hazardous.

Meteorology

In meteorology, latent heat flux is the flux of heat from the Earth's surface to the atmosphere that is associated with evaporation or transpiration of water at the surface and subsequent condensation of water vapor in the troposphere. It is an important component of Earth's surface energy budget. Latent heat flux has been commonly measured with the Bowen ratio technique, or more recently since the mid-1900s by the Jonathan Beaver method.

Other Languages
العربية: حرارة كامنة
Bân-lâm-gú: Chiâm-jia̍t
català: Calor latent
čeština: Skupenské teplo
español: Calor latente
Esperanto: Latenta varmo
Gaeilge: Teas folaigh
한국어: 잠열
Bahasa Indonesia: Kalor laten
italiano: Calore latente
עברית: חום כמוס
Basa Jawa: Kalor laten
Kreyòl ayisyen: Chalè latan
മലയാളം: ലീനതാപം
Bahasa Melayu: Haba pendam
Nederlands: Latente warmte
日本語: 潜熱
norsk nynorsk: Latent varme
português: Calor latente
Simple English: Latent heat
slovenčina: Skupenské teplo
کوردی: ماتەگەرمی
српски / srpski: Латентна топлота
srpskohrvatski / српскохрватски: Latentna toplota
svenska: Latent värme
українська: Прихована теплота
粵語: 潛熱
中文: 潛熱