Latent heat is the heat energy that is released or absorbed, by the body or thermodynamic system, during a constant temperature process - usually a first-order transition phase.
Latent heat can be understood as heat energy in hidden form supplied or extracted to alter the state of a substance without changing its temperature. An example is latent heat of fusion and latent heat of evaporation involved in phase change, ie a substance that condenses or evaporates at a given temperature and pressure.
The term was introduced around 1762 by the English chemist Joseph Black. It comes from Latin latere ( for hidden lies ). Black uses the term in the context of calorimetry in which heat transfer causes volume changes in the body while temperature is constant.
In contrast to latent heat, a reasonable heat is the heat transfer that results in changes in temperature in the body.
Video Latent heat
Usage
The term "sensible heat" and "latent heat" see the type of heat transfer between the body and its surroundings, they depend on the properties of the body Sensible heat is felt or felt in the process as a change in body temperature Latent heat is heat which are transferred in a process without changes in body temperature, for example, in phase change (solid/liquid/gas).
Both plausible and latent heat are observed in many processes of energy transfer in nature. Latent heat is associated with changes in the atmospheric or oceanic phase, evaporation, condensation, freezing or fusion, whereas a reasonable heat is transferred energy that is evident in changes in atmospheric or ocean temperature, or ice, without such phase change. , although it is associated with changes in pressure and volume.
The original use of the term, as introduced by Black, applies to systems that are deliberately held at a constant temperature. Such use refers to
When a body is heated at a constant temperature by thermal radiation in a microwave field for example, it can inflate with the amount described by its latent heat in terms of volume or latent heat of expansion, or increase its pressure by the amount described by its latent latitude in relation to the pressure . Latent heat is energy that is released or absorbed, by the body or thermodynamic system, during a constant temperature process. The two common forms of latent heat are latent heat of fusion (melting) and latent heat of evaporation (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 changes are endothermic, which means that the system absorbs energy. For example, when water evaporates, energy is required for water molecules to overcome the tensile strength between them, the transition from water to vapor requires energy input.
If the vapor then condenses into liquid on the surface, then the latent energy of the vapor absorbed during evaporation is released as a plausible hot liquid to the surface.
The great value of the vapor condensation enthalation is the reason that steam is a heating medium much more effective than boiling water, and more dangerous.
Meteorology
In meteorology, latent heat flux is the heat flux from the Earth's surface to the atmosphere associated with evaporation or transpiration of water on the surface and subsequently condensing water vapor in the troposphere. This is an important component of the Earth's surface energy budget. Latent heat flux is usually measured by the Bowen ratio technique, or later since the mid-1900s by Jonathan Beaver's method.
Maps Latent heat
History
The latent word latent comes from the Latin lat? Ns , which means lying hidden . The term latent was introduced to the calorimetry of about 1750 when Joseph Black, commissioned by the Scotch whiskey producer to find the ideal amount of fuel and water for their refining process, to study system changes, such as volume. and pressure, when a thermodynamic system is held at a constant temperature in a hot water bath. James Prescott Joule characterizes latent energy as the interaction energy in a particular particle configuration, a potential energy form, and a reasonable heat as the energy indicated by a thermometer, connecting the latter with heat energy.
Specific latent heat
A spesifik laten panas ( L ) menyatakan jumlah energi dalam bentuk panas ( Q ) yang diperlukan untuk sepenuhnya mempengaruhi perubahan fasa dari suatu satuan massa ( m ), biasanya 1 kg , dari suatu zat sebagai properti intensif:
Intensive properties are material characteristics and do not depend on the size or level of the sample. Commonly cited and tabulated in the literature is the specific latent heat of fusion and specific latent heat from evaporation to many substances.
Dari definisi ini, panas laten untuk massa suatu zat dihitung oleh
where:
- Q is the amount of energy released or absorbed during the phase phase change (in kJ or in BTU),
- m is the substance mass (in kg or in lb), and
- L is the specific latent heat for certain substances (kJ kg -1 ) or both f for fusion, or L v for evaporation.
Tables specific to latent heat
The following table shows specific latent heats and changes in phase temperature (at standard pressure) from some common liquids and gases.
Specific latent heat for water condensation in the cloud
Panas laten spesifik dari kondensasi air dalam kisaran suhu dari -25 ° C hingga 40 ° C diperkirakan oleh fungsi kubik empiris berikut:
di mana suhu dianggap sebagai nilai numerik dalam  ° C.
Untuk sublimasi dan pengendapan dari dan ke dalam es, panas laten spesifik hampir konstan dalam rentang suhu dari -40 ° C hingga 0 ° C dan dapat diperkirakan oleh fungsi kuadrat empiris berikut:
Variasi dengan suhu (atau tekanan)
When the temperature (or pressure) rises to the critical point, LHOV falls to zero:
See also
- Bowen Ratio
- Eddy covariance flux (eddy flux correlation)
- Sublimation (physics)
- Specific heat capacity
- Enthalpy fusion
- Enthalpy evaporation
References
Source of the article : Wikipedia
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