Latent heat – wikipedia electricity projects for 4th graders

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.

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. History [ edit ]

The English word latent comes from Latin latēns, meaning lying hidden. [5] [6] The term latent heat was introduced into calorimetry around 1750 when Joseph Black, commissioned by producers of Scotch whisky in search of ideal quantities of fuel and water for their distilling process, [7] to studying system changes, such as of volume and pressure, when the thermodynamic system was held at constant temperature in a thermal bath. James Prescott Joule characterised latent energy as the energy of interaction in a given configuration of particles, i.e. a form of potential energy, and the sensible heat as an energy that was indicated by the thermometer, [8] relating the latter to thermal energy. Specific latent heat [ edit ]

A specific latent heat ( L) expresses the amount of energy in the form of heat ( Q) required to completely effect a phase change of a unit of mass ( m), usually 1 kg, of a substance as an intensive property: L = Q m . {\displaystyle L={\frac {Q}{m}}.}

Intensive properties are material characteristics and are not dependent on the size or extent of the sample. Commonly quoted and tabulated in the literature are the specific latent heat of fusion and the specific latent heat of vaporization for many substances.

where: Q is the amount of energy released or absorbed during the change of phase of the substance (in kJ or in BTU), m is the mass of the substance (in kg or in lb), and L is the specific latent heat for a particular substance (kJ kg −1 or in BTU lb −1), either L f for fusion, or L v for vaporization. Table of specific latent heats [ edit ]

The specific latent heat of condensation of water in the temperature range from −25 °C to 40 °C is approximated by the following empirical cubic function: L water ( T ) = ( 2500.8 − 2.36 T + 0.0016 T 2 − 0.00006 T 3 ) J/g , {\displaystyle L_{\text{water}}(T)=(2500.8-2.36T+0.0016T^{2}-0.00006T^{3})~{\text{J/g}},} [10]

For sublimation and deposition from and into ice, the specific latent heat is almost constant in the temperature range from −40 °C to 0 °C and can be approximated by the following empirical quadratic function: L ice ( T ) = ( 2834.1 − 0.29 T − 0.004 T 2 ) J/g . {\displaystyle L_{\text{ice}}(T)=(2834.1-0.29T-0.004T^{2})~{\text{J/g}}.} [10] Variation with temperature (or pressure) [ edit ]