latent heat


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heat

 [hēt]
1. energy that raises the temperature of a body or substance.
2. estrus.
3. a rise in temperature.
4. to cause to increase in temperature.

Heat is associated with molecular motion, and is generated in various ways, including combustion, friction, chemical action, and radiation. The total absence of heat is absolute zero, at which all molecular activity ceases.
Body Heat. Heat Production. Body heat is the byproduct of the metabolic processes of the body. The hormones thyroxine and epinephrine increase metabolism and consequently increase body heat. Muscular activity also produces body heat. At complete rest (basal metabolism) the amount of heat produced from muscular activity may be as low as 25 per cent of the total body heat. During exercise or shivering the percentage may rise to 60 per cent. Body temperature is regulated by the thermostatic center in the hypothalamus. A body temperature above the normal range is called fever.
Heat Loss. Loss of body heat occurs in three ways: by radiation (heat waves), by conduction to air or objects in contact with the body, and by evaporation of perspiration. Some body heat is lost in exhalation of air and in elimination of urine and feces.
Applications of External Heat. Purposes. Local applications of heat may be used to provide warmth and promote comfort, rest, and relaxation. Heat is also applied locally to promote suppuration and drainage from an infected area by hastening the inflammatory process; to relieve congestion and swelling by dilating the blood vessels, thereby increasing circulation; and to improve repair of diseased or injured tissues by increasing local metabolism.
Effects. Factors that determine the physiologic action of heat include the type of heat used, length of time it is applied, age and general condition of the patient, and area of body surface to which the heat is applied. Moist heat is more penetrating than dry heat. Prolonged applications of heat produce an increase in skin secretions, resulting in a softening of the skin and a lowering of its resistance. Extreme heat produces constriction of the blood vessels; moderate heat produces vascular dilation. Repeated applications of heat will result in an increased tolerance to heat so that the individual may be burned without being aware of it. Elderly persons and infants are more susceptible to burns from high temperatures.

Heat applied to an infected area can localize the infection; for this reason, external heat should not be applied to the abdomen when appendicitis is suspected, because it may lead to rupture of the inflamed appendix.
heat exhaustion a disorder resulting from overexposure to heat or to the sun; long exposure to extreme heat or too much activity under a hot sun causes excessive sweating, which removes large amounts of salt and fluid from the body. When salt and fluid levels fall too far below normal, heat exhaustion may result. Called also heat prostration.
Symptoms. The early symptoms are headache and a feeling of weakness and dizziness, usually accompanied by nausea and vomiting. There may also be cramps in the muscles of the arms, legs, or abdomen. These first symptoms are similar to the early signs of sunstroke, or heat stroke, but the disorders are not the same and should be treated differently. In heat exhaustion, the person turns pale and perspires profusely. The skin is cool and moist, pulse and breathing are rapid, and body temperature remains at a normal level or slightly below (in sunstroke the body temperature may be dangerously elevated). The patient may seem confused and may find it difficult to coordinate body movements; loss of consciousness seldom occurs.
Treatment. In cases of heat exhaustion, the victim should lie quietly in a cool place until transported to an emergency facility. The restoration of normal blood volume will be a priority. Stabilization of electrolytes is also important. If the person is able to safely swallow, sips of cool replacement fluid should be provided. Measures to reduce body temperature are employed.

If the condition is accompanied by cramps, the pain may be relieved by lightly stretching the affected muscles in addition to administering replenishing fluids. In cases of severe heat exhaustion and cramps, hospitalization may be necessary. Serum electrolyte levels are monitored to guide adequate replacement.
Prevention. Heat exhaustion and other heat disorders may be prevented by avoiding long exposure to sun or heat. The elderly, the very young, individuals with chronic diseases, and athletes exercising in the sun are at high risk. When the weather is very hot, or when working in an extremely hot place, it is essential to maintain adequate hydration. Regular rest periods are necessary. In the event of weakness or dizziness, persons should stop working at once and rest in a cool place.

It is possible for indoor temperatures to exceed the outdoor temperature. Poor ventilation can lead to an unhealthy situation that contributes to heat exhaustion. For this reason, adequate temperature control indoors is important in prevention of serious health problems.
latent heat the amount of heat absorbed or given off by a body without changing temperature, as when it undergoes a change of state.
prickly heat (heat rash) miliaria.
specific heat the ratio of the heat capacity of a substance to that of water; it is equivalent to the amount of heat required to raise the temperature of one gram of the substance by one degree Celsius, since the corresponding value for water is defined as 1.0.

la·tent heat

the amount of heat that a substance may absorb without an increase in temperature, as in conversion from solid to liquid state (ice to water at 0°C), or from liquid to gaseous state (water to steam at 100°C). Compare: sensible heat.

latent heat

Etymology: L, latere, to be concealed; AS, haetu
the heat absorbed by a substance when it changes from a solid to a liquid or from a liquid to a gas without an accompanying rise in temperature.

latent heat

The caloric or heat energy absorbed by matter changing from solid to liquid or from liquid to vapor with no change in temperature.
See also: heat
References in periodicals archive ?
6) range, [degrees]C([degrees]F) Latent heat of fusion, J x 230,132 (98.
Monitoring results of an interior sun protection system with integrated latent heat storage, Energy and Buildings 43(9): 2468-2475.
Through modelling the energy balance equation with SEBAL, it has shown that the basic parameters (albedo, vegetation index and surface temperature) obtained from the satellite imagery leads to determine the latent heat flux (LE) as the residual term of this equation.
Metabolic heat generated in the body is dissipated to the environment as sensible heat through the skin and as latent heat by evaporation.
The latent heat of the steam provides heat to the interface zone between the steam finger and cool oil sand.
If we capture the latent heat of vaporisation from the condensing pure water, we can be as efficient as, or even better than, a reverse osmosis system--and no C[O.
The cooling of the water releases latent heat which is then heats the mine during winter and the melting ice helps cool the mine during summer.
But if crystallization begins at the droplet's surface, latent heat can more easily transfer to the surrounding air.
By surrounding the batteries with slow-melting wax (the "ice"), the batteries would be kept at a stable temperature because the wax would absorb the excess heat as it melts in the form of latent heat.
Can you tell me how to work out the latent heat of naphthelene?
As boundary conditions in the simulation are modified, the time required for removal of latent heat from different regions within the product structure is changed.