| 释义 |
latent heat
latent heatn. The quantity of heat absorbed or released by a substance undergoing a change of state, such as ice changing to water or water to steam, at constant temperature and pressure. Also called heat of transformation.latent heat n (General Physics) (no longer in technical usage) the heat evolved or absorbed by unit mass (specific latent heat) or unit amount of substance (molar latent heat) when it changes phase without change of temperature la′tent heat′
n. heat absorbed or radiated during a change of phase at constant temperature and pressure. [1750–60] la·tent heat (lāt′nt) The quantity of heat absorbed or released by a substance undergoing a change of state, such as ice changing to water or water changing to ice, at constant temperature and pressure.latent heat1. The quantity of heat which is absorbed or released by a substance during a change of state (fusion or vaporization) at constant temperature.2. Heat released or absorbed when a substance changes state without a change in temperature.Thesaurus| Noun | 1. | latent heat - heat absorbed or radiated during a change of phase at a constant temperature and pressureheat of transformationheat, heat energy - a form of energy that is transferred by a difference in temperatureheat of condensation - heat liberated by a unit mass of gas at its boiling point as it condenses into a liquid; "the heat of condensation is equal to the heat of vaporization"heat of fusion - heat absorbed by a unit mass of a solid at its melting point in order to convert the solid into a liquid at the same temperature; "the heat of fusion is equal to the heat of solidification"heat of solidification - heat liberated by a unit mass of liquid at its freezing point when it solidifiesheat of sublimation - heat absorbed by a unit mass of material when it changes from a solid to a gaseous stateheat of vaporisation, heat of vaporization - heat absorbed by a unit mass of a material at its boiling point in order to convert the material into a gas at the same temperature |
latent heat
latent heat, heat change associated with a change of state or phase (see states of matterstates of matter,
forms of matter differing in several properties because of differences in the motions and forces of the molecules (or atoms, ions, or elementary particles) of which they are composed.
..... Click the link for more information. ). Latent heat, also called heat of transformation, is the heatheat,
nonmechanical energy in transit, associated with differences in temperature between a system and its surroundings or between parts of the same system. Measures of Heat
..... Click the link for more information. given up or absorbed by a unit mass of a substance as it changes from a solid to a liquid, from a liquid to a gas, or the reverse of either of these changes. It is called latent because it is not associated with a change in temperature. Each substance has a characteristic heat of fusion, associated with the solid-liquid transition, and a characteristic heat of vaporization, associated with the liquid-gas transition. The latent heat of fusion for ice is 80 calories per gram (see caloriecalorie,
abbr. cal, unit of heat energy in the metric system. The measurement of heat is called calorimetry. The calorie, or gram calorie, is the quantity of heat required to raise the temperature of 1 gram of pure water 1°C;.
..... Click the link for more information. ). This amount of heat is absorbed by each gram of ice in melting or is given up by each gram of water in freezing. The latent heat of vaporization of steam is 540 calories per gram, absorbed during vaporizationvaporization,
change of a liquid or solid substance to a gas or vapor. There is fundamentally no difference between the terms gas and vapor, but gas is used commonly to describe a substance that appears in the gaseous state under standard conditions of pressure and
..... Click the link for more information. or given up during condensationcondensation,
in physics, change of a substance from the gaseous (vapor) to the liquid state (see states of matter). Condensation is the reverse of vaporization, or change from liquid to gas.
..... Click the link for more information. . For a substance going directly from the solid to the gas state, or the reverse, the heat absorbed or given up is known as the latent heat of sublimationsublimation
, change of a solid substance directly to a vapor without first passing through the liquid state. The term is also used to describe the reverse process of the gas changing directly to the solid again upon cooling.
..... Click the link for more information. .latent heat[′lāt·əŋt ′hēt] (thermodynamics) The amount of heat absorbed or evolved by 1 mole, or a unit mass, of a substance during a change of state (such as fusion, sublimation or vaporization) at constant temperature and pressure. latent heatThe amount of heat which is absorbed or evolved in changing the state of a substance without changing its temperature, e.g., in freezing or vaporizing water.latent heat
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 heatthe 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 heatThe caloric or heat energy absorbed by matter changing from solid to liquid or from liquid to vapor with no change in temperature. See also: heatAcronymsSeeleft handlatent heat
Related to latent heat: Latent heat of fusion, Latent heat of vaporizationSynonyms for latent heatnoun heat absorbed or radiated during a change of phase at a constant temperature and pressureSynonymsRelated Words- heat
- heat energy
- heat of condensation
- heat of fusion
- heat of solidification
- heat of sublimation
- heat of vaporisation
- heat of vaporization
|