| 释义 |
specific heat
specific heatn.1. The ratio of the amount of heat required to raise the temperature of a unit mass of a substance by one unit of temperature to the amount of heat required to raise the temperature of a similar mass of a reference material, usually water, by the same amount.2. The amount of heat, measured in calories, required to raise the temperature of one gram of a substance by one Celsius degree.specif′ic heat′
n. the number of calories required to raise the temperature of one gram of a substance 1°C, or the number of Btu's per pound per degree F. [1825–35] specific heat1. The ratio of the amount of heat needed to raise the temperature of a certain amount of a substance by one degree to the amount of heat needed to raise the temperature of the same amount of a reference substance, usually water, by one degree. Because molecules of different materials have different weights and sizes, they require different amounts of energy to be heated to a given temperature. Knowing the specific heat of a material makes it possible to calculate how much energy is needed to raise the material's temperature by a given number of degrees.2. The amount of heat, measured in calories, needed to raise the temperature of one gram of a substance by one degree Celsius.Thesaurus| Noun | 1. | specific heat - the heat required to raise the temperature of one gram of a substance one degree centigradeheat, heat energy - a form of energy that is transferred by a difference in temperature |
specific heat
specific heat, ratio of the heat capacityheat capacity
or thermal capacity,
ratio of the change in heat energy of a unit mass of a substance to the change in temperature of the substance; like its melting point or boiling point, the heat capacity is a characteristic of a substance.
..... Click the link for more information. of a substance to the heat capacity of a reference substance, usually water. Heat capacity is the amount of 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. needed to change the temperature of a unit mass 1°. The heat capacity of water is 1 calorie per gram per degree Celsius (1 cal/g-°C;) or 1 British thermal unit per pound per degree Fahrenheit (1 Btu/lb-°F;). Thus, the specific heat of some other substance relative to water will be numerically equal to its heat capacity; for this reason, "specific heat" is often used when the heat capacity actually is meant. Because the heat capacities of most substances vary with changes in temperature, the temperatures of both the specified substance and the reference substance must be known in order to give a precise value for the specific heat. The heat capacity of water at 15°C; is a frequently used value. Like specific gravity, specific heat is a dimensionless quantity, i.e., a pure number having no unit of measurement associated with it.Specific heat A measure of the heat required to raise the temperature of a substance. When the heat ΔQ is added to a body of mass m, raising its temperature by ΔT, the ratio C given in Eq. (1) is defined as the heat capacity of the body. The quantity c defined in Eq. (2) is (1)  (2)  called the specific heat capacity or specific heat. A commonly used unit for heat capacity is joule · kelvin-1 ( J · K-1); for specific heat capacity, the unit joule · gram-1 · K-1 ( J · g-1 · K-1) is often used. Joule should be preferred over the unit calorie = 4.18 J. As a unit of specific heat capacity, Btu · lb-1 · °F-1 = 4.21 J · g-1 · K-1 is also still in use in English-language engineering literature. If the heat capacity is referred to the amount of substance in the body, the molar heat capacity cm results, with the unit J · mol-1 · K-1. If the volume of the body is kept constant as the energy ΔQ is added, the entire energy will go into raising its temperature. If, however, the body is kept at a constant pressure, it will change its volume, usually expanding as it is heated, thus converting some of the heat ΔQ into mechanical energy. Consequently, its temperature increase will be less than if the volume is kept constant. It is therefore necessary to distinguish between these two processes, which are identified with the subscripts V (constant volume) and p (constant pressure): CV, cV, and Cp, cp. For gases at low pressures, which obey the ideal gas law, the molar heat capacities differ by R, the molar gas constant, as given in Eq. (3), where R = 8.31 J · mol-1 · K-1; that is, the expanding gas heats up less. (3)  For solids, the difference between cpand cVis of the order of 1% of the specific heat capacities at room temperature. This small difference can often be ignored. See Heat capacity, Thermodynamic processes specific heat[spə′sif·ik ′hēt] (thermodynamics) The ratio of the amount of heat required to raise a mass of material 1 degree in temperature to the amount of heat required to raise an equal mass of a reference substance, usually water, 1 degree in temperature; both measurements are made at a reference temperature, usually at constant pressure or constant volume. The quantity of heat required to raise a unit mass of homogeneous material one degree in temperature in a specified way; it is assumed that during the process no phase or chemical change occurs. specific heatThe ratio of the quantity of heat required to raise the temperature of a given mass of any substance 1 degree to the quantity required to raise the temperature of an equal mass of water 1 degree.specific 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.spe·cif·ic heatthe amount of heat required to raise any substance through 1°C of temperature, compared with that raising the same volume of water 1°C.specific heatThe heat needed to raise the temperature of 1 g of a substance 1°C.See also: heatSee SPhT
See SPhTspecific heat
Words related to specific heatnoun the heat required to raise the temperature of one gram of a substance one degree centigradeRelated Words |