In physics and chemistry, heat is energy transferred from one body to another by thermal interactions. The transfer of energy can occur in a variety of ways, among them conduction, radiation, and convection. Heat is not a property of a system or body, but instead is always associated with a process of some kind, and is synonymous with heat flow and heat transfer.
Heat flow from high to low temperature occurs spontaneously, and is always accompanied by an increase in entropy. This flow of energy can be harnessed and partly converted into useful work by means of a heat engine. The second law of thermodynamics prohibits heat flow directly from low to high temperature, but with the aid of a heat pump external work can be used to transport internal energy indirectly from a low to a high temperature body.
Heat is a characteristic of macroscopic processes and is described by thermodynamics, but its origin and properties can be understood in terms of microscopic constituents using statistical mechanics. For instance, heat flow can occur when the rapidly vibrating molecules in a high temperature body transfer some of their energy (by direct contact, radiation exchange, or other mechanisms) to the more slowly vibrating molecules in a lower temperature body.
The SI unit of heat is the joule. Heat can be measured by calorimetry, or determined indirectly by calculations based on other quantities, relying for instance on the first law of thermodynamics. In physics, especially in calorimetry, and in meteorology, the concepts of latent heat and of sensible heat are used. Latent heat produces changes of state without temperature change, while sensible heat produces temperature change.
Read more about Heat: Overview, Microscopic Origin of Heat, History, Notation and Units, Estimation of Quantity of Heat, Internal Energy and Enthalpy, Latent and Sensible Heat, Specific Heat, Entropy, Heat Transfer in Engineering, Practical Applications, Usage of Words
Other articles related to "heat":
... Heat exchangers are widely used in industry both for cooling and heating large scale industrial processes ... The type and size of heat exchanger used can be tailored to suit a process depending on the type of fluid, its phase, temperature, density, viscosity, pressures, chemical composition and various ... In many industrial processes there is waste of energy or a heat stream that is being exhausted, heat exchangers can be used to recover this heat and put it to use by heating a different stream in the process ...
... The carotid rete is a counter-current heat exchanging organ in some ungulates ... brain, flows via a network of vessels where heat is discharged to the veins of cooler blood descending from the nasal passages ... rest of the body, and therefore aids in tolerating bursts in metabolic heat production such as associated with outrunning cheetahs (during which the body temperature exceeds the maximum ...
... metal from ore (smelting) or in oil refineries and other chemical plants, for example as the heat source for fractional distillation columns ... to a direct fired heater, used in boiler applications in chemical industries or for providing heat to chemical reactions for processes like cracking, and is part of the standard English names for many ... The heat energy to fuel a furnace may be supplied directly by fuel combustion, by electricity such as the electric arc furnace, or through induction heating in induction furnaces ...
... Further information Countercurrent exchange in biological systems "Countercurrent" heat exchangers occur naturally in the circulation system of fish, whales and other marine mammals ... causing the warm arterial blood to exchange heat with the cold venous blood ... This reduces the overall heat loss in cold waters ...
... A heat exchanger is a piece of equipment built for efficient heat transfer from one medium to another ... The classic example of a heat exchanger is found in an internal combustion engine in which a circulating fluid known as engine coolant flows through radiator coils and air flows past the coils, which cools ...
Famous quotes containing the word heat:
“She knows the heat of a luxurious bed.
Her blush is guiltiness, not modesty.”
—William Shakespeare (15641616)
“As in hoary winters night stood shivering in the snow,
Surprised I was with sudden heat which made my heart to glow;
And lifting up a fearful eye to view what fire was near,
A pretty Babe all burning bright did in the air appear;”
—Robert Southwell (1561?1595)
“Nowadays men cannot love seven night but they must have all their desires: that love may not endure by reason; for where they be soon accorded and hasty, heat soon it cooleth. Right so fareth love nowadays, soon hot soon cold: this is no stability. But the old love was not so.”
—Thomas Malory (c. 14301471)