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":
... Countercurrent exchange in biological systems "Countercurrent" heat exchangers occur naturally in the circulation system of fish, whales and other marine mammals ... cold blood, causing the warm arterial blood to exchange heat with the cold venous blood ... This reduces the overall heat loss in cold waters ...
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... The carotid rete is a counter-current heat exchanging organ in some ungulates ... flows via a network of vessels where heat is discharged to the veins of cooler blood descending from the nasal passages ... the rest of the body, and therefore aids in tolerating bursts in metabolic heat production such as associated with outrunning cheetahs (during which the ...
... 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 ...
... 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 ... 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 ...
Famous quotes containing the word heat:
“Glories, like glow-worms, afar off shine bright,
But looked to near, have neither heat nor light.”
—John Webster (15801625)
“And oh, I knew, I knew,
And said out loud, I couldnt bide the smother
And heat so close in; but the thought of all
The woods and town on fire by me, and all
The town turned out to fight for me that held me.”
—Robert Frost (18741963)
“Why does man freeze to death trying to reach the North Pole? Why does man drive himself to suffer the steam and heat of the Amazon? Why does he stagger his mind with the mathematics of the sky? Once the question mark has arisen in the human brain the answer must be found, if it takes a hundred years. A thousand years.”
—Walter Reisch (19031963)