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53-465: An ember , also called a hot coal , is a hot lump of smouldering solid fuel , typically glowing , composed of greatly heated wood , coal , or other carbon -based material. Embers (hot coals) can exist within, remain after, or sometimes precede, a fire . Embers are, in some cases, as hot as the fire which created them. They radiate a substantial amount of heat long after the fire has been extinguished, and if not taken care of properly can rekindle

106-411: A thermodynamic system and its surroundings by modes other than thermodynamic work and transfer of matter. Such modes are microscopic, mainly thermal conduction , radiation , and friction , as distinct from the macroscopic modes, thermodynamic work and transfer of matter. For a closed system (transfer of matter excluded), the heat involved in a process is the difference in internal energy between

159-431: A fire that is thought to be completely extinguished and can pose a fire hazard. In order to avoid the danger of accidentally spreading a fire, many campers pour water on the embers or cover them in dirt. Alternatively, embers can be used to relight a fire after it has gone out without the need to rebuild the fire – in a conventional fireplace , a fire can easily be relit up to 12 hours after it goes out, provided that there

212-406: A large fire, with the right conditions, embers can be blown far ahead of the fire front, starting spot fires several kilometres/miles away. A number of practical measures can be undertaken by homeowners to reduce the consequences of such an " ember attack " that bombards especially wooden structures and starts property fires. Heat In thermodynamics , heat is energy in transfer between

265-665: A system absorbs heat from its surroundings, it is positive ( Q > 0 ). Heat transfer rate, or heat flow per unit time, is denoted by Q ˙ {\displaystyle {\dot {Q}}} , but it is not a time derivative of a function of state (which can also be written with the dot notation) since heat is not a function of state. Heat flux is defined as rate of heat transfer per unit cross-sectional area (watts per square metre). In common language, English 'heat' or 'warmth', just as French chaleur , German Hitze or Wärme , Latin calor , Greek θάλπος, etc. refers to either thermal energy or temperature , or

318-576: Is a tremulous ... motion of the particles of matter, which ... motion they imagined to be communicated from one body to another." John Tyndall 's Heat Considered as Mode of Motion (1863) was instrumental in popularizing the idea of heat as motion to the English-speaking public. The theory was developed in academic publications in French, English and German. Unstated distinctions between heat and “hotness” may be very old, heat seen as something dependent on

371-427: Is assessed through quantities defined in the surroundings of the body. It is supposed that such work can be assessed accurately, without error due to friction in the surroundings; friction in the body is not excluded by this definition. The adiabatic performance of work is defined in terms of adiabatic walls, which allow transfer of energy as work, but no other transfer, of energy or matter. In particular they do not allow

424-429: Is based on the work of Carathéodory (1909), referring to processes in a closed system. Carathéodory was responding to a suggestion by Max Born that he examine the logical structure of thermodynamics. The internal energy U X of a body in an arbitrary state X can be determined by amounts of work adiabatically performed by the body on its surroundings when it starts from a reference state O . Such work

477-464: Is enough space for air to circulate between the embers and the introduced fuel. They are often used for cooking, such as in charcoal barbecues . This is because embers radiate a more consistent form of heat, as opposed to an open fire, which is constantly changing along with the heat it radiates. An ember is formed when a fire has only partially burnt a piece of fuel, and there is still usable chemical energy in that piece of fuel. This happens because

530-668: Is implicitly expressed in the last sentence of his report. I successively fill'd the Vessels with one, two, three, &c. Parts of hot boiling Water, and the rest cold ... And having first observed where the Thermometer stood in cold Water, I found that its rising from that Mark ... was accurately proportional to the Quantity of hot Water in the Mixture, that is, to the Degree of Heat. In 1748, an account

583-478: Is not quite the same as defining an adiabatic transformation as one that occurs to a body enclosed by walls impermeable to radiation and conduction. He recognized calorimetry as a way of measuring quantity of heat. He recognized water as having a temperature of maximum density . This makes water unsuitable as a thermometric substance around that temperature. He intended to remind readers of why thermodynamicists preferred an absolute scale of temperature, independent of

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636-509: Is nothing but the motion of the constituent particles of objects, and in 1675, his colleague, Anglo-Irish scientist Robert Boyle repeated that this motion is what heat consists of. Heat has been discussed in ordinary language by philosophers. An example is this 1720 quote from the English philosopher John Locke : Heat , is a very brisk agitation of the insensible parts of the object, which produces in us that sensation from whence we denominate

689-620: Is often partly attributed to Thompson 's 1798 mechanical theory of heat ( An Experimental Enquiry Concerning the Source of the Heat which is Excited by Friction ), postulating a mechanical equivalent of heat . A collaboration between Nicolas Clément and Sadi Carnot ( Reflections on the Motive Power of Fire ) in the 1820s had some related thinking along similar lines. In 1842, Julius Robert Mayer frictionally generated heat in paper pulp and measured

742-421: Is reached from state O by a process with two components, one adiabatic and the other not adiabatic. For convenience one may say that the adiabatic component was the sum of work done by the body through volume change through movement of the walls while the non-adiabatic wall was temporarily rendered adiabatic, and of isochoric adiabatic work. Then the non-adiabatic component is a process of energy transfer through

795-582: Is the watt . Btu per hour (Btu/h) is sometimes used in North America and the United Kingdom - the latter for air conditioning mainly, though "Btu/h" is sometimes abbreviated to just "Btu". MBH —thousands of Btu per hour—is also common. The Btu should not be confused with the Board of Trade Unit (BTU), an obsolete UK synonym for kilowatt hour (1 kW⋅h or 3,412 Btu). The Btu is often used to express

848-554: Is used in natural gas and other industries to indicate 1,000 Btu. However, there is an ambiguity in that the metric system (SI) uses the prefix "M" to indicate ' Mega- ', one million (1,000,000). Even so, "MMbtu" is often used to indicate one million Btu particularly in the oil and gas industry. Energy analysts accustomed to the metric "k" (' kilo- ') for 1,000 are more likely to use MBtu to represent one million, especially in documents where M represents one million in other energy or cost units, such as MW, MWh and $ . The unit ' therm '

901-432: Is used to represent 100,000 Btu. A decatherm is 10 therms or one million Btu. The unit quad is commonly used to represent one quadrillion (10 ) Btu. One Btu is approximately: A Btu can be approximated as the heat produced by burning a single wooden kitchen match or as the amount of energy it takes to lift a one-pound (0.45 kg) weight 778 feet (237 m). The SI unit of power for heating and cooling systems

954-450: The British thermal unit (BTU) and the calorie . The standard unit for the rate of heating is the watt (W), defined as one joule per second. The symbol Q for heat was introduced by Rudolf Clausius and Macquorn Rankine in c.  1859 . Heat released by a system into its surroundings is by convention, as a contributor to internal energy, a negative quantity ( Q < 0 ); when

1007-430: The quantity of a hot substance, “heat”, vaguely perhaps distinct from the quality of "hotness". In 1723, the English mathematician Brook Taylor measured the temperature—the expansion of the liquid in a thermometer—of mixtures of various amounts of hot water in cold water. As expected, the increase in temperature was in proportion to the proportion of hot water in the mixture. The distinction between heat and temperature

1060-487: The 1850s to 1860s. In 1850, Clausius, responding to Joule's experimental demonstrations of heat production by friction, rejected the caloric doctrine of conservation of heat, writing: The process function Q was introduced by Rudolf Clausius in 1850. Clausius described it with the German compound Wärmemenge , translated as "amount of heat". James Clerk Maxwell in his 1871 Theory of Heat outlines four stipulations for

1113-609: The Btu that differ slightly. This reflects the fact that the temperature change of a mass of water due to the addition of a specific amount of heat (calculated in energy units, usually joules) depends slightly upon the water's initial temperature. As seen in the table below, definitions of the Btu based on different water temperatures vary by up to 0.5%. Units of kBtu are used in building energy use tracking and heating system sizing. Energy Use Index (EUI) represents kBtu per square foot of conditioned floor area. "k" stands for 1,000. The unit Mbtu

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1166-460: The United States the price of natural gas is quoted in dollars per the amount of natural gas that would give 1 million Btu (1 "MMBtu") of heat energy if burned. A Btu was originally defined as the amount of heat required to raise the temperature of one pound of liquid water by one degree Fahrenheit at a constant pressure of one atmospheric unit . There are several different definitions of

1219-441: The ball of a mercury thermometer with ether and using bellows to evaporate the ether. With each subsequent evaporation , the thermometer read a lower temperature, eventually reaching 7 °F (−14 °C). In 1756 or soon thereafter, Joseph Black, Cullen’s friend and former assistant, began an extensive study of heat. In 1760 Black realized that when two different substances of equal mass but different temperatures are mixed,

1272-403: The caloric theory of heat. To account also for changes of internal energy due to friction, and mechanical and thermodynamic work, the caloric theory was, around the end of the eighteenth century, replaced by the "mechanical" theory of heat, which is accepted today. As scientists of the early modern age began to adopt the view that matter consists of particles, a close relationship between heat and

1325-422: The changes in number of degrees in the two substances differ, though the heat gained by the cooler substance and lost by the hotter is the same. Black related an experiment conducted by Daniel Gabriel Fahrenheit on behalf of Dutch physician Herman Boerhaave . For clarity, he then described a hypothetical but realistic variant of the experiment: If equal masses of 100 °F water and 150 °F mercury are mixed,

1378-436: The conversion-efficiency of heat into electrical energy in power plants. Figures are quoted in terms of the quantity of heat in Btu required to generate 1 kW⋅h of electrical energy. A typical coal-fired power plant works at 10,500 Btu/kWh (3.1 kWh/kWh), an efficiency of 32–33%. The centigrade heat unit (CHU) is the amount of heat required to raise the temperature of one pound of water by one Celsius degree. It

1431-458: The definition of heat: In 1907, G.H. Bryan published an investigation of the foundations of thermodynamics, Thermodynamics: an Introductory Treatise dealing mainly with First Principles and their Direct Applications , B.G. Teubner, Leipzig. Bryan was writing when thermodynamics had been established empirically, but people were still interested to specify its logical structure. The 1909 work of Carathéodory also belongs to this historical era. Bryan

1484-482: The embers are actually combustion; the combustion is just not happening at a fast enough rate to create a flame . Once the embers are completely 'burned through', the remains are oxidized minerals like carbon, calcium and phosphorus. At that point they are called ashes . Embers play a large role in forest fires, wildland fires or wildland urban interface fires. Because embers are typically burnt leaves and thus small and lightweight, they can easily become airborne. During

1537-487: The final and initial states of a system, and subtracting the work done in the process. For a closed system, this is the formulation of the first law of thermodynamics . Calorimetry is measurement of quantity of energy transferred as heat by its effect on the states of interacting bodies, for example, by the amount of ice melted or by change in temperature of a body. In the International System of Units (SI),

1590-663: The following research and results to a society of professors at the University of Glasgow. Black had placed equal masses of ice at 32 °F (0 °C) and water at 33 °F (0.6 °C) respectively in two identical, well separated containers. The water and the ice were both evenly heated to 40 °F by the air in the room, which was at a constant 47 °F (8 °C). The water had therefore received 40 – 33 = 7 “degrees of heat”. The ice had been heated for 21 times longer and had therefore received 7 × 21 = 147 “degrees of heat”. The temperature of

1643-441: The heat released by respiration , by observing how this heat melted snow surrounding his apparatus. A so called ice calorimeter was used 1782–83 by Lavoisier and his colleague Pierre-Simon Laplace to measure the heat released in various chemical reactions. The heat so released melted a specific amount of ice, and the heat required for the melting of a certain amount of ice was known beforehand. The modern understanding of heat

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1696-589: The human perception of these. Later, chaleur (as used by Sadi Carnot ), 'heat', and Wärme became equivalents also as specific scientific terms at an early stage of thermodynamics. Speculation on 'heat' as a separate form of matter has a long history, involving the phlogiston theory, the caloric theory , and fire . Many careful and accurate historical experiments practically exclude friction, mechanical and thermodynamic work and matter transfer, investigating transfer of energy only by thermal conduction and radiation. Such experiments give impressive rational support to

1749-413: The ice had increased by 8 °F. The ice had now absorbed an additional 8 “degrees of heat”, which Black called sensible heat , manifest as temperature change, which could be felt and measured. 147 – 8 = 139 “degrees of heat” were also absorbed as latent heat , manifest as phase change rather than as temperature change. Black next showed that a water temperature of 176 °F

1802-408: The matter of heat than water.” In his investigations of specific heat, Black used a unit of heat he called "degrees of heat"—as opposed to just "degrees" [of temperature]. This unit was context-dependent and could only be used when circumstances were identical. It was based on change in temperature multiplied by the mass of the substance involved. If the stone and water ... were equal in bulk ...

1855-529: The motion of those particles was widely surmised, or even the equivalency of the concepts, boldly expressed by the English philosopher Francis Bacon in 1620. "It must not be thought that heat generates motion, or motion heat (though in some respects this be true), but that the very essence of heat ... is motion and nothing else." "not a ... motion of the whole, but of the small particles of the body." In The Assayer (published 1623) Galileo Galilei , in turn, described heat as an artifact of our minds. ... about

1908-534: The object hot ; so what in our sensation is heat , in the object is nothing but motion . This appears by the way, whereby heat is produc’d: for we see that the rubbing of a brass nail upon a board, will make it very hot; and the axle-trees of carts and coaches are often hot, and sometimes to a degree, that it sets them on fire, by the rubbing of the nave of the wheel upon it. When Bacon, Galileo, Hooke, Boyle and Locke wrote “heat”, they might more have referred to what we would now call “temperature”. No clear distinction

1961-408: The obvious heat source—snow melts very slowly and the temperature of the melted snow is close to its freezing point. In 1757, Black started to investigate if heat, therefore, was required for the melting of a solid, independent of any rise in temperature. As far Black knew, the general view at that time was that melting was inevitably accompanied by a small increase in temperature, and that no more heat

2014-456: The passage of energy as heat. According to this definition, work performed adiabatically is in general accompanied by friction within the thermodynamic system or body. On the other hand, according to Carathéodory (1909), there also exist non-adiabatic, diathermal walls, which are postulated to be permeable only to heat. For the definition of quantity of energy transferred as heat, it is customarily envisaged that an arbitrary state of interest Y

2067-726: The properties of a particular thermometric substance. His second chapter started with the recognition of friction as a source of heat, by Benjamin Thompson , by Humphry Davy , by Robert Mayer , and by James Prescott Joule . He stated the First Law of Thermodynamics , or Mayer–Joule Principle as follows: He wrote: He explained how the caloric theory of Lavoisier and Laplace made sense in terms of pure calorimetry, though it failed to account for conversion of work into heat by such mechanisms as friction and conduction of electricity. Having rationally defined quantity of heat, he went on to consider

2120-500: The proposition “motion is the cause of heat”... I suspect that people in general have a concept of this which is very remote from the truth. For they believe that heat is a real phenomenon, or property ... which actually resides in the material by which we feel ourselves warmed. Galileo wrote that heat and pressure are apparent properties only, caused by the movement of particles, which is a real phenomenon. In 1665, and again in 1681, English polymath Robert Hooke reiterated that heat

2173-480: The second law, including the Kelvin definition of absolute thermodynamic temperature. In section 41, he wrote: He then stated the principle of conservation of energy. He then wrote: On page 46, thinking of closed systems in thermal connection, he wrote: On page 47, still thinking of closed systems in thermal connection, he wrote: On page 48, he wrote: A celebrated and frequent definition of heat in thermodynamics

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2226-401: The temperature rise. In 1845, Joule published a paper entitled The Mechanical Equivalent of Heat , in which he specified a numerical value for the amount of mechanical work required to "produce a unit of heat", based on heat production by friction in the passage of electricity through a resistor and in the rotation of a paddle in a vat of water. The theory of classical thermodynamics matured in

2279-428: The unit of measurement for heat, as a form of energy, is the joule (J). With various other meanings, the word 'heat' is also used in engineering, and it occurs also in ordinary language, but such are not the topic of the present article. As a form of energy, heat has the unit joule (J) in the International System of Units (SI). In addition, many applied branches of engineering use other, traditional units, such as

2332-401: The usable chemical energy is so deep into the center that air (specifically oxygen) does not reach it, and it therefore does not combust (carbon-based fuel + O 2 → CO 2 + H 2 O + C + other chemicals involved). It continues to stay hot and does not lose its thermal energy quickly because combustion is still happening at a low level. The small yellow, orange and red lights often seen among

2385-419: The wall that passes only heat, newly made accessible for the purpose of this transfer, from the surroundings to the body. The change in internal energy to reach the state Y from the state O is the difference of the two amounts of energy transferred. British thermal unit While units of heat are often supplanted by energy units in scientific work, they are still used in some fields. For example, in

2438-430: The water temperature increases by 20 ° and the mercury temperature decreases by 30 ° (both arriving at 120 °F), even though the heat gained by the water and lost by the mercury is the same. This clarified the distinction between heat and temperature. It also introduced the concept of specific heat capacity , being different for different substances. Black wrote: “Quicksilver [mercury] ... has less capacity for

2491-404: The water was heated by 10 degrees, the stone ... cooled 20 degrees; but if ... the stone had only the fiftieth part of the bulk of the water, it must have been ... 1000 degrees hotter before it was plunged into the water than it is now, for otherwise it could not have communicated 10 degrees of heat to ... [the] water. It was known that when the air temperature rises above freezing—air then becoming

2544-420: Was a physicist while Carathéodory was a mathematician. Bryan started his treatise with an introductory chapter on the notions of heat and of temperature. He gives an example of where the notion of heating as raising a body's temperature contradicts the notion of heating as imparting a quantity of heat to that body. He defined an adiabatic transformation as one in which the body neither gains nor loses heat. This

2597-421: Was made between heat and temperature until the mid-18th century, nor between the internal energy of a body and the transfer of energy as heat until the mid-19th century. Locke's description of heat was repeatedly quoted by English physicist James Prescott Joule . Also the transfer of heat was explained by the motion of particles. Scottish physicist and chemist Joseph Black wrote: "Many have supposed that heat

2650-435: Was needed for the vaporization; again based on the time required. The modern value for the heat of vaporization of water would be 967 “degrees of heat” on the same scale. A calorimeter is a device used for measuring heat capacity , as well as the heat absorbed or released in chemical reactions or physical changes . In 1780, French chemist Antoine Lavoisier used such an apparatus—which he named 'calorimeter'—to investigate

2703-449: Was needed to melt an equal mass of ice until it was all 32 °F. So now 176 – 32 = 144 “degrees of heat” seemed to be needed to melt the ice. The modern value for the heat of fusion of ice would be 143 “degrees of heat” on the same scale (79.5 “degrees of heat Celsius”). Finally Black increased the temperature of and vaporized respectively two equal masses of water through even heating. He showed that 830 “degrees of heat”

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2756-670: Was published in The Edinburgh Physical and Literary Essays of an experiment by the Scottish physician and chemist William Cullen . Cullen had used an air pump to lower the pressure in a container with diethyl ether . The ether boiled, while no heat was withdrawn from it, and its temperature decreased. And in 1758 on a warm day in Cambridge , England, Benjamin Franklin and fellow scientist John Hadley experimented by continually wetting

2809-418: Was required than what the increase in temperature would require in itself. Soon, however, Black was able to show that much more heat was required during melting than could be explained by the increase in temperature alone. He was also able to show that heat is released by a liquid during its freezing; again, much more than could be explained by the decrease of its temperature alone. In 1762, Black announced

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