Thermal equilibrium refers to the condition that the internal temperature of an object in contact with the outside world is uniform everywhere and equal to the outside temperature.In heat balance, there is no heat exchange between parts of the object and the outside world.In thermal engineering and chemistry, if the heat absorbed and released by an object at the same time exactly offset each other, the object is also in thermal balance.[1]
If there is no heat transfer between the components of a single system and no heat transfer with the outside world, the system is in heat balance.At this time, the temperature of each part of the system is equal to the external temperature.
Between two systems
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A system in any equilibrium state is called thermal contact (orheat exchange）。TwoThermodynamic systemDuring thermal contact, the originalEquilibrium stateGenerally, it will change;After a long enough time, the heat exchange stops;At this time, it can be considered that the two systems are in thermal equilibrium.If the state of the two systems does not change when they are in thermal contact, it means that the two systems are already hot to each otherbalanceOf.It can be considered that the two systems, which are in heat balance with each other, have the same cold and hot degree and the same temperature.
Between the three systems
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If A, B, and C are in an arbitrarily determinedEquilibrium stateSystem A and system B are mutually adiabatic.Let A and B contact with system C at the same time. After a long enough time, both A and B will reach thermal contact with Cbalance。At this time, A and B are no longer adiabatic and are in thermal contact with each other. Experiments show that the states of A and B are unchanged, that is, A and B are also in thermal equilibrium.This experimental fact shows that if twoThermodynamic systemIf they are in thermal equilibrium with the third thermodynamic system, they must be in thermal equilibrium with each other.This experimental conclusion is called the transmissibility of heat balance, orHeat balance law。
Heat balance law
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If each of the two thermodynamic systems is in thermal equilibrium (at the same temperature) with the third thermodynamic system, they must also be in thermal equilibrium with each other.
Heat balance lawIt is a basic experimental law in thermodynamics. Its significance lies in that it is the basis for scientific definition of the concept of temperature and the basis for measuring temperature with a thermometer.In thermodynamics, temperature, internal energy and entropy are three basic factorsState function, internal energy is determined byFirst law of thermodynamicsaffirmatory;Entropy is determined byThe second law of thermodynamicsaffirmatory;The temperature is determined by the law of heat balance.So the law of heat balance, like the first law and the second law, is also the basic experimental law in thermodynamics, and its importance is no less than the first and second laws of thermodynamics. However, people realized the importance of this law only after they fully understood the first and second laws of thermodynamics, so the famous British physicist RH. Fowler calls itZeroth law of thermodynamics。[2]
Heat balance calculation
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Q release=Q suction.
Find out the ways of heat absorption of the system first, and then conduct quantitative analysis;Then find out the ways of heat release of the system, and make quantitative analysis;Finally, the heat absorbed or released by the system through a certain path is solved by using the formula of system heat balance Q release=Q absorption.
Heat balance analysis of electric furnace
Heat balance calculation is usually widely used in heat and mass transfer, refrigeration and heating, boiler calculation and other fields requiring thermal analysis.
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Heat balance of engine body
AnimalisticHeat productionandHeat dissipationEqual is heatbalance。In the process of normal metabolism, animal body continuouslyThermogenesisanddissipate heat, asThermostatic animalIn order to maintain a relatively constant body temperature and ensure that the organs and tissues of the body perform normalphysiological function。
Thermally balanced carrier
The electrons in the semiconductor are all in a certain energy band, but only the electrons in the conduction band and the holes in the valence band can participate in the conduction. They are called carriers.Under the condition of constant temperature, the number of electron holes generated per unit time is equal to the number of electron holes recombined and disappeared per unit time. At this time, the concentration of electron holes in semiconductors maintains a constant, called heat balance.[3]
