Coefficient of thermal conductivity of air

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2018-03-18 20:36:12

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Joseph black in the distant 1754 empirically proved to the world that the earth's atmosphere (i.e., air) is composed of a mixture of different gases, the main ones being oxygen and nitrogen. He also entered such concept, as coefficient of thermal conductivity of air.

All living organisms on earth to the existence of air is required, rather, the basis of air - oxygen. The ongoing process of oxidation oxygen entering the body from the ambient air, produce energy, without which there is no continuation of life.

Oxygen is widely used in manufacturing and in daily life - while burning there is an allocation of fuel, and internal combustion engines - mechanical energy. By its liquefaction produces noble gases.

The Composition of atmospheric air has a significant impact on the lives and health of every person. The perfect (“correct”), the composition contains 75% nitrogen, 24% oxygen and a small admixture of various gases - methane, neon, krypton, hydrogen, carbon dioxide, etc.

The Presence of industrial enterprises, increase in the number of vehicles emitted into the atmosphere millions of biological and chemical particles (aldehydes, ammonia, oxides of heavy metals), significantly pollute the atmosphere, and the conductivity of the air decreases, which adversely affect living organisms. Emissions from automobile motors (they are in the air of large cities is not less than 60 percent) are most harmful for the human body. Second place belongs to thermal power plants pollution, the third is the chemical industry.

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The Main property of air is its thermal conductivity. After conducting numerous tests and experiments, scientists were able to determine that the heat in the gas medium is distributed in three main ways: thermal radiation (the electromagnetic-wave transfer of energy), convection (movement of energy flows through the motion of layers of gas in space),thermal conductivity ( chaotic motion of molecules that contribute to the reception of heat from the layer of gas with higher temperature to less than “warm”layer of gas). In the process of heat transfer molecule that contains more energy, transfer it to the molecules with lower energy content. Characterized by the ability to conduct heat is a physical parameter coefficient of thermal conductivity of air. The thermal conductivity coefficient of air is determined by the equation:

λ= -d2Qt/gt/gn*dF*dt.

Coefficient of thermal conductivity of air is numerically equal to the quantity of heat passing over a period of time through a unit of isothermal surfaces with concomitant condition that gradt=1. Its direct dimension value is considered as the ratio of W/(m·K).

The results of the tests and experiments created cross-reference table by which we can determine the values of the coefficient of thermal conductivity of air and other substances. For most substances, the heat transfer coefficient can be represented as linear functions

λ= λ0 *[1+b*(t-to)]

Where λ0 is the value of the coefficient acting on the thermal conductivity at t0=0 degrees Celsius;

B — constant determined experimentally.

Worst of all gases conduct heat. The heat transfer coefficient of gases increases with increasing temperature and is 0,006÷0.6 W/(m·K), where the upper value belongs to helium and hydrogen. Their direct conductivity, five, and even ten times higher than in other gases. The heat transfer coefficient of air at zero degrees Celsius is equal to 0,0243 W/(m·K).

The Amount of heat transported by layers of gas in the heat exchange process, if the temperature difference over a period of time constant, determined by the law of the famous scientist Fourier.


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Alin Trodden - author of the article, editor
"Hi, I'm Alin Trodden. I write texts, read books, and look for impressions. And I'm not bad at telling you about it. I am always happy to participate in interesting projects."

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