Joseph Black back in 1754 empirically proved to the world that the earth's atmosphere (ie, air) consists of a mixture of various gases, most important of which are oxygen and nitrogen.He also introduced a concept such as the thermal conductivity of air.
all living organisms on Earth need air to exist, or rather, the basis of air - oxygen.The ongoing process of oxidation of oxygen entering the body from the air, produces energy, without which there is no continuation of life.
Oxygen is widely used in industry and everyday life - is released during the combustion of fuel, and in internal combustion engines - mechanical energy.By its liquefaction produce the noble gases.
composition of air has a significant impact on the lives and health of each individual.Perfect ("correct") the composition contains up to 75 percent nitrogen, 24 percent oxygen, and a small admixture of different gases - methane, neon, krypton, hydrogen, carbon dioxide and others.
presence of industrial production, increase in the number of vehicles which emit into the atmosphere millions of biologicaland chemical microparticles (aldehydes, ammonia, oxides, heavy metals), considerably pollute the atmosphere, wherein the thermal conductivity of air is reduced, which negatively affects the living organisms.Emissions from the operation of automobile engines (them in the air of large cities at least 60 percent) of the most harmful to the human body.Second place belongs to thermal power units on pollution, chemical industry occupies the third.
main properties of air is its thermal conductivity.After carrying out numerous tests and experiments, scientists were able to determine that the heat in the gaseous medium is distributed in three main ways: heat radiation (electromagnetic-wave energy transfer), convection (movement of energy flows through the movement of the gas layers in space), thermal conductivity (the chaotic motion of molecules, promotingreceiving heat from the gas layer with a higher temperature to less "warm" gas layer).During heat molecules containing more energy transmitting its molecules with less energy.The characteristic ability to conduct heat is a physical parameter of the thermal conductivity of air.The thermal conductivity of air is determined by the equation:
λ = -d2Qt / gt / gn * dF * dt.
coefficient of thermal conductivity air is numerically equal to the amount of heat passing through a period of time for the unit insulated surfaces with a concomitant condition when gradt = 1.Its close dimensional value is regarded as the ratio of W / (m · K).
The results of the tests and experiments designed checklist, on which you can determine the values of the thermal conductivity of air and other agents.For most materials the heat transfer coefficient can be expressed as a linear function
λ = λ0 * [1 + b * (t-to)],
where λ0 is the value of the coefficient acting on the thermal conductivity based on t0 = 0 degrees Celsius;
b - constant, determined experimentally.
worst conductors of heat gases.The heat transfer coefficient increases with increasing gas temperature, and is 0.006 ÷ 0.6 W / (m · K), wherein the upper value belongs helium and hydrogen.Their direct thermal conductivity five or even ten times higher than that of other gases.The heat transfer coefficient of air at Zero degrees Celsius is 0.0243 W / (m · K).
amount of heat carried by gas layers during the heat when the temperature difference in a time constant, determined by the law of the well-known scholar of Fourier.
