tailieunhanh - Computational Fluid Mechanics and Heat Transfer Third Edition_16

Tham khảo tài liệu 'computational fluid mechanics and heat transfer third edition_16', kỹ thuật - công nghệ, điện - điện tử phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 574 Radiative heat transfer of these ideas in the mid-twentieth century major advances have been made in our knowledge of the radiative properties of gases and in the tools available for solving gas radiation problems. In particular band models of gas radiation and better measurements have led to better procedures for dealing with the total radiative properties of gases see in particular References and . Tools for dealing with radiation in complex enclosures have also improved. The most versitile of these is the previously-mentioned Monte Carlo method which can deal with nongray nondiffuse and nonisothermal walls with nongray scattering and nonisothermal gases. An extensive literature also deals with approximate analytical techniques many of which are based on the idea of a gray gas one for which 8 and are independent of wavelength. However as we have pointed out the gray gas model is not even a qualitative approximation to the properties of real Finally it is worth noting that gaseous radiation is frequently less important than one might imagine. Consider for example two flames a bright orange candle flame and a cold-blue hydrogen flame. Both have a great deal of water vapor in them as a result of oxidizing H2. But the candle will warm your hands if you place them near it and the hydrogen flame will not. Yet the temperature in the hydrogen flame is higher. It turns out that what is radiating both heat and light from the candle is soot small solid particles of almost thermally black carbon. The CO2 and H2 O in the candle flame actually contribute relatively little to radiation. Solar energy The sun The sun continually irradiates the earth at a rate of about kW. If we imagine this energy to be distributed over a circular disk with the earth s diameter the solar irradiation is about 1367 W m2 as measured by satellites above the atmosphere. Much of this energy reaches the ground where it sustains the processes of life.

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