How to calculate the surface thermal radiation force

1. Q = QR + QA + QD
1 = QR / Q + QA / Q + QD / Q
= R + A + d
R -- reflectivity; A -- absorptivity; D -- transmittance
when the absorptivity a = 1, it indicates that the object can absorb all the heat rays projected on its surface, which is called absolute blackbody
when the reflectivity r = 1, it indicates that the object can reflect all the heat rays projected on its surface, which is called absolute white body, or white body for short
when it is mirror reflection (incidence angle = reflection angle), it is called mirror body
when d = 1, it is called absolute transparent body, or transparent body for short, also known as dielectric and diathermal body.

2. Yes, blackbody radiation is also thermal radiation. Radiation mainly occurs on the surface of an object. In real life, a cavity object with a small hole made of opaque material is often used as a blackbody model. The electromagnetic wave emitted from the small hole into the cavity is absorbed and reflected many times on the inner wall of the cavity, and only a small part of the energy is emitted from the small hole, The object that can absorb all the electromagnetic waves of various wavelengths projected on its surface without reflection and projection is called blackbody. The radiation and absorption of blackbody are mainly on the surface. In nature, blackbody does not exist. It can be considered that the small holes in the cavity are equivalent to the surface of blackbody, and the thermal radiation is also mainly on the surface of the object. Therefore, the radiation on the surface of blackbody is stronger than that inside

3. I suggest you take a look at the content of blackbody radiation in college physics. I can't remember the specific formula, so I should read the relevant contents σ It's a formula. I hope I can help you

4. Solar constant * 4 π R ^ 2 (R is the distance between the sun and the earth)
total solar radiation flux / 4 π R ^ 2 (R is the radius of the solar line) to get the solar radiation emittance π R ^ 2 is the surface area formula of the ball

5.

Law of calculation: according to the basic law of infrared radiation, when the surface radiation coefficient of a measured object is fixed, its radiation power is proportional to the fourth power of its absolute temperature T

Relevant factors of radiation power: the radiation power of an object is closely related to its material, structure, size, shape, surface properties, heating conditions, surrounding environment and whether there are faults and defects in it. When other conditions of the measured object remain unchanged, only faults and defects occur, then the surface temperature field distribution will change accordingly; If the material properties of the object to be measured are abnormal, the surface temperature will change accordingly. Therefore, the application of infrared temperature detection can provide excellent information for analyzing the existing state of the object to be measured

radiation coefficient ε Importance in infrared temperature measurement an important parameter in infrared temperature measurement is emissivity. It directly affects the temperature measurement results, also known as "emissivity" or radiation coefficient

The emissivity of an object is a parameter that characterizes the radiation ability of the surface of an object. It is the ratio of the heat energy radiated by the object at a certain temperature to that radiated by the blackbody at the same temperature. In infrared temperature measurement, only after the emissivity of the object in the measured temperature range is determined can the surface temperature of the object be obtained by optical or electronic compensation. If we know nothing about the value of C, we can not determine the difference between the temperature measurement results and the real temperature. If there is an error in the set radiation coefficient, the error will be caused to the temperature measurement results. The analysis is as follows:

let the surface temperature of a measured object be T0, and the real radiation coefficient be 0 ε 0, the measured temperature is T1, and the set radiation coefficient is 0 ε 1, then

radiation energy W= ε 0 δ 6T04= ε one δ T14

temperature measurement error △ t = | t1-t0 |

radiation coefficient setting error: △ t ε=|ε 1- ε 0 |

then △ t = t0 [1 - (1 - △ ε/ε 1)]1/4

△T/T0=1-(1-△ ε/ε 1) 1 / 4

results show the relationship between relative error of temperature measurement and relative error of radiation, and the calculation results are listed in table 12-3

6. Blackbody radiation
Open classification: Science, physics, nature, natural phenomena, quantum mechanics

[Chinese]: blackbody radiation
[English]: blacd body radiation

any object has the ability to continuously radiate, absorb and emit electromagnetic waves. The radiated electromagnetic wave is different in each band, that is, it has a certain spectral distribution. This kind of spectrum distribution is related to the characteristics of the object itself and its temperature, so it is called thermal radiation. In order to study the law of thermal radiation which does not depend on the specific physical properties of matter, physicists defined an ideal object, black body, as the standard object of thermal radiation research

the so-called black body means that all the incident electromagnetic waves are absorbed, neither reflected nor transmitted (of course, the black body still radiates outwards). A black hole may be an ideal blackbody.

according to Kirchhoff's law of radiation, the ratio of the energy radiated and absorbed by an object in thermal equilibrium has nothing to do with the physical properties of the object itself, but only with the wavelength and temperature. According to Kirchhoff's radiation law, at a certain temperature, the blackbody must be the object with the greatest radiation ability, which can be called the complete radiator

Planck's radiation law gives the specific spectral distribution of blackbody radiation. At a certain temperature, the energy radiated by a unit area blackbody in unit time, unit solid angle and unit wavelength interval is

B λ， T)=2hc2 / λ 5 ·1/exp(hc/ λ RT)-1

B( λ， T) - spectral radiance of blackbody (W, m-2, SR-1, μ M-1)
blackbody spectral emissivity M λ， T) The formula of the relationship between wavelength and thermodynamic temperature:
m = C1/[ λ^ 5(exp(c2/ λ T) 1), where C1 = 2 π HC ^ 2, C2 = HC / K.
blackbody energy density formula:
e * D ν= C1 * V ^ 3 * DV / [exp (C2 * V / T) - 1)]
e * DV represents the blackbody radiation energy density in the frequency range (V, V + DV)< br /> λ— Radiation wavelength μ m)

t-absolute temperature of blackbody (k, t = t + 273k)

c-speed of light (2.998 × 108 m · s-1)

h-planck constant, 6.626 × 10-34 J · s

k-boltzmann constant, 1.380 × The basic physical constants of 10-23 J · k-1 are

as can be seen from Figure 2.2:

① at a certain temperature, there is an extreme value of spectral radiance of blackbody, and the position of the extreme value is related to temperature, which is Wien's law of displacement

λ m T=2.898 × 103 ( μ m·K)

λ M - wavelength at the maximum blackbody spectral radiance μ m)

t-absolute temperature (k) of blackbody, λ m ～0.48 μ M (green). This is the approximate maximum spectral radiance of solar radiation

when t ~ 300K, λ m～9.6 μ m. This is the approximate maximum spectral radiance of the earth's object radiation

② at any wavelength, the spectral radiance of high temperature blackbody is absolutely greater than that of low temperature blackbody, regardless of whether this wavelength is the maximum spectral radiance

If b λ， T) By integrating all wavelengths and all radiation directions, Stefan Boltzmann law can be obtained. The total energy radiated by a blackbody with absolute temperature T in each direction of space in unit time is B (T)

b (T)= δ T4 (W·m-2 )

δ Is Stefan Boltzmann constant, equal to 5.67 × 10-8 w · m-2 · K-4

but there is no such ideal blackbody in the real world, so what can be used to describe the difference? For any wavelength, the emissivity is defined as the ratio of the radiation energy of the real object to that of the blackbody at the same temperature within a tiny wavelength interval of the wavelength. Obviously, emissivity is a positive number between 0 and 1. Generally, emissivity depends on material properties, environmental factors and observation conditions. If the emissivity has nothing to do with the wavelength, the object can be called grey body, otherwise it is called selective radiator

I don't know why the sun can also be calculated as a blackbody, it is so bright...
(blackbody's & quot; Black & quot; It's really about color!)

7. The heat radiation of a heat generator is directly proportional to the quartic equation of its surface temperature (absolute temperature, i.e. Kjeldahl temperature).

8. The heat always radiates from the high temperature object to the low temperature object. The way that the object directly radiates energy e to its own temperature is called thermal radiation. The higher the temperature is, the stronger the radiation is. The radiation energy satisfies the equation w = ks1s2 (T1-T2) / R2, where k is the thermal radiation constant, T1-T2 is the temperature difference, S1 is the area of high temperature object, S2 is the area of low temperature object, and R is the distance between two objects

Basic Law of thermal radiation:
1. Blackbody radiation law
blackbody has the largest absorption force α= 1) At the same time, it also has the maximum radiation force ε= 1)
there is no absolute blackbody in the real object, so the artificial blackbody is introced, and almost all the incident energy is absorbed by the cavity. The radiation field system in the cavity is composed of the emission and reflection of the cavity surface. It is isotropic and must have the same properties as the radiation selected from the small hole< Second, Planck's law describes the variation of monochromatic radiation force with wavelength and temperature. At a certain temperature, the radiation energy of blackbody is different in different wavelength range< (3) Stefan Boltzmann law
EB= σ bT4W/m2< br /> σ B = 5.67 * 10-8w / (m2k4)
the variation of blackbody radiation force with surface temperature is described. The radiation force in a certain wavelength range can also be calculated< Fourth, Lambert's cosine law includes the following contents:
in hemispheric space, the radiation intensity of blackbody is independent of direction. The surface with the same radiation direction is called diffuse radiation surface. The radiation force on a diffuse surface is a function of radiation intensity π Times< The maximum monochromatic radiation force EB increases with the increase of temperature T λ, The peak wavelength corresponding to max λ Max graally moves to the direction of short wave. λ maxT=2897.6 μ K

9. The instrial revolution, which first started in England in the 1830s, promoted the unprecedented development of proctive forces. The development of proctive forces has opened up a broad road for the development and growth of natural science. The subject of heat transfer is developed in this background
the two basic heat transfer modes of heat conction and convection have been known for a long time. The third heat transfer mode was confirmed by the discovery of infrared ray in 1803, which is the heat radiation mode. The establishment of the three basic theories has gone through their own unique process. It was not until the beginning of the 20th century that heat transfer became an independent discipline. At present, through the study of heat conction, convection and radiation, heat transfer has a relatively complete theoretical basis and formed a relatively mature discipline system
at the beginning of the 19th century, Lambert, bealwood and Fourier all started their research from the experimental study of one-dimensional heat conction of solids. In 1804, according to the experiment, bealwood put forward a formula that the heat conction per unit area per unit time is positively proportional to the temperature difference on both sides of the surface, and inversely proportional to the wall thickness. The proportional coefficient is the physical property of the material. This formula improves the understanding of the law of heat conction, but it is a little rough. Fourier in the experimental research at the same time, attaches great importance to the use of mathematical tools, very characteristic. He constantly improved his theoretical formula from the comparison of theoretical solution and experiment, and made remarkable progress. In 1807, he proposed the separation of variables method for solving field differential equations and the concept that the solution can be expressed as a series of arbitrary functions, which has been paid attention to by the academic circles. In 1812, the French Academy of Sciences set up a competition prize with the title of "the mathematical theory of the law of heat transfer and the comparison between theoretical results and accurate experiments". After efforts, Fourier published his famous work "analytical theory of heat" in 1822, and successfully completed the task of establishing the theory of heat conction. His heat conction law correctly summarizes the results of heat conction experiment, now known as Fourier's law, which lays the foundation of heat conction theory. Fourier is recognized as the founder of heat conction theory
the theory of fluid flow is a necessary prerequisite for the theory of convective heat transfer. Navier's flow equation in 1823 can be applied to incompressible fluid. This equation was improved to Navier Stokes equation by Stokes in 1845, and the task of establishing the basic equation of fluid flow was completed. In 1880, Reynolds put forward a non dimensional physical quantity group which has a decisive influence on the flow. From 1880 to 1883, Reynolds carried out a large number of experimental studies. It was found that the transition of flow layer to turbulent flow occurred between the Reynolds number of 1800 and 2000, which clarified the confusion between the experimental results and made a significant contribution to guiding the experimental research. The breakthrough is e to the contributions of two papers written by Nusselt in 1909 and 1915. He made dimensional analysis on the basic differential equations and boundary conditions of forced convection and natural convection, and obtained the principle relationship between dimensionless numbers. Under the guidance of the principle of dimensionless number, a basic method of solving the problem of convective heat transfer through experimental research is developed, which greatly promotes the development of the research of convective heat transfer. In 1921, inspired by the concept of flow boundary layer, bohausen introced the concept of thermal boundary layer. In 1930, in cooperation with Schmidt and Beckman, he successfully solved the natural convection heat transfer of the air near the vertical wall. Prandtl analogy in 1925, Carmen analogy in 1939 and Martinelli's extension in 1947 record the track of early development. Due to the importance of turbulence in application, the research of turbulence calculation model has developed rapidly with the deepening of the understanding of turbulence mechanism, and has graally become a hot topic in heat transfer research. It also strongly promotes the development of theoretical solution. It should also be mentioned that in the modern development of convective heat transfer theory, McAdam, Bert and Eckert have made important contributions
in the early research of thermal radiation, it is very important to understand the importance of blackbody radiation and to use artificial blackbody for experimental research to establish the theory of thermal radiation. In 1889, LUMO et al. Measured the experimental data of spectral energy distribution of blackbody radiation. At the end of the 19th century, J. Stefan established the rule that the radiation force of blackbody is proportional to the fourth power of its absolute temperature according to the experiment, which was later confirmed by Boltzmann in theory. This law is called Stephen Boltzmann law. The biggest challenge in the basic theory of thermal radiation is to determine the spectral energy distribution of blackbody radiation. In 1896, Wien deced a formula by semi theoretical and semi empirical method. Although the formula is in good agreement with the experiment in the short wave band, it is not in good agreement with the experiment in the long wave band. A few years later, Rayleigh derived a formula theoretically. This formula was improved by Jenkins in 1905, and later people called it Rayleigh Jenkins formula. This formula is in good agreement with the experimental results in the long wave band, but it is far from the experimental results in the short wave band, and with the increase of frequency, the radiation energy will increase to infinity, which is obviously very absurd. Rayleigh - gins formula has encountered insurmountable difficulties in the high frequency part, that is, the ultraviolet part. It is a theoretical disaster, so it is called "ultraviolet disaster"“ The appearance of "ultraviolet disaster" makes people strongly realize that there are problems in the classical physics theory which was originally thought to be quite perfect. The solution of the problem depends on a new breakthrough in concept. Planck is determined to find a new formula which is consistent with the experimental results. After hard work, he finally put forward a formula in 1900. The subsequent experiments show that the Planck formula is completely consistent with the actual situation in the whole spectrum. In seeking the physical explanation of this formula, he boldly put forward a new hypothesis, which is fundamentally different from the concept of continuity in classical physics, that is, the Energon hypothesis. According to the Planck's law established by quantum theory, the law of spectral distribution of blackbody radiation energy is correctly revealed, which lays the foundation of thermal radiation theory. In 1935, Pollock referred to the net radiation method proposed by business settlement, the exchange factor method proposed by hotel in 1954 and improved in 1967, and the simulated network method proposed by Oppenheim in 1956, which are three important calculation methods. They have contributed to the improvement of the calculation method of such complex problems
for more than 100 years, heat transfer researchers have carried out extensive and in-depth research on heat transfer phenomena, published a large number of scientific works and research reports, and published a large number of valuable academic monographs. The research results have been widely used in instry, agriculture, space, biotechnology and other fields, and have proced significant economic benefits in improving heat transfer efficiency, recing material consumption and proct cost. It is of great significance to summarize and summarize the existing work, including the basic concepts and laws of heat transfer, and point out the existing problems and the future development direction. In a word, heat transfer itself is a basic interdisciplinary subject of cross instry professional technology, which is mainly in the fields of Mathematics (mainly differential equation theory), thermodynamics, thermodynamics, heat transfer and so on It is developed on the basis of fluid mechanics and quantum mechanics, and it must also be based on experiments. Therefore, on the one hand, the development of heat transfer depends on the progress of mathematics, thermodynamics, fluid mechanics and quantum mechanics, on the other hand, it also needs the continuous development of scientific measurement technology