# C 热辐射 辐射换热（C thermal radiation for heat transfer）

C 热辐射 辐射换热（C thermal radiation for heat transfer） This paper is contributed by hdyu123156 The PPT document may not have a good browsing experience at the WAP end. It is recommended that you choose TXT, or download the source file to the native view. Heat Transfer in Heat Transfer Chapter viii radiation transfer This chapter firstly from the viewpoint of electromagnetic radiation, to realize the this mass and thermal radiation and some of the features of radiant energy transfer process, and some of the features of radiant energy transfer process, thermal radiation of a few basic law, simple calculation of radiation heat transfer. This law, the simple calculation of radiation heat transfer. The characteristics of this chapter are more basic concepts. The characteristics of this chapter are more basic concepts Liang xiu of huabei power university Heat Transfer in Heat Transfer The basic concept of § 8-1 thermal radiation One, radiation and thermal radiation Radiation is the object through the phenomenon of electromagnetic wave energy. Radiation is the object through the phenomenon of electromagnetic wave energy. Is the object through the phenomenon of electromagnetic wave energy There are many kinds of forms of radiation, there are many kinds of forms of radiation, the difference is to launch electric magnetic wave incentives, magnetic wave excitation in a different way, and external performance is the wavelength of the radiation is not the same, and absorb the radiation energy effect caused by different. After, and absorb the effect caused by different after radiation energy. Thermal radiation is object because of heat generated by the radiation. Radiation is because of thermal radiation generated by the object. It is an object because of thermal radiation generated by the role: objects absorb radiant energy turned them into their internal energy. After role: objects absorb radiant energy turned them into their internal energy. After the wavelength range: 0.1 ~ 1000 mu m wavelength range: 0.1 1000 microns Liang xiu of north China electric power university Heat Transfer in Heat Transfer Huabei power university Liang Xiujun Heat Transfer in Heat Transfer The purple blue Blue, green, huang Orange red Visible wavelength range: 0.38 visible wavelength range: 0.38 ~ 0.76 mu m mu m Liang xiu of huabei power university Heat Transfer in Heat Transfer Second, absorption, reflection and transmission absorption, Project 1, radiation surrounding object in unit time drop shot into the unit surface area on the radiation, said unit W/m. To use G, said unit W/m2. 2, absorption, reflectance and transmittance absorption ratio, absorbed by the object and absorbed by the object, reflection and transmission part of the total share respectively called projection radiation absorption than alpha, reflectance rho and transmittance tau. The alpha rho G G G + tau tau alpha + rho = 1 rho = alpha = tau = G G G Liang xiu of huabei power university Heat Transfer in Heat Transfer 4, black, white body and portholes blackbody, 1 object called a blackbody called a blackbody. Absorption than alpha = 1 object called a blackbody. 1 objects called white body or the lens body). The object is called white body (reflectance rho = 1 object called a white body (or mirror). 1 object called a transparent body called portholes, transmittance tau = 1 object called a transparent body. Black and white body and portholes are ideal objects, bold in the nature, white body and portholes are ideal objects, Does not exist, the main studies law of radiation use them as reference. Do not exist, mainly use them as reference of the research on the rules of radiation. Especially the concept of blackbody, especially the concept of blackbody, is the theoretical basis of the thermal radiation research and engineering application. The theoretical basis. Huabei power university Liang Xiujun Heat Transfer in Heat Transfer About the color of the object We can see the object color is due to the monochromatic light (radiation) from the surface into our eyes. Monochromatic light (radiation) into our eyes. The radiation from the surface may be its own launch, and the radiation from the surface may be its own launch, can also be to visible light is reflected in its surface. Visible light is reflected in its surface. Huabei power university Liang Xiujun Heat Transfer in Heat Transfer Iii. Radiation strength and radiation intensity 1, the spectral radiation Objects in unit time per unit area to the hemisphere space launch all direction from lambda to + wavelength, radiant energy, called spectral radiation emission from to lambda + d lambda wavelength of radiant energy is called spectral radiation, said unit for W/m, E lambda said with symbols, unit for W/m3. 2, the objects in unit time per unit area, radiation to the hemisphere space all directions all emission wavelength range of radiation called radial force, direction of all emission wavelength range of radiant energy is called radiation, said the unit symbols for W/m E, said unit for W/m2. E = ∫ E lambda d lambda. 0 up Huabei power university Liang Xiujun Heat Transfer in Heat Transfer The fundamental laws of § 8-2 blackbody radiation One, black body and black body model Blackbody is an ideal object to absorb more than equal to 1. Black is an ideal object to absorb more than equal to 1. It is the nature of the biggest temperature radiation ability. Under the nature of the largest radiation ability. Although does not exist in nature bold, although does not exist in nature bold, but with artificial method can produce very close to the blackbody model. You can create very close to the blackbody model. Such as: cavity on the holes. The holes. Huabei power university Liang Xiujun Heat Transfer in Heat Transfer The temperature of the cavity wall should be uniform, the temperature of the cavity wall should be uniform, the area of the holes for as far as possible small. Total area as far as possible little. Holes in the actual surface absorption ratio on the impact is not big. This impact is not big. Liang xiu of huabei power university Heat Transfer in Heat Transfer The basic rule of blackbody radiation law is summed up in three - the basic rule of blackbody radiation law is summed up in three - Planck s law, stefan boltzmann s law and linkbase specific Planck s law, Planck s law Stefan respectively introduce below. Law. The following is introduced respectively. Two, Planck s law Planck in 1900 (the Planck) in 1900, the Planck (M.P lanck) on the basis of the quantum hypothesis, theoretically determine of the blackbody radiation spectrum distribution, based on the theoretically determine of the blackbody radiation spectrum distribution, also is the Planck s law. So that s the Planck s law. 5 C1 lambda sub b lambda lambda is equal to f of T, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, lambda, Planck s first constant, 742 times Planck s first constant, C2 - Planck s second constant, C2 = 1.439 x 10-2 mK. Planck s second constant, 439 times Planck s second constant Liang xiu of huabei power university Heat Transfer in Heat Transfer According to the black radiation curve, the following pattern can be obtained by the black body radiation curve: (1) the higher the temperature, the greater the radiation force of the spectra. At a certain temperature, the spectral radiation force of the blackbody changes with the wavelength, and at a certain wavelength, it has a maximum. Continuous change, with a maximum at a certain wavelength; With the increase of temperature, (3) with the increase of temperature, radiation spectrum to achieve the maximum wave Max becomes more and more small Namely in the lambda. More and more small, long lambda Max becomes more and more small, the position in the lambda coordinates to the short-wave direction Optical pyrometer and the principle of temperature measuring instrument, optical pyrometer and the principle of temperature measuring instrument. Mobile. Mobile. Liang xiu of huabei power university Heat Transfer in Heat Transfer Based on the rules of the black body radiation curve (3), the relation of Venn s displacement law is calculated, and the following relation is calculated according to the law (3). Lambda Max T = 2.8976 x 103 is approximately 2.9 x 103 mK Type is called Wayne displacement law. The type is called Wayne displacement law. When calculating temperature of 300 K to 5800 K respectively 300 K and maximum spectral radiation calculation temperature of 300 K and 5800 K respectively when the wavelength of the maximum spectral radiation lambda Max. The corresponding wavelength lambda Max. 2.9 x 103 m K T = 300 K, lambda Max = 9.67 m material T is equal to 5800 K, lambda Max Huabei power university 300 K 2.9 x 103 m K = = 0.5 m 5800 K Liang Xiujun Heat Transfer in Heat Transfer Three, stefan boltzmann s law Stefan blackbody radiation of the relationship between radial force and temperature follow stefan blackbody radiation of the relationship between radial force and temperature follow stefan - wave boltzmann s law:, boltzmann s law: Eb is the integral of E lambda d lambda lambda is equal to the integral 0 up up 0 Eb is equal to sigma T 4, 4 T Eb is equal to C0 100 C0 = 5.67 W/(m2 K4) Huabei power university C1 lambda 5 d lambda lambda is equal to sigma T 4 C2 / (lambda T) e 1 Sigma = 5.67 x 108 W/m2 K4. Liang Xiujun Heat Transfer in Heat Transfer The calculation of radiant force in the band range Eb is the integral of Eb lambda lambda d lambda lambda 1 lambda 2 lambda. Type in order to calculate the type, in order to calculate, first calculate the radiation (0 - lambda) accounts for the percentage of the total radiation force: force: the percentage of lambda five exabytes lambda d lambda lambda 1 c1 lambda ∫ lambda (0) = 0 F = ∫ c2 / lambda (T) lambda 4 4 0 sigma sigma b T T d e 5 lambda T 1 c1 lambda = ∫ c2 / lambda (T), d (T) lambda = F (T) lambda 5 0 sigma T e 1 blackbody radiation function table is given, and numerical. Table 8-2 blackbody radiation function table are given, namely, the value of F (T) lambda. Liang xiu of huabei power university Heat Transfer in Heat Transfer Lambda T/(mK) Fb (0 - lambda) / % Lambda T/(mK) Fb (0 - lambda) / % Huabei electric university of north China (2) 0.434 0.434 0.782 The total value of the products is estimated to be 65,000 77.66, 80.83.468.089.089.094.94.5999.7.3897.3898.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.98.89 Heat Transfer in Heat Transfer Example: calculation of solar radiation in the proportion of visible light. Examples: calculation of solar radiation in the proportion of visible light. K blackbody bold, solution: the sun can be considered as the surface temperature of blackbody T = 5762 K, the wavelength of visible light range is 0.38 0.76 0.38 to the wavelength of visible light range is 0.38 ~ 0.76 m, namely the lambda. 1 = 0.38 m, lambda 2 = 0.76 m, so Lambda. 1 t = 2190 mK Lambda 2T = 4380 mK Fb (0 lambda. 2) = 54.59% The black body radiation function table can be found Lambda Fb (0 1) = 9.94% The proportion of visible light is Fb (lambda 1 lambda 2) = Fb (0 lambda 2) Fb (0 lambda 2) = 44.65 % Liang xiu of huabei power university Heat Transfer in Heat Transfer § 8-3 of the actual object and gray body radiation For the actual radiation properties of solid and liquid is compared with black body Is The actual radiation of solid and liquid, respectively, the actual radiation of solid and liquid, respectively, with directional radiation intensity and spectral radiation temperature of blackbody, in comparison with numerical and directional radiation intensity and compared with the temperature of the blackbody numerical, from black degrees) and emissivity of epsilon (black), spectral emissivity (lambda) (monochrome black epsilon degrees) and directional emissivity epsilon (theta) directional black degrees). The concept of the concept of directional black (degrees). E epsilon = Eb Huabei power university E lambda epsilon of lambda is equal to Eb lambda L (theta) epsilon (theta) = Lb Liang Xiujun Heat Transfer in Heat Transfer 1. The spectral radiative force of the actual objects is the E lambda and the spectral emission rate epsilon (lambda). E lambda = epsilon (lambda) Eb lambda Epsilon (lambda) < 1 Huabei power university Liang Xiujun Heat Transfer in Heat Transfer The radiation and emissivity of the actual object E = epsilon Eb E of 0 epsilon of lambda d lambda d lambda epsilon is equal to the eeb sigma T 4 up In engineering, it is possible to think that the surface of the actual object will be uniformly radiated in all directions, which is diffuse. Liang xiu of huabei power university Heat Transfer in Heat Transfer 3. The spectral absorption of actual objects is more than alpha (lambda). G (lambda) alpha alpha (lambda) = G (lambda.) Huabei power university Liang Xiujun Heat Transfer in Heat Transfer The greenhouse is using glass to absorb radiation Huabei power university Liang Xiujun Heat Transfer in Heat Transfer About the color of the object of radiation emitted from the surface an object may be its own launch, radiation from the surface of the object could be launched itself, may also be a reflection of the visible light into its surface. Visible light may be reflected in its surface. If all objects absorb all kinds of visible light, it is black; If the object absorbs all kinds of visible light, it is black; If the object all reflects various visible light, it is white; If the object all reflects various visible light, it is white; If the object reflects a wavelength of visible light, only if the objects only reflects a wavelength of visible light, it will take on the colour of the reflected radiation. Take on the colour of the reflected radiation. Purple Huabei power university blue Blue, green, huang Orange red Liang Xiujun Visible wavelength range: 0.38 visible wavelength range: 0.38 ~ 0.76 mu m mu m Heat Transfer in Heat Transfer Actual object spectral absorption ratio of choice in the wavelength of the radiation with this situation caused a lot of inconvenience for engineering calculation of radiation heat transfer. Sexual selection that caused a lot of inconvenience for e