Lecture 7:Radiation Between Surfaces
Lecture 7: Radiation Between Surfaces
Introduction Definition:energy emitted by matter that is at a finite temperature Nature of thermal radiation ■ all matters radiate it is dependent on the temperature and nature of the material The Electromagnetic Spectrum
Introduction Definition: energy emitted by matter that is at a finite temperature Nature of thermal radiation all matters radiate it is dependent on the temperature and nature of the material The Electromagnetic Spectrum
X Rays Microwave Gamma rays hermal radiation 10-5 104 10-3 102 101 10 102 103 10 2(4m) FIGURE 12.3 Spectrum of electromagnetic radiation
Frequency and wavelength of the electromagnetic waves v=c/九 Transparent,semitransparent,and opaque materials Two features:spectral and directional distribution
Frequency and wavelength of the electromagnetic waves Transparent, semitransparent, and opaque materials Two features: spectral and directional distribution c /
Emissive power E,Irradiation G and Radiosity J Radiosity.J Total emissive power E 00 E(T)= E(A,T)da Incident Radiation Total irradiation G 00 G G(T)= Gi(A,T)da Total radiosity J J(T)= J(A,T)da
Emissive power E, Irradiation G and Radiosity J G E
Blackbody Radiation ▣An ideal surface Absorbs all incoming radiation; Emits the maximum radiation at the same temp. No reflection,no transmission Radiation independent of direction: diffuse emitter
Blackbody Radiation An ideal surface Absorbs all incoming radiation; Emits the maximum radiation at the same temp. No reflection, no transmission Radiation independent of direction: diffuse emitter
Continued The Plank Distribution E e9r-] C1=3.742*108w·m4/m2 C2=1.438*104um~K Whenλ=const T1一E元b↑
Continued The Plank Distribution [ 1] 5 / 1 2 b C T e C E C m K C w m m 4 2 8 4 2 1 1.438 *10 3.742 *10 / When λ=const T E,b
Continued Wien's Displacement Law AaxT=C3 C3=2897.8um·K Sun,at 5800K,as black body, =C3/5800K=0.5m Visible Range
Continued Wien’s Displacement Law maxT C3 C3 2897 .8m K Sun, at 5800K, as black body, max C3 / 5800K 0.5m Visible Range
109 visible spectral region 8 入maxT=28984mK Solar radiation 05 1 5800K 2000K 104 1000K 800K 10 300K 100K 102 103 50K 104 0.1 0.2 0.40.6 1 2 46 10 200 4060100 Wavelength,入(um) FIGURE 12.13 Spectral blackbody emissive power. Plank distribution curve
Plank distribution curve
Continued ▣Total Emissive Power E,Ead。7 0 C [exp(C2 /AT)-1] ◇Eh=OT4 g=5.67*10-8Wm2.K4
Continued Total Emissive Power 0 0 2 5 1 , [exp( / ) 1] d C T C Eb E bd 4 Eb T 8 2 4 5.67*10 W / m K