上海交通大学：《生物传热学教与学 Bioheat Transfer》课程教学资源（电子讲义）lecture 7 Radiation Between Surfaces

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 .8m  K Sun, at 5800K, as black body, max  C3 / 5800K  0.5m 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  