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 10：Radiation

Lecture 10:Radiation

Lecture 10: Radiation

Introduction 目 Definition:energy emitted by matter that is at an infinite 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 an infinite 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 L 105 104 10-3 10-2 101 10 102 103 10 2(4m) FIGURE 12.3 Spectrum of electromagnetic radiation

Frequency and wavelength of the electromagnetic waves V=c/λ 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 ν = c / λ

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 Eba C lecstar C1=3.742*108w:4m4/m2 C2=1.438*104um·K Whenλ=const T1一EAb↑

Continued  The Plank Distribution [ 1] 5 / 1 2 − = b C T e C E λ λ λ C m K C w m m = ⋅ = ⋅ μ μ 4 2 8 4 2 1 1.438 *10 3.742 *10 / When λ=const T Eλ,b

Continued Wien's Displacement Law AT=C3 C3=2897.8,Um·K Sun,at 5800K,as black body, λ=C3/5800K=0.5m max Visible Range

Continued  Wien’s Displacement Law λmaxT = C3 C3 = 2897 .8μm ⋅ K Sun, at 5800K, as black body, λmax = C3 / 5800K = 0.5μm Visible Range

109 visible spectral region 入maxT=2898以m-K Solar radiation 10 5800K 2000K 104 1000K 800K 10 300K 100K 102 10-3 50K 104 0.1 0.2 0.40.6 1 2 46 10 20 4060100 Wavelength,入(um) FIGURE 12.13 Spectral blackbody emissive power. Plank distribution curve

 Plank distribution curve

Continued ▣Total Emissive Power E=fExda=l C exp(C2/λT)I刂 ◇E6=o4 0=5.67*10-8W/m2.K4 ▣Band Emission

Continued  Total Emissive Power  Band Emission   ∞ ∞ − = = 0 0 2 5 1 , [exp( / ) 1] λ λ λ λ λ d C T C Eb E bd 4 Eb =σT 8 2 4 = 5.67*10 W / m ⋅K − σ

Real Surface Radiation 目 Emissivity E(,T) Spectral E(T) emissivity Eō(2，T月 E(T total emissivity E=」E(,T)dM 广cE(,IdM c,Eu(,T)）d几 ￡= OT4 E(T)=OT4 e=1 Blackbody

Real Surface Radiation  Emissivity λ λ λ ε λ λ = ( , ) ( , ) E , T E T b = ε ( ) ( ) E T E T b   ∞ ∞ = = 0 , 0 ( , ) ( ) ( , ) ε λ λ λ λ λ λ λ E T d E T E T d b 4 Eb ( T ) = σT 4 0 , ( , ) T E T d b σ ε λ λ ε  λ λ ∞ = ε = 1 Blackbody total emissivity Spectral emissivity