summerschool hornberg 2013 optical and thermal ii 4.ppt · > sollab 2013 > pernpeintner...

Measuring Optical and Thermal Properties of High and Medium Temperature Absorbers II

Johannes Pernpeintner

Institute of Solar Research

> SOLLAB 2013 > Pernpeintner 2013/05/13

Outline

1. Introduction

2. Reflectance measurements with off-the-bench spectrophotometers and integration sphere- integrating sphere properties- pitfalls

3. Other methods

www.DLR.de • Folie 2


Introduction

Benz et al.: A new receiver for parabolic trough collectors, Proceedings of SolarPACES Conference 2004, Oaxaca, Mexico


Goal

- absoptance α

- emittance ε

Conservation of energy

Kirchhoffs law

1

''


Spectrometer System – Typical Reflectance Measurement

white light source


monochromator/FTIR

integration sphere

sample/ reference

detector


Integrating Spheres I

Properties of the sphere surface1. reflectance labertian

→ from 2nd reflection on sphere: homogenious flux surface of sphere

2. reflectance very high (spectralon or gold)

reflectance transmittance

22

21 4 RdAdF dd

exchange factor F


Integrating Spheres II

Calibration- measurement of reference- (measurement of sphere

multiplyer) )1(1 fAL

s

inSphere

)1(1 fM

,MA

Ls

inSphere

sphere multiplyer


Integrating Spheres III

Pitfalls1. reflectance typically not measured

as function of incidence angle


T-Runde-Almeria – Johannes Pernpeintner – 23/04/2009

Isolators

Angular distribution of thermal radiationa wet ice, b wood, c glass, d paper, e clay, f copper oxide, g gray aluminum oxide

- physical model: Fresnel equations

Ni, polished

Ni, mat

Conductors

Angular distribution of thermal radiation



conductors

isolators




as function of incidence angle2. reflectance typically not measured

as function of temperature





as function of temperature3. throughput is dependent on

reflection angle





as function of temperature3. throughput is dependent on

reflection angle4. measurement of curved surfaces


Other Methods: Other Integrating Sphere Geometries

Sample Center Mount Hemispherical illumination

Benz: Schott Absorberrohr und das DLR als Entwicklungspartner, Sonnenkolloquium2011, Jülich, Germany

Artificial sky

Te, εe

Ts, εs

Sample

Pel

Other Methods: Other Integrating Sphere Geometries

Calorimetric Emittance Measurement

Elliptical Mirror Dome


Conclusion


- Users of off-the-bench spectrophotometers should be aware of limitations of their machines

- Throughput of real integration spheres is dependent on reflection angle

- Near normal emittance is not equal to hemispherical emittance

- References should be similar to the sample in terms of reflectance and specularity

- Alternative methods exist.


Conclusion


- Users of off-the-bench spectrophotometers should be aware of limitations of their machines

- Throughput of real integration spheres is dependent on reflection angle

- Near normal emittance is not equal to hemispherical emittance

- References should be similar to the sample in terms of reflectance and specularity

- Alternative methods exist.

Thank you for your attention!


Other Methods: Hemispherical illumination

Benz: Schott Absorberrohr und das DLR als Entwicklungspartner, presentation at theSonnenkolloquium 2011, Jülich, Germany

Calorimetric Emissivity Test Bench



SPF – Solartechnik Prüfung Forschung Rapperswil



Qualtiy Engineering, Inglas – TIR100

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