Measuring Optical and Thermal Properties of High Temperature Receivers

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Measuring Optical and Thermal Properties of High

Temperature Receivers

Johannes Pernpeintner, Thomas Fend

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Part I:

Thermal properties of receivers for

SOLAR TOWER TECHNOLOGY

 Thomas Fend

Part II:

Optical and thermal properties of tube receivers for

PARABOLIC TROUGH TECHNOLOGY

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Why Solar Tower Technology?

• Higher losses at higher temperatures

• Higher concentration ratio

• Efficiency limited by thermal engine

• Higher temperatures – higher

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Receivers for Solar Tower Technology

• volumetric receivers

• tube receivers

• direct medium receivers

• …

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Tube Receivers

• absorption on outer tube surface

• transport of heat through tube wall to a medium

• media: liquid salt, liquid metal, water, air

‐ thermal resistance

‐ non homogeneous heating

‐ tube surface temperature is higher than medium temperature

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Tube Receivers

Solar Two

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Tube Receivers

Source: torresolenergy

Gemasolar

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Tube Receivers

PS10/PS20

Source: desertec UK

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Volumetric Receivers

• Radiation absorbed in the porous volume of the receiver

• Front temperature lower than medium temperature

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Volumetric Receivers

0.8 mm 2 mm

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Volumetric Receivers

Solar Tower Jülich Tower: 60m 2153 Heliostats (8.2 m²) 22.7 m² receiver aperture 1 h thermal storage 500°C/ 30 bar 1.5 MW_elturbine

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Thermal Performance Prediction

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Thermal Performance Prediction

• Absorption

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Thermal Performance Prediction

• Absorption

• Conductive resistance in tube wall • Convective resistance

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Thermal Performance Prediction

• Absorption

• Conductive resistance in tube wall • Convective resistance

 tables

 standard techniques

 optimization of process by

geometry and thermal properties of the employed material

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Thermal Performance Prediction: Heat

Transfer Enhancing Concepts

• Increased heat transfer surface

• Enhanced heat transfer by gradation in radial direction

• Thermal properties of porous material needed

• Proposed in Korean/Swiss/German project CMC4CSP

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Thermal Performance Prediction:

Volumetric Receiver

• Conductive resistance and

• Convective resistance in porous

volume

 Advanced experimental techniques necessary if non uniform pore

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Thermal Performance Prediction

volume

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Thermal Performance Prediction

volume

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Thermal Conductivity of Porous Materials

• Transient Plane Source Technique + Measurement of characteristic volumes + mesurement yields ‐ effective thermal conductivity ‐ effective thermal diffusivity ‐ heat capacity

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Thermal Conductivity of Porous Materials

• Transient Plane Source Technique + Measurement of characteristic volumes + mesurement yields ‐ effective thermal conductivity ‐ effective thermal diffusivity ‐ heat capacity

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Effective Thermal Conductivity of Porous

Materials: Metal Foams

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Convective Resistance in Porous Volume

0 )

(

2

_

_



_S _v _S _F eff

T



A

T



0 )

(







_v _S _F F P

A

T

dx

dT

C

m

_



• two phase approach in continuum model

• Additional term in energy equations of solid and fluid phase

A_v: volumetric convective heat transfer coefficient

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Experimental Set-Up for Volumetric

Convective Heat Transfer Coefficient

Av: AAF-method

1 x=0 x=L Absorber sample Insulation Air T(t,0) T(t,L) Heat Element DT(t,0) _DT(t,L) Df t t

‐ Air flow with alternating temperature profile induced

‐ Porous sample causes phase shift and amplitude attenuation

‐ Av determined

1. ) _{Alternating Air flow method after Younis}

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Experimental Set-Up for Volumetric

Convective Heat Transfer Coefficient

Av: AAF-method

x=0 x=L Absorber sample Insulation Air T(t,0) T(t,L) Heat Element DT(t,0) _DT(t,L) Df t t 10 mm Cordierite 20 ppi CB SiC 45 ppi

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Experimental Set-Up for Volumetric

Convective Heat Transfer Coefficient

Av: AAF-method

x=0 x=L Absorber sample Insulation Air T(t,0) T(t,L) Heat Element DT(t,0) _DT(t,L) Df t t y = 0,15x0,62 y = 0,42x0,62 y = 0,08x0,62 0 2 4 6 8 10 0 50 100 150 200 Re Nu 76 all 45 76 all 20 76 all 10

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Experimental Set-Up for Volumetric

Convective Heat Transfer Coefficient

Av: AAF-method

x=0 x=L Absorber sample Insulation Air T(t,0) T(t,L) Heat Element DT(t,0) _DT(t,L) Df t t y = 0,15x0,62 y = 0,42x0,62 y = 0,08x0,62 0 2 4 6 8 10 0 50 100 150 200 Re Nu 76 all 45 76 all 20 76 all 10 62 . 0 1 . 1

Re

8 .

4 





 PPI

n

Nu

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Experimental Set-Up for Volumetric

Convective Heat Transfer Coefficient

Av: AlAv-method

1 1. ) _{AlphaAv‐method after Brendelberger et al.} blower mass flow measurement sample beamer IR camera

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Experimental Set-Up for Volumetric

Convective Heat Transfer Coefficient

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The AlAv-method: Results on Metal

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Conclusions

• For the prediction of the thermal performance of high temperature components characteristic quantities are needed

• Transient plane Source Technique for thermal conductivity measurement

• AAF and AlAV method for volumetric convective heat transfer properties