Measuring Optical and Thermal Properties of High...
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Measuring Optical and Thermal Properties of High Temperature Receivers
www.DLR.de • Folie 1 > Vortrag > Autor • Dokumentname > Datum
Johannes Pernpeintner, Thomas Fend
4th SFERA Summerschool, May 15-16, 2013, Burg Hornberg
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> Vortrag > Autor • Dokumentname > Datumwww.DLR.de • Folie 2
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
Johannes Pernpeitner
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Why Solar Tower Technology?
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• Higher losses at higher temperatures• Higher concentration ratio
• Efficiency limited by thermal engine• Higher temperatures – higher
efficiencies
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Solar Tower Technology: Example
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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 ReceiversSolar Two
• 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
Source: torresolenergy
Gemasolar
• 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 ReceiversPS10/PS20
Source: desertec UK
• 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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Volumetric Receivers
• Radiation absorbed in the porous volumeof the receiver
• Front temperature lower than medium temperature
• Medium: air, pressurized air
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Volumetric Receivers
0.8 mm
2 mm
• Radiation absorbed in the porous volumeof the receiver
• Front temperature lower than medium temperature
• Medium: air, pressurized air
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Volumetric Receivers
Solar Tower Jülich
Tower: 60m2153 Heliostats (8.2 m²)22.7 m² receiver aperture1 h thermal storage500°C/ 30 bar1.5 MWel turbine
• Radiation absorbed in the porous volumeof the receiver
• Front temperature lower than medium temperature
• Medium: air, pressurized air
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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
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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: HeatTransfer 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 techniquesnecessary if non uniform poregeometries are used
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Thermal Performance Prediction
• Conductive resistance and• Convective resistance in porous
volume
Advanced experimental techniquesnecessary if non uniform poregeometries are used
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Thermal Performance Prediction
• Conductive resistance and• Convective resistance in porous
volume
Advanced experimental techniquesnecessary if non uniform poregeometries are used
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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
Nickel base alloy
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Convective Resistance in Porous Volume
0)(2 FSvSeff TTAT
0)( FSvF
P TTAdxdTCm
• two phase approach in continuum model
• Additional term in energyequations of solid andfluid phase
Av: volumetric convectiveheat transfer coefficient
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Experimental Set-Up for VolumetricConvective Heat Transfer CoefficientAv: 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)
Dft t
‐ Air flow with alternating temperatureprofile induced
‐ Porous sample causes phase shift andamplitude attenuation
‐ Av determined
1. ) Alternating Air flow method after Younisand Viskanta
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Experimental Set-Up for VolumetricConvective Heat Transfer CoefficientAv: AAF-method
x=0 x=L
Absorber sample
Insulation
Air
T(t,0) T(t,L)
Heat Element
DT(t,0) DT(t,L)
Dft t
10 mm
Cordierite 20 ppi CB SiC 45 ppi
SSiC 10 ppi
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Experimental Set-Up for VolumetricConvective Heat Transfer CoefficientAv: AAF-method
x=0 x=L
Absorber sample
Insulation
Air
T(t,0) T(t,L)
Heat Element
DT(t,0) DT(t,L)
Dft t
y = 0,15x0,62
y = 0,42x0,62
y = 0,08x0,62
0
2
4
6
8
10
0 50 100 150 200Re
Nu
76 all 4576 all 2076 all 10
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Experimental Set-Up for VolumetricConvective Heat Transfer CoefficientAv: AAF-method
x=0 x=L
Absorber sample
Insulation
Air
T(t,0) T(t,L)
Heat Element
DT(t,0) DT(t,L)
Dft t
y = 0,15x0,62
y = 0,42x0,62
y = 0,08x0,62
0
2
4
6
8
10
0 50 100 150 200Re
Nu
76 all 4576 all 2076 all 10
62.01.1 Re8.4
PPInNu
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Experimental Set-Up for VolumetricConvective Heat Transfer CoefficientAv: AlAv-method1
1. ) AlphaAv‐method after Brendelberger et al.
blowermass flowmeasurement
sample beamer
IR camera
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Experimental Set-Up for VolumetricConvective Heat Transfer CoefficientAv: AlAv-method
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The AlAv-method: Results on MetalFoams
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Conclusions
• For the prediction of the thermal performance of high temperature components characteristic quantities areneeded
• Transient plane Source Technique for thermal conductivitymeasurement
• AAF and AlAV method for volumetric convective heat transferproperties