Measuring Optical and Thermal Properties of High...

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

> 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

Why Solar Tower Technology?

• Higher losses at higher temperatures• Higher concentration ratio

• Efficiency limited by thermal engine• Higher temperatures – higher

efficiencies

Solar Tower Technology: Example

Receivers for Solar Tower Technology

• volumetric receivers• tube receivers• direct medium receivers• …

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

Tube ReceiversSolar Two

Tube Receivers

Source: torresolenergy

Gemasolar

Tube ReceiversPS10/PS20

Source: desertec UK

Volumetric Receivers

• Radiation absorbed in the porous volumeof the receiver

• Front temperature lower than medium temperature

• Medium: air, pressurized air

0.8 mm

Solar Tower Jülich

Tower: 60m2153 Heliostats (8.2 m²)22.7 m² receiver aperture1 h thermal storage500°C/ 30 bar1.5 MWel turbine

Thermal Performance Prediction

• Absorption

• Absorption• Conductive resistance in tube wall

• Absorption• Conductive resistance in tube wall• Convective resistance

tables standard techniques optimization of process by

geometry and thermal properties of the employed material

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

Thermal Performance Prediction: Volumetric Receiver

• Conductive resistance and• Convective resistance in porous

volume

Advanced experimental techniquesnecessary if non uniform poregeometries are used

volume

Thermal Conductivity of Porous Materials

• Transient Plane Source Technique+ Measurement of characteristic volumes

+ mesurement yields‐ effective thermal conductivity‐ effective thermal diffusivity‐ heat capacity

Thermal Conductivity of Porous Materials

• Transient Plane Source Technique+ Measurement of characteristic volumes

+ mesurement yields‐ effective thermal conductivity‐ effective thermal diffusivity‐ heat capacity

Effective Thermal Conductivity of Porous Materials: Metal Foams

Nickel base alloy

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

Experimental Set-Up for VolumetricConvective Heat Transfer CoefficientAv: AAF-method 1

x=0 x=L

Absorber sample

Insulation

T(t,0) T(t,L)

Heat Element

DT(t,0) DT(t,L)

‐ Air flow with alternating temperatureprofile induced

‐ Porous sample causes phase shift andamplitude attenuation

‐ Av determined

1. ) Alternating Air flow method after Younisand Viskanta

Experimental Set-Up for VolumetricConvective Heat Transfer CoefficientAv: AAF-method

x=0 x=L

Absorber sample

Insulation

T(t,0) T(t,L)

Heat Element

DT(t,0) DT(t,L)

Cordierite 20 ppi CB SiC 45 ppi

SSiC 10 ppi

x=0 x=L

Absorber sample

Insulation

T(t,0) T(t,L)

Heat Element

DT(t,0) DT(t,L)

y = 0,15x0,62

y = 0,42x0,62

y = 0,08x0,62

0 50 100 150 200Re

76 all 4576 all 2076 all 10

x=0 x=L

Absorber sample

Insulation

T(t,0) T(t,L)

Heat Element

DT(t,0) DT(t,L)

y = 0,15x0,62

y = 0,42x0,62

y = 0,08x0,62

0 50 100 150 200Re

76 all 4576 all 2076 all 10

62.01.1 Re8.4

PPInNu

Experimental Set-Up for VolumetricConvective Heat Transfer CoefficientAv: AlAv-method1

1. ) AlphaAv‐method after Brendelberger et al.

blowermass flowmeasurement

sample beamer

IR camera

Experimental Set-Up for VolumetricConvective Heat Transfer CoefficientAv: AlAv-method

The AlAv-method: Results on MetalFoams

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

Measuring Optical and Thermal Properties of High...

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