thermal storage in packed beds: pressure drop & heat transfer k.g. allen, t.w. von backström,...
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Packed bed characteristics Prediction of packed bed characteristics: Pressure drop (apparent friction factor) Heat transfer coefficient & thermocline (temperature) Influence of: Particle shape? Roughness? Alignment? Why? Estimate cost …TRANSCRIPT
Thermal storage in packed Thermal storage in packed beds: pressure drop & heat beds: pressure drop & heat transfertransfer
K.G. Allen, T.W. von Backström, D.G. KrögerK.G. Allen, T.W. von Backström, D.G. KrögerSolar Thermal Energy Research GroupSolar Thermal Energy Research GroupUniversity of StellenboschUniversity of Stellenbosch
Energy Postgraduate Conference 2013
Packed bed thermal storage for CSP
• Store thermal energy from gas turbine exhaust or central receiver
• Stored heat (500 - 600 ºC) used for steam power cycle
Example of packed bed use: SUNSPOT combined cycle
Packed bed characteristics
Prediction of packed bed characteristics:•Pressure drop (apparent friction factor)•Heat transfer coefficient & thermocline (temperature)Influence of:Particle shape?Roughness?Alignment?
Why? Estimate cost …
Experimental work
Sample materials and test section/wind tunnel
Friction factor – crushed rockRange of values obtained…
1.3 & 4.1 mm data from Allen et al., 2013. Powder Technology 246:590-600
How does a packed bed store heat?
Ideal bed Actual bed
Temperature profile?Heat transfer – h ?
ThermoclineRock size dependent
Temperature prediction? (I)
Glass spheres; Bi ≈ 0.18; Re ≈ 490
Temperature prediction? (II)
Crushed rock (ΣVp/ΣAp = 1.3 mm); Bi ≈ 0.12; Re ≈ 280
Thermal decomposition Thermal cycling – cracking and disintegration
Availability of suitable rock?
Other considerations
Conclusion• Pressure drop
Importance of shape, roughness, alignmentNo general correlation
• Temperature profile & heat transferExisting correlations work well up to ≈ 100 ºC
Thermal radiation at higher temperatures?