Abstract
An effective device for the collection of solar energy is the so-called parabolic-cylindrical solar collector. In this device, a circular receiver tube is enclosed by a concentric glass envelope and situated along the focal line of a parabolic trough reflector. The heat transfer processes which occur in the annular space between the receiver tube and the glass envelope are important in determining the overall heat loss from the receiver tube. In typical high temperature receiver tube designs the rate of energy loss by combined thermal conduction and natural convection is of the same order of magnitude as that due to thermal radiation, and can amount to approximately 6% of the total rate at which energy is absorbed by the solar collector. The elimination of conduction and natural convection losses can significantly improve the performance of a large collector field.
This work was supported by the United States Department of Energy.
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Abbreviations
- a:
-
accommodation coefficient
- g:
-
acceleration of gravity
- k:
-
thermal conductivity
- kef :
-
effective thermal conductivity
- L:
-
length of receiver tube
- ℓ,Δr:
-
gap size
- NRa :
-
Rayleigh number
- P:
-
pressure
- Q:
-
heat loss
- ro :
-
inner radius of glass envelope
- ri :
-
outer radius of receiver tube
- ΔT:
-
temperature difference
- α:
-
thermal diffusivity
- β:
-
coefficient of volumetric thermal expansion
- δ:
-
molecular diameter
- ε:
-
eccentricity
- εir :
-
thermal emissivity
- γ:
-
ratio of specific heats
- λ:
-
mean free path
- μ:
-
dynamic viscosity
- ρ:
-
density
References
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Ortabasi, U., “Indoor Test Methods to Determine the Effect of Vacuum on the Performance of a Tubular Flat Plate Collector,” ASME Paper 76-WASOL-24.
Kraussold, H., “Wärmeabgabe von zylindrischen Flüssigkeitsschichten bei natürlicher Konvektion,” Forsch Hft. Ver. Dt. Ing., Vol. 5, No. 4, 1934, pp. 186–191.
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Gartling, D. K., “Convective Heat Transfer by the Finite Element Method,” Comp. Meth. Appl. Mech. Eng., (to appear in 1977).
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© 1978 Purdue Research Foundation
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Ratzel, A.C., Hickox, C.E., Gartling, D.K. (1978). Energy Loss by Thermal Conduction and Natural Convection in Annular Solar Receivers. In: Mirkovich, V.V. (eds) Thermal Conductivity 15. Springer, Boston, MA. https://doi.org/10.1007/978-1-4615-9083-5_46
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DOI: https://doi.org/10.1007/978-1-4615-9083-5_46
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