Physics of a Porous Solar Pond

概要

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A solar pond is a useful system for storing solar energy only if convection is strictly prevented. The temperature difference of 50℃ between the bottom and the top is obtained with a pond of 1 m depth in one week (radiative heating time), if conduction loss to the ground is neglected. It takes two and a half months (conduction time), however, for the pond to settle in a quasi-stationary state. Then, 90% of the solar energy flux can be utilized. The variation principle is generalized to prove that length scales of thermal conduction and viscous forces acting in a porous pond are reduced so much that the Rayleigh number may be lowered below the critical value for the onset of convection. Piles of coarse sheets of transparent artificial lawn or vertical strings or rods, one in each 4-mm-square area, will be sufficient to prevent convection. The conduction equation is solved, giving the daily variation of temperature as less than 1℃ at the bottom and negligible at the top.
社団法人応用物理学会の論文
1993-03-15