667. 高圧気体中の介在する水平環状断熱層の伝熱特性,(I)

内外面一定温度に対する解析

抄録

Natural convective heat transfer in horizontal annular thermal insulation layer which are vital in very high temperature reactor (VHTR) piping technologies are analyzed.
The product of Rayleigh number and Darcy number RaDa and the ratio of outer and inner radius of the annular layer r₀/r_i are found to be governing parameters of the mean heat transfer characteristics.
Relatlve increase of mean effective thermal conductivity(λ_e/λ)_m is formulated from numerical analysis as follows:
(λ_e/λ)_m=0.168(r₀/r_i-0.924)(RaDa)^1/2, (1.25≤r₀/r_i≤3.0, (λ_e/λ)_m≥1).
In the region for (λ_e/λ)_m≥1, the amplitude of local heat flux and effective conductivity increase notably With RaDa and r0/ri, Because of mentioned above, thermal design of annular insulation with empirical thermal conduction model is found to be insufficient.