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What are the ratios of the conductivities ?
i.e. k1/k2 ? Here's a quick answer: make two dimensionless parameters epsilon=k1/k2 and eta characteristic length tube/characteristic length plate, make sure they are << 1. Denote them as epsilon and eta. Now expand both expression you've written in powers of epsilon and eta. The one with the higher order O(epsilon^n), O(eta^n) is the more accurate. |