The Statistical Character of Packed-bed Heat Transport Properties

Packed beds are essentially heterogeneous on a pellet scale. For random packed beds this heterogeneity causes a statistical character both on a pellet and bed scale. We discuss experimental results which deal with bed-scale statistics. For packed beds on a laboratory scale, the results indicate that the beclscale statistical behaviour introduces a spread up to a factor of three in correlations for the effective radial heat conductivity, ,&, and the heat transfer coefficient at the wall, a,. This spread of a factor of three roughly equals the spread between correlations available in the literature. For cooled tubular reactors the statistical spread in the behaviour of the individual tubes will have a large influence on reactor operation.