A note on computing finite difference interblock transmissivities

A formula is developed for computing interblock transmissivities for the case where the transmissivity varies more or less linearly between block centers. The error in interblock flow rates resulting at steady state conditions, when either the arithmetic or harmonic mean of ( T /Δ x ) is used for adjacent blocks for the interblock transmissivity, can be significant for some variations of block size and transmissivity.