Basic heat-transfer and pressure-drop results for laminar airflow through arrays of in-line or staggered plate segments have been determined from numerical solutions of the fluid flow and energy equations. The results depend on only a single dimensionless parameter which encompasses the relevant geometrical and fluid flow quantities. Application of the results was made to compare the performance of the two types of segmented-plate arrays with each other and with the parallel-plate channel. At constant mass flow rate and constant heat-transfer surface area, the heat-transfer effectiveness ε. of the segmented arrays is appreciably higher than that of the parallel-plate channel, both in the range of small and intermediate effectiveness values. In addition, for a fixed heat duty corresponding to an intermediate ε value and for a constant mass flow, the heat-transfer area of the segmented arrays is only about a third of that for the parallel-plate channel. Under constant pumping power and constant surface area conditions, the heat transfer for the segmented arrays exceeds that for the parallel-plate channel when the effectiveness of the latter is less than 0.65-0.75. Under most conditions, the staggered array yields better performance than the in-line array, but situations are identified where the reverse is true.