A study was conducted on the cross flow and mixing between water flowing in two semiopen channels. Measurements were made of the quantity of heat transferred between the hot and cold channels in a square array of parallel rods to determine the correlation between the ratio of the overall effective diffusivity for heat e to the kinematic viscosity v and the flow Reynolds number Re. The result e/v = 0.0061 Re0.98 is in general agreement with previous results, but contains numerical coefficients not previously obtained for the present geometry.