Vertical Temperature Profiles in Open-Channel Flow

This study presents methods for predicting vertical mixing of heated surface effluents in the far-field mixing region. A set of laboratory flume experiments covered a range of flows from well-mixed to nearly stably stratified conditions, over a range of conditions commonly encountered in practice. The data, together with analysis based on the convection-diffusion equation, were used to determine: (1) The distance for nearly complete mixing; (2) a bulk mixing coefficient, K_y, for rapidly mixing flows; and (3) the vertical distribution of the overall vertical heat transfer coefficient, E_Ty, at downstream cross sections. Buoyancy effects are reflected in the vertical distribution of E_Ty. Stratification sharply inhibits vertical mixing near the surface and reduced vertical mixing throughout most of the depth. For rapidly mixing flows the vertical heat transfer coefficient agrees closely with the turbulent mass and momentum transfer coefficient.