Enhancement of transfer processes on a channel wall covered with regular small-size ribs

Experiments were carried out to study hydrodynamics and heat transfer in a channel with discrete roughness elements on walls. Semicircle ribs with the height of 1.4 % of the hydraulic diameter of the channel were considered. Various rib geometries and positions were examined: solid ribs and ribs with slits, various streamwise and spanwise pitches, inline and staggered rib arrangements. Heat transfer enhancement and thermal-hydraulic performance were estimated. Integral and local values of the heat transfer coefficient were measured. Optical measurements yielded the fields of velocities and turbulent characteristics of the flow. Simultaneous analysis of hydrodynamic and thermal parameters of flow was carried out. Formation mechanisms of the kinematic structure of flow and heat transfer on roughened walls were considered. The distribution of heat transfer coefficient was shown to depend on the turbulent structure of flow, namely the vertical fluctuation of velocity in the near-wall region.