Local Heat Transfer Dependency on Thermal Boundary Condition in Ribbed Cooling Channel Geometries

The present study is geared toward quantifying the effects of imposed thermal boundary condition in cooling channel applications. In this regard, tests are conducted in a generic passage, with evenly distributed rib type perturbators at 90 deg, with a 30% passage blockage ratio and pitch-to-height ratio of 10. Uniform heat-flux is imposed on the external side of the slab which provides Biot number and solid-to-fluid thermal conductivity ratio around 1 and 600, respectively. Through infrared thermometry measurements over the wetted surface and via an energy balance within the solid, conjugate heat transfer coefficients are calculated over a single rib-pitch. The local heat extraction is demonstrated to be a strong function of the conduction effects, observed more dominantly in the rib vicinity. Moreover, the aero-thermal effects are investigated by comparing the findings with analogous aerodynamic literature, enabling heat transfer distributions to be associated with distinct flow structures. Furthermore, the results are contrasted with the iso-heat-flux wetted boundary condition test case. Neglecting the thermal boundary condition dependence, and thus the true thermal history of the boundary layer, is demonstrated to produce large errors in heat transfer predictions.