Thermal performance of developing flow in a radially rotating parallelogram channel with 45° ribs

An experimental study was performed to measure the full-field Nusselt number (Nu) distributions over two opposite leading and trailing ribbed walls, the pressure drop coefficients (f) and the overall thermal performance factors (TPF) of a rotating parallelogram channel with radially outward flow. The test conditions in terms of Reynolds (Re), rotation (Ro) and buoyancy (Bu) numbers were respectively in the ranges of 5000 ≤ Re ≤ 15,000, 0 ≤ Ro ≤ 0.3 and 0.001 ≤ Bu ≤ 0.23. The full-field Nu data generated by the infrared thermography method were examined to study the isolated and interdependent Re, Ro and Bu impacts on the detailed Nu distributions as well as on the rib-wise averaged Nusselt numbers (Nu) at rib and mid-rib locations over the leading and trailing walls. With rotation, the Nu distribution over the trailing wall followed the Nu₀ pattern in the static channel; but underwent considerable modification from the Nu₀ pattern on the leading wall by generating a haloed high Nu region at the obtuse entry corner. A parametric analysis which examined the detailed Ro and Bu impacts on Nu at rib and mid-rib locations enlightened the streamwise developments of rotational effects on heat transfer performances over leading and trailing walls. This parametric analysis led to the generation of a set of physically consistent empirical Nu correlations which assisted to evaluate the individual and interdependent Ro and Bu effects on Nu at rib and mid-rib locations over the developing flow region. As an indication of the combined effects of Coriolis force, rotating buoyancy and the geometric features emulated by the present parallelogram ribbed channel, the area-averaged Nusselt numbers on the leading and trailing walls were modified to the respective ranges of 0.78-1.34 and 1.09-1.38 times of the non-rotating Nusselt numbers; while the f coefficients were raised to 1.05-5.2 times of the stationary levels, leading the TPF factors to the range of 0.979-1.575.