5. For present type of sharp-bend ribbed-wavy channels with large changes in the gradients of fluid velocity and temperature, the linear increase of St against f ensures the applicability of Reynolds’ analogy. Acting by the flow phenomena relevant to present wavy sidewalls, the TPF values for present test channels of AR(e/H) = 0.5(0.05), 1(0.1) and 2(0.2) are generally raised above the TPF references collected from the two-pass ribbed channels with flat sidewalls to the respective ranges of 1.74–1.62, 2.42–2.24 and 2.51–2.28. The present undulant channel sidewalls with skewed sinusoidal waves are demonstrated as an effective and efficient HTE measure to boost the thermal performances for a twopass ribbed channel with 180 sharp bends.