Homogenization of fin layers in tube-fin structures subjected to compression and bending: Analyses and experiments

• Fin-homogenization is verified for finite element analysis of heat exchanger cores.
• A first order homogenization is proposed to evaluate the homogenized stiffnesses of fin layers.
• Fin-homogenization-based and full-scale analyses give good agreements to each other.
• The Bernoulli-Euler assumption is not satisfied under longitudinal bending.
• This is because the homogenized shear stiffness responsible for the bending is very low.

This paper verifies fin-homogenization for finite element analysis of heat exchanger cores with stacking of flat tubes and thin wavy fins. A first-order homogenization method is proposed on the assumption that uniform deformation prevails a short distance away from each fin layer in the stacking direction while the wavy fins have periodicity in the in-layer directions. Using this homogenization method, the homogenized elastic stiffness values of outer and inner fin layers in an intercooler are evaluated by considering real and sinusoidal shapes of the wavy fins. The homogenized elastic stiffness values attained are examined by performing fin-homogenization-based (fin-h-based) analyses, full-scale analyses, and experiments of tube-fin layered specimens subjected to compression and bending. It is shown that the fin-h-based and full-scale analyses give good agreements to each other even in the presence of macro-strain gradients in the outer and inner fin layers though the homogenization method is of first-order. Moreover, it is shown that the fin-h-based analyses reproduce well the experiments if the homogenized elastic stiffness values obtained for the real shapes of outer and inner fins are used in the analyses. It is also shown that the Bernoulli-Euler assumption is not satisfied in the homogenized outer fin layers under longitudinal bending because the homogenized elastic shear stiffness responsible for the bending is very low.