Optimization study of cross-cut flow control for heat transfer enhancement in wavy fin heat exchangers: Concept of cross-cut reference length

The numerical study to find the optimum cross-cut length in wavy fin heat exchangers with various corrugation angle is conducted in this paper. Two-dimensional five-waved wavy fin with various corrugation angles is used as a simulation domain. The space ratio (fin pitch divided by wavelength) of wavy fin is fixed at 0.15. Non-dimensionlized conservation equations for steady laminar flow are used with working fluid of water. To track the optimum cross-cut length conveniently, the concept of cross-cut reference length (CRL) is devised and applied. As a result of parametric study, the optimal heat transfer performance is achieved when the cross-cut is applied with 0.4 CRL in all corrugation angles. Qualitatively, the heat transfer performance increases until the cross-cut length reaches 0.4 CRL, by up to 21.71% compared with typical wavy, then decreases thereafter. However, the degree of heat transfer enhancement is dependent on the corrugation angle and Reynolds number. The pressure drop (pressure difference between entrance and exit of wavy fin) also increases when the cross-cut is applied optimally; however, the increment is smaller compared to the heat transfer enhancement. Evaluating the overall thermal performance (j/f) considering the degree of pressure drop shows that the optimum cross-cut length is changed to 0.5 CRL in certain cases.