A numerical study of flow structure and heat transfer in a square channel with ribs combined downstream half-size or same-size ribs

摘要

The present study employs square cross-section ribbed channels with different arrangements of downstream half-size ribs to determine the most optimal configurations for augmenting heat transfer rates with minimized pressure drop penalties. The channel inlet Reynolds number ranges from 20,000 to 160,000. The influence of downstream ribs arrangement on the overall performance characteristics of ribbed duct is observed with six different cases. A case of an array of six big continuous ribs installed on one wall with a pitch ratio of P/e = 20, is first designed (Case A). Four cases are then designed with inserting half-size and same-size ribs downstream the big ribs (Case B, Case C, Case D and Case E, respectively). The last case has a different pitch ratio and half-size ribs in the middle of two neighbor big ribs (Case F). The details of turbulent flow structure temperature fields, local heat transfer, normalized heat transfer, and thermal performance factor were obtained using Computation Fluid Dynamics (CFD) with the v~2f turbulence model and constant heat flux thermal boundary conditions applied to all surfaces. The overall performances of six ribbed channel are evaluated and compared. The results reveal that the usage of downstream ribs is a suitable way to decrease the pressure loss and improve the flow structure, while keeps comparable enhancement in heat transfer as expected. Compared with Case A, all other cases yield the lower friction factor except for Case B. Case D and Case F present the prominent effect of their thermal enhancement factor, suggesting that the two cases exhibit individual advantage when different performances are taken into account to augment the heat transfer of ribbed channels.