Numerical Study of Staggered Tube Bundle in Turbulent Cross Flow for an Optimum Arrangement

A numerical study was conducted to evaluate optimum arrangement of staggered tube bundle in cross flow based on heat transfer rate, friction factor and compactness of bundle; utilizing CFD code FLUENT. The RNG (Re-Normalization Group) k-ε turbulent model with modified constant of dissipation term in ε equation was applied. The Reynolds numbers (based on maximum mean velocity inside tube bundle and hydraulic diameter of tubes) of 1000, 5000, 10000, 100000; dimensionless spacing ratios between tubes parallel and normal to flow direction (Sp/D and Sn/D) in range of 0.6-3.0 and 1.0-2.9 respectively, and isothermal boundary condition on twelve rows of tubes inside symmetry computational domain were considered. According to the results, the model improves global heat transfer rate prediction, particularly in high Reynolds numbers, compared with standard k-ε model in previous studies. A discussion was made in behaviour of global Nusselt number and friction factor for different tube bundle arrangements by utilizing flow stream lines and temperature contours as well as local Nusselt number on tubes. The results show that both heat transfer rate and friction factor are almost independent of Sp/D for Sp/D higher than specific value. Finally, by defining a performance parameter, the optimum arrangements for array of staggered tubes in cross flow was found Sn/D=1.5, 1.3 and S p/D=1.15, 1.05 respectively.