CFD-Based Correlation Development for Air Side Performance of Wavy Fin Tube Heat Exchangers using Small Diameter Tubes
Airside heat transfer, airside friction, CFD, correlations, wavy fin
A great deal of effort is spent on the design and optimization of air-to-refrigerant heat exchangers in HVAC&R applications. One path towards improving their performance is the transition to smaller hydraulic diameter flow channels. In particular, tube diameters below 5mm need to be investigated. The in-tube refrigerant flow characteristics are well understood for small diameter tubes and reliable heat transfer and pressure drop correlations are available in the literature. On the air side, however, most of what is available in the literature has no, or very limited, applicability to small tube diameter heat exchangers. In these situations numerical methods such as CFD are commonly employed in the performance evaluation of tube and fin surfaces. Although CFD has been a powerful and reliable tool it is still computationally expensive if used for evaluating a large number of parameterized geometries. This work presents new CFD-based correlations for wavy-finned tube heat exchangers with tube diameter ranging from 2mm to 5mm. Herringbone wavy fin profiles are analyzed in this study. The methodology implemented in this work consists of analyzing air-side heat transfer and pressure drop characteristics by using Parallel Parameterized CFD (PPCFD) which helps in reducing engineering time significantly. The CFD models are verified using the Grid Convergence Index (GCI) method. The verified CFD model are then used to generated air-side performance data for a wide range of geometrical parameters such tube diameters, spacing and fin density and operating parameters such as tube wall temperature and inlet air state. The resulting data is reduced into correlations that can be easily implemented in various heat exchanger analyses tools. As new experimental data becomes available, the correlations will be updated. In the meanwhile, researchers and engineers can use these correlations for evaluating the performance of small tube diameter heat exchangers.