Numerical investigation of thermal and hydraulic performances of a condenser coil with oblique-shaped tubes
Abstract High efficiency condenser coil providing higher heat removal capacity with lower air-side pressure drop is desirable. However, coil designs with different fin patterns for higher heat transfer incur large air-side pressure drop and thus consume more energy. In this study, the thermal and hydraulic performances of the condenser coil design with plain fin, corrugated fin, and novel oblique-shaped tube are evaluated numerically with a 3-fin and 3-tube model in comparison with a conventional circular tube coil. This novel oblique-shaped tube design features smaller air recirculation zone behind the tube so as to increase effective heat transfer area and to lower air-side pressure drop. The numerical results show that, for the plain fin configuration, the shape of the oblique tube is important in reducing the recirculation zone on the fin, thus increasing effective heat transfer area and heat transfer amount up to 14% and reducing the air-side pressure drop up to 14% at the same inlet air velocity as compared with the circular tube coil. With corrugated fin guiding and promoting air speed, causing more flow separation zones, it is detrimental to the thermal-hydraulic performance of the oblique tube coil. The discussion of choice of materials for tube and fin, such as copper, brass, and aluminium, is provided with possible manufacturing processes required for realizing potential high performance coil design. Parametric optimisation on the best performing plain fin oblique tube design shows that, for the design of condenser coil with oblique tube, there is no optimal FPI, but it is recommended to keep the ratio of tube pitch to tube frontal length/diameter to about 3 to 3.5.