Thermo-fluid characteristics of fin-and-tube heat exchangers with various fin details for air conditioning applications
The need for more efficient air conditioning systems requires an in depth understanding about the performance of its components. One of the key components in the air conditioning plant is the fin-and-tube cooling coil, which is investigated here. The main focus of the work is concerned with the analysis of fin-and-tube cooling coils having two classes of passive enhancement techniques known as corrugated and turbulated fins with particular reference of developing flow region. Initially, two-dimensional modelling was done to establish the scope of later three-dimensional modelling in terms of dominant variables, meshing strategies and convergence criteria. The results gave key insights into required modelling strategies needed for the more complex three-dimensional problem of the composite fin-and-tube cooling coil. Three-dimensional CFD modelling of fin-and-tube cooling coils having turbulated, corrugated and flat-fin geometries have been investigated with particular reference to the dry-hot arid climate. Five modelling approaches have been considered based on an isothermal fin-and-tube, periodic boundaries, conjugate heat transfer, tube-row temperature gradient and the effect of manufacturing defects. The last three approaches are novel contributions to this field of research. The influences of the key design parameters of fin pitch, fin material, and fin thickness have also been investigated parametrically for all fin types. To provide confidence in these models, experimental studies on these cooling coils were carried out to acquire data for comparison between the predicted and measured values of heat transfer and friction, and to investigate the effect of range of design conditions on the cooling coils performance. The detailed results of this work can be used to optimise the air-conditioning coil designs. The turbulated fin coil was found to give the highest values of Nusselt number at given friction factor followed by the corrugated fin coil. At a given pressure drop (dP = 52 N/m2 corresponding to 14, = 2.3 m/s), the heat transfer coefficient of the corrugated and turbulated fin coils was higher than that of flat fin by 16 % and 36 % respectively. For typical operating conditions, the corrugated and turbulated fin coils required core volumes of 19 % and 40 % less than that of flat fin coil respectively for the same performance. The cooling coils employing corrugated and turbulated fin geometries contribute significantly to the energy conservation and volume reduction of the air conditioning plant.