NUMERICAL INVESTIGATION OF HEAT TRANSFER IMPROVEMENT OF A DOUBLE PIPE HEAT EXCHANGER WITH KOCH SNOWFLAKE FRACTAL AND LONGITUDINAL FIN DESIGNS

The effects of the inner pipe design of a double pipe heat exchanger (DPHE) on the thermal performance were numerically investigated by using a three-dimensional computational fluid dynamics (CFD) method under various Reynolds numbers and steady state conditions. Two different passive heat transfer enhancement methods were applied to the DPHE, and the heat exchanger was tried to be compact. The first method is the addition of a conventional longitudinal fin to the outer surface of the inner pipe. The other method is the fractal application; the fractal pattern applied in heat exchangers in the available literature is generally used in the fin geometry. But in this study, the fractal pattern was used in the geometry of the inner pipe. Heat transfer occurred over the entire wall of the inner pipe due to using the fractal pattern to the inner pipe of the heat exchanger. The heat exchanger model with the Koch Snowflake fractal pattern cross-section showed the highest heat transfer rate values. It was easily observed that the total pressure drop values increased as the number of iterations increased. As a result of fin attachment, relatively lower increases were observed in heat transfer rate values. In general, the n = 1 fractal model has both high heat transfer and relatively low pressure drop values that make this model more remarkable than the others. The heat transfer rate and pressure drop (cold side) values of this model varied between nearly 6-18 kW and 1.2-13 kPa, respectively. The numerical results were compatible with the values obtained from the literature and theoretical calculations.