ABSTRACT

Optimization studies were performed for helically finned tubes to investigate the performance of two correlation methods for use within the optimization procedure. Geometric parameters and operating conditions were determined based on maximization of the heat transfer enhancement efficiency index. The first correlation procedure used an artificial neural network (ANN) model found previously to yield highly accurate prediction of the measured friction factor and the Colburn j factor. The second used empirical correlations for the friction factor and j factor developed using symbolic regression based on a genetic programming technique. The optimization performed using the ANN was found to be invalid, producing physically unrealistic results in some regions of the parameter space and leading to a false optimum. The optimization using the symbolic regression correlations performed well and provided reasonable values for optimum geometric and operating parameters. The results showed that the highest efficiency index was obtained using a combination of parameters that promoted a swirling rather than a skimming flow. The optimization study highlights the fact that great care must be exercised when using ANNs for optimization and design purposes, particularly in cases for which the available experimental data are not evenly and densely distributed throughout the parameter space. In contrast, symbolic regression correlations using a relatively small number of additive terms appear to be well suited for optimization purposes due to their increased accuracy over conventional correlations and their robust predictive/generalization behavior relative to ANNs.