Multi-objective optimization of plate-fin heat exchangers Ottimizzazione multiobiettivo degli scambiatori di calore a piastre e alette

Abstract The design of plate-fin heat exchangers (PFHEs) requires the simultaneous consideration of thermal performance, hydraulic losses, and manufacturing cost, since geometric modifications that enhance heat transfer generally increase pressure drop and production complexity. This thesis develops a multi-objective optimisation framework for PFHE design aimed at identifying balanced configurations under realistic engineering constraints. The study considers compact PFHEs equipped with offset strip fins and wavy fins, with particular focus on OSF-OSF and OSF-Wavy arrangements. Established and validated thermo–hydraulic and cost models are employed within a virtual evaluation framework to predict heat transfer rate, outlet pressure drop, and production cost for different geometric configurations and working fluids, including oil, coolant, and charge air. The optimisation problem is formulated in terms of a reduced set of decision variables, objective functions, and feasibility constraints, ensuring consistency with the deterministic PFHE evaluation framework employed throughout the study. The resulting reduced design space is then explored using the Non-dominated Sorting Genetic Algorithm II (NSGA-II), which is adopted to maximise heat transfer rate while minimising pressure losses and cost. The optimisation produces Pareto-front approximations that explicitly reveal the trade-offs between the competing objectives for the investigated fin configurations and fluid types. A dedicated sensitivity analysis of the NSGA-II hyperparameters is also performed to assess the influence of population size, number of generations, crossover probability, and mutation probability on solution quality, convergence behaviour, and computational cost. This analysis is used to establish a robust and reproducible optimisation setup. To support practical design selection, the feasible non-dominated solutions are further ranked using the Technique for Order Preference by Similarity to Ideal Solution (TOPSIS). This combined NSGA-II--TOPSIS framework enables systematic identification of preferred PFHE designs by balancing thermal, hydraulic, and economic criteria. The overall methodology provides a structured and industrially relevant tool for the multi-objective design and decision support of compact plate-fin heat exchangers.