Thermodynamic Optimization of a Plate-fin Heat Exchanger by Oppositional-Differential Evolution

Douglas Mayer Rieger¹; Viviana Cocco Mariani¹; Emerson Martim¹

¹ Pontifícia Universidade Católica do Paraná

doi:10.20906/CPS/CILAMCE2017-0630

Resumo

In the present study, a plate-fin heat exchanger (PFHE) equipped with offset-strip fins was thermodynamically optimized. Commonly used for gas-gas operations, the PFHEs are extremely compact (high heat transfer area per equipment volume), granting very light models, and are also able to reach up to 25 times the heat transfer area (by weight) of the shell and tube types. The more generated entropy in the exchanger, greater is the loss of potential work or heat/mass transfer, therefore, the minimization of the number of entropy generation was the main objective of the study. Also, many of heat transfer parameters were determined in order to verify the exchanger's effectiveness. The method used for the modelling was the effectiveness-NTU, which is especially useful when the fluids' outlet temperatures are unknown. The process fluids are hot ammonia (NH3), referred as fluid A, and cold air, fluid B. The fluids enter the exchanger as superheated vapors, with pressure of 101325 Pa and temperatures of 400 K (ammonia) and 200 K (air). The equipment is single-pass, with cross flow and unmixed fluids. The heat transfer coefficients were determined by the appropriate Chilton-Colburn correlations. The used optimization method was the Oppositional Differential Evolution (ODE), a stochastic evolutionary-based method. An initial population of possible solutions is generated and through mutation, crossover and selection (among other vectors) it is possible to achieve the optimum one that respects previously established conditions. The ODE is an adaptation of the original Differential Evolution (ED), in which, for each analyzed solution, its opposite vector is also determined and considered as another optimal value. It is known from the literature that the oppositional-based optimization grants faster convergence. The variables subjected to the ODE were the exchanger's length for each fluid, La and Lb, the number of fin layers for A, Na, the external height, H, thickness, t, frequency, n, and the lance length, l, of the fins. Th

Palavras-chave: Oppositional Differential Evolution; Effectiveness; Entropy Number; Plate Fin Heat Exchanger; Optimization