Performance improvement of a tubular heat exchanger by tube arrangement optimization using simulated annealing algorithm and blocked-off method

In this study, the performance of a two-dimensional cross-flow tube heat exchanger, which has been widely applied in the energy recovery processes, is optimized. The main contribution is to propose the most optimum tube arrangements so that the outlet temperature and the pressure drop are optimized based on fluid characteristics. While the flow regime is assumed to be laminar and is affected by buoyancy force, the hot fluid participates in radiation through emitting, scattering, and absorbing. The Simulated Annealing has been used as the optimization algorithm to find the optimal arrangement. Meanwhile, fluid and thermal characteristics of HE are analyzed by concurrently solving set of governing equations, including Navier Stocks and energy equations, for which a Cartesian-based program has been developed in FORTRAN. The discretized form of equations has been obtained and solved using the finite-volume method and SIMPLE algorithm. To simulate the volumetric radiation in the gas domain, the discrete-ordinates method is applied. Furthermore, the Blocked-off region has been implemented to identify the tube circular boundaries inside the Cartesian coordinates system. The applied computational fluid dynamic techniques are validated with the experimental data, while the performance of Simulated Annealing is evaluated by single-objective, multi-objective, and coupled set point parameter cases. A comparison between the results of conventional (in-line and staggered) optimum configurations indicates that more than 20% improvement in pressure drop can be achieved. Moreover, in multi-objective optimization, the findings show that at higher values of optical thickness, the tubes should be placed in the vicinity of lateral boundaries.