Otimização do projeto de trocadores de calor do tipo air-cooler

Abstract

Air-coolers are heat exchangers based in an air stream that is blown by fans through a finned tube bundles. This equipment is used in industrial units where the availability of water is limited. Despite of the importance and sensibility of the design in the economic performance of the equipment, just a little amount of scientific works has studied automatic techniques related to this equipment design. In this context, the present work aims the optimization of the air-coolers design, in order to minimize the associated costs. The optimization problem has as an objective function that should be minimized, the total cost of the project, which includes the investment and maintenance in the heat exchanger, pump of the process stream, piping and valves, together with the operational costs related to the energy required by the operation of the pump and the fans. In the proposed approach, each point of search space corresponds to one project alternative, which is represented by a vector with the optimization variables. In the formulation of the optimization procedure, were investigated the following variables: outside tube diameter, fin frequency, fin height, pitch ratio, number of passes inside the tubes, tube length, number of tube rows, number of tubes per bundle, number of bundles per bay, number of bays, coverage percentual of the fans and air outside temperature. The constraints are presented fundamentally by a minimum excess of area which determines the technical availability of the equipment. Each evaluation of the objective function and restrictions implies in the actuation of the termofluidodynamic simulation associated to the investigated configuration. The methods that were developed to the optimization are: a stochastic method called simulated annealing and a deterministic method. Both methods reached a trajectory showing the cost decrease, however, the simulated annealing presented better results since it is global optimization method