Simultaneous Optimization For Heat Transfer Enhancement Equipment Size Of Heat Exchanger And Heat Exchanger Network

In heat exchanger network(HEN)optimization,considering the use of enhanced heat transfer equipment in heat exchangers is an effective way to improve heat transfer performance and increase energy efficiency.At present,the study of HEN optimization considering heat transfer enhancement technology,in order to simplify the mathematical model and reduce the difficulty of solving,the heat transfer enhancement equipment size of heat exchanger is often set to fixed value,only considering the effect of enhanced heat transfer equipment on the performance of the HEN.However,setting the size of the enhanced heat transfer equipment to a fixed value simplifies the mathematical model.At the same time,it also separates the design of the heat transfer enhancement equipment from the HEN.This narrows the search scope of the optimized algorithm and makes it difficult to achieve overall optimization.Therefore,this paper establishes a mixed integer nonlinear programming(MINLP)mathematical model for the HEN simultaneous synthesis optimization considering the type and size optimization of heat transfer enhancement equipment,solving with genetic/simulated annealing algorithm(GA/SA)to achieve the overall optimization between the heat transfer enhancement equipment type,the heat transfer equipment size as well as structural parameters of the HEN.At the same time,a sequential synthesis optimization calculation of the heat transfer enhancement equipment size and the HEN is performed,and the optimization results are compared with the simultaneous synthesis optimization.(1)First based on the stage-wise superstructure of the HEN synthesis and the enhanced heat transfer equipment design model,a MINLP model of sequential optimization and simultaneous optimization for the enhanced heat transfer equipment size and HEN was established.The minimum annual total cost is the objective function,including the cost of the heat exchanger equipment,the cost of the enhanced heat transfer equipment,the utility cost,and the operating cost caused by the pressure drop,with logic constraints for enhanced heat transfer equipment and pressure drop constraints considering in the model.Whether or not to use enhanced heat transfer equipment,enhanced heat transfer equipment types and the heat capacity flow rate and heat load in the HEN are set to be the optimized variables in sequential optimization,and whether or not to use enhanced heat transfer equipment,enhanced heat transfer equipment types and size of the enhanced heat transfer equipment and the heat capacity flow rate and heat load in the HEN are set to be the optimized variables in the simultaneous optimization.(2)The sequential optimization strategy of size of the enhanced heat transfer equipment of heat exchanger with HEN synthesis was proposed.First,through the design model of the heat transfer enhancement device and the performance evaluation index of the heat exchanger,the size of the heat transfer enhancement equipment is calculated when the heat exchanger performance is optimal,and this size is used as the initial parameter of HEN optimization.Then the HEN synthesis considering the use of heat exchanger enhancement heat transfer equipment is performed,considering the influence of the pressure drop changes caused by the use of the heat transfer enhancement equipment.The GA/SA algorithm was used to solve the problem,and the optimal heat exchanger network structure and the type of the heat exchanger enhanced heat transfer equipment were obtained.Compared with the literature results,this sequential synthesis optimizes the annual total cost reduction by 5.19% through the 5*1 case analysis.(3)The simultaneous optimization strategy of size of the enhanced heat transfer equipment of heat exchanger with HEN synthesis was proposed.The design variables are coded by genetic genes,and genetic optimization of crossover and mutation are adopted to realize the simultaneous optimization of enhanced heat transfer equipment size and HEN.At the same time,the influence of pressure drop variation caused by the use of heat exchanger and heat transfer enhancement equipment is taken into account in the objective function.The optimal heat exchanger network structure and the type and size of enhanced heat transfer equipment are obtained by using the GA/SA algorithm.The total cost of the simultaneous optimization is reduced by 2.25%,10.98% and 6.11% respectively through the comparison of 2*2 cases with literature results,and comparison of 5*1 cases with the results of the literature and sequential optimization.The validity of the proposed simultaneous optimization model and the solution strategy is verified.