Research On Parameter Optimization Of Corrugated Plate Dryer

For some PWR nuclear power plants,corrugated plate dryer is a significant part in steam generator.It determines the steam quality and affects safe operation of turbine.With the comprehensive consideration of research on miniaturization technique of steam generator and improvement in inherent safety of steam generator,reducing the volume of corrugated plate dryer and keeping its working capacity are important issues.To this end,the inlet steam velocity must be increased,which can lead to re-entrainment phenomenon and affect the separation performance of corrugated plate dryer.To avoid this problem,the structure and operating parameters of corrugated plate dryer need to be investigated and that with better separation performance would be the optimal choice.This thesis is divided into two sections.For one,experiments on effects of drainage tank structures on performance of corrugated plate dryer were carried out under room temperature.This aspect aims to design different drainage tank structures and obtain their corresponding changes in separation efficiency as well as pressure drop with the variation of inlet airflow rate through experiments,thereby to seek one reasonable structure with better separation performance considering the parameter of estimated critical airflow rate.The factors of baffles number in drainage tank and the depth of tank were investigated.For another,parameter optimization of corrugated plate dryer was done by means of response surface method(RSM)and non-dominated sorting genetic algorithm(NSGA-Ⅱ).This aspect aims to seek more suitable depth of drainage tank(from 226 mm to 286mm),baffles number in tank(from 1 piece to 3 pieces),plate spacing(from 13 mm to 15.8mm),inlet humidity(from 3% to 8%)and inlet velocity(from 3m/s to 15m/s)to accomplish the goal of better separation performance and maximum critical airflow rate based on multi-objective optimization theory.The minimum pressure drop and maximum separation efficiency of corrugated plate dryer are taken as the objective functions for this research.RSM is applied to figure out the relation between design variables and objective functions.Once the relation is obtained,a set of Pareto optimal solutions that meet the optimization requirements could be given through MATLAB based on NSGA-Ⅱ.Through the above research the conclusions were as follows.(1)Separation efficiency,pressure drop and critical airflow rate will increase,remain and decrease respectively as the inlet humidity increases.When the inlet velocity becomes larger,separation efficiency will drop after rising to a high stable stage while pressure drop will go up exponentially.Besides,with the increasing number of vertical baffles distributed evenly in drainage tank there will be an upward trend in critical airflow rate and separation efficiency.The critical airflow rate and separation efficiency for the structure with three vertical baffles can be approximately 1.15 and 1.01 times larger than those for the structure with one vertical baffle.However,the number of baffles has no obvious effect on the pressure drop.In addition,as the depth of drainage tank increases in the certain range,the separation performance of corrugated plate dryer will be poorer.(2)During the experimental process,it was found that experimental repeatability was not good.To solve this problem,error of electromagnetic flow meter mounted on feed water pipe was verified.Finally it was concluded that the flow deviation of flow meter is one of reasons for bad experimental repeatability.To minimize the systematic error of experiments,water tightness of experimental equipments should be ensured and the working status of nozzles for each working condition needs to be kept unchanged as much as possible.(3)It can be seen from Pareto optimal solutions obtained by NSGA-Ⅱ that the recommended values of inlet humidity,plate spacing,baffles number in drainage tank and the depth of tank are basically fixed,about 8%(for the optimization of dryer with drainage tank structures this value is 5.5%),14.6mm,3 pieces and 226 mm respectively,which meets the law that the conclusion(1)gives.The selection of plate spacing is based on the same importance of separation efficiency and pressure drop.By adjusting the proportion of ranking for each objective function in non-dominated sorting process,the designer of corrugated plate dryer could get a different set of Pareto optimal solutions.Besides,the recommended inlet velocity for the dryer in this thesis mostly ranges from 7.58m/s to9.44m/s(for the optimization of dryer with drainage tank structures this range is about9.37m/s to 10.81m/s).