Performance Analysis Of Organic Rankine Cycle And Optimization Design Of Evaporator Under Considering The Pressure Drop

The Organic Rankine Cycle(ORC)power generation is an effective technology to recovery low grade waste heat,which has the advantages of simple structure,high thermal efficiency and relatively low evaporating pressure.Considering the flow pressure drop,this paper analyzed the effects of operation parameters on the overall performance of the system,In addition,a multi-objective optimization was carries out for the evaporator to achieve better operation parameters and structure parameters.The research will play an significant guiding role in the industrial application of ORC power generation technology.The main contents and conclusions are as follows:1)The model of flow pressure drop and thermal analysis of the ORC system were established.Then the ORC evaporator and condenser according to the given parameters were designed.The heat transfer area of finned tube evaporator and plate condenser is 46.26m~2 and 27.58 m~2 respectively,in addition,the length of tube is 159.6m and the plate number is 57.Based on the principle of ORC system fluids selection,R245 fa,R123,R600 a,R141b,R134 a and R236 ea were selected as working fluids.On this basis,the reliability of the model was verified by the literature.2)The effects of operation parameters(evaporating pressure,superheating temperature,pinch point temperature difference)and heat source temperature on flow pressure drop were investigated.In addition,the influence of flow pressure drop affects on net output power,thermal efficiency,exergy efficiency,heat recovery efficiency and irreversible loss were examined.Results indicate that the flow pressure drop of the ORC system is mainly composed of evaporator pressure drop,which is mainly influenced by the evaporating pressure.When the evaporating pressure is lower than 0.8MPa,flow pressure drop will further affect to the performance of the whole system,and the decrease in the performance index increases.For dry working fluid,the influence of pinch point temperature and superheating temperature on the flow pressure drop is small.Under the different pinch point temperature difference,the affect of flow pressure drop on the performance of the system is less than 10%.The flow pressure drop increases with the increase of heat source temperature.Working fluids is the important factors affect the flow pressure drop and performance of the system.Among the selected working fluids,R141 b and R245 fa is more suitable than others.3)The flow pressure drop,net output power,thermal efficiency and heat recovery efficiency of the ORC system were selected as the optimization goals.The thermal parameters(evaporating pressure,superheating temperature,pinch point temperature difference)and structure parameters(the single length of heat exchange tube,single pipe number,fin height,fin thickness,fin spacing)of the evaporator were chosed as the design variables.The ORC system evaporator was optimized using simulated annealing optimization algorithm,which adopts working fluid R245 fa and R141 b.Then,the effect of evaporator structure parameters and thermal parameters of system on the thermal performance of the ORC system were analyzed.Results indicate that it existes opposite and game phenomena among the system performance indexes.Among the evaporator thermal parameters,the evaporating pressure has the greatest effect on the value of objective function.The best evaporating pressure of R245 fa is 2.5MPa in the optimized conditions.Among the structural parameters of the evaporator,finned tube structure is the most important factor that affects system thermal performance.In addition,the influence of heat exchanger tube arrangement on the thermal performance of the system can be ignored.For the working fluid R245 fa,the optimized size parameters are as follows: fin height 34 mm,fin thickness 7.3mm,fin spacing 3.5mm.