Performance Analysis And Optimization Design Of Organic Rankine Cycle Generation System Driven By Solar Heat Source Of Medium-Low Temperature

With the development of industrialization,the problem of energy consumption and environmental pollution are important challenges to the development of our society.The reduction of fossil energy brings unprecedented pressure to energy application and also leads to series of environmental problems such as haze,global warming and so on.Energy saving and emission reduction especially in electric power production is an important part for the remission of energy problems.Under this circumstance,many renewable energy resources have attracted worldwide attention,such as solar energy,wind energy,tidal energy and geothermal energy,etc.Currently,the research on solar energy is mainly concentrated in the field of photovoltaic power generation.However,some drawbacks,such as high pollution,high cost of photovoltaic panels,have exposed in the production process during the past years.In addition,the generated power being forced to be immediately transported to the power grid leads to the power waste during the period of valley power demand.Because the solar energy resource is abundant and economical,the solar organic rankine cycle(ORC)power generation system has been favored by many scholars in recent years because it makes up many disadvantages of photovoltaic power generation.In this dissertation,the design and optimization of solar ORC systems are studied.Firstly,the principles of the system are briefly introduced,and then the physical and mathematical models of each component are developed.The heat transfer model of evaporator is calculated accurately by using the method of micro-element partition.According to the performance of solar collector and average solar radiation capacity in typical areas,the fluid temperature from solar collectors to ORC system is set to be in the range of 100-180℃.Some kinds of working fluids have been compared towards the system efficiency.Finally,the working fluid R245fa is determined as a most appropriate working medium,which has obvious advantages in environmental protection,safety,and system efficiency.Based on the theoretical model of each component,the calculation program of the system simulation model is developed.Using the developed system simulation model,the impact of design parameters of the solar ORC system,such as heat source temperature,evaporation temperature,superheat,and the flow ratio of working fluid to heat source medium,on the performance of the system(including the thermal efficiency,exergy efficiency and system output power of the system)are investigated.The simulation results show that the maximum system exergy efficiency and thermal efficiency are 66.6%and 16.7%,respectively,and the maximum output power generated by unit evaporation area is 0.45W/m~2.However,the influence of system parameters on the performance of different targets is different,so the system can not achieve the optimal values of multiple target performance parameters at the same time.In order to obtain the optimal design parameters of the system,the normalization method is used to fit different system parameters into one comprehensive formula so that the system performance could be better evaluated.This multi-objective function and multi optimal parameters can be obtained by means of the genetic algorithms.The multi-objective function can set the ratio of different target parameters according to the designer’s specific requirements.By comparing the results of multi-objective optimization method and single-objective optimization method,it is found that the general performance parameters of the system under the multi-objective optimization method can reach more than 80%of their respective optimal performance.The exergy efficiency optimization method is the best among all the single objective simulation methods,and the general performance parameters are more than 70%of their respective optimal values.The performance of multi-objective optimization system is better than that of single objective optimization system.It is also found that the optimal parameter design value of the system is not unique,but the optimal solution of the system performance is unique,which proves that the system has the highest performances,which can be realized by appropriate design parameters.The simulation results show that the ideal evaporation temperature and the flow ratio of thermal conduction oil to working fluid is between 125℃-140℃and 1:0.8 to 1:1,respectively.Besides,higher solar collecting temperature and lower superheat will increase the system overall performance.In this dissertation,the basic design parameters of the solar ORC system are discussed through theoretical analysis and numerical simulation,which is of certain reference to the system designers.