Thermodynamic Optimization Of A Novel Composition Adjusement Zeotropic Organic Rankine Cycle With Liquid-separation Condensation And Variable Operating Conditions Analysis

China has many low-grade energy sources such as solar energy,geothermal energy,and industrial waste heat.The effective use of low-grade energy can solve the energy shortage and environmental pollution problems.Organic Rankine Cycle(ORC)uses low-grade heat energy to generate electricity.The development prospect is broad and has become the research focus of scholars at home and abroad.Changes in ambient temperature will have a greater impact on the performance of the ORC system.When the system deviates from the design conditions,the system performance deteriorates.This paper focuses on improving the thermodynamic performance of the system under variable conditions.Thermodynamic optimization of zeotropic working fluid ORC with variable composition(OZORC): when the operating condition changes,different operating conditions require different temperature slips to better match the heat exchange with cold and heat sources.In response to this problem,an ORC system with variable composition was proposed.Using MATLAB to model and fix the monthly pinch temperature difference,a loop iteration method was used to optimize the maximum net output power,and the variable composition ORC system was obtained for each month within a year.The best composition and the maximum net output power,and compared with the traditional variable ORC system(TZORC).The results show that when the working fluids are R245fa/R365 mfc,R245fa/R113 and R245ca/R113,the net output power of the OZORC system is increased by 4.48%,9.15% and 2.95% compared to the TZORC system.The composition adjustment ORC system(LZORC)based on the liquid separation condenser is proposed,its control range is optimized and analyzed: working liquids of different composition can be obtained by liquid separation condensation,then stored in different liquid storage tanks,when the working condition changes,the best composition can be obtained by mixing the working fluids of different composition in different storage tanks in different proportions.Since the range of the composition after liquid separation is affected by the dryness of the liquid and the initial compo sition injected into the system,the theoretically obtained optimal composition may not be achieved due to system limitations.Therefore,to optimize the liquid dryness and initial composition,MATLAB programming uses the sequence quadratic programming method,using the UA value under the design conditions as a constraint,with the maximum net output power as the goal,the changing condensing pressure working conditions and the constant condensing pressure working conditions are optimized to obtain the best liquid dryness and the best initial composition.The results show that compared with the variable condensing pressure working conditions,the constant condensing pressure working conditions have a higher dependence on the composition;when different mixtures are used as the working fluid,the optimal liquid dryness and the optimal initial composition are different,and the economics of the LZORC system compared to the TZORC system are also different.Analysis and optimization of composition control zeotropic working fluid ORC system(ARORC)with liquid separation condensation constrained by thermal conductivity h A under variable operating conditions: ORC systems are usually designed under a specific operating condition,when the operating condition changes,the performance of the system deteriorates,however,the change of composition can alleviate the performance deterioration problem.In order to explore the performance advantages of the composition control system,the ARORC system was modeled and analyzed.By establishing the thermal conductivity h A constraint under variable operating conditions,a strict heat exchanger model was avoided.The research results show that when the lowest ambient temperature is selected as the design condition in January,the ambient temperature increases,the temperature difference between the pinch points of the heat exchange process increases,resulting in the heat transfer deteriorates.ARORC system can produce different temperature slips,which can better match the changing cold source and reduce the temperature difference between the pinch points.ARORC system also can increase the average endothermic temperature and reduce the average exothermic temperature compared to the TZORC system,thereby improving system performance.During the optimization of the system under variable operating conditions,the UA value calculated by the parameter h A decreases as the heat exchange load decreases,when the mixtures are R124/R245 ca,R134a/R245 fa,R245fa/R365 mfc,R236fa/R123 and R245ca/R113,the thermodynamic properties of the composition adjustable system compared with the traditional ORC system are 3.77%,1.31%,4.51%,1.81% and 9.79%,respectively.