Applied Research To Assess Heat Transfer Performances Of Zeotropic Mixture And Nanorefrigerant By Pearson Correlation Coefficient

Evaporator is one of the four main component in ORC system,and the selection of working fluid can affect the heat dynamics performance of evaporator and the whole system.Temperature glide of zeotropic mixture in evaporator and Brownian movement of nanoparticles in flowing condition,which are research hot spots currently,both can enhance heat transfer performance of evaporator.Because there exist several factors which influence results and contradict the multiobjective optimization,dependence relationships of influence factors and target functions can only be shown qualitatively.Therefore,in this papers,Pearson correlation coefficient will be introduced to study the effect of influence factors on research targets and calculated the degree and direction of correlation quantitatively.On the one hand,taking single-tube evaporator of ORC as the research object,correlationships and degree of correlation between influences factors and thermodynamic performances of evaporator have been analyzed through Pearson correlation coefficient under the conditions of different distributions of R245fa and R601 and different evaporating temperatures by numerical simulation.The results show that the temperature glide has the significant positive correlation and significant negative correlation with thermal efficiency and system total exergy loss,respectively.But the correlationship between temperature and log-mean temperature difference enhances from weak negative correlation to significant negative correlation.Under the guidance of Pearson correlation coefficient,the problem of interaction between influence factors in multiobjective optimization can be solved,and the analytical process and thermodynamics results can also be optimized.On the other hand,this paper also presents an experimental investigation of variation tendency of heat transfer coefficient,log-mean temperature difference and differential pressure of pure R123 and 20nm Al₂O₃-R123 nanorefrigerants with four various volume concentrations,0.03%,0.13%,0.18%,0.23%flowing inside the single-tube evaporator of organic Rankine cycle system under the conditions of various heat source temperatures and flow rates.Heat source temperatures are in the range of 50?to 90?at an interval of 10?,and heat source flow rates are 0.7 m³/h,1.3 m³/h and 1.8 m³/h.Pearson correlation coefficient validated above and polynomial fitting will be applied to analyses the experimental results as a auxiliary method.Results show an increment of heat transfer coefficient along flowing direction for both pure R123 and four Al₂O₃-R123 nanorefrigerants with the increment of heat source temperature and flow rate,and that of four nanorefrigerants are higher than that of pure R123.There is no optimum value of heat transfer coefficient when operation condition is changed for the loading carrying capacity increasing with the increasing intensity of operation condition.Meanwhile,suspending nanoparticles and increasing heat source temperature can change the variation tendency of heat transfer coefficient along flowing direction except pure R123 and 0.13 vol%nanorefrigerant.In addition,0.13 vol%as a whole is the optimum volume concentration for both log-mean temperature difference and differential pressure.