Study On The Performance Of Low-temperature Flue Gas Waste Heat Recovery ORC System Of Nano-mixed Working Fluid

With the rapid development of national industrialization brought about by the large-scale waste heat resources has become the focus of our concern.At present,the high temperature waste heat is basically fully utilized,but the medium and low temperature waste heat,especially the low temperature waste heat due to its low grade and related technology development immature has not been effectively used.Some domestic and foreign studies showed that by adding nano particles to enhance the heat transfer performance of working fluid is effective,but has not yet been systematically research on nano mixed refrigerant enhanced organic Rankine cycle system of heat transfer mechanism and characteristics.In this paper,On the basis of studying the thermophysical properties of nano particles on mixed refrigerants,a model of heat transfer calculation for nano mixed refrigerants has been constructed.The main contents and main conclusions are as follows:(1)Based on the PR equation of state and the Vander Waals covolume mixing rule,the calculation method of the thermodynamic properties of the non-azeotropic mixture is constructed.On this basis,the thermodynamic analysis of the ORC system is used to optimize the circulating working fluid,and the optimization of the cycle parameters of the R245fa/R123 non azeotropic mixed refrigerant ORC system is studied.The results show that the non azeotropic mixture of R245fa/R123 can improve the low temperature flue gas waste heat recovery system of ORC’s exergy efficiency,mass ratio of R245fa/R123(0.9/0.1)ORC system with maximum exergy efficiency(53.1%).(2)The mechanism of nano-fluid heat transfer enhancement of non-azeotropic mixtures was studied;The main factors affecting the nano-working fluid are the solid-liquid interface nanometer layer,the agglomeration effect of particles,and the Brownian motion;The main reason for the enhancement of the thermal conductivity of nanofluids is the static mechanism,and the contribution of the static mechanism increases with the increase of particle concentration;Agglomeration degree increased,increasing the thermal conductivity of nanofluids,however excessive agglomeration or high concentration of particles will also make fluid viscosity increase,in practical application,recommend the use of low concentration nanofluids have a certain degree of Loosely agglomerated nanofluids.(3)A thermodynamic performance calculation model for Low Temperature Flue Gas heat recovery of nano mixed refrigerant ORC was established,Comparison of several kinds of nano-working fluid as a circulating refrigerant low temperature flue gas waste heat recovery ORC system performance,The multi-objective exergy economic optimization method is used to analyze the main performance of the system,Analysis results:With the increase of the concentration of nanoparticles,the net output power of the system increases,but the net output power increases slowly when the effective volume concentration of nanoparticles over 0.6 vol%;Ethanol and R245fa as the base of the nano-working fluid than the amount of ethanol or R245fa pure system of comprehensive performance is better;Using Cu + R245fa/R123(0.9/0.1)in the evaporation temperature range of 75～105 ℃ with a multi-objective function of the smallest,But the evaporation temperature is in the range of 105～115 ℃,Cu + R245fa/R123(0.8/0.2)has the least objective function value.