Research On The Performance Of Zeotropic Mixtures Used In Organic Rankine Cycle System

The shortage of fossil energy makes people more aware of the importance of low grade waste heat.Organic Rankine Cycle,as one of the key technologies to made use of low grade waste heat,had drawn many scholars' attention.This paper conducted simulation experiment on Organic Rankine Cycle using zeotropic mixtures as working fluid under both subcritical and supercritical evaporation pressure.Meanwhile,this paper analyzed pure-working-fluid-using Organic Rankine Cycle and how load capacity and heat source temperature affected system performance with experimental research methods.All their physical parameters analyzed,7 kinds of suitable organics were selected,which were R227ea,R152a,R134a,R113,R11,R21 and R245fa.With R245fa as the basic working fluid,6 different zeotropic mixtures were made by mixing R245fa with other organics.Thermodynamic models were built to study how system performance,parameters varied with 6 different types of zeotropic mixtures.When the evaporation pressure was in the subcritical state and the heat absorption of the working fluid stayed stable,the zeotropic mixtures could better improve the output power and thermal efficiency than the pure working fluid.With the pure working fluid R245fa used,the maximum output power was 11.98 kW and the maximum thermal efficiency was 6.07%.Compared with the pure working fluid,when zeotropic mixtures R113/R245fa(0.7:0.3)were taken,the output power and thermal efficiency were increased by 22.87%and 22.89%respectively.In addition,there was an inverse relationship between the entranspy dissipation and the system net power.When zeotropic mixtures R113/R245fa(0.7:0.3)reached the maximum net power,.the entranspy dissipation was 5778.3 K kW,the minimum value in the six mixtures.As the evaporation pressure was in the supercritical state,different mixtures had different optimum evaporation pressures.Under its optimum evaporation pressure of 3.87MPa,the system thermal efficiency which used R11/R245fa(0.8:0.2)as working fluid was 14.59%,and its net output power was 68.58 kW,which both reached the maximum value among the 6 mixtures.After the exergy efficiency of 6 different mixtures were studied,it was found that when R113/R245fa(0.7:0.3)was under the evaporation pressure of 3.03MPa,its exergy efficiency reached 48.28%,the maximum value among the 6 different mixtures.A further analysis on exergy loss was carried out,which showed the maximum exergy loss happened in the evaporator.And when the evaporation pressure grew,the exergy loss in the pump and the expander would go down,while that in the evaporator and the condenser would go up.A 5kW integrated power generation system of organic Rankine cycle was set up during our experimentation.Based on that,this paper studied how system performance parameters would vary with different expander speeds when the heat source temperature was 105? and 120 ?,and the load capacity was 1.5 kW and 3 kW.The experimental results show that when the load capacity was 3 kW,along with increasing revolving speed and heat source temperature,the thermal efficiency of the system would be on the rise.When the heat source temperature was 105? and 120?,the maximum thermal efficiency of the system would reach 2.88%and 2.52%.When the heat source temperature was 105?and the load capacity was 3 kW,the maximum electric efficiency of the system would be 4.66%.When the load capacity was 1.5 kW,the maximum electric efficiency of the system was 2.66%.