The impact of working fluid charge on performance of organic Rankine cycle using zeotropic mixture under design condition

Mass-based analysis of thermodynamic cycle can be a link to realize the matching between the working fluid properties, performance of components, and operation parameters. The present paper proposes a working fluid charge-oriented analysis for ORC systems operated with zeotropic fluid mixture. It combines the fundamental equations with the working fluid mixture variation analysis during heat transfer processes, focusing on evaporator and condenser as the phase-change components. This proves to be an effective way to investigate the impact of working fluid mass on performance of ORC systems. Results indicated that liquid-phase zones in both heat exchangers account for more than 60% of total working fluid mass. Since the largest composition shift occurs during condensation, this relation affects the masses and composition shifts in other components as well as the overall system. Moreover, the relationship between the total mass and composition shift of zeotropic mixture are analyzed. It is found that the increase of total mass of working fluid leads to a decrease of mass in the two-phase regions and an increase of mass in the single-phase zones. It therefore causes a reduction of the average composition shift in the system. The system performance analysis shows the highest net output work of 2.42 kW, which occurs when the total mass of working fluid rises to 130% of the design value. However, further increases in mass will have a negative impact on system performance.     «

Mass-based analysis of thermodynamic cycle can be a link to realize the matching between the working fluid properties, performance of components, and operation parameters. The present paper proposes a working fluid charge-oriented analysis for ORC systems operated with zeotropic fluid mixture. It combines the fundamental equations with the working fluid mixture variation analysis during heat transfer processes, focusing on evaporator and condenser as the phase-change components. This proves to b...     »