An examination of exergy destruction in organic Rankine cycles

Abstract

SUMMARYThe exergy topological method is used to present a quantitative estimation of the exergy destroyed in an organic Rankine cycle (ORC) operating on R113. A detailed roadmap of exergy flow is presented using an exergy wheel, and this visual representation clearly depicts the exergy accounting associated with each thermodynamic process. The analysis indicates that the evaporator accounts for maximum exergy destroyed in the ORC and the process responsible for this is the heat transfer across a finite temperature difference. In addition, the results confirm the thermodynamic superiority of the regenerative ORC over the basic ORC since regenerative heating helps offset a significant amount of exergy destroyed in the evaporator, thereby resulting in a thermodynamically more efficient process. Parameters such as thermodynamic influence coefficient and degree of thermodynamic perfection are identified as useful design metrics to assist exergy-based design of devices. This paper also examines the impact of operating parameters such as evaporator pressure and inlet temperature of the hot gases entering the evaporator on ORC performance. It is shown that exergy destruction decreases with increasing evaporator pressure and decreasing turbine inlet temperatures. Finally, the analysis reveals the potential of the exergy topological methodology as a robust technique to identify the magnitude of irreversibilities associated with real thermodynamic processes in practical thermal systems.

Exergy Analysis of Organic Rankine Cycle and Electric Turbo Compounding for Waste Heat Recovery

“…The losses in ORC are higher compared to the ETC. This is due to the evaporator, which is the main contributor in exergy losses in the ORC due its irreversibility associated with heat transfer [25]. In addition, existence of multiple components in the ORC system also adds up to the total losses in exergy.…”

“…Other study has recorded higher exergy efficiency for ORC using different organic fluid [17]. The exergy efficiency can be increased up to 36% by using modified ORC to include turbine bleeding or regenerative ORC [15,25]. Since ORC has higher available exergy, it is possible to use larger capacity electric generator.…”

The Exergy Loss Distribution and the Heat Transfer Capability in Subcritical Organic Rankine Cycle

“…Hung et al [13] discussed the irreversible loss of the key parts in ORC and found that the maximum irreversible loss happens in the evaporator. Analogously, Wei et al [14] showed that the greatest irreversible loss occurs in the evaporator when waste heat temperature varies from 610 K to 650 K. Usually, the greatest exergy loss is in the evaporator under the given conditions [15][16][17][18] and the smallest exergy loss is in the pump in ORC. But the magnitude of exergy loss conditions [15][16][17][18] and the smallest exergy loss is in the pump in ORC.…”

“…Also, many investigations on ORC are mainly focused on the choices of the working fluid [7][8][9][10][11][12] and its performance [13][14][15][16][17][18][19][20][21]. Hung et al [13] discussed the irreversible loss of the key parts in ORC and found that the maximum irreversible loss happens in the evaporator.…”

Performance Evaluation of a Solar-Powered Regenerative Organic Rankine Cycle in Different Climate Conditions

“…In addition, they investigated the effect of mass flow rate on the system performance and found out that as the mass flow rate increased the turbine inlet pressure and turbine rotational speed increased while the regenerator efficiency decreased. Mago et al [21] examined exergy destruction in basic and R-ORCs using the network topological methodology. It was found that the evaporator contributed the most to the exergy loss of both cycles, but the loss of exergy was reduced in the regenerative cycle.…”