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Thermodynamic efficiency is a crucial factor of a power cycle. Most of the studies indicated that efficiency increases with increasing heat source temperature, regardless of heat source type. Although this assumption generally is right, when the heat source temperature is close to the critical temperature, increasing the heat source temperature can decrease efficiency. Therefore, in some cases, the increase in the source temperature, like using improved or more collectors for a solar heat source can have a double negative effect by decreasing efficiency while increasing the installation costs. In this paper, a comparison of the CO2 subcritical cycle and the Trilateral Flash Cycle will be presented to show the potential negative effect of heat source temperature increase.
Aram Mohammed Ahmed; Attila R. Imre. Effect of high temperatures on the efficiency of sub-critical CO2 cycle. Pollack Periodica 2021, -1, 1 .
AMA StyleAram Mohammed Ahmed, Attila R. Imre. Effect of high temperatures on the efficiency of sub-critical CO2 cycle. Pollack Periodica. 2021; -1 (aop):1.
Chicago/Turabian StyleAram Mohammed Ahmed; Attila R. Imre. 2021. "Effect of high temperatures on the efficiency of sub-critical CO2 cycle." Pollack Periodica -1, no. aop: 1.
The increase of the maximal cycle temperature is considered as one of the best tools to increase cycle efficiency for all thermodynamic cycles, including Organic Rankine Cycles (ORC). Technically, this can be done in various ways, but probably the best solution is the use of hybrid systems, i.e., using an added high-temperature heat source to the existing low-temperature heat source. Obviously, this kind of improvement has technical difficulties and added costs; therefore, the increase of efficiency by increasing the maximal temperature sometimes has technical and/or financial limits. In this paper, we would like to show that for an ideal, simple-layout ORC system, a thermodynamic efficiency-maximum can also exist. It means that for several working fluids, the thermodynamic efficiency vs. maximal cycle temperature function has a maximum, located in the sub-critical temperature range. A proof will be given by comparing ORC efficiencies with TFC (Trilateral Flash Cycle) efficiencies; for wet working fluids, further theoretical evidence can be given. The group of working fluids with this kind of maximum will be defined. Generalization for normal (steam) Rankine cycles and CO2 subcritical Rankine cycles will also be shown. Based on these results, one can conclude that the increase of the maximal cycle temperature is not always a useful tool for efficiency-increase; this result can be especially important for hybrid systems.
Aram Mohammed Ahmed; László Kondor; Attila R. Imre. Thermodynamic Efficiency Maximum of Simple Organic Rankine Cycles. Energies 2021, 14, 307 .
AMA StyleAram Mohammed Ahmed, László Kondor, Attila R. Imre. Thermodynamic Efficiency Maximum of Simple Organic Rankine Cycles. Energies. 2021; 14 (2):307.
Chicago/Turabian StyleAram Mohammed Ahmed; László Kondor; Attila R. Imre. 2021. "Thermodynamic Efficiency Maximum of Simple Organic Rankine Cycles." Energies 14, no. 2: 307.