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Operational Issues
Published in Reinhard Radermacher, Yunho Hwang, Vapor Compression Heat Pumps, 2005
Reinhard Radermacher, Yunho Hwang
An inherent feature of zeotropic mixtures is the different boiling points of their components that result in different vapor and liquid mass fractions at equilibrium. As shown in Figure 9.9.1, the saturated vapor contains more low boiling point component while the saturated liquid contains more high boiling point component when the temperature is between its saturated liquid and vapor temperature (Tsl and Tsv). This mass fraction difference brings new design issues: Mass fraction shift within the cycle.Mass fraction shift due to leakage.Mass fraction shift during refrigerant transfer between containers.Cycle performance effects due to the mass fraction shift.
Refrigerants
Published in Vasile Minea, Industrial Heat Pump-Assisted Wood Drying, 2018
Zeotropic (also called non-azeotropic) refrigerants (e.g., HFC-245fa/HCF-134a, which is used as the working fluid for heat pumps generating steam at >120°C) are chemical mixtures (blends) of two (or more) fluids of which the composition of the liquid phase within the two-phase range is always different from that of the vapor phase, because the very different boiling points of the individual components. They undergo phase changes at varying temperatures during constant-pressure evaporation/boiling and condensation process. In other words, these processes achieve temperature glides, contrary to pure single-component refrigerants that evaporate and condense at constant temperatures.
Thermodynamic analysis of solar power organic Rankine cycle based on experimental data
Published in International Journal of Ambient Energy, 2021
Deepak Tiwari, Ahmad Faizan Sherwani, Deepali Atheaya
Figure 4 shows the effect of variation of mass fraction in evaporation and condensation temperature glide. It is observed from Figure 4 that as mass fraction of mixture’s constituents increases, the temperature glide during evaporation and condensation process increases first and goes to a maximum and it decreases. The highest condensation temperature glide (62.65 K) and highest evaporation temperature glide (61.51 K) are achieved at the same mass fraction 0.45/0.55. It is because when mass fraction of zeotropic mixture constituents increases, the boiling point also increases. The temperature glides in condensation and evaporation proportional to the difference of boiling point temperature of zeotropic mixture’s constituents.
Thermodynamic and multi-objective optimisation of solar-driven Organic Rankine Cycle using zeotropic mixtures
Published in International Journal of Ambient Energy, 2019
Deepak Tiwari, Ahmad Faizan Sherwani, Akhilesh Arora
Pure working fluids have isothermal phase change during evaporation and condensation. Mixtures of pure fluids are mostly zeotropic in nature. The zeotropic mixtures are prepared by mixing of different pure fluids having similar chemical properties with a significant difference in boiling temperatures of pure components (Geng, Du, and Yang 2016). The zeotropic mixtures represent nonhomogeneous composition in vapour and liquid phases and isobaric temperature glide during evaporation and condensation (Lu et al. 2016). The temperature glide is the difference between the temperature of saturated vapour (dew point) and saturated liquid (bubble point). The isobaric temperature glide of zeotropic mixtures during the phase change process brings better thermal match between heat source and working fluid in the evaporator as well as between the cooling medium in the condenser thereby reducing the exergy destruction in heat exchangers due to reduction in finite temperature difference up to a significant level (Wang, Zhao, and Wang 2010; Wang et al. 2010; Aghahosseini and Dincer 2013; Zhao and Bao 2014b). The application of the zeotropic mixture has explored the new range of the working fluid (Feng et al. 2015). In this study five zeotropic mixtures of hydrocarbon butane/isopentane, butane/pentane, isobutane/pentane, isopentane/isobutane and cyclohexane/R123 are used. The considered working fluids are not only thermodynamically efficient in comparison with pure fluids, but also have a very less harmful impact on the environment. The flammability issue limits the application of hydrocarbons. The flammability of hydrocarbon is suppressed by mixing of hydrofluoro carbon and hydrofluoric-olefin (Abadi and Kim 2017).
Optimization and thermo-economic performance analysis of organic Rankine cycles using mixture working fluids driven by solar energy
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2019
Deepak Tiwari, Ahmad Faizan Sherwani, Nishant Kumar
The issue while using zeotropic mixture is the lower value of heat transfer coefficient which results in higher heat exchanger area leading to more cost than pure working. The composition shift phenomenon of the zeotropic mixture during phase change occurs due to the difference in composition of the charged mixture, and circulating mixture results in lower network output of the ORC system. Furthermore, the existence of wider temperature glide of >15 K results in the phenomena of fractionating of zeotropic mixture.