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SUMMARY This paper performed a comparative analysis of organic Rankine cycle (ORC) using different working fluids, in order to recover waste heat from a solid oxide fuel cell-gas turbine hybrid power cycle. Depending on operating parameters, criteria for the choice of the working fluid were identified. Results reveal that due to a significant temperature glide of the exhaust gas, the actual ORC cycle thermal efficiency strongly depends on the turbine inlet temperature, exhaust gas temperature, and fluid's critical point temperature. When exhaust gas temperature varies in the range of 500 K to 600 K, R123 is preferred among the nine dry typical organic fluids because of the highest and most stabilized mean thermal efficiency under wide operating conditions and its reasonable condensing pressure and turbine outlet specific volume, which in turn results in a feasible ORC cycle for practical concerns. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

SUMMARY A thermal-economic analysis of a transcritical Rankine power cycle with reheat enhancement using a low-grade industrial waste heat is presented. Under the identical operating conditions, the reheat cycle is compared to the non-reheat baseline cycle with respect to the specific net power output, the thermal efficiency, the heat exchanger area, and the total capital costs of the systems. Detailed parametric effects are investigated in order to maximize the cycle performance and minimize the system unit cost per net work output. The main results show that the value of the optimum reheat pressure maximizing the specific net work output is approximately equal to the one that causes the same expansion ratio across each stage turbine. Relative performance improvement by reheat process over the baseline is augmented with an increase of the high pressure but a decrease of the turbine inlet temperature. Enhancement for the specific net work output is more significant than that for the thermal efficiency under each condition, because total heat input is increased in the reheat cycle for the reheat process. The economic analysis reveals that the respective optimal high pressures minimizing the unit heat exchanger area and system cost are much lower than that maximizing the energy performance. The comparative analysis identifies the range of operating conditions when the proposed reheat cycle is more cost effective than the baseline. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: For clarify main affecting factors on air-source transcritical CO2 heat pump water heaters, and the influence extent of these main affecting factors, at fixed water inlet temperature of 12 °C, an experimental research was conducted on a prototype in a range of ambient temperatures (−15 °C–35 °C) and water outlet temperatures (55 °C–80 °C). Based on the experimental results, effect of water outlet temperatures and ambient temperatures on the optimal discharge pressure and system COP was illustrated, and with change of water outlet temperatures and ambient temperatures, variation of CO2 gas cooler outlet temperatures, evaporating temperatures and other cycle variables was presented and interpreted. According established simulation model, we conducted simulation for the prototype and the cycle respectively adopted another two gas coolers with difference heat transfer surface. As one conclusion, for an established plant, correlation for the optimal discharge pressure as the function of ambient temperatures and water outlet temperatures can be achieved by fitting numerous simulation or experimental results. [Copyright &y& Elsevier]

Highlights: [•] A prototype of transcritical CO2 heat pump water heater was introduced. [•] Experiment was conducted for a prototype of transcritical CO2 heat pump water heater. [•] Simulation was conducted for two categories of gas coolers. [•] Variation of the optimal pressure with heat transfer area was illustrated. [•] Variation of the optimal pressure with CO2 mass flux was illustrated. [ABSTRACT FROM AUTHOR]