“…Conventionally, these losses are categorized as primary and parasitic losses. Primary losses, 21 such as incidence loss, viscous loss, tip clearance loss, and exit kinetic energy loss, occur in the primary flow path 1-2-3, as shown in Figure 1.Figure 1.Meridional view of inward flow radial turbine with backface flowpath.…”
Section: Parasitic Loss Mechanisms and Modelsmentioning
Inward flow radial (IFR) supercritical CO2 (sCO2) turbines are smaller in size and operate at considerably higher speeds in comparison to similar capacity conventional gas or steam turbines. The compact size and high speed of IFR turbines result in significant parasitic (leakage and disk friction) losses at the rotor backface. This paper presents CFD investigations to understand the mechanism of parasitic losses of IFR turbines in the kW to MW power scales. The first part of the paper presents a parametric study to quantify the effect of backface flowpath dimensions, rotor inlet radius, and rotational speed on the magnitude of parasitic losses. Subsequently, the paper proposes the implementation of a radial labyrinth seal on the rotor backface to curtail the parasitic losses. The second part of the paper examines how the power scale of the turbine and its design parameters, specific speed and velocity ratio, influence the magnitude of parasitic losses. The investigation reveals that parasitic losses cause an efficiency drop of 8%–15% for 100 kW and 4%–9% for 1 MW IFR sCO2 turbines. In addition, IFR turbines designed for low specific speeds and high velocity ratios result in notably higher parasitic losses, leading to a decline in turbine efficiency. Finally, the paper presents optimal turbine design parameters accounting for the parasitic losses to maximize turbine efficiency.
“…Conventionally, these losses are categorized as primary and parasitic losses. Primary losses, 21 such as incidence loss, viscous loss, tip clearance loss, and exit kinetic energy loss, occur in the primary flow path 1-2-3, as shown in Figure 1.Figure 1.Meridional view of inward flow radial turbine with backface flowpath.…”
Section: Parasitic Loss Mechanisms and Modelsmentioning
Inward flow radial (IFR) supercritical CO2 (sCO2) turbines are smaller in size and operate at considerably higher speeds in comparison to similar capacity conventional gas or steam turbines. The compact size and high speed of IFR turbines result in significant parasitic (leakage and disk friction) losses at the rotor backface. This paper presents CFD investigations to understand the mechanism of parasitic losses of IFR turbines in the kW to MW power scales. The first part of the paper presents a parametric study to quantify the effect of backface flowpath dimensions, rotor inlet radius, and rotational speed on the magnitude of parasitic losses. Subsequently, the paper proposes the implementation of a radial labyrinth seal on the rotor backface to curtail the parasitic losses. The second part of the paper examines how the power scale of the turbine and its design parameters, specific speed and velocity ratio, influence the magnitude of parasitic losses. The investigation reveals that parasitic losses cause an efficiency drop of 8%–15% for 100 kW and 4%–9% for 1 MW IFR sCO2 turbines. In addition, IFR turbines designed for low specific speeds and high velocity ratios result in notably higher parasitic losses, leading to a decline in turbine efficiency. Finally, the paper presents optimal turbine design parameters accounting for the parasitic losses to maximize turbine efficiency.
“…Several authors tried to extend the validity of existing correlations developed for ideal gas to organic medium either by combining several loss models [14,15] or by means of the introduction of calibration coefficients and optimization strategies [16]. In the present work it was decided to use the correlation set provided by Meroni et al [16], as it was deemed the most appropriate thanks to the applicability to on-and off-design points and high expansion ratio turbines.…”
In recent years, Organic Rankine Cycle (ORC) technology has received growing interests, thanks to its high flexibility and to the capability to exploit energy sources at temperature levels difficult to be approached with conventional power cycles. These features allow exploiting renewable and renewable-equivalent energy sources, by either improving the energy conversion efficiency of existing plants or using waste heat from industrial process. As far as the expander is concerned, a high potential solution is represented by turbo-expanders, which allow reduction of plant clutter and complexity, so enhancing the potential impact on the diffusion of small power ORC-based plants. The present work concerns the design of a RadialInflow Turbine for a bottoming Organic Rankine Cycle in the tens of kW scale. Design boundary conditions are retrieved by a zero-dimensional model of a solar-assisted micro gas turbine in cogenerating mode. The design process is started by means of an in-house mean-line design code accounting for real gas properties. The code is used to carry out parametric analyses to investigate the design space for several working fluids encompassing different classes, namely refrigerants and siloxanes. The program is used to assess the effect of design variables and working fluid on the turbine performance and turbine design characteristics. Subsequently, the most promising design candidates are selected and three-dimensional first guess stator and rotor geometries are built on these preliminary designs. Stationary and rotating passages are then meshed and analyzed by means of RANS CFD based solution of the stator – rotor interaction.
“…In terms of loss calculation, Persky et al [13] developed a loss model matching method for analyzing CO 2 and the performance of an R143a working medium turbine. They proposed a loss model with higher accuracy through the preferred physical model and the data were derived directly from their experiment.…”
Combining one-dimensional parameter optimization and three-dimensional modeling optimization, a 30 kW radial inflow turbine for ocean thermal energy conversion was designed. In this paper, the effects of blade tip clearance, blade number, twist angle, and wheel–diameter ratio on the radial inflow turbine were analyzed. The results show that the model prediction method based on 3D numerical simulation data can effectively complete secondary optimization of the radial turbine rotor. The prediction model can be used to directly obtain the optimal modeling parameter of the rotor. The tip clearance, blade number, twist angle, wheel–diameter ratio, and shaft efficiency were found to be 0.273 mm, 16, 43.378°, 0.241, and 88.467%, respectively. The optimized shaft efficiency of the turbine was found to be 2.239% higher than the one-dimensional design result, which is of great significance in reducing the system’s power generation costs and promoting the application of this approach in engineering power generation using ocean thermal energy.
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