Design and Optimization of a Radial Inflow Turbine for Use with a Low Temperature ORC

This study aims to design and optimize an organic Rankine cycle (ORC) and radial inflow turbine to recover waste heat from a polymer exchange membrane (PEM) fuel cell. ORCs can take advantage of low-quality waste heat sources. Developments in this area have seen previously unusable, small waste heat sources become available for exploitation. Hydrogen PEM fuel cells operate at low temperatures (70 °C) and are in used in a range of applications, for example, as a balancing or backup power source in renewable hydrogen plants. The efficiency of an ORC is significantly affected by the source temperature and the efficiency of the expander. In this case, a radial inflow turbine was selected due to the high efficiency in ORCs with high density fluids. Small scale radial inflow turbines are of particular interest for improving the efficiency of small-scale low temperature cycles. Turbines generally have higher efficiency than positive displacement expanders, which are typically used. In this study, the turbine design from the mean-line analysis is also validated against the computational fluid dynamic (CFD) simulations conducted on the optimized machine. For the fuel cell investigated in this study, with a 5 kW electrical output, a potential additional 0.7 kW could be generated through the use of the ORC. The ORC’s output represents a possible 14% increase in performance over the fuel cell without waste heat recovery (WHR).

Design Parameter Influence on Losses and Downstream Flow Field Uniformity in Supersonic ORC Radial-Inflow Turbine Stators

The design of organic Rankine cycle (ORC) turbines often requires dealing with transonic flows due to the cycle efficiency requirements and the matching of the temperature profiles with heat sources and sinks, as well as the nature of organic fluids, often featuring high molecular weight. Consequently, the use of convergent–divergent turbine stators has been widely established as a solution in the published literature for use in both axial- and radial-inflow machines. With respect to the latter layout in particular, the available design guidelines are still limited. The present work shows the results of an investigation into a series of ORC radial-inflow convergent–divergent nozzles that differ with respect to the vane count and the designed metal angle of the outlet. These stators were designed by fitting the divergent portion of a sharp-edged minimum-length nozzle, designed by means of the method of characteristics (MoC) adapted to dense gases, into a radial-inflow turbine stator. The geometries were analysed by means of steady-state RANS CFD calculations, and the results were used to assess the influence of the design parameters on the nozzle losses and downstream flow field uniformity, showing that conflicting trends exist between optimum stator efficiency and optimum downstream flow field uniformity.

Leakage flow characteristic of radial inflow turbine adopted in CAES system: Review on progress

Compressed Air Energy Storage (CAES) System is an important power output component of the energy storage technology. Radial inflow turbine is the main power output device in CAES system, it is operated at extraordinary operation condition (inlet pressure ≥ 75 bar and inlet temperature < 500 K) which is different from gas turbine and other turbomachinery. Therefore, clearance existing in the CAES radial inflow turbine will result in special leakage flow characteristic and higher flow loss, which decreases the aerodynamic performance and the economic efficiency of the CAES system. However, most of researches for CAES radial inflow turbine mainly focus on the performance prediction of CAES system with one-dimensional model, the detailed leakage flow loss mechanism based on three-dimensional analysis, which significantly influences the flow structure and efficiency, are still needed to be further conducted. In present study, the progress on leakage flow characteristic in the CAES radial inflow turbine is reviewed. The effects of tip clearance, case-shroud clearance and back cavity of rotors are summarized, the leakage flow mechanism and loss reduction method are also analyzed and discussed. Suggestions for the future work on leakage flow of CAES radial inflow turbine are also proposed. The present review can provide a guide for new design and optimization of the radial inflow turbine adopted in CAES system.

Numerical investigation on the performance of impeller back seal configuration in a supercritical CO2 radial-inflow turbine

Radial-inflow turbine is a core component in supercritical CO2 (SCO2) Brayton cycle. The leakage from the nozzle outlet towards the impeller back brings a great challenge to the efficiency and security of the power system. In this paper, the labyrinth seal (LS) and dry gas seal (DGS) are arranged on the impeller back of a SCO2 radial-inflow turbine and the influence on the comprehensive performance is investigated. Results demonstrate that both LS and DGS configurations can significantly reduce leakage of the impeller back and DGS configuration performs better. Compared with the configuration without leakage, the power and efficiency of DGS configuration are only reduced by 0.27% and 0.35% respectively. The seal clearance and the inlet width have a greater effect on LS configuration. The thermo-mechanical seal deformation values of DGS configurations are all less than 8 μm, which verifies the feasibility. Finally, a novel combined seal configuration with both LS and DGS is proposed and excellent performance is achieved, providing a potential approach for the sealing problem of SCO2 radial-inflow turbine.

Three-Dimensional Performance Analysis of a Radial-Inflow Turbine for Ocean Thermal Energy Conversion System

Turbine is one of the key components of the ocean thermal energy conversion system (OTEC), and its aerodynamic performance and geometric dimension affect the performance of the system directly. This paper proposes a design method for the radial inflow turbine suitable for the ocean thermal energy conversion based on the parameter optimization of the ocean thermal energy conversion system. Aiming at the application characteristics of marine thermal energy conversion in a small temperature difference environment and the special thermophysical properties of the organic working fluid in this environment, one-dimensional design and three-dimensional CFD analysis of the turbine is separately done, of which the results were compared. At the same time, the performance of the turbine was verified by changing the inlet and outlet conditions of the radial turbine under the design conditions. The conclusion is that the three-dimensional CFD results of the turbine are in good agreement with the one-dimensional design, and the internal flow field of the turbine is stable, without obvious backflow and eddy current, which meets the application requirements of the ocean thermal energy conversion.