Hugh Russell

The University of Queensland refrigerant and supercritical CO2 test loop

The use of organic refrigerants or supercritical CO (sCO ) as a working fluid in closed loop power cycles has the potential to revolutionise power generation. Thermodynamic cycle efficiency can be improved by selecting bespoke working fluids that best suit a given combination of heat source and heat sink temperatures, but thermal efficiency can be maximised by pairing this with a custom made turbine. This work describes the development and design of a new 100kW thermal laboratory-scale test loop at the University of Queensland. The loop has capabil-ities for characterising both simple and recuperated refrigerant and sCO organic Rankine cycles in relation to overall cycle performance and for the experimental characterisation of radial inflow turbines. The aim of this facility is to generate high quality validation data and to gain new insight into overall loop performance, control operation, and loss mechanisms that prevail in all loop components, including radial turbines when operating with supercritical fluids. The paper describes the current test loop and provides details on the available test modes: An organic Rankine cycle mode, a closed loop Brayton cycle mode, and heat exchanger test mode and their respective operating ranges. The bespoke control and data acquisition system has been designed to ensure safe loop operation and shut down and to provide high quality measurement of signals from more than 60 sensors within the loop and test turbine. For each measurement, details of the uncertainty quantification in accordance with ASME standards are provided, ensuring data quality. Data from the commissioning of the facility is provided in this paper. This data confirms controlled operation of the loop and the ability to conduct both cycle characterisation tests and turbomachinery tests.

[Retracted publication] Design and Testing Process for a 7Kw Radial Inflow Refrigerant Turbine At the University of Queensland

The Queensland Geothermal Energy Centre of Excellence (QGECE) has been developing a small 7 kW refrigerant radialinflow turbine assembly. Such turbines, when used with organic fluids (e.g. refrigerants), result in power cycles that can have a superior thermodynamic efficiency compared to traditional power cycles and turbines in the low to medium temperature range (100-250°C). The intended use for the UQ 7kW turbine unit is validation of CFD simulations, characterisation of turbomachinery loss mechanisms, and validation of 1-D design methodologies. This paper describes the structural and aerodynamic design process that has led to completion of the turbine unit. The first generation aerodynamic design (rotor and stator) and operating points were selected using the QGECEs 1-D mean line design software TOPGEN, to obtain a simple and robust turbine. Results from preliminary CFD simulations to verify the volute and stator operation and stage simulations to provide design and off-design performance characteristics and structural loads are presented. The turbine assembly was designed with modularity in mind to allow future turbine design iteration. Design information is provided for the overall turbine concept and the modular sub-components, including volute, magnetic coupling, bearing chamber design, shaft rotordynamics, FEA analysis and the instrumentation scheme. The paper concludes with a summary of the planned tests.

Rotating Shaft Thermal Analysis for Supercritical Carbon Dioxide Radial Inflow Turbines

Supercritical carbon dioxide (sCO) in power cycles has been shown to have high efficiencies at high temperatures. Good heat transfer properties and high power density reduce cycle complexity and component size when compared with conventional steam cycles. A key design challenge with sCO turbomachinery is the reduced size due to the high power density. This is particularly true for radial inow turbines which are currently more common in low power output applications. This results in reduced space between critical components, requiring a thermal management strategy for safe operation. This paper presents and analyses an active cooling system for the main rotor shaft in a radial inow turbine operating with sCO and utilizing sCO as the cooling fluid. A coupled thermal-fluid-structural heat transfer analysis is conducted. Predicted temperature distributions show that large temperature differences can be achieved over short lengths due to the high convective heat transfer coefficients of sCO under these flow regimes. Performance trends of the cooling system with respect to cooling fluid mass flow rate and coolant inlet temperature are presented.