- Title
- Design, modelling, and optimization of inlet control valves for gas expanders for extended efficiency
- Creator
- Hossain, Md Shazzad
- Date
- 2024
- Type
- Text; Thesis; PhD
- Identifier
- http://researchonline.federation.edu.au/vital/access/HandleResolver/1959.17/204859
- Identifier
- vital:20102
- Abstract
- The Organic Rankine Cycle (ORC) is a promising process in energy systems due to its compact design and efficient operation with low-temperature heat sources. These attributes make it particularly suitable for small-scale power plants utilizing waste heat and renewable energy, contributing to the broader goal of sustainable energy solutions. A critical component in ORC systems is the gas expander, whose performance greatly influences the overall efficiency of the power plant. Among gas expanders, positive displacement machines, especially rotary type limaçon expanders, are highly advantageous for small-scale applications due to their ability to operate effectively at low speeds, low flow rates, and high-pressure ratios. These machines exhibit favourable pressure characteristics, offering significant efficiency and reliability advantages over conventional expander systems. Traditional gas expansion systems often rely on uncontrolled inlet ports or cam-operated valves that allow working fluid into the expander chamber but lack the ability to regulate the fluid flow effectively. This constraint leads to the wastage of high-quality working fluid and limited adaptability to varying loads. In contrast, a controlled inlet valve with an appropriate control scheme can address this issue by regulating fluid flow, thereby enhancing expander performance. This potential for enhancement, whilst it offers hope for the future of these energy conversion systems, underscores the significance of research projects focusing on designing, modelling, and controlling inlet valves to ensure desirable performance levels are achieved. This research initially proposes two direct-drive rotary valves actuated by a stepper motor and a rotary solenoid. Their performance is examined through mathematical models, and a comparative analysis of their impact on the limaçon gas expander’s performance is provided. The effects of temperature, friction, pressure, and leakage are also analyzed. The study finds that including the stepper motor valve can increase the isentropic and volumetric efficiencies of the expander considerably. However, this valve’s performance is sensitive to inlet pressure, which can degrade expander performance at higher pressures. Conversely, though less sensitive to pressure changes, the rotary solenoid valve yields improvements to these efficiencies to a lesser extent. A fast and accurate mathematical model is essential for optimizing and controlling complex systems such as a valved expander. Traditional analytical models, which are complex and time-consuming, are often computationally intensive and less suited for optimization and control applications. To address this limitation, an artificial neural network model is developed to predict the complex input-output relationships within the limaçon expander-stepper motor valve system. This model achieves high accuracy, with a normalized mean square error of 0.0014 and a coefficient of determination of 0.98, and is computationally efficient, outperforming simpler interpolation methods by 5.07%. The model’s efficiency and reduced computational loads make it suitable for optimizing and controlling the expander-valve system. The inlet valve must be optimized to achieve fast and accurate response characteristics. Thus, a push-pull solenoid valve is optimized using a Simultaneous perturbation stochastic approximation (SPSA) method. This optimization results in a 56-58% improvement in valve response speed. Analytically testing the optimized valve on a generic non-optimized limaçon expander shows that a faster valve alone can enhance the expander’s isentropic and volumetric efficiencies by 2.24% and 5.04% respectively. It is also observed that the optimized valve is robust and performs well even at lower pressures. However, future research will attempt to optimize a complex system that combines a valve and an expander. This thesis offers critical insights into the design and optimization of inlet valves for gas expanders, demonstrating their significant potential to enhance expander performance, particularly within ORC-based power generation. By addressing existing challenges and proposing innovative solutions, this work advances the prior understanding of limaçon expander technology and highlights the untapped potential of controlled inlet valves to improve performance. These findings lay the groundwork for future developments in small-scale renewable energy systems, significantly impacting the commercial viability of ORC-based power generation. However, further research is needed to translate these insights into practical, commercially viable applications.; Doctor of Philosophy
- Publisher
- Federation University Australia
- Rights
- All metadata describing materials held in, or linked to, the repository is freely available under a CC0 licence
- Rights
- Copyright Md Shazzad Hossain
- Rights
- Open Access
- Subject
- Organic Rankine cycle; Energy conversion; Limaçon gas expander; Control valve actuators; Mathematical modelling; Optimization
- Full Text
- Thesis Supervisor
- Sultan, Ibrahim
- Hits: 98
- Visitors: 100
- Downloads: 13
Thumbnail | File | Description | Size | Format | |||
---|---|---|---|---|---|---|---|
View Details Download | SOURCE2 | Australian Digital Thesis | 8 MB | Adobe Acrobat PDF | View Details Download |