Multi-Stage Sliding Vane Rotary Expander for Waste Heat Recovery
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Sliding vane rotary expanders in waste heat recovery systems suffer from low pressure expansion ratio and mechanical efficiency due to internal leakage and increased friction at higher rotational speeds, limiting their effectiveness in converting waste heat into useful work.
Innovation Solution
A multi-stage rotary expander design with radially movable vane assemblies and balanced fluid coupling between stages, including a high pressure chamber, intermediate pressure chambers, and a low pressure chamber, along with a balance valve to manage flow imbalances and a gearbox for meeting speed requirements, enhances mechanical efficiency and volumetric efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If rotational speed of sliding vane expander is increased to improve volumetric efficiency, then volumetric efficiency is improved, but sliding friction of vanes against housing increases leading to deterioration in mechanical efficiency
Solution Approach 1:
The expander is divided into multiple stages (first stage with high pressure chamber and first intermediate pressure chamber, second stage with second intermediate pressure chamber and low pressure chamber). Each stage has its own vane assembly that operates independently, allowing optimization of each stage's performance characteristics while managing the trade-off between volumetric and mechanical efficiency across different pressure ratios.
Solution Approach 2:
The patent changes operational parameters by introducing a balance valve that controls fluid coupling between stages. This allows dynamic adjustment of pressure differentials and flow rates, optimizing the balance between volumetric efficiency (benefiting from higher speeds) and mechanical efficiency (suffering from friction at high speeds).
2Stress or pressure
If multi-stage design is implemented to improve pressure expansion ratio, then pressure expansion ratio is improved, but device complexity increases
Solution Approach 1:
Multiple expander stages are merged into a single integrated housing with shared intermediate pressure chambers. The first and second intermediate pressure chambers are fluidly coupled to one another, allowing the stages to operate as a unified system rather than separate units, thereby reducing overall device complexity while maintaining high pressure expansion ratio.
Solution Approach 2:
The intermediate pressure chambers serve dual functions: they act as discharge chambers for the first stage and intake chambers for the second stage. This multi-functionality reduces the need for separate chambers and piping, simplifying the overall device structure while achieving the desired pressure expansion ratio.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The multi-stage design improves the mechanical and volumetric efficiency of the rotary expander, effectively converting waste heat into useful work while maintaining mechanical integrity, thereby enhancing fuel economy and system efficiency.
Implementation Method 1
a working fluid receives heat rejected by an EGR cooler. The recovered waste heat is converted into useful work through an expander
Implementation Method 2
The performance of sliding vane expander is typically not very good due to a low pressure expansion ratio relating to its low volumetric efficiency resulting from internal leakage. Increasing rotational speed of a sliding vane expander improves the volumetric efficiency, however, the siding friction of the vanes against its housing also increases
Data Source
AI summary
A sliding vane rotary expander is used in a waste heat recovery system for a power plant. One example rotary expander has multiple stages with the vane assemblies disposed in bearing supported rings. Another example rotary expander has multiple stages with the vane assemblies disposed in an elliptical cavity. A balance valve equalizes the flow within the stages. Single stage rotary expanders may also be used.