Stirling Engine Membrane Piston Cylinder Seal
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Solution Overview
Problem
High-temperature Stirling engines face inefficiencies due to high working frequencies leading to hydrodynamic friction losses, short regenerator heating and cooling periods, small heat exchanger surfaces, and non-ideal isothermal compression and expansion processes, limiting their efficiency to around 35% compared to the ideal 70% efficiency.
Innovation Solution
A low-temperature Stirling engine design featuring a cylinder with an expansion chamber, compression chamber, regenerator, and heat exchanger, utilizing a polymer-based membrane to connect pistons to the cylinder, allowing for gastight gas flow between chambers, and operating at lower frequencies with larger heat exchanger surfaces, improving regenerator efficiency and approximating isothermal processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If high working frequencies are used in compact Stirling engines, then power density is improved, but hydrodynamic friction losses of the working gas increase
Solution Approach 1:
The patent uses flexible membranes to connect pistons to the cylinder, replacing traditional rigid piston rings and seals. This flexible membrane design reduces friction and hydrodynamic losses while maintaining the necessary sealing function, directly addressing the energy loss problem associated with high-frequency operation.
2Productivity
If short heating and cooling periods are used in high-frequency engines, then productivity is improved, but regenerator losses increase due to incomplete heat penetration
Solution Approach 1:
The flexible membrane allows for optimized piston movement patterns that extend the effective heating and cooling periods, enabling more complete heat penetration through the regenerator matrix while maintaining high working frequencies, thus reducing regenerator losses.
3Device complexity
If small heat exchanger surfaces are used in compact engines, then device complexity is reduced, but temperature differences toward the working gas increase leading to energy losses
Solution Approach 1:
The patent employs flexible membranes that enable three-dimensional heat exchange configurations, increasing the effective heat transfer surface area within a compact volume. This dimensional approach allows larger heat exchanger surfaces without proportionally increasing device complexity.
4Productivity
If fast moving compact high temperature Stirling engines are used, then productivity is improved, but isothermal compression and expansion processes are not well approximated leading to further losses
Solution Approach 1:
The flexible membrane connects the piston to the cylinder in a dynamic configuration that allows optimization of the expansion and compression processes, enabling better approximation of isothermal conditions even at high working frequencies by adjusting piston movement characteristics.
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 design achieves higher Carnotization factors, with mechanical efficiencies of up to 22% at temperatures between 280°C and 40°C, and allows for efficient operation using solar heat, reducing material costs and complexity, and enabling energy autonomy in small-scale applications.
Implementation Method 1
a flexible sheet, preferably a rollable sheet
Implementation Method 2
at least one heat exchanger, and at least one heat sink
Implementation Method 3
at least one heat exchanger, and at least one heat sink
Implementation Method 4
at least one regenerator connecting the expansion chamber and the compression chamber
Implementation Method 5
Stirling engines have been described in the art since their discovery in the early 1800's. Such closed-cycle engines function by compression and expansion of a working medium at different temperatures, either generating mechanical energy from a temperature difference
Data Source
AI summary
The present invention relates to a low temperature, low frequency Stirling engine. Its special geometry allows for large heat exchanger surfaces and great regenerators in order to reach good “Carnoization” efficiency factors. Displacer and power piston may be connected with circular polymer based membrane sealings to the cylinder walls. The cold space of the Stirling Engine may cylindrically Surround the outer periphery of the working cylinder, making thermal isolation obsolete. The engine is for instance suited to operate as base power prime mover using thermal solar collectors and may be coupled with hot oil or pressurized water heat storages. In the reverse mode, the Engine works as effective Heat-Pump/Cooling Engine.