Method for improving gas bearing function at low thermal cooling power
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Solution Overview
Problem
Free piston Stirling heat pumps face gas bearing effectiveness decline at higher steady state freezer operating temperatures, leading to potential piston-cylinder contact and frictional wear due to reduced piston amplitude, limiting the higher temperature boundary of the operating range.
Innovation Solution
Implementing a variable frequency AC power source to increase the operating frequency of the Stirling heat pump, which reduces thermal cooling power and piston amplitude, thereby maintaining gas bearing effectiveness and preventing failure by increasing gas flow through the gas bearings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the steady state operating temperature of the freezer is increased to reduce thermal cooling power requirements, then energy efficiency is improved, but gas bearing effectiveness deteriorates due to reduced piston amplitude
Solution Approach 1:
The patent applies dynamics by making the drive frequency variable rather than fixed. The control system dynamically adjusts the drive frequency of the linear electric motors based on real-time piston amplitude measurements. When piston amplitude decreases (indicating potential gas bearing failure), the system increases the drive frequency to restore adequate amplitude, thereby maintaining gas bearing effectiveness while allowing operation at higher steady state temperatures that reduce thermal cooling power requirements.
Solution Approach 2:
The patent changes the operational parameter of drive frequency to resolve the contradiction. By varying the drive frequency within a specified range (e.g., 50-100 Hz), the system can maintain piston amplitude above critical thresholds even when operating at higher temperatures. This parameter change allows the system to decouple the relationship between steady state temperature and gas bearing effectiveness, enabling energy-efficient operation without compromising reliability.
2Loss of energy
If piston amplitude is reduced to decrease thermal cooling power, then energy consumption is reduced, but piston-cylinder contact and frictional wear increase
Solution Approach 1:
The patent implements feedback control by continuously monitoring piston amplitude and using this information to adjust drive frequency. The control system receives feedback from piston amplitude measurements and automatically increases frequency when amplitude approaches critical levels, preventing piston-cylinder contact. This closed-loop feedback mechanism ensures that energy reduction strategies do not compromise mechanical protection, as the system self-corrects before harmful contact occurs.
Solution Approach 2:
The system takes preliminary action by detecting trends in piston amplitude degradation and increasing drive frequency before actual piston-cylinder contact occurs. The control method monitors piston amplitude continuously and proactively adjusts operating parameters to prevent the harmful condition rather than reacting after damage has occurred. This preliminary intervention maintains gas bearing effectiveness throughout the operational cycle.
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
This approach allows the Stirling heat pump to safely operate at higher steady state temperatures by maintaining effective gas bearing operation, preventing piston-cylinder contact and wear, and extending the higher temperature boundary of the operating range.
Implementation Method 1
The pistons and displacer are reciprocated at a constant frequency near their resonant frequency. Although the displacer motion is not balanced, the displacer 16 has a low mass so its contribution to casing vibrations is small and generally acceptable.
Implementation Method 2
a gas bearing system which lubricates the pistons to minimize or prevent contact between the pistons and their cylinders and resulting excessive wear
Data Source
AI summary
A method for increasing working gas flow rate through gas bearings of a free piston, gamma configured Stirling heat pump to avoid failure of the gas bearings while maintaining thermal cooling power. The Stirling heat pump lifts heat from a storage chamber and has pistons that are driven in reciprocation at an operating frequency by linear electric motors. A temperature control maintains a steady state storage chamber temperature by sensing storage chamber temperature and modulating piston amplitude. The invention comprises (a) driving the pistons with linear electric motors that are driven by a variable frequency, AC power source; (b) sensing the pistons' amplitude of reciprocation; and (c) if the sensed piston amplitude is less than a selected piston activation amplitude, increasing the frequency of the AC power source to increase the Stirling heat pump's operating frequency. That decreases thermal cooling power which causes the temperature control to increase piston amplitude.