System and method for dynamically determining refrigerant film thickness and dynamically controlling refrigerant film thickness at rolling-element bearing of an oil free chiller
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Solution Overview
Problem
Oil-free centrifugal chillers face challenges in maintaining adequate refrigerant film thickness at rolling-element bearings, especially during start-up and shutdown, due to the lack of residual refrigerant on bearing surfaces.
Innovation Solution
A computerized controller device dynamically determines and controls refrigerant film thickness by monitoring temperature, pressure, and rotation speed, using equations like Formula 1 and Formula 2 to adjust the refrigerant flow and temperature, ensuring a minimum film thickness is maintained between rolling elements and races.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If refrigerant is used as bearing lubricant in oil-free chillers, then the chiller avoids oil contamination and meets environmental requirements, but little or no residual refrigerant remains on bearing surfaces after shutdown causing inadequate lubrication at startup
Solution Approach 1:
The system introduces a preliminary lubrication phase where liquid refrigerant is delivered to the bearing before the compressor impeller reaches full rotational speed. This preliminary action ensures that the bearing surface is coated with refrigerant film before the centrifugal forces during high-speed rotation would otherwise drain or evaporate the lubricant, thereby resolving the contradiction between avoiding residual oil and ensuring adequate startup lubrication.
2Quantity of substance
If liquid refrigerant is delivered to the bearing for lubrication, then adequate film thickness is maintained during operation, but the refrigerant drains away or boils off during shutdown leaving dry bearings
Solution Approach 1:
The system dynamically adjusts refrigerant delivery based on operational state. During operation, liquid refrigerant is delivered to maintain adequate film thickness. During shutdown, the delivery is modulated or stopped to prevent excessive accumulation that would lead to draining or boiling off. This dynamic control resolves the contradiction between maintaining sufficient refrigerant quantity for lubrication and preventing refrigerant loss during transition phases.
3Use of energy by moving object
If the chiller uses a variable speed-driven motor, then energy efficiency is improved, but the bearing experiences varying rotational speeds and loads requiring dynamic refrigerant delivery control
Solution Approach 1:
The system incorporates feedback control where the refrigerant delivery rate is continuously adjusted based on the actual rotational speed and load conditions of the variable speed motor. Sensors monitor bearing temperature, vibration, and operational parameters to dynamically modulate the refrigerant flow, ensuring adequate lubrication across varying speeds while optimizing energy efficiency. This feedback mechanism resolves the contradiction by automating the complexity of dynamic control.
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 solution ensures continuous lubrication and prevents damage by maintaining an adequate refrigerant film thickness, even during start-up and shutdown, thereby extending the operational life of the chiller components.
Implementation Method 1
the liquid refrigerant is provided (1) to the rolling element bearings... for lubrication
Implementation Method 2
to the drive motor of the chiller's compressor for motor cooling purposes
Data Source
AI summary
Methods are directed towards dynamically determining refrigerant film thickness at the rolling-element bearing and for dynamically controlling refrigerant film thickness at the rolling-element bearing. Further, an oil free chiller system is configured for dynamically determining refrigerant film thickness at the rolling-element bearing of the oil free chiller system, wherein the oil free chiller system is also configured for dynamically controlling refrigerant film thickness at the rolling-element bearing of the oil free chiller system.