Refrigerated Container Oil Return Cycle to Prevent Compressor Failure
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Solution Overview
Problem
Refrigerated truck systems fail to maintain accurate temperature set points, particularly for fresh goods, due to oil logging in eutectic plates when switching from eutectic plate evaporators to blower evaporators, which can lead to compressor oil level reduction and potential failure.
Innovation Solution
A control module is used to manage the flow of a refrigerant and oil mixture through eutectic plates and evaporators, increasing compressor speed to drive refrigerant out of eutectic plates and back to the compressor, then switching to the blower evaporator, ensuring minimal oil logging and maintaining safe refrigerant levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the eutectic plates are closed off from the rest of the system when running the blower evaporator, then the temperature control for fresh goods is improved, but oil logging in the plates occurs which reduces compressor oil level and may cause failure
Solution Approach 1:
The control module performs preliminary action by initiating an oil return cycle before switching to the blower evaporator. The compressor operates at increased speed for a predetermined time period to drive refrigerant and oil from the eutectic plates back to the compressor, ensuring oil is recovered before the plates are closed off, thus preventing oil level reduction and compressor failure
Solution Approach 2:
The system dynamically adjusts compressor speed based on operational phase. The compressor operates at increased speed during the oil return cycle and at normal speed during regular cooling operation. The control module also dynamically switches between eutectic plate evaporator and blower evaporator based on temperature requirements, enabling the system to adapt to different loading conditions and prevent oil logging
2Reliability
If the compressor speed is increased to drive refrigerant out of eutectic plates, then oil return to compressor is improved, but energy consumption increases
Solution Approach 1:
The system implements periodic action by operating the compressor at increased speed only for a predetermined time period during the oil return cycle, rather than continuously. The control module timers the high-speed operation to last only long enough to recover oil from the eutectic plates, then returns the compressor to normal operating speed, thus minimizing energy consumption while ensuring adequate oil return
Solution Approach 2:
The system uses its own compressor to perform the oil return function by temporarily increasing its speed. The refrigerant circulation system self-regulates to drive oil back to the compressor during the predetermined time period, eliminating the need for separate oil return mechanisms and reducing overall system energy requirements
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 effectively reduces oil logging in eutectic plates, maintaining accurate temperature control and preventing compressor failures, thereby enhancing the reliability of refrigerated truck systems for transporting both frozen and fresh goods.
Implementation Method 1
A compressor compresses a refrigerant
Implementation Method 2
A eutectic plate cools a refrigerated space, and a mixture of the refrigerant and an oil flows through the eutectic plate to cool the eutectic plate
Implementation Method 3
An evaporator cools the refrigerated space, and the mixture also flows through the evaporator
Data Source
AI summary
A compressor compresses a refrigerant. A eutectic plate cools a refrigerated space. An evaporator cools the refrigerated space. A mixture of the refrigerant and an oil flows through the evaporator and the eutectic plate. A control module controls the compressor, a first valve that permits or prevents flow of the mixture to the eutectic plate, and a second valve that permits or prevents flow of the mixture to the evaporator. In response to a temperature of the refrigerated space being greater than a predetermined temperature, the control module: increases a speed of the compressor; operates the compressor at the increased speed for a predetermined time period; after the predetermined period: opens the second valve; and closes the first valve, where the control module opens the second valve before closing the first valve, and decreases the speed of the compressor after closing the first valve.