CO₂ Refrigeration Ejector Bypass for Low Ambient Temperature Operation
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Solution Overview
Problem
Carbon dioxide-based refrigeration systems are sensitive to ambient temperature fluctuations, leading to subcritical or transcritical operating conditions, especially in low ambient temperatures, where the low-pressure lift ejector fails to provide sufficient pressure lift, necessitating additional energy consumption through a refrigerant pump.
Innovation Solution
Incorporating a bypass line and a bypass control valve in the refrigerant circuit, allowing the system to switch between ejector and bypass modes based on ambient temperature, thereby avoiding low-pressure lift operations and reducing energy consumption by bypassing the ejector when necessary.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a low pressure lift ejector is used in a CO2 refrigeration system, then the system can operate at ambient temperatures of around 17-18°C with sufficient pressure lift, but the ejector fails to provide sufficient pressure lift in low ambient temperature conditions (e.g., winter)
Solution Approach 1:
The system dynamically switches between two operational modes (ejector mode and bypass mode) based on ambient temperature conditions. A control valve automatically directs refrigerant flow through the ejector when ambient temperature is above a threshold (providing sufficient pressure lift) and through the bypass line when ambient temperature is below the threshold (avoiding insufficient pressure lift). This dynamic adaptation resolves the contradiction between reliable ejector operation and adaptability across temperature ranges.
2Reliability
If an additional refrigerant pump is used to overcome insufficient pressure lift across the ejector in low temperature conditions, then the pressure lift problem is solved, but energy consumption increases
Solution Approach 1:
The invention extracts the ejector component from the mandatory flow path and provides an alternative bypass route. Instead of relying on the ejector to provide pressure lift in all conditions (which would require an additional pump to compensate for insufficient lift), the system allows refrigerant to bypass the ejector entirely when pressure lift is insufficient. This eliminates the need for an additional energy-consuming pump while maintaining reliable operation across all temperature conditions.
3Device complexity
If the ejector is operated in low pressure lift conditions, then the system can maintain simplicity without additional pumps, but the ejector provides no benefits and acts merely as a high-pressure valve
Solution Approach 1:
The control valve dynamically routes refrigerant flow based on operating conditions. When ambient temperature is high, the valve directs flow through the ejector where it can provide its full performance benefit (pressure lift, flash gas removal). When ambient temperature is low, the valve bypasses the ejector, preventing it from operating in its ineffective low-pressure-lift regime. This ensures the ejector only operates when productive, maintaining system simplicity without sacrificing performance.
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 configuration reduces system complexity and energy consumption, enabling efficient operation in both low and high cooling load conditions by acting as a simple single-stage vapor-compression system, optimizing performance based on external conditions without the need for additional pumps.
Implementation Method 1
the low pressure lift ejector is able to operate to provide a pressure lift, entraining and mixing the low pressure fluid from the suction inlet (from the evaporator) with the high pressure fluid from the motive inlet
Implementation Method 2
the liquid outlet of the receiver is connected via the expansion device to an inlet of the heat absorbing heat exchanger
Implementation Method 3
heat absorbing heat exchanger... the ejector secondary inlet is arranged to receive fluid from an outlet of the heat absorbing heat exchanger
Implementation Method 4
heat rejecting heat exchanger... the ejector primary inlet is arranged to receive fluid from an outlet of the heat rejecting heat exchanger
Data Source
AI summary
A refrigeration system for a carbon dioxide based refrigerant fluid, wherein the refrigeration system includes a refrigerant circuit, the refrigerant circuit including a compression device, a heat rejecting heat exchanger, an ejector, a receiver, an expansion device, and a heat absorbing heat exchanger; wherein the ejector includes a primary inlet, a secondary inlet and an outlet; wherein the receiver includes an inlet, a liquid outlet and a gas outlet; wherein the ejector primary inlet is arranged to receive fluid from an outlet of the heat rejecting heat exchanger, the ejector secondary inlet is arranged to receive fluid from an outlet of the heat absorbing heat exchanger, and the ejector outlet is arranged to direct flow to the receiver inlet; wherein a suction inlet of the compression device is arranged to receive refrigerant fluid from the gas outlet of the receiver.