Principles and advantages of three common oil return methods for refrigeration units

Principles and advantages of three common oil return methods for refrigeration units

1. Injector oil return technology
As a key fluid dynamic equipment, the injector (or jet) plays an important role in the oil return system. Its working principle is based on the injection effect in fluid mechanics. When the refrigerant passes through the nozzle of the injector at high speed, according to the principles of fluid mechanics, a significant low-pressure area will be formed here.

This low-pressure area is like a powerful "suction source" that can attract lubricating oil or other fluids in the surrounding environment. In the injector return oil system, lubricating oil is usually first thoroughly mixed with refrigerant fluid through pipelines or oil separators and other devices. Subsequently, the injector, with its unique structure and working mode, accurately guides the oil in the mixed fluid from the low-pressure area to the suction end of the compressor. Dry filters and sight glasses are usually required in the system to prevent impurities from entering the compressor and monitor the return oil status.

advantage
Efficient oil return: The injector utilizes the kinetic energy of the refrigerant to achieve oil return without the need for external pumps or complex mechanical devices. In complex refrigeration systems, this oil return method can efficiently bring oil back to the compressor, ensuring system lubrication.
Energy and cost savings: Compared to traditional oil return pump systems, injector oil return technology does not require additional power drive and can operate solely on the fluid power source within the system. The primary flow rate can be adjusted through solenoid valves and angle valves to further optimize the return oil efficiency.
Strong adaptability: Suitable for systems of various scales, especially for long pipelines or complex layout scenarios.

2. Direct oil return technology
Direct oil return technology optimizes pipeline design to allow lubricating oil to mix with refrigerant and flow back directly to the compressor without the need for an oil gas separator. The specific process is as follows: after mixing with refrigerant in the evaporator, the lubricating oil flows back directly to the suction end of the compressor through carefully designed pipelines (such as orifice plates or electronic expansion valves to control flow). Strict control of the return oil volume is required to avoid liquid compression issues, which can be optimized through exhaust temperature monitoring.
advantage
Simplify system design: Save on oil separators and return pumps, reducing design complexity.
Reduce costs and energy consumption: Reduce equipment investment and maintenance costs, and improve energy efficiency.
Improve oil return efficiency: Ensure fast and stable oil return, maintain compressor lubrication.
Reduce system failure rate: reduce the number of mechanical components and enhance reliability

3. Gravity return oil
The core of gravity oil return is to use gravity to naturally flow lubricating oil from the high point of the system to the suction end of the compressor by designing the pipeline slope and height difference reasonably. The evaporator position should be higher than the compressor to create sufficient height difference to drive oil reflux. After mixing with the refrigerant, the lubricating oil is separated in the evaporator and then refluxed through a well-designed oil passage.
advantage
Simplify system structure: reduce complex equipment and facilitate maintenance.
Reduce energy consumption: No need for oil pump, significant energy-saving effect.
High reliability: independent of external devices, low failure rate.
Reduce maintenance costs: It is necessary to precisely control the evaporator liquid level through high/low pressure float valves or electronic expansion valves to ensure stable oil return. .

summarize
Each of the three oil return methods has its own advantages and disadvantages:
Injector oil return: suitable for complex systems, requiring attention to power source and filtration monitoring;
Direct oil return: efficient and energy-saving, but the risk of liquid compression needs to be controlled;
Gravity oil return: Depending on the evaporator position and heat exchanger design, suitable for simple systems.
In practical applications, it is necessary to select appropriate solutions based on system requirements and optimize operational effects by combining control components.

Shanghai KUB Refrigeration Equipment Co., Ltd.

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