Transcritical Air Conditioner Flow Control for Radiator Oil Return
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Solution Overview
Problem
Air-conditioning apparatuses using natural refrigerants like carbon dioxide face challenges with refrigerating machine oil accumulation in transcritical cycles, particularly in outdoor heat exchangers and radiators, where existing oil-return technologies are ineffective, and partial load conditions are not adequately addressed.
Innovation Solution
An air-conditioning apparatus with a flow regulating mechanism and flow control means that increases refrigerant flow velocity at the radiator outlet if it falls below a threshold, ensuring refrigerating machine oil is returned to the compressor until the velocity exceeds a second threshold, maintaining reliability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If high-viscosity refrigerating machine oil is used in a transcritical cycle with natural refrigerants, then the lubrication performance is improved, but the oil accumulates in the radiator and heat exchanger due to low solubility
Solution Approach 1:
The system performs periodic oil-return operations by controlling the expansion mechanism to create reverse flow conditions. The expansion mechanism is switched between normal cooling mode and oil-return mode, where in oil-return mode the high-pressure side and low-pressure side are reversed, creating periodic cycles that prevent oil accumulation while maintaining lubrication performance.
Solution Approach 2:
The invention changes the operating parameters of the expansion mechanism to enable oil return. By adjusting the expansion mechanism to operate in reverse mode, the pressure distribution and flow direction are altered, allowing oil to be carried back to the compressor. This parameter change enables the system to switch between normal operation and oil-return operation.
2Productivity
If the refrigerant flow velocity at the radiator outlet is low, then the system operates efficiently under partial load, but the refrigerating machine oil accumulates in the radiator
Solution Approach 1:
The control unit monitors the refrigerant flow velocity at the radiator outlet and compares it against a predetermined threshold. When the velocity falls below the threshold, the control unit activates the oil-return operation by controlling the expansion mechanism. This feedback mechanism ensures that oil accumulation is prevented while allowing efficient operation at higher flow velocities.
Solution Approach 2:
The system dynamically switches between normal cooling mode and oil-return mode based on real-time flow velocity conditions. The expansion mechanism is controlled to create dynamic flow patterns that adapt to varying load conditions, enabling the system to maintain both efficiency and prevent oil accumulation under different operating conditions.
3Reliability
If existing oil-return technologies are applied to transcritical cycles, then oil return may be achieved in vapor compression cycles, but they are ineffective in supercritical refrigerant systems with radiators
Solution Approach 1:
The invention adapts the oil-return mechanism to work specifically with transcritical cycles using supercritical refrigerants and radiators. The expansion mechanism serves dual functions: normal cooling operation and oil-return operation. By controlling the expansion mechanism to reverse flow conditions, the system achieves oil return capability specifically tailored for transcritical cycles, making the technology adaptable to this specific application.
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
Effectively returns refrigerating machine oil to the compressor, enhancing the reliability of the air-conditioning apparatus by preventing oil accumulation and ensuring consistent performance across various load conditions.
Implementation Method 1
If a refrigerant flow velocity, in which the refrigerant is in a supercritical state, at an outlet side of the radiator is lower than a predetermined threshold value, the refrigerant flow velocity at the outlet side of the radiator is increased by the flow control means so that oil-return operation that returns the refrigerating machine oil discharged from the compressor to the compressor is performed
Data Source
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AI summary
In an air-conditioning apparatus that uses a refrigerant, which operates in a transcritical cycle, and refrigerating machine oil, which has low miscibility with the refrigerant, in a refrigerant circuit for a refrigeration cycle connected to a compressor, a radiator, an expansion mechanism, and an evaporator, the air-conditioning apparatus includes a flow regulating mechanism provided in the refrigerant circuit, and flow control means that controls the flow regulating mechanism. If a refrigerant flow velocity at an outlet side of the radiator is lower than a predetermined threshold value, the refrigerant flow velocity at the outlet side of the radiator is increased by the flow control means so that oil-return operation that returns the refrigerating machine oil discharged from the compressor to the compressor is performed for at least a predetermined time period.