Transcritical CO2 Oil Return Control at Radiator Outlet

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

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, where existing oil-return technologies are ineffective, and partial load conditions are not accounted for, leading to reduced reliability and heat transfer performance.

Innovation Solution

The implementation of a flow regulating mechanism in the refrigerant circuit with flow control means that increases refrigerant flow velocity at the radiator outlet if it falls below a threshold, ensuring the return of refrigerating machine oil to the compressor for an extended period, thereby enhancing oil return operations and system reliability.

Engineering Contradictions & Design Principles

VSEngineering 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 outdoor heat exchanger and reduces heat transfer performance

Engineering Contradiction:

Improvelubrication performanceVSAvoidheat transfer performance

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The system performs periodic oil-return operations by controlling the flow regulating mechanism to increase refrigerant flow velocity through the outdoor heat exchanger at specific intervals or under specific conditions, thereby preventing oil accumulation while maintaining high-viscosity oil for lubrication

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The system changes the refrigerant flow velocity parameter dynamically by adjusting the flow regulating mechanism (such as expansion valve opening degree or compressor capacity), creating conditions that promote oil return to the compressor while maintaining optimal lubrication conditions

Inventive Principle:

Principle #35Parameter changes

2Use of energy by moving object

If the refrigerant flow velocity at the radiator outlet is low, then the system operates efficiently under partial load, but the oil accumulates in the outdoor heat exchanger

Engineering Contradiction:

Improveenergy efficiencyVSAvoidoil accumulation prevention

Core Design Contradiction:

Use of energy by moving objectVSReliability

Solution Approach 1:

The flow control means monitors refrigerant flow velocity and provides feedback control by adjusting the flow regulating mechanism when velocity falls below the threshold value, thereby preventing oil accumulation while maintaining energy efficiency

Inventive Principle:

Principle #23Feedback

Solution Approach 2:

The system dynamically adjusts the refrigerant flow velocity based on operating conditions by controlling the flow regulating mechanism, allowing the system to adapt between energy efficiency and oil return requirements

Inventive Principle:

Principle #15Dynamics

3Reliability

If existing oil-return technologies are applied to transcritical cycles, then oil return in subcritical systems is improved, but the technologies are ineffective in supercritical refrigerant systems

Engineering Contradiction:

Improveoil return effectivenessVSAvoidapplicability to transcritical cycle

Core Design Contradiction:

ReliabilityVSAdaptability or versatility

Solution Approach 1:

The invention addresses the inapplicability of existing oil-return technologies by changing the control parameters specifically for transcritical cycles, using refrigerant flow velocity threshold values and flow regulation methods that are effective in supercritical refrigerant systems where traditional technologies fail

Inventive Principle:

Principle #35Parameter changes

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 returns refrigerating machine oil to the compressor, improving the reliability and efficiency of the air-conditioning apparatus by maintaining optimal refrigerant flow and preventing oil accumulation, even under partial load conditions and transcritical cycle operations.

Implementation Method 1

flow control means that controls the flow regulating mechanism. 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

Methodology Applied

Scientific EffectFluid flow regulation:

Data Source

PatentUS9163864B2Air-conditioning apparatus with oil return in a transcritical cycle

Publication Date: 2015.10.20 MITSUBISHI ELECTRIC CORP

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 controller 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 controller 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.