Cooling system with oil return to oil reservoir

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Solution Overview

Problem

Cooling systems using certain primary refrigerants like carbon dioxide face issues where oil gets stuck in low side heat exchangers, leading to compressor failure and reduced efficiency, as it cannot be effectively cycled back to the compressor.

Innovation Solution

The cooling system operates in three modes: normal, oil drain, and oil return modes, where oil from low side heat exchangers is drained into vessels and then pushed back to the compressor using compressed refrigerant, ensuring efficient oil circulation and prevention of oil buildup.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If certain primary refrigerants (e.g., carbon dioxide) are used in the cooling system, then the cooling system can effectively cool various spaces, but the oil gets stuck in the low side heat exchanger and cannot be cycled back to the compressor

Engineering Contradiction:

Improvecooling efficiencyVSAvoidoil circulation

Core Design Contradiction:

ProductivityVSReliability

Solution Approach 1:

The system periodically switches between normal operation mode and oil return mode. During normal operation, cooling is prioritized. When oil accumulation is detected or at scheduled intervals, the system transitions to oil return mode where the fourth valve opens and the fifth valve closes, directing compressed refrigerant to the low side heat exchanger to push oil back to the compressor. This periodic action resolves the contradiction by temporarily sacrificing cooling efficiency to maintain oil circulation reliability.

Inventive Principle:

Principle #19Periodic action

Solution Approach 2:

The low side heat exchanger serves as an intermediary vessel for oil collection and return. Instead of allowing oil to accumulate and cause damage, or requiring direct modification of the compressor, the system uses the low side heat exchanger as a temporary holding area. Compressed refrigerant acts as a mediator to push the accumulated oil from the heat exchanger back to the compressor, resolving the oil circulation problem while maintaining the integrity of the primary cooling function.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Duration of action of stationary object

If the compressor continues to operate without oil return mechanism, then the cooling system maintains continuous operation, but the compressor begins losing oil which eventually leads to breakdown or failure

Engineering Contradiction:

Improvecontinuous operationVSAvoidcompressor lifespan

Core Design Contradiction:

Duration of action of stationary objectVSReliability

Solution Approach 1:

The system implements self-service oil return functionality. The compressor's own discharged refrigerant is redirected through the fifth valve to the low side heat exchanger, where it naturally pushes the accumulated oil back toward the compressor without requiring external power or additional pumping mechanisms. This self-service approach maintains continuous operation while preserving compressor lifespan by preventing oil loss.

Inventive Principle:

Principle #25Self-service

3Reliability

If oil is allowed to drain into a vessel during oil drain mode, then the oil in the low side heat exchanger is removed, but the cooling operation is interrupted

Engineering Contradiction:

Improveoil removalVSAvoidcooling operation

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The system employs periodic action by alternating between normal cooling mode and oil drain/return mode. During normal mode, the first and second valves are closed while the third valve is open, maintaining standard cooling operation. When oil accumulation becomes problematic, the system periodically switches to oil management mode where the fourth valve opens and fifth valve closes to facilitate oil return. This periodic switching resolves the contradiction by temporarily interrupting cooling to maintain system reliability, then resuming full cooling operation.

Inventive Principle:

Principle #19Periodic action

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 prevents oil buildup in low side heat exchangers, improves compressor efficiency, and extends its lifespan by ensuring oil is regularly returned to the compressor, thus maintaining system performance.

Implementation Method 1

the first low side heat exchanger uses primary refrigerant from the flash tank to cool a secondary refrigerant

Methodology Applied

Scientific EffectHeat transfer: Heat Exchanger

Implementation Method 2

compressed refrigerant is directed to the vessel to push the oil in the vessel back towards a compressor

Methodology Applied

Scientific EffectPressure-driven flow: Pressure Gradient

Data Source

PatentUS11384969B2Cooling system with oil return to oil reservoir

Publication Date: 2022.07.12 HEATCRAFT REFRIGERATION PRODUCTS LLC

AI summary

A cooling system drains oil from low side heat exchangers to vessels and then uses compressed refrigerant to push the oil in the vessels back towards a compressor. Generally, the cooling system operates in three different modes of operation: a normal mode, an oil drain mode, and an oil return mode. During the normal mode, a primary refrigerant is cycled to cool one or more secondary refrigerants. As the primary refrigerant is cycled, oil from a compressor may mix with the primary refrigerant and become stuck in a low side heat exchanger. During the oil drain mode, the oil in the low side heat exchanger is allowed to drain into a vessel. During the oil return mode, compressed refrigerant is directed to the vessel to push the oil in the vessel back towards a compressor.