Trans-Critical CO2 Ejector Cooling System to Reduce Throttling Losses

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Solution Overview

Problem

Aircraft cooling systems face inefficiencies due to significant throttling losses and reduced coefficient of performance (COP) in gas-based systems, which are bulky and fail to effectively manage varying ambient conditions.

Innovation Solution

The implementation of a cooling system that includes a first heat exchanger, an expander, at least one compressor, an ejector, and a liquid separator, with a two-stage compression and recuperative heat exchanger, using CO2 as a refrigerant to span the temperature range and improve system performance, and incorporating redundancy and independent compressor operation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a gas-based cooling system is used to accommodate wide ambient operating conditions, then the system can cover the range of conditions, but the system becomes bulky and less efficient

Engineering Contradiction:

Improveability to cover range of ambient conditionsVSAvoidsystem bulk

Core Design Contradiction:

Adaptability or versatilityVSWeight of moving object

Solution Approach 1:

The patent uses CO2 refrigerant which allows trans-critical operation, changing the thermodynamic parameters to achieve both compact size and adaptability. The system operates above the critical point of CO2 at high ambient temperatures and pressures, enabling efficient cooling across wide ambient conditions without requiring a bulky gas-based system.

Inventive Principle:

Principle #35Parameter changes

2Stress or pressure

If an expansion valve is used to expand refrigerant to the required pressure, then the pressure control is achieved, but significant throttling losses occur and COP is reduced

Engineering Contradiction:

Improvepressure controlVSAvoidthrottling losses

Core Design Contradiction:

Stress or pressureVSLoss of energy

Solution Approach 1:

The patent replaces the traditional expansion valve (mechanical throttling device) with an ejector that uses fluid dynamics principles. The ejector uses a motive stream to create a low-pressure region that draws in and compresses the refrigerant, eliminating the isenthalpic throttling process and its associated energy losses while maintaining pressure control.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Device complexity

If a single compressor is used, then the system is simpler, but the system lacks redundancy and flexibility for varying conditions

Engineering Contradiction:

Improvesystem simplicityVSAvoidsystem redundancy

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent divides the compression function into multiple independent compressors that can operate individually or in combination. This segmentation provides redundancy (if one compressor fails, others can continue operation) and flexibility (compressors can be independently controlled to match varying cooling demands), while keeping each individual compressor unit relatively simple.

Inventive Principle:

Principle #1Segmentation

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 enhances the coefficient of performance (COP) and reduces throttling losses, providing efficient cooling across a wide range of ambient conditions while maintaining system reliability and flexibility.

Implementation Method 1

an ejector configured to receive the refrigerant from the expander as a motive stream that evacuates and compresses the refrigerant from an evaporator

Methodology Applied

Scientific EffectEjector effect: Injector

Implementation Method 2

a first heat exchanger for cooling a refrigerant

Methodology Applied

Scientific EffectHeat exchange: Heat Exchanger

Implementation Method 3

an expander configured to receive the refrigerant from the first heat exchanger

Methodology Applied

Scientific EffectExpansion:

Implementation Method 4

at least one compressor configured to compress the refrigerant

Methodology Applied

Scientific EffectCompression:

Implementation Method 5

a liquid separator coupled to an output of the ejector and configured to provide liquid refrigerant to an evaporator loop and vapor refrigerant to the at least one compressor

Methodology Applied

Scientific EffectPhase separation:

Implementation Method 6

the evaporator configured to receive the refrigerant from the expansion device, heat the refrigerant from a heat load

Methodology Applied

Scientific EffectEvaporation:

Data Source

PatentUS10773818B2Trans-critical CO2 cooling system for aerospace applications

Publication Date: 2020.09.15 ROLLS ROYCE CORP

AI summary

A cooling system includes a first heat exchanger for cooling a refrigerant, an expander configured to receive the refrigerant from the first heat exchanger at least one compressor configured to compress the refrigerant, an ejector configured to receive the refrigerant from the expander as a motive stream that evacuates and compresses the refrigerant from an evaporator, and a liquid separator coupled to an output of the ejector and configured to provide liquid refrigerant to an evaporator loop and vapor refrigerant to the at least one compressor. The evaporator loop includes an expansion device positioned to expand the liquid refrigerant from the liquid separator, and the evaporator configured to receive the refrigerant from the expansion device, heat the refrigerant from a heat load, and pass the refrigerant to the ejector.