Two-Stage Centrifugal Compressor Recirculation for Part-Load Stability

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Solution Overview

Problem

Refrigerant compressors face challenges in efficiently managing capacity control during part-load operating conditions, particularly in maintaining optimal flow angles and velocities, which can lead to instability and reduced efficiency.

Innovation Solution

The implementation of a centrifugal refrigerant compressor system with a recirculation flow path and an economizer flow path, where fluid from these paths is introduced into the main flow path through strategically located ports, either adjacent to the return channel between impellers or downstream of the second impeller, to stabilize operation and improve efficiency.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If variable inlet guide vanes are used to regulate capacity, then capacity control is improved, but device complexity increases

Engineering Contradiction:

Improvecapacity controlVSAvoiddevice complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent removes the variable inlet guide vanes from the system entirely, replacing them with a recirculation flow path that extracts excess refrigerant from the discharge side and returns it to the suction side, thereby simplifying the device while maintaining capacity control capability

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces a recirculation flow path as an intermediary mechanism between the discharge and suction sides of the compressor, using this intermediate path to control capacity by regulating the amount of recirculated refrigerant rather than using complex inlet guide vanes

Inventive Principle:

Principle #24Intermediary (Mediator)

2Adaptability or versatility

If variable-geometry diffusers are added to improve capacity control, then capacity control is improved, but device complexity increases

Engineering Contradiction:

Improvecapacity controlVSAvoiddevice complexity

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent eliminates the variable-geometry diffusers from the system, replacing their flow control function with the recirculation flow path that achieves capacity control through refrigerant recirculation rather than geometric adjustment of diffuser passages

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The recirculation flow path serves as an intermediary mechanism that performs the capacity control function previously achieved by variable-geometry diffusers, but with simpler construction and fewer moving parts

Inventive Principle:

Principle #24Intermediary (Mediator)

3Adaptability or versatility

If recirculation is implemented without proper port location, then capacity control is improved, but stability deteriorates due to surge conditions

Engineering Contradiction:

Improvecapacity controlVSAvoidoperational stability

Core Design Contradiction:

Adaptability or versatilityVSStability of the object's composition

Solution Approach 1:

The patent strategically locates the recirculation port upstream of the impeller inlet, allowing recirculated refrigerant to mix with incoming refrigerant before entering the impeller, which preliminary stabilizes the flow and prevents surge conditions

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The patent positions the recirculation port at a specific location upstream of the impeller inlet where the recirculated refrigerant can be properly mixed with the main flow, creating local flow conditions that prevent surge while maintaining overall system stability

Inventive Principle:

Principle #3Local quality

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 stability and efficiency of the compressor during part-load conditions, extends the operating range, and reduces the likelihood of surge conditions, while also simplifying the mechanical components and eliminating the need for inlet guide vanes or variable geometry diffusers.

Implementation Method 1

a recirculation flow path from the discharge side of the compressor to the suction side

Methodology Applied

Scientific EffectRecirculation flow:

Implementation Method 2

an economizer flow path from the economizer to the main flow path of the compressor

Methodology Applied

Scientific EffectFlash gas:

Implementation Method 3

Fluid from a recirculation flow path and an economizer flow path is introduced into a main flow path of the compressor by way of the at least one port

Methodology Applied

Scientific EffectFluid mixing:

Implementation Method 4

a centrifugal compressor having a first impeller and a second impeller downstream of the first impeller

Methodology Applied

Scientific EffectCentrifugal compression: Centrifugal Force

Data Source

PatentUS9382911B2Two-stage centrifugal compressor with extended range and capacity control features

Publication Date: 2016.07.05 DANFOSS AS

AI summary

One exemplary embodiment of this disclosure relates to a centrifugal refrigerant compressor system. The system includes a condenser, an evaporator, and an economizer between the condenser and the evaporator. The system further includes a centrifugal compressor having a first impeller and a second impeller downstream of the first impeller. The compressor includes at least one port. Fluid from a recirculation flow path and an economizer flow path is introduced into a main flow path of the compressor by way of the at least one port.