Two-Stage Centrifugal Compressor Diffuser Layout for Part-Load Surge

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Solution Overview

Problem

Existing multi-stage centrifugal compressors with fixed, vaneless diffusers face efficiency losses and early surge at part-load conditions due to sensitivity to flow angle variations, limiting their operational stability and efficiency.

Innovation Solution

A two-stage centrifugal compressor design featuring a variable geometry diffuser downstream of the first stage impeller and a fixed diffuser downstream of the second stage impeller, eliminating the need for variable inlet guide vanes, with the variable geometry diffuser capable of adjusting its geometry to optimize flow and pressure regulation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If fixed, vaneless diffusers are used in multi-stage centrifugal compressors, then the structure is simple, but efficiency losses and early surge occur at part-load conditions

Engineering Contradiction:

Improvediffuser structureVSAvoidcompressor efficiency

Core Design Contradiction:

Device complexityVSLoss of energy

Solution Approach 1:

The patent applies a variable geometry diffuser in the first compression stage that can dynamically adjust its geometry to optimize flow angles at different operating conditions. This dynamic adjustment capability allows the diffuser to maintain high efficiency across part-load and full-load conditions, resolving the contradiction between simple fixed structure and efficient performance.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The variable geometry diffuser changes its geometric parameters (such as diffuser angle and passage area) based on operating conditions. By adjusting these parameters, the system optimizes flow characteristics and prevents early surge, thereby improving compressor efficiency without significantly increasing structural complexity.

Inventive Principle:

Principle #35Parameter changes

2Adaptability or versatility

If variable inlet guide vanes are used for capacity control, then operational flexibility is improved, but device complexity increases

Engineering Contradiction:

Improvecapacity control flexibilityVSAvoidinlet guide vane mechanism

Core Design Contradiction:

Adaptability or versatilityVSDevice complexity

Solution Approach 1:

The patent removes the variable inlet guide vane mechanism from the system entirely. Instead, capacity control is achieved through variable speed drive of the compressor, which simplifies the overall device structure while maintaining operational flexibility. The variable geometry diffuser compensates for the removed inlet guide vanes by optimizing flow at different capacity conditions.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent replaces the mechanical variable inlet guide vane system with an electrical/electronic variable speed drive system. This substitution reduces mechanical complexity while maintaining or improving capacity control flexibility, as speed can be adjusted precisely through electronic control.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Adaptability or versatility

If variable speed capability is added for capacity control, then operational flexibility is improved, but surge characteristics deteriorate at part-load conditions

Engineering Contradiction:

Improvevariable speed operationVSAvoidsurge characteristics

Core Design Contradiction:

Adaptability or versatilityVSReliability

Solution Approach 1:

The variable geometry diffuser dynamically adjusts its configuration in response to changing operating conditions, particularly at part-load speeds. This dynamic adaptation prevents flow separation and maintains stable flow patterns, thereby improving surge characteristics while preserving variable speed operation benefits.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The system incorporates feedback mechanisms that monitor operating conditions and adjust the variable geometry diffuser accordingly. This feedback control ensures that the diffuser geometry is optimized for current flow conditions, preventing surge and maintaining reliable operation across the variable speed range.

Inventive Principle:

Principle #23Feedback

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 design enhances compressor efficiency by 4-7% and improves surge characteristics at part-load conditions, providing better operational stability and efficiency compared to traditional rotatable inlet guide vane arrangements.

Implementation Method 1

first and second-stage diffusers are arranged in the housing with the first-stage diffuser arranged fluidly between the first-stage impeller outlet and the second compressor inlet

Methodology Applied

Scientific EffectDiffusion: Diffusion

Implementation Method 2

first- and second-stage impellers are arranged in the housing with the first-stage impeller arranged fluidly between the first-stage inlet and outlet

Methodology Applied

Scientific EffectCentrifugal force: Centrifugal Force

Data Source

PatentUS10072663B2Variable-speed multi-stage refrigerant centrifugal compressor with diffusers

Publication Date: 2018.09.11 DANFOSS AS

AI summary

A refrigeration system includes a chiller having a refrigerant loop. A compressor is part of and in fluid communication with the refrigerant loop. The compressor has two stages, one with a variable geometry diffuser and one with a fixed geometry diffuser.