Mixed-Flow Centrifugal Compressor for Low-Pressure Refrigerants
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Solution Overview
Problem
Existing centrifugal compressors are too large for applications using new low-pressure refrigerants, exceeding available space due to their large diameter, which is necessary for accommodating high speeds.
Innovation Solution
A centrifugal compressor design with a mixed flow configuration, featuring a conical impeller with angled vanes and a cylindrical diffuser structure with additional vanes that reduce the Mach number of fluid flow, allowing for a reduced footprint by limiting fluid rotation and optimizing fluid flow angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the compressor diameter is increased to accommodate high speeds for low-pressure refrigerants, then the compressor can handle the required refrigerant flow, but the compressor size exceeds the available packaging space
Solution Approach 1:
The patent transitions from a conventional radial-flow centrifugal compressor to a mixed-flow compressor where the fluid flow has both radial and axial components. The impeller blades are angled to discharge fluid at approximately 45 degrees relative to the radial direction, creating a mixed flow pattern that combines centrifugal and axial flow characteristics. This dimensional change in flow direction allows the compressor to achieve higher refrigerant capacity without increasing the radial footprint, as the axial component of flow utilizes the length dimension more effectively.
2Area of stationary object
If the impeller speed is increased to maintain pressure ratio in a smaller compressor, then the compressor size is reduced, but the fluid flow becomes highly turbulent and inefficient
Solution Approach 1:
The patent employs adjustable inlet guide vanes that can be positioned at different angles to optimize the fluid flow entering the impeller. By dynamically adjusting the vane angle based on operating conditions, the system maintains optimal flow angles into the impeller blades, reducing turbulence and improving efficiency across varying speed and load conditions. This dynamic adjustment allows the smaller compressor to operate efficiently without excessive turbulence even at higher speeds.
Solution Approach 2:
The patent changes the flow angle parameter by using mixed-flow impeller blades discharged at approximately 45 degrees instead of conventional radial discharge. This parameter change in blade angle creates a more favorable flow pattern that reduces turbulence and improves efficiency. Additionally, the diffuser vane angles are optimized to match the mixed flow discharge angle, creating smooth flow transitions that minimize energy losses despite higher operating speeds in the compact design.
3Area of stationary object
If a mixed-flow configuration with angled vanes is used to reduce compressor size, then the footprint is reduced by 40% in radius and 10% in length, but the device complexity increases due to additional diffuser vanes and modified impeller design
Solution Approach 1:
The diffuser vanes in this design serve multiple functions: they convert kinetic energy to pressure (diffusion), guide the mixed-flow discharge from the impeller, and can be adjusted to optimize performance at different operating conditions. The inlet guide vanes similarly serve multiple purposes by controlling flow angle into the impeller and acting as a throttle. This multi-functionality reduces the need for separate components, managing complexity while achieving the compact mixed-flow design.
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
The design achieves a substantial size reduction of up to 40% in radius and 10% in length, improving compressor performance and making it suitable for low and medium pressure refrigerants while maintaining high pressure ratios in a single stage.
Implementation Method 1
Rotation of the impeller increases a pressure and/or velocity of a fluid or gas moving across the impeller
Implementation Method 2
a diffuser section arranged within the casing, the diffuser section being positioned adjacent the impeller
Implementation Method 3
at least one deswirl vane is positioned adjacent the outlet end of the diffuser section, the deswirl vane being arranged at the interface between the axial flow passage and the passageway to limit rotation of the fluid flow about the axis
Data Source
Figure 1
Figure 2
Figure 3A~3B
AI summary
An impeller (46) mountable within a centrifugal compressor (10) includes a hub (50) having a front side (52) and a back side (54), the hub (50) being rotatable about an axis of rotation and a plurality of vanes (56) extending outwardly from the front side (52) of the hub (50) such that a plurality of passages (62) is defined between adjacent vanes (56). The plurality of vanes (56) is oriented such that a flow output from the plurality of passages (62) adjacent the back side (54) of the impeller (46) is arranged at an angle to the axis of rotation of less than 20 degrees.