Centrifugal Compressor Rotor Cooling Through Shaft Axial Grooves
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Solution Overview
Problem
Conventional centrifugal compressor motor cooling techniques are insufficient when using low-pressure refrigerants like R1233zd, leading to elevated rotor and stator temperatures and excessive refrigerant flow rates that cause motor drag, and are not effective for low global warming potential refrigerants such as R1234ze or R1234yf.
Innovation Solution
A centrifugal compressor design with a cooling medium delivery structure that includes an inlet and outlet conduit system, utilizing axial passageways between the shaft and rotor to enhance cooling, and optimizing the cross-sectional area of the flow path to manage refrigerant flow and pressure differences effectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If conventional motor cooling techniques are used with low-pressure refrigerants, then motor cooling is achieved, but rotor and stator temperatures become excessively high
Solution Approach 1:
The motor cooling system is segmented into multiple cooling paths: one for the stator and another for the rotor. The rotor cooling path includes axial grooves on the shaft that direct refrigerant flow specifically to the rotor, separating it from the stator cooling path. This segmentation allows independent optimization of cooling for each component, ensuring adequate temperature control for both stator and rotor when using low-pressure refrigerants.
2Temperature
If refrigerant flow rate is increased to improve motor cooling, then cooling effectiveness improves, but motor drag increases
Solution Approach 1:
The cooling system applies local quality by directing refrigerant flow to specific locations where it is most needed. Axial grooves are provided on the shaft at specific positions to channel refrigerant directly to the rotor cooling zones. The cross-sectional area of the flow path is optimized locally to ensure adequate cooling without excessive flow rates that would cause drag. This localized approach allows efficient cooling with minimal refrigerant flow.
Solution Approach 2:
The cross-sectional area of the refrigerant flow path is optimized to achieve the right balance between cooling effectiveness and drag prevention. By carefully controlling the flow path dimensions and refrigerant flow parameters, the system achieves adequate motor cooling without excessive flow rates that would create harmful drag on the motor.
3Device complexity
If conventional cooling flow paths are used, then simple structure is maintained, but inadequate cooling occurs with low-pressure refrigerants
Solution Approach 1:
The shaft serves multiple functions: it mechanically transmits power to the impeller and simultaneously acts as a cooling medium delivery structure with integrated axial grooves. The cooling channels are merged into the shaft structure itself, eliminating the need for separate cooling components. This merging maintains structural simplicity while providing adequate cooling for both stator and rotor when using low-pressure refrigerants.
4Quantity of substance
If cooling medium flow path cross-sectional area is increased to improve cooling, then refrigerant flow improves, but system complexity increases
Solution Approach 1:
The shaft is designed as a multi-functional component that simultaneously provides mechanical support, power transmission, and refrigerant distribution. The axial grooves on the shaft serve as cooling channels while the shaft itself remains a simple mechanical component. This universal design provides adequate refrigerant flow to both stator and rotor without adding separate complex flow distribution systems.
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 ensures adequate motor cooling without causing drag, effectively managing refrigerant flow and temperature control for both low-pressure and low global warming potential refrigerants, improving thermal management and efficiency.
Implementation Method 1
The inlet conduit is located to supply the cooling medium through the gap and the at least one axial passageway to cool the rotor
Data Source
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AI summary
A centrifugal compressor (22, 22') includes a casing (30), an inlet guide vane (32a, 32b), an impeller (34a, 34b), a motor (38), a diffuser (36a, 36b) and a cooling medium delivery structure (SS, SR, RS, RR, IC, OC, G, 80). The motor (38) includes a rotor (62) mounted on the shaft (42) and a stator (60) disposed radially outwardly of the rotor (62) to form a gap (G) between the rotor (62) and the stator (60). The cooling medium delivery structure (SS, SR, RS, RR, IC, OC, G, 80) includes inlet (IC) and outlet (OC) conduits located to supply and discharge a cooling medium to and from the motor (38). The shaft(42) has an external shape different than an internal shape of the rotor (62) to form at least one axial passageway (80) between the shaft (42) and the rotor (62). The cooling medium is supplied through the gap (G) and the at least one axial passageway (80) to cool the rotor (62).