Centrifugal Compressor Diaphragm Ducting for Recirculation Control
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Solution Overview
Problem
Centrifugal compressors face issues with fluid recirculation and swirl between the impeller shroud and diaphragm, leading to increased axial thrust, larger balance drums and thrust bearings, higher power consumption, and reduced rotor-dynamic stability due to radial pressure gradients and swirl-induced instability.
Innovation Solution
A diaphragm design with a duct system that redirects fluid from a high-pressure area to a low-pressure area near the impeller, incorporating seals to limit backflow and swirl, with ducts oriented to reduce tangential velocity and enhance rotor-dynamic stability, and additional seals to further restrict fluid recirculation and increase axial counter-thrust.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If seals are used between rotating and static elements to reduce leakage, then fluid recirculation is limited, but device complexity increases
Solution Approach 1:
A seal element is introduced as an intermediary component between the rotating impeller shroud and the static diaphragm. This seal element physically blocks the gap through which fluid recirculates, preventing high-pressure fluid from leaking back to the low-pressure inlet region. The seal element acts as a mediator that resolves the energy loss problem without requiring fundamental redesign of the compressor architecture.
Solution Approach 2:
The seal solution divides the gap region into separate zones using multiple seal elements positioned at different locations. Rather than attempting to seal the entire gap with a single complex structure, the gap is segmented into multiple smaller sealing zones, each handled by a simpler seal element. This segmentation reduces the complexity of each individual seal while collectively achieving effective recirculation prevention.
2Force
If balance drums and thrust bearings are increased in size to compensate for axial thrust, then axial thrust compensation is improved, but device complexity and power consumption increase
Solution Approach 1:
The seal elements are positioned to prevent fluid recirculation before the recirculated fluid can generate significant axial thrust. By sealing the gap upstream, the system prevents the formation of the radial pressure gradient that would otherwise create harmful axial thrust. This preliminary action eliminates the need for oversized balance drums and thrust bearings that would be required if sealing were not implemented.
Solution Approach 2:
The seal elements create a preliminary counter-action to the potential axial thrust by blocking the recirculation path that generates the radial pressure gradient. Rather than allowing the harmful axial thrust to develop and then compensating for it with large balance drums, the seal elements preemptively prevent the thrust-generating mechanism from occurring in the first place.
3Stability of the object's composition
If swirl brakes are used to reduce swirl, then rotor-dynamic stability is improved, but device complexity increases
Solution Approach 1:
The seal elements serve as an intermediary mechanism that indirectly reduces swirl by preventing recirculation. Rather than using dedicated swirl brake devices that would directly interact with the rotating fluid to dissipate tangential velocity, the seal elements block the recirculation path that sustains the swirl. This intermediary approach reduces swirl as a secondary effect of preventing recirculation, rather than requiring direct swirl-braking action.
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 solution effectively reduces fluid recirculation and swirl, decreasing the size of balance drums and thrust bearings, increasing compressor efficiency, and improving rotor-dynamic stability by minimizing power consumption and enhancing operational safety.
Implementation Method 1
The inlet is located on the rear surface at a point where the static pressure is higher with respect to the static pressure at the outlet
Data Source
AI summary
A diaphragm 1 for a centrifugal compressor having a rear surface 2 configured to at least partly face an impeller 3, the rear surface 2 having a first portion 2a defining at least in part a diffuser 4 and a second portion 2b facing the impeller 3; the diaphragm has a duct 5 provided with an inlet 6 and an outlet 7, the outlet 7 being located on the second portion 2b of the rear surface 2, the inlet 6 being located on the rear surface 2 at a point where the static pressure is higher with respect to the static pressure at the outlet 7.