Compressor Diaphragm Duct Layout for Swirl and Axial Thrust
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Solution Overview
Problem
In centrifugal compressors, the recirculation of fluid between the impeller shroud and diaphragm causes swirl, leading to increased axial thrust, larger balance drums and thrust bearings, higher power consumption, and reduced rotor-dynamic stability, which existing swirl brakes only partially mitigate.
Innovation Solution
A diaphragm design with strategically placed ducts and seals that redirect fluid flow to reduce swirl, featuring a second portion of the duct oriented to impart tangential velocity opposite to the impeller's rotation, and additional seals to limit backflow, enhancing rotor-dynamic stability and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If seals are placed on the impeller eye to limit recirculation, then fluid leakage is reduced, but the swirl in the diaphragm/shroud gap persists causing increased axial thrust and power consumption
Solution Approach 1:
The harmful swirl is extracted and removed from the system by providing a dedicated escape path through the duct. The duct connects the diaphragm/shroud gap to the diffuser, allowing the swirled fluid to be diverted away from the harmful recirculation zone and directed toward the diffuser where it can be harmlessly discharged into the main flow.
Solution Approach 2:
The duct acts as an intermediary element that mediates between the diaphragm/shroud gap and the diffuser. Instead of allowing direct recirculation that creates harmful swirl, the duct provides an intermediate pathway that redirects the fluid flow, eliminating the harmful effect while maintaining the sealing function.
2Loss of energy
If the diaphragm/shroud gap is reduced to minimize recirculation, then fluid leakage decreases, but manufacturing precision requirements increase
Solution Approach 1:
The duct serves as an intermediary that provides a controlled pathway for fluid redirection. This allows the diaphragm/shroud gap to maintain a practical size for manufacturing while the duct handles the precise flow control function, separating the sealing requirement from the precision requirement.
Solution Approach 2:
Instead of controlling recirculation solely through the radial gap dimension, the invention introduces a new dimensional pathway through the duct. This allows fluid flow control to occur in a different spatial dimension, reducing the stringency of gap tolerance requirements.
3Force
If larger balance drums and thrust bearings are used to compensate for increased axial thrust, then thrust compensation improves, but device complexity and size increase
Solution Approach 1:
The harmful swirl and recirculation are converted into a beneficial flow path through the duct. By redirecting the swirled fluid through the duct to the diffuser, the harmful recirculation that increased axial thrust is transformed into a controlled flow path that actually helps manage the fluid dynamics and reduces the thrust burden on the balance drum and bearing.
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 effectively reduces fluid recirculation, decreases axial thrust, and increases compressor efficiency by stabilizing the rotor and reducing the size of balance drums and thrust bearings, thereby improving overall performance.
Implementation Method 1
a duct (5) directed towards a diffuser (4) of the centrifugal compressor. The duct (5) comprises an inlet (6) communicating with a gap (10) defined between a shroud (3c) of the impeller (3) and a diaphragm (1) and an outlet (7) communicating with a diffusion passage of the diffuser (4)
Implementation Method 2
centrifugal compressors, in which the mechanical energy operates on gas input to the compressor by way of centrifugal acceleration which accelerates the gas particles
Implementation Method 3
A seal placed on the impeller eye, namely the lower diameter of the external side of the shroud, has the purpose to limit such recirculation
Implementation Method 4
an impeller which is capable of providing kinetic energy to the input gas
Implementation Method 5
the mechanical energy operates on gas input to the compressor by way of centrifugal acceleration which accelerates the gas particles
Implementation Method 6
a diffuser which converts the kinetic energy of the gas leaving the impeller into pressure energy
Data Source
Figure 1
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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.