Designing a Brush Seal for a Cryogenic Centrifugal Pump

Overview

Flowserve Bethlehem tasked our team to design a brush seal for a centrifugal pump capable of withstanding the cryogenic conditions of liquid hydrogen. The seal is located between the rotating impeller shaft of the pump and the pump casing and reduces the amount of backflow into the pump inlet reservoir. Typically this is accomplished in water pumps using a wear ring with an engineered clearance, but due to liquid hydrogen’s smaller size, extreme temperatures, and low viscosity, a new seal must be developed to attempt to withstand as much flow as possible.

Objectives

The team’s main two objectives assigned by Flowserve were to research materials for the seal design and to create a theoretical seal design that could be manufactured and tested for efficiency.

Approach

• Created a consistent method of contact between the sponsor and our team.
• Established goals, project deliverables, and general timeline.
• Developed a list of customer needs through the initial meetings with the sponsors.
• Conducted research on materials capable of withstanding cryogenic conditions.
• Conducted research on materials resistant to hydrogen embrittlement.
• Conducted research on different brush seal designs and how bristle packing affects porosity.
• Conducted research on calculating porosity and velocity through a brush seal through a set pressure gradient.
• Ran calculations on a multitude of different seal designs by changing the packing geometry and determining their porosities until the final design was discovered with the lowest porosity.
• Ran calculations to determine when diminishing returns occurred with the addition of more bristle rows in the seal to estimate final seal design parameters.
• Developed CAD models through Solidworks of the different potential designs to validate results.
• Developed a testing rig for the CAD Models.
• Performed CFD Analysis on the models to confirm the results through the guidance of the sponsor.

Outcomes

• The best materials for the seal design were found to be Stainless Steel 316L and Inconel 718 with a Teflon coating, which the sponsor can use to develop the brush seal.
• The best packing geometry was determined that achieved a porosity of 9%, 4% lower than standard brush seals, with design schematics available for Flowserve to use during development.
• The ideal number of rows was found to be from 10-15, yielding in a brush seal with 21,500-32,250 bristles depending on pump requirements, with a graph demonstrating the diminishing returns up to a 46,000-bristle brush that Flowserve can reference.
• CAD models, CFD testing rigs, and simulation data showing an increase in pressure at the inlet over alternative methods that can be referenced by Flowserve to perform further analysis.