Currently, the shuttle engine turbopump is required to boost propellant pressures to 30 MPa with proposed second-generation engines requiring propellants to be delivered at pressures to 50 MPa. The problem of fluid leaking past the sealing surfaces in rotating machinery is compounded with cryogenics, high pressure, large temperature gradients, very high speeds of rotation, and static seal requirements. At lower pressure and rotation speeds, self-energizing pumping seals with very close clearances have been successfully employed in a variety of sealing applications [1]. These seals frequently have very large length-to-hydraulic diameter ratio (L/D) passages. At the proposed operating pressures, design innovations to minimize losses are required, but choked flow data and models to make such calculations are lacking. A similar problem occurs in very long cryogenic transmission lines.
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