Experimental and numerical investigation of liquid film phase change in textured mechanical seals with inner herringbone and spiral grooves

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Abstract
Liquid film phase change critically degrades mechanical seal performance. Experimental data on phase change evolution and groove-type differences for typical hydrodynamic grooves remain scarce. In this study, phase change experiments were conducted on mechanical seals with these two groove types using high-temperature hot water as the working medium. The effects of rotational speed and medium temperature on phase change were investigated, back-surface temperature was synchronously measured, and film thickness effects were analyzed numerically. The numerical predictions agree well with experimental data. The results demonstrate that, compared with the inner spiral groove seal, the inner herringbone groove seal exhibits a 6.44%–33.61% higher phase change rate, an 18.4%–35.4% lower leakage rate, and an average back-surface temperature up to 4.88 K lower. Phase change in the inner spiral groove seal concentrates at the low-pressure inner-diameter side and propagates outward along the spiral grooves, whereas in the inner herringbone groove seal it is additionally distributed on the leeward side of the grooves. This difference arises from the coupled effects of non-uniform liquid film thickness between the groove and dam regions and localized low-pressure zones. The phase change rate decreases with increasing rotational speed but increases significantly with medium temperature. Film thickness analysis reveals a stable operating interval and a phase-change-sensitive interval. The dimensionless friction torque gradually attenuates and plateaus as film thickness increases, while the leakage rate exhibits a continuous upward trend.

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