Enver Karakas and Sinan Ozcan, Ebara Elliott Energy, USA, analyse cavitation at pump inducers, cavitation inception, and propagation in LNG pumping applications and consider safe pump operation in low suction pressure conditions.
avitation is the formation of vapour bubbles or cavities in the low-pressure region within a liquid flow field. The formation of vapour bubbles starts when the static pressure in the liquid reaches the vapour pressure of the liquid for a given temperature. Cavitation causes damage to the material surfaces close to the area where the bubbles collapse when they enter higher pressure regions. Cavitation occurs in different forms and is highly detrimental to centrifugal pumps. Collapsing bubbles result in cavitation erosion, which is direct and can destroy inducer and impeller blades.
The cavitation behaviour of a centrifugal pump is an important performance characteristic for safe pump operation in the event of low suction pressure conditions. To better understand the destructive nature of vapour bubbles and how to minimise the damage they cause, Ebara Elliott Energy has conducted computational fluid dynamics (CFD) simulations, using LNG as the process fluid, to observe the performance characteristics of a variable pitch inducer (axial flow impeller) with various sweep back angles in both non-cavitating – meaning no vapour formation – and cavitating operating conditions.
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