drop. The effective combination of
advanced computational methods and
basic fluid dynamics experiments with
water safely showed the way to increase
the capacity of the valve.
The pressure drop produced by control
valves is one source of cavitation, but
far from the only one that should concern plant operators.
Cavitation frequently occurs with
both centrifugal and reciprocating
pumps, particularly when head loss
from flow restriction exists. For example, Alden Research Laboratory has
been working with the U.S. Nuclear
Power Commission and nuclear plant
operators to design better screens for
plants’ Emergency Core Cooling Systems (ECCS). Fibers, particles and
other debris generated by a pipe rupturing inside a reactor can accumulate on
the ECCS intake screen, reducing the
water flow, increasing the head loss and
causing the pump to cavitate, which
impairs its ability to recirculate cooling
Entrained gasses are also a concern.
A fluid-handling system can be
designed to discourage cavitation of the
primary fluids processed, but other
gasses in the fluid can cavitate with
pressure changes that do not affect the
main fluid. For example, gasses in
lubrication oil can cavitate, causing pitting and flaking of bearing surfaces
used to support power turbine rotors.
Also of concern, however, is operator
error. In 1996, during a turnaround at
a refinery hydrogen production unit, the
water level in a tank was allowed to
drop, causing the pump to cavitate.
Since that pump was not immediately
shut down by the operators, when the
cavitation started and no cavitation
sensor with an automatic pump shutoff
existed, hydrogen flowed back into the
tank and ignited. The explosion damaged the tank, 15 vehicles and windows
on nine buildings.
Since cavitation was first described
by John Strutt almost 100 years ago,
the scientific understanding of this phenomenon has continued to advance.
Companies also continue to develop
1. Lauterborn W; Boll H (1975): Experimental investigation of cavitation-bubble collapse in the neighborhood of a solid boundary. J. Fluid Mechanics, 72, pp. 391-399.
2. Matula TJ (2000): Single-bubble sonolumi-nescence in microgravity. Ultrasonics, 38, pp.
3. Tomita Y; Shima A (1985): Mechanisms of
impulsive pressure generation and damage
pit formation by bubble collapse. J. Fluid
Mechanics, 169, pp. 535-564
new technologies to prevent cavitation
and minimize its damage. However, no
product can be built to meet the needs
of all the unique plant designs. Each
design requires a careful analysis of the
exact plant conditions so the proper
solutions can be applied. VM
LUDWIG HABER is a senior flow engineer at
Alden Research Laboratory. He has worked on
improving performance in a wide range of fluid
dynamics applications ranging from turboma-chinery to nuclear strainer systems. MARTIN
WOSNIK is an assistant professor of Mechanical
Engineering at the University of New Hampshire and a technical consultant to Alden. He
conducts research on cavitation and bubbly
flows, turbulent boundary layers and renewable
The OEM Approach To Repair
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