Page 67 - Energize April 2022

TECHNICAL

An alternative emerges
In the early 1980s, a graduate student
named Ali Broukhiyan published his
honours thesis on a new method
of control valve aerodynamic noise
reduction called ‘A Modal Coincidence
Suppression Device’ (Figure 2).
The design consisted of a series
of carefully sized concentric rings and
partitions around a pipe, with the device
to be installed downstream of a noise
producing control valve. The different
sized rings were specifically designed
to resonate at a particular range of
frequencies. When put together, it was
theorised that the set of concentric rings
would produce destructive interference
across a broad range of frequencies,
effectively reducing the total sound
emitted by the valve.
Early trials of the core technology
Figure 2: This diagram shows the original concept of a modal coincidence suppression device, designed
were encouraging, but there was no to reduce the aerodynamic noise produced by a control valve. The series of chambers are each sized to
feasible way to economically construct produce destructive interference across a small range of frequencies.
such a device capable of handling the
pressures and temperatures encountered 600 lb (about 68, 136 and 273 kg) (Figure 3). Its pressure ratings generally match the
in typical processes. After several flange rating sizes, and the maximum temperature is 650°F (343°C). The new modal
attempts, the concept was abandoned suppressor utilises a similar construction to the original design but incorporates several
and shelved for decades. improvements (Figure 4). The inner pipe is a full-bore perforated liner which allows a
pipeline pig to pass through it with no restriction. The new design also includes a larger
Resurrection through additive number of concentric cavities to provide an average 10 dB noise reduction across a
manufacturing broader range of frequencies. In addition, the rings have been modified to allow the
The advent of additive manufacturing device to be self-draining, so process liquids do not collect in the rings and negatively
and 3D metal printing enabled impact noise reduction performance.
Emerson to create complicated metal
components that could not have been
economically fabricated in the past.
New and innovative anti-cavitation
and low noise trims were the focus of
early additive manufacturing efforts,
but attention eventually turned to
the modal coincidence suppression
device. A series of preliminary trials
proved the modal suppression device
held promise and suggested the new
manufacturing techniques might be
employed to fabricate the device at an
affordable price. After several years,
Emerson engineers developed and
patented a method that allows the sound
suppression device to be produced as a
casting.
Emerson’s WhisperTube was
released for sale in late 2021 in sizes
from 2 in. (50 mm) to 12 in. (300 mm) Figure 3: The forged WhisperTube (6 inch model shown) undergoing noise testing at the Emerson
with flange ratings of 150, 300 and Innovation Centre Flow Laboratory.

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