Noise reduction with
RECEMAT^® metal foam

RECEMAT International has specialized in the development of parts made of metal foam for many different applications. The major field of development, however is the development and manufacture of low noise internals for newly designed as well as existing control valves.

RECEMAT LOW NOISE INTERNALS

The porous structure of RECEMAT metal foam offers stochastic tortuous paths to flow. As is well known, noise is caused by highly turbulent flows and is very much dependant on the mass flow through the valve and the pressure conditions up stream and down stream of the valve.

Without going into too much theoretical detail one may state that being able to influence the following parameters of flow, will positively reduce noise generated:

Velocity :

The lower the velocity in the pressure reducing process, the lower the noise that is being generated. One of the tricks, very impractical however, could be to build a very long pipe into the control valve and reduce the pressure by use of the length of the pipe.

Mass flow:

Observations show, that control valves under the same operating conditions but of different size generate different levels of noise. The explanation is simple: The control valve or silencer dissipates energy and one of the elements in the conversion of energy from a higher level to a lower level is that part of the dissipated energy is converted into high turbulent flow. Turbulence is inherent with pressure fluctuations. It is the pressure fluctuation transmitted to the ear, which is being observed as noise. In a smaller pressure reducing element the resulting Reynolds numbers are lower, thus the levels of turbulence are lower.
The same effect is generally being observed with valves operating under lower flow conditions.

Peak frequency:

The peak frequency of the turbulent flow is directly dependant on the size of the passage an the velocity through it.

All of the above effects may be intelligently manipulated by the use of RECEMAT metal foam.

Velocity

The velocity in the pressure reduction process will be reduced as the foam acts as an effective restrictor.

Mass flow

Due to the unlimited number of stochastic passages, the flow per unit passage is very small and therefore the energy flowing through each "individual" passage is extremely small.

Peak frequency

Since the inherent diameter of the passages is very small, the peak frequency of the discharge flow is pushed up to very high levels. High frequency noise is much easier to attenuate than low frequency noise.

RECEMAT metal foam for LOW NOISE APPLICATIONS

RECEMAT International has successfully developed blow down silencers for the gas industry and other industries as shown in the photograph and drawings attached. The major advantages of the RECEMAT Silencers are the extreme small sizes, which have resulted in the supply portable silencers blowing down natural gas from 60 bar-g to atmosphere with extremely low noise levels.

Most important however, is the development of low noise internals for existing conventional control valves. In all cases the internals have been inserted successfully with little or no change to the existing control valve. The well known Fisher 99 gas regulator is a perfect example. For many gas distribution companies we are manufacturing the inserts and we have been able to reduce the noise level by about 30 dBA.

Many control valve manufacturers use our designs not only to bring their standard design valves in line with the regulations, but also to develop new low noise models. In all cases we engineer, develop and manufacture the trim inserts.

Testing has shown that the RECEMAT Low Noise Internals even reduce to levels which get below the background noise of existing test facilities. Noise reductions recorded, but limited by the test facilities have been in the range of 35 dBA. With more advanced test facilities available noise levels recorded are expected to come considerably lower than presently measured.

An interesting observation has been made on a German test facility. The control valve with the RECEMAT insert reduced the noise level by about 25 dBA and at the same time passed more flow (about 15%). This can be explained simply by the fact that the RECEMAT metal foam is also a very good flow distributor. Flow passing through conventional valves normally has an extreme asymmetric pattern, reducing the actual flow passing area considerably.

CONCLUSION:

RECEMAT metal foam has great potential in the field of control valves and silencers. We offer the possibility, in most cases, to reduce the noise levels to any required level. Dependant on the type of basic valve design higher flows than the original anticipated capacity could be passed.

We will be pleased to assist manufacturers and users in their fight against noise.