Provided is a flow modification component for use with a muffler, which can be a Helmholtz resonator muffler, a side branch muffler, or a Y-pipe. The flow modification component includes a porous plate adapted for incorporation into a passage to a sound muffling portion connected to a through passage pipe of the muffler or Y-pipe. One or more openings are formed on the porous plate to allow low frequency acoustic waves to pass through into the passage to the sound muffling portion while reducing large-scale turbulent eddies that produce undesirable resonant tones within the aperture tube to small-scale turbulent eddies. The openings having sufficient porosity such that the resulting sound frequency is determined by size, shape, number, and spacing of the openings. The flow modification component can also include a dissipative material component in an internal port passage of the muffler to further reduce resonant tones.

An apparatus for regulating pressure of exhaust gas of a fuel cell system includes porous foam mounted in an exhaust tube and having a plurality of pores therein and a regulator that compresses or expands the porous foam to regulate a differential pressure of the exhaust gas flowing through the exhaust tube.

An apparatus for regulating pressure of exhaust gas of a fuel cell system includes porous foam mounted in an exhaust tube and having a plurality of pores therein and a regulator that compresses or expands the porous foam to regulate a differential pressure of the exhaust gas flowing through the exhaust tube.

Provided is a flow modification component for use with a muffler, which can be a Helmholtz resonator muffler, a side branch muffler, or a Y-pipe. The flow modification component includes a porous plate adapted for incorporation into a passage to a sound muffling portion connected to a through passage pipe of the muffler or Y-pipe. One or more openings are formed on the porous plate to allow low frequency acoustic waves to pass through into the passage to the sound muffling portion while reducing large-scale turbulent eddies that produce undesirable resonant tones within the aperture tube to small-scale turbulent eddies. The openings having sufficient porosity such that the resulting sound frequency is determined by size, shape, number, and spacing of the openings. The flow modification component can also include a dissipative material component in an internal port passage of the muffler to further reduce resonant tones.

A mesh apparatus for use in a downspout of a drainage system of a building to reduce noise of passing rainwater is provided. The mesh apparatus includes a mesh assembly having a mesh sheet with a rolled portion, the mesh sheet having a plurality of wires connected together to form a plurality of openings disposed throughout the sheet, and a fastener coupled to the mesh assembly to retain the rolled portion of the mesh sheet in a rolled configuration. The mesh assembly is inserted into the downspout. Rainwater passing through the downspout contacts any portion of the connected wires in the rolled portion of the sheet assembly, thereby diffusing the rainwater.

Noise attenuation units are disclosed that are connectable in a system as part of a fluid flow path. Such units include a housing defining an internal cavity and having a first port and a second port each connectable to a fluid flow path and in fluid communication with one another through the internal cavity, and a noise attenuating member seated in the internal cavity of the housing within the flow of the fluid communication between the first port and the second port. The noise attenuating member enables the fluid communication between the first port and the second port to flow through the noise attenuating member.

Noise attenuation units are disclosed that are connectable in a system as part of a fluid flow path. Such units include a housing defining an internal cavity and having a first port and a second port each connectable to a fluid flow path and in fluid communication with one another through the internal cavity, and a noise attenuating member seated in the internal cavity of the housing within the flow of the fluid communication between the first port and the second port. The noise attenuating member enables the fluid communication between the first port and the second port to flow through the noise attenuating member.

Noise attenuation units are disclosed that are connectable in a system as part of a fluid flow path. Such units include a housing defining an internal cavity and having a first port and a second port each connectable to a fluid flow path and in fluid communication with one another through the internal cavity, and a noise attenuating member seated in the internal cavity of the housing within the flow of the fluid communication between the first port and the second port. The noise attenuating member enables the fluid communication between the first port and the second port to flow through the noise attenuating member.