Sn V

where fe = vortex frequency, Hz

D = a characteristic dimension of the generation source, ft (m) V = flow velocity in the pipe, ft/s (m/s)

For flow past tubes, D is the tube diameter, and for branch piping excitation, D is the diameter of the branch pipe. The basic Strouhal equation is further defined in Table 1, items 4A and B. As an example, flow at 100 ft/s (30 m/s) past a 12-in diameter (0.3-m) stub line would exhibit instability tendencies at a frequency of approximately 50 Hz. If the stub is acoustically resonant at a frequency near 50 Hz, rather large pulsation amplitudes can result.

When a centrifugal pump is operated at flows less than or greater than best efficiency capacity, noise is usually heard around the pump casing. The magnitude and frequency of this noise vary from pump to pump and are dependent on the magnitude of the pump head being generated, the ratio of NPSH required to NPSH available, and the amount by which pump flow deviates from ideal flow. Noise is often generated when the vane angles of the inlet guide, impeller, and casing (or diffuser) are incorrect for the actual flow rate. Another major source contributing to this noise is referred to as recirculation.4,5

Before the pressure of the liquid flowing through a centrifugal pump is increased, the liquid must pass through a region where its pressure is less than that existing in the suction pipe. This is due in part to acceleration of the liquid into the eye of the impeller. It is also due to flow separation from the impeller inlet vanes. If flow is in excess of design and

TABLE 1 Piping vibration excitation forces

Generation mechanism Excitation frequency fe, Hz

Generation mechanism Excitation frequency fe, Hz

TABLE 1 Piping vibration excitation forces

Renewable Energy Eco Friendly

Renewable Energy Eco Friendly

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable.

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