IEC 60534-8-3:2010 pdf – Industrial-process control valves – Part 8-3: Noise considerations- Control valve aerodynamic noise prediction method.
The mechanical stream power as well as acouslical efficiency factors are calculated for v arious flow regimes. These acoustical efficiency factors glv e the proportion of the mechanical stream power which is cony erted Into internal sound power.
This method also prov ides for the calculation of the internal sound pressure and the peak frequency for this Sound pressure, which Is of special importance in the calculation of the pipe transmission loss.
At present, a common requirement by v alv e users is the knowledge of the sound pressure 1ev el outside the pipe, typically I m downstream of the v sly a or expander and I m from the pipe wall. This standard of fers a method to establish this value.
The equations en this standard make use of the v alv e sizing factors as used in IEC 60534.1 and
IEC 60534-2-i
In the usual control v alv e. little noise tray els through the wall of the v sly a. The noise of interest is only that which tray els downstream of the v alv e and inside of the pipe and then escapes through the wall of the pipe to be measured typically at I m downstream of the v alv e body and I m away from the outer pipe wail,
Secondary noise sources may be created where the gas exits the v alv e outlet at higher Mach numbers, This method allows for the estimation of these additional sound 1ev els which can then be added logarithmically to the sound 1ev els created within the v aN e.
Although this prediction method cannot guarantee actual results in the field, it yields calculated predictions within 5 dB(A) for the majority of noise data from tests under laboratory conditions (see IEC 60534-8-1). The current edition has increased the level of confidence of the calculation. In some cases the results of the prey ious editions were more conservative,
The bulk of the test data used to v alidate the method was generated using air at moderate pressures and temperatures. However, it is believ ed that the method is generally applicable to other gases and v apours and at higher pressures, Uncertainties become greater as the fluid behav as less perfectly for extreme temperatures and for downstream pressures far different from atmospheric, or near the critical point. The equations include terms which account for fluid density and the ratio of specific heat.
NOTE Laboratory air leMs conducted With U to I 830 bPa (18.3 bar) upeream pressure and up to 1 600 kPa (18,0 bar) downstream pressure and steam Lasts up to 225 C s5owed good aeement with the calculated values.
A rigorous analysis of the transmission loss equations is beyond the scope of this standard. The method considers the interaction between the sound way es edsting in the pipe fluid and the lrst coincidence frequency In the pipe wall. In addition, the wide tolerances In pipe wall thickness allowed In commercial pipe sev erely limit the v alue of the v ery complicated mathematical approach required for a rigorous analysis. Therefore, a simplified method is used.
Examples of calculations are giv en m Annex A.
This method is based on the IEC standards listed in Clause 2 and the references giv en in the Bibliography.
3Terms and definitions
For the purposes of this document, all of the terms and definitions giv en in the IEC 60534series and the f ollowing apply:
acoustical efficiencyn
ratio of the stream power conv erted into sound power propagating downstream to the streampower of the mass flow
external coincidence frequencyf
frequency at which the external acoustic wav espeed is equal to the bending wav espeed in aplate of equal thickness to the pipe wall
internal coincidence frequencyfo
lowest frequency at which the internal acoustic and structural axial wav e numbers are equalfor a giv en circumferential mode, thus resulting in the minimum transmission loss
fluted vane butterfly valve
butterfly v alv e which has flutes (groov es) on the face(s) of the disk. These flutes areintended to shape the f low stream without altering the seating line or seating surface
independent flow passage
flow passage where the exiting f low is not affected by the exiting f low from adjacent f low passages
peak frequencyp
frequency at which the internal sound pressure is maximum
valve style modifierFa
ratio of the hydraulic diameter of a single flow passage to the diameter of a circular orifice,
the area of which is equiv alent to the sum of areas of all identical flow passages at a giv entravel.