Development
This article presents a set of results that have been obtained in the application of noise assessment and control methodologies in different situations.
application-methodologies-for-noise-control-in-companiesThese solutions have effectively contributed to the development of production systems and, above all, to the improvement of human safety, health and well-being conditions.
1. Citrus Company of Jagüey Grande
In the company of the Citrus of Jagüey Grande a diagnosis was made of the Sound Pressure Levels that are emitted by the compressors that the company has, it has 5 compressors, of which 2 are of a type, whose fundamental characteristic is that the fan that has this facing the street, which causes a higher level of sound pressure in that direction, the other three compressors its fan has the flow up.
At the time of carrying out the study, two compressors were operating, one of each type. Measurements were carried out using a decibel meter and measuring at various points in order to determine the sound pressure level that is emitted from each of the compressors and sum of levels, that is, assuming the operation of all at the same time, determine the level that is emitted by all, compare it with the norm and be able to reach conclusions on the subject.
The results of the sound pressure level measurement are shown below, in addition a sketch was made to represent the points where the measurements were taken.
Results of the diagnosis of sound pressure levels
Table 1 shows the sound pressure levels that were taken with the instrument and that correspond to the points shown in the sketch.
Table 1. Sound Pressure Levels at each of the measured points.
Analysis of each of the values obtained
Tables 2 (a and b) show the results obtained, when all the company's compressors are operating at the same time.
Table 2.a. Results obtained when all the compressors work A.
In this investigation, the sound pressure values that reach the houses adjacent to this company, and the values found near the fence that divide the company and the houses were also analyzed. The obtained values are shown in the following tables. It is important to point out that the impact this has on a social level, with its damages and consequences, is an extremely important element.
Table 3. Analysis of the values in front of the fence.
Table 6 presents the final sound pressure level values in each of the areas that were studied.
Table 6. NPS values in the evaluated areas.
Analysis of the NPS values with the Maximum Levels Admitted in NC 19-01
The Cuban standard states that the maximum sound pressure level admitted is 85 decibels (A), which is emitted by the compressors is higher than this.
It is valid to emphasize that the value measured in the points is only with the operation of the two compressors, so this value is higher when all the equipment is put into operation.
That is why measures must be taken so that the noise that is produced by this equipment does not affect the people who live in these houses.
Recommendations for the elimination of noise
The following is the proposed solution that was made to the citrus company, with a view to solving the problem caused by high noise levels in the population and in the company itself, for its workers.
1. One of the recommendations to eliminate these sound pressure levels is the sowing in front of the tree compressors, they must have the following characteristics:
- They must be large trees
- They must have as many leaves as possible
- They should drink as much close to each other.
These characteristics of the trees will allow them to act as a great wall and will greatly attenuate the level of sound pressure that is emitted by the compressors.
2. It is recommended to build a wall at a distance of 2.5 m from the place where the compressors are located to allow the escape of air that is needed by the compressors. The wall should be 28m long by 3m high. In its upper part it must have a crescent-shaped, semicircular, concave structure (seen from the compressor side), one meter in radius. The construction material for this wall should be as solid as possible.
3. It is recommended to replace the zinc roof with another material, since it causes more vibrations, causing more noise.
2. Matanzas Dairy Products Combine
The work was carried out in the Matanzas City Dairy Products Combine, specifically in the area of milk liters filling, where the work environment is characterized by high noise exposure.
Here 8 workers work. The sound environment is determined by various sources of noise, such as that produced by the filling machine, the beating of the liters against each other as they pass through the conveyor mat, but predominantly there is equipment whose sound pressure level is significantly higher than rest of the equipment: the vacuum pump. This is located 0.10 m from a wall that divides this area with a warehouse, built of 0.20 m blocks, where workers usually do not work. Given these conditions, the construction of a capsule is proposed, but with the particularity that it is necessary to leave openings for air circulation and engine cooling. These openings were built into the existing block wall with lattices,so that the noise that escaped through them made it to the area where the workers do not work and allowed the passage of air. The rest of its contours would be delimited by the walls of the capsule.
Encapsulation was performed by wrapping the entire noise source. Its effectiveness was given in preventing the propagation of noise through the air, being locked inside the capsule.
The degree of reduction is defined by the characteristics of the envelope materials.
The measurements were made with a Polish sound level meter "Sound Level Meter", brand Sonopan, with external filter that allows to assess the noise by octave bands.
The measurements made in the filling area are presented in table 7.
Table 7. NPS values obtained in the area.
According to what the measurements show, the noise level in the filling part is very high, directly affecting the personnel who work there, especially in the high frequencies from 2000 Hz, being the most interesting for this study, whose level Maximum Allowable noise is 78 dB.
The steps followed for your project are detailed below:
1. Determination of the attenuation to be achieved by the capsule.
Required: Noise level to reduce (dB).
Lexistent: Existing noise level (dB).
Recommended L: Allowed noise level (dB).
2. Characteristics of the capsule
It is built by two brick walls and two panel-type galvanized plywood zinc doors, separated with a chamber made of inert material, which in this case used poly-foam.
Data necessary to perform the calculations:
Lower frequency of interest = 2000 Hz
NPS for this frequency = 78 dB
Recommended L = 78 dB, according to the table of the Cuban standard 19-01-05
Length of the vacuum pump, L = 0.84 m
Vacuum pump width, A = 0.64 m
Vacuum pump height, H = 0.90 m
Transmission losses for zinc plated plants, R = 0.52
Transmission losses for 0.12 m thick common brick, R = 0.45
Brick thickness, E1 = 0.12 m
Thickness of the zinc plate, E2 = 0.03 m
Absorption coefficient of the brick, α = 0.02 sabinos / m2
Absorption coefficient of the plate, α = 0.01 sabinos / m2
3. Determination of the dimensions of the capsule.
Where:
C = speed of sound, 343 m / s
Fmi = minimum frequency of interest, 2000 Hz
D = distance between the vacuum pump and the interior walls of the capsule, m
Substituting we have that:
Therefore,
D = 0.1715 / 4
D = 0.0428 m
Internal dimensions of the capsule.
Length = L + 2D
Length = 0.94 m
Width = A + D + 0.10 *
Width = 0.79 m
* 0.10: distance from the capsule to the wall, m.
Note: the value of D is added once, since the other distance is fixed, which is the average between the pump and the wall.
Height = H + D
Height = 0.95 m
Capsule exterior dimensions
Length = L + 2D + 2E1
Length = 1.18 m
Width = A + D + 0.10 + E2
Width = 0.82 m
Height = H + D + E2
Height = 0.98 m
The problem What was presented is that the capsule was built by two different materials that have different values of R (losses by transmission) and alpha (values of the absorption). The calculations were made with the values of the material that has less R (brick). so that the values obtained for noise will be less than what is theoretically obtained.
Calculation of attenuation you will achieve
Where
:: expected attenuation, dB.
Sc: outer surface of the capsule.
Ac: sound absorption surface equivalent to the area limited by the capsule.
Sc = 2 (Lc + Hc) +2 (Ac + Hc) + (Lc + Ac)
Sc = 4.88 m2
Ac = α * Sintc
Where:
α: absorption coefficient (of the brick 0.02 sab / m2)
Sintc: inner surface of the capsule, m2
Sintc = 4,029 m2
Therefore,
Ac = 0.08 sab
Substituting, we have that:
= 27.2 dB
With the obtained attenuation value that the capsule achieved was equal to 27.2 dB and only 7 dB needed to be reduced, we concluded that the design was effective, that is, that the 8 workers who work in that plant, the noise levels that exceeded the standards, are now below the permitted limits and therefore are not exposed to the pathologies that this risk imposes.
3. Sugar Plant "Mario Muñoz"
A noise study has been carried out at the "Mario Muñoz" sugar mill in the Matanzas province, where it has been obtained that there is a risk of hearing damage to the safety valve of one of the boilers from the frequency of 125 Hz. The existing sound pressure level is 98 dB. The fluid temperature is 179 0C and the valve diameter is 0.1016 m. We want to design a silencer to avoid any damage to the health of workers.
Solution:
The data offered to me in this problem are:
L = 98 dB
fm = 125 Hz
T0 = 179 0C + 273 K = 452 K (the temperature must be given in K)
D = 0.1016 m
Step 1. Noise evaluation.
In this case, the frequency and the existing sound pressure level, for which noise begins to be harmful, are already shown in the data. Considering that the muffler is built for the frequency of least interest.
Step 2. Determine the speed of sound.
Where:
c: Speed of sound, (m / s).
t: Fluid temperature, (K).
Step 3. Determine the wavelength of the sound (λ).
Where:
f: Minimum frequency of interest, (Hz).
Step 4. Determine the wave number.
Where:
k: Amount of compressions and depressions of the wave.
Step 5. Determine the length of the silencer (L).
Step 6. Determine the section of the silencer (S2), (m2).
Where:
S1: Section of the tube through which the fluid escapes, (m2).
m: Constant obtained from Figure 2.19, with the variables:
- ∆ Ls: Difference between the real NPS and the normed NPS for the minimum frequency of interest.
- k * L: wave number (k) multiplied by the length (L).
r: radius of the silencer (m).
In this case the values to obtain am are:
Therefore, entering the table with these values, we obtain that m = 4.
Step 7. Determine the diameter of the silencer D (m).
In order to determine the diameter of the silencer, it is necessary to know the radius, as well as the sections that form it.
Where:
r: Radius of the silencer, (m).
