Canopy Design and Fabrication for Reducing Noise

Journal of Refrigeration, Air Conditioning, Heating and Ventilation ISSN: 2394-1952(online) Volume 3, Issue 3 www.stmjournals.com

Canopy Design and Fabrication for Reducing Noise Level Generated at Work Place without Affecting Equipment/Machine Performance Sunhara Kadam, Shivaji Shelar*, Aurelius D’souza, Lionel D’souza, Amar Kulkarni Department of Mechanical Engineering, St. John College of Engineering and Management, Palghar, Maharashtra, India Abstract Laws governing the safety and health of employed people exist in most countries of the world, the purpose being to create a suitable working environment and eliminate unsafe practices and processes. Work areas should be designed and laid out so that they are satisfactory both, from the environmental and safety points of view. In this connection, safety also implies that noise is kept at a level, which is not likely to cause hearing damage. A noise control program should involve the following: (1) The preparation of a noise map after making measurements in all areas. (2) The setting of target noise levels for all areas. 3. A description of all measures planned, a cost analysis, and the attenuation expected. 4. The setting of priorities within a plan to achieve the agreed targets, stating start and finish times. In the context pertaining to our project, we use the concept of isolating the sound at the source itself by using a canopy system. The properties of sound absorptive materials are studied and put into practice. Research has led to combining materials with good tensile strength along with its absorptive properties into one system without affecting the system performance. We get a successful drop of 15 dB with our canopy system after conducting the various tests that are present in the following chapters of this report. Keywords: Canopy, sound, sound intensity, medium density fibre (MDF) board, heat transfer, sound damping

*Author for Correspondence E-mail: [email protected]

INTRODUCTION Industries and various laboratories have elements leading to high discharge of noise. This noise, if over permissible level can cause health hazards to the people working in these industries/laboratories [1, 2]. If the machines causing this noise have a vital role in that particular industry, it cannot be changed or modified. Consideration of cost factor that affects the change in the set-up also has to be taken. Canopy (for noise reduction) is a casing used to conceal the noise of the machine without affecting the machine’s performance [3]. It is the easiest and effective way to reduce the noise generated by a machine without changing the machine specifications. The paper gives you the detailed data required for the design and construction of the canopy. This report is made considering the standards set for noise. We have kept the cost and spatial factors, so that the canopy can be handled easily by any worker in the factory.

System Design The system consists of a cuboidal shaped box which is made of medium density fibre board (MDF) and the inner side is lined with foam. Inside the canopy, there are two vents fitted which are also made of MDF and lined with foam. In addition, there are two identical fans (one suction and one exhaust). The machine (noise source) selected is the IDAC 30, 8 bar compressor (Figure 1). Modelling Taking into consideration factors such as area, volume, ease of machining, distribution of sound and installation of the compressor (noise source) into the system, a cuboidal shaped canopy is modelled on Solidworks 2015 (Figure 2). The system also includes a ventilation system, which consists of two fans as shown in Figure 3 and two vents in Figure 2 to control the ambient temperature within the canopy, as well as to control supply of air, to

JoRACHV (2016) 24-29 © STM Journals 2016. All Rights Reserved

Page 24

Canopy for Reducing Noise Level at Work Place

Shelar et al.

and fro the canopy. The vents are made of MDF and lined with foam and placed inside the canopy one at suction side and the other at exhaust side of compressor. Working of Canopy System The compressor is placed in the canopy facing the suction and exhaust vents respectively. The compressor is then switched on. As soon as the compressor starts filling, the lid is placed on the canopy as seen in Figure 4. Once the compressor is filled, it gets cut off and is ready to supply air to the required systems via the canopy.

ANALYSIS AND CALCULATIONS The compressors noise intensity is first measured in an open environment, with the help of a noise tachometer and it was found to be 89 dB. Factory limits of sound intensity being 75 to 80 dB during the day. This sound intensity is exceeded [4]. However, when the air compressor is placed in the canopy, the sound intensity achieved on the noise tachometer during filling of the compressor was 78 dB, which is within factory limits.

Fig. 3: Ventilation System.

Fig. 1: IDAC30, 8 bar Air Compressor. Fig. 4: Canopy System with Lid On.

Fig. 2: Canopy Modelling on Solidworks.

Experiment 1 Aim An experiment to find out effectiveness of the foam. Experimental Setup The foam was placed between the noise tachometer and noise source. With respect to the noise tachometer the source was placed at two different positions. Position A: 20 cm from the measuring devices. Position B: 15 cm from the measuring devices.


Page 25

Journal of Refrigeration, Air Conditioning, Heating and Ventilation Volume 3, Issue 3 ISSN: 2394-1952(online)

Observation At Source: Sound intensity =89 dB. Frequency =1830 Hz. At Position A: Material: Foam, Sound intensity =80 dB. Frequency =2247 Hz. At Position B (Figures 5 and 6): Material: Acoustic Foam. Sound intensity =87 dB. Frequency =2492 Hz. Acoustic Foam average frequency =2383 Hz.

Calculation and Result Calculation for wavelength [1]:

λ=

c n

(1)

Where, c is velocity of sound and n is frequency of sound waves. Wavelength of sound waves passed through acoustic foam is:

λ=

330 = 0.138m = 13.8cm 2383

Fig. 5: Sound Intensity Graph.

Fig. 6: Frequency Graph.


Page 26


Shelar et al.

Fig. 7: Noise Intensity with and without Canopy vs. Distance.

Fig. 8: Temperature in the Canopy vs. No. of Cut-Offs. Table 1: Observation Table for Noise Intensity with and without Canopy. Sr. No.

Distance of Sound Tachometer from Noise Source (ft.)

Noise Intensity without Canopy (dB) A

Noise Intensity with Canopy (dB) B

Percent Decrease in Noise Intensity (%) A B  100 A

1

0

89

78

12.36

2

3

85

73

14.12

3

6

84

69

17.86

4

9

83

69

16.87

5

12

83

68

18.07


Page 27

Journal of Refrigeration, Air Conditioning, Heating and Ventilation Volume 3, Issue 3 ISSN: 2394-1952(online)

Experiment 2 Once the foam effectiveness was calculated, a second experiment on the canopy system was conducted. An individual with the noise tachometer stood at different distances away from the canopy system when the compressor was placed inside and filling (Figure 7). The following observations were noted (Table 1).

Shearing Stress due to Friction

Average decrease in noise intensity = 15.86. On an average there is a 15.86% decrease in the sound intensity (dB).

Local Convective Heat Transfer Coefficient

Experiment 3 The third experiment focuses on, the calculation of accumulation of heat in the canopy with respect to the number of times it is filled [3]. As the heat increases, the specific density of the air decreases (Charle’s Law). This increases the work of the motor. The following results were achieved (Figure 8). Thermal Conductivity Velocity of air leaving the canopy due to forced convection: U=2 m/s. Reynold’s Number (Re) Height at which the layer of air is considered (x) Kinematic viscosity (ʋ)

Re = Re =

Ux

(2)

 2× 0.7 16.04×10 6

=87281.8>4000 Hence, the flow is turbulent.

0.664 Re

(3)

Average Friction Coefficient

1.328 Re

1.328 87281.8 = 4.495×103 =

1.1374× 22 2

= 5.1126×103

1 1 k (6) hx 0.332× ×  Re  2 ×  Pr 3 x 1 1 0.11 = 0.332× × 87281.8 2 ×  0.7 3 0.7 =13.685 W/m2K Average Convective Heat Transfer Coefficient h = 2×13.685 =27.37 W/m2K Rate of Heat Transfer by Convection Q = hAdt (7) = 27.37  0.7  0.386   55.5  35.1 =150.086 W Total Drag Force on Foam

Fd  τ  A = 0.7  0.386  5.1126 10  3 = 1.381103

(8)

m  ρ  A U = 1.1374  0.009  0.009  2 = 1.85 104 kg / s  2 104 kg / s

(9)

RESULTS AND CONCLUSIONS

0.664 87281.8 = 2.2475×103 =

Cf 

= 2.2475×103 ×

(5)

Mass Flow Rate through Fans

Local Coefficient of Friction (Cfx)

C fx 

ρU 2   Cfx× 2

(4)

1. There is a 15.86% decrease in the sound intensity (dB). 2. Theoretically when the loudness doubles, there is an increase in sound intensity by 10 dB. 3. Therefore, with a decrease in 10 dB we conclude that the sound intensity is halved. 4. This consideration is not ideal, as every human being can perceive the same sound intensity with a different loudness,


Page 28


5. But this conclusion can stand true for the fact that, sound in an atmosphere with pressure can never be 0 dB. 6. The temperature reached by the compressor in open condition is 55°C. 7. At the 6th cut off, the temperature in the canopy crosses the maximum temperature attained by the compressor. 8. Hence we can conclude, with the canopy we can use the compressor continuously up to five cut offs and then the canopy lid has to be opened, to cool off the compressor. 9. To increase the heat transfer the mass flow rate has to be increased which can be achieved by increasing the area of the opening for the fan or the rpm of the fan or both. FUTURE SCOPE  An extra casing can be added outside the canopy casing to study the dampening effect of air.  The effect of reflective materials inside the canopy can be studied.  Additional fans can be added to increase the number of continuous cut-offs before removing the lid of the canopy.  Maximum fan speeds can be calculated to cool the compressor without affecting the air intake of the compressor.  Bituminous rubber can be added between the foam and wood for further dampening. [5–9].

REFERENCES 1. Avadhanulu MN, Kshrisagar PG. A Textbook of Engineering Physics. Architectural Acoustics. Chapter 9. S. Chand & Company Ltd.; 2014; 277–294p.

Shelar et al.

2. Ch. Rama Rao V, Rama Murthy MB, Srinivasa Rao K. A Perceptual Approach to Reduce Musical Noise Using Critical Bands Tonality Coefficients and Masking Thresholds. Int J Communications Network and System Sciences (IJCNS). 2009; 2: 742–745p. 3. https://engineeringtoolbox.com 4. http://en.m.wikipedia.org/wiki/Noise_Red uction_Coefficient 5. Fotini Kehagia, Sofia Mavridou. Noise Reduction in Pavement Made of Rubberized Bituminous top Layer. Open Journal of Civil Engineering (OJCE). 2014; 4: 198–208p. 6. Paolo Guidorzi, Massimo Garai. Advancement in Sound Reflection and Airborne Sound Insulation Measurement on Noise Barriers. Open Journal of Acoustics (OJA). 2013; 3: 25–38p. 7. Nobuyuki Miyake, Tetsuya Takiguchi, Yasuo Ariki. Sudden Noise Reduction based on GMM with Noise Power Estimation. J Software Engineering & Applications (JSEA). 2010; 3: 341–346p. 8. http://www.moef.gov.in/citizen/specinfo/n oise.html 9. http://www2.siba.fi/akustiikka/?id=38&la =en

Cite this Article Sunhara Kadam, Shivaji Shelar, Aurelius D’souza, et al. Canopy Design and Fabrication for Reducing Noise Level Generated at Work Place without Affecting Equipment/Machine Performance. Journal of Refrigeration, Air Conditioning, Heating and Ventilation. 2016; 3(3): 24–29p.


Page 29