Faculty of Mechanical Engineering

Transcription

1 Faculty of Mechanical Engineering PADDY FIBER AS AN ALTERNATIVE SUSTAINABLE ACOUSTIC ABSORBER MATERIAL Yasseer bin Abdullah Master of Science in Mechanical Engineering 2014

2 PADDY FIBER AS AN ALTERNATIVE SUSTAINABLE ACOUSTIC ABSORBER MATERIAL YASSEER BIN ABDULLAH A thesis submitted in fulfillment of the requirements for the degree of Master of Science in Mechanical Engineering Faculty of Mechanical Engineering UNIVERSITI TEKNIKAL MALAYSIA MELAKA 2014

3 DECLARATION I declare that this thesis entitle Paddy fiber as an alternative sustainable acoustic absorber material is the result of my own research except as cited in the references. The thesis has not been accepted for any degree and is not concurrently submitted in candidature of any other degree. Signature :... Name :... Date :...

4 APPROVAL I hereby declare that I have read this thesis and in my opinion this thesis is sufficient in terms of scope and quality for the award of Master of Science in Mechanical Engineering Signature :... Supervisor Name :... Date :...

5 DEDICATION To my beloved parents and wife

6 ABSTRACT The use of synthetic materials as acoustic absorbers is still applied extensively in building industry. These non-biodegradable materials do not only cause pollution to the environment, but also contribute significantly in increasing the CO 2 causing the effect of global warming. Therefore researchers have now driven their attentions to find sustainable and eco-friendly materials to be an alternative sound absorber. This study discusses the use of natural waste fibers from dried paddy as fibrous acoustic material. Since this is one of common natural waste materials found across South East Asia, the usage will also minimize the production cost. Samples of sound absorbers from paddy fibers were fabricated and the acoustic properties were determined through experiment. The paddy fibers are found to have good acoustic performance with normal incidence absorption coefficient greater than 0.5 from 1 khz and can reach the average value of 0.8 above 2.5 khz. The sound absorption performance can be further increased at lower frequency range by 50% with a layer of polyester cloth added to its front surface. The absorption coefficient result from sample with weight of 3 grams and thickness of 20 mm is found to be comparable against that from the commercial synthetic glass wool. i

7 ABSTRAK Penggunaan bahan-bahan sintetik sebagai penyerap bunyi masih lagi digunakan secara meluas di dalam industri pembinaan. Bahan yang tidak-terbiodegradasi ini tidak hanya akan menyebabkan punca pencemaran kepada alam sekitar, tetapi juga menyumbang kepada peningkatan CO 2 yang boleh menyebabkan kesan pemanasan global. Justeru, para penyelidik telah didorong untuk mencari bahan-bahan yang mampan dan mesra alam untuk menjadi penyerap bunyi alternatif. Kajian ini membincangkan mengenai bahan buangan semulajadi daripada padi sebagai bahan akustik berserat. Memandangkan bahan-bahan buangan semulajadi ini biasanya terdapat di seluruh Asia Tenggara, penggunaannya juga dapat mengurangkan kos pengeluaran. Panel penyerap bunyi dari jerami padi telah dibentuk dan ciri-ciri akustiknya telah dikaji melalui eksperimen. Panel ini didapati mempunyai prestasi penyerapan bunyi yang baik dengan pekali penyerap bunyi yang melebihi 0.5 pada 1 khz dan mencapai nilai purata 0.8 pada frekuensi melebihi 2.5 khz. Prestasi bunyi dapat ditingkatkan lebih 50% pada frekuensi rendah dengan menambah kain polyester pada permukaannya. Manakala hasil untuk sampel yang seberat 3 gram dengan ketebalan 20 mm adalah setanding dengan penebat gentian bulu kaca yang terdapat di pasaran kini. ii

8 ACKNOWLEDGEMENTS In the name of Allah, The Beneficient, The Merciful This research was made possible through contributions, support, and encouragement from many individuals. Unfortunately, it is not possible to acknowledge each of them here. First and foremost, I would like to thank ALLAH SWT for the blessing and ability given to me to eventually complete my Master thesis. I would like to give sincere tribute to my supervisor, Dr. Azma Putra for everything. From preliminary ideas to data processing, invaluable guidance, continuous encouragement and excellent supervision in making this research possible. I really appreciate the consistent support he provided me throughout the research. The good advise, support and friendship of my second supervisor, Prof. Dr. Md Razali bin Ayob has been invalueable on both academic and personal level for which I am extremely grateful. I wish to express my gratitude to my parents, Hj Abdullah and Hjh Maliah, for their unlimited love. It is because of their prayer that I have become what I am. I could not find a appropriate words that could properly describe my appreciation for their devotion, support and faith in pursuing my dreams. Also for my parents in law, Allahyarham Hasan and Hjh Rossnah for their sincere kindness. Also not to forget staff in the Faculty of Mechanical Engineering, UTeM which their names are too numerous to mention, who help me directly or indirectly throughout the whole project. For my colleagues in Acoustics and Vibration Group, thank you for the brilliant discussion which gives much input to my work. Finally but most importantly, for my beloved wife, Noraini, to whom this work is lovingly dedicated. Her unconditional love, support, encouragement and sacrifices has given me a peaceful heart during my study. And also for her gifts from heaven, Muhammad Adam Hafiey and Muhammad Afif Hakimi, who have cheered up my days. iii

9 TABLE OF CONTENTS PAGE DECLARATION APPROVAL DEDICATION ABSTRACT ABSTRAK ACKNOWLEDGEMENT LIST OF TABLES LIST OF FIGURES LIST OF ABBREVIATIONS LIST OF SYMBOLS LIST OF PUBLICATIONS CHAPTER i ii iii i ii iii vi vii ix x xii xii 1 INTRODUCTION Background Problem Statement Objectives Scope Thesis Layout 5 2 LITERATURE REVIEW Sound Absorption Porous absorbers Natural Fibers Factors influencing sound absorption Established works on natural fiber as sound absorber Paddy 20 iv

10 3 METHODOLOGY Testing methods for absorption coefficient Reverberation chamber method Impedance tube method Design of an impedance tube Cross-section Choosing working frequency range Length of the impedance tube Microphones Test sample holder Signal processing equipment Loudspeaker Signal generator Loudspeaker termination Thermometer and barometer Test specimen mounting Signal processing Fabrication of impedance tube Validation of impedance tube Fabrication of flow resistivity instrument Experimental setup for absorption coefficient test Fabrication of samples Density, porosity and water absorption test Density Porosity Water absorption Flammability test Microscopic test 53 4 RESULT AND DISCUSSION Measured density, porosity and water absorption Flammability test result Microscopic view of the sample Measured absorption coefficient 58 5 CONCLUSION AND RECOMMENDATIONS FOR FUTURE RESEARCH Conclusion Recommendations 68 REFERENCES 69 v

11 LIST OF TABLES TABLE TITLE PAGE 1.1 Comparison between natural and man-made fibers Comparison of properties of paddy fibers (average) compared with other natural fibers Summary between two testing methods to measure absorption coefficient Relative distance of the microphones Frequency limit of measurement Equipment used in the experiment List of equipment used in the experiment Determination of airflow resistance according to ISO The measured density for 10 mm thick samples The measured density for 20 mm thick samples The measured porosity for different weight of samples The water absorption test results Flammability rating summary Flammability results. 58 vi

12 LIST OF FIGURES FIGURE TITLE PAGE 1.1 (a) Practical noise insulations in a building and (b) glass fiber; synthetic fibrous material common used as sound absorber Assessment on Global Warming Potential Reflection, absorption and transmission of sound energy (a) Schematic representation of sound propagation in a room and (b) schematic representation of the functioning of sound barriers Typical frequency range of sound sources Types of porous absorber Ilustration of porous absorber cross section Energy transfer of particle velocity Classification of fibers Paddy field after harvesting season External anatomy of paddy The flowchart of research methodology Measurement of sound absorber inside a reverberation chamber A complete system of a commercial impedance tube Different diameters of impedance tube: (a) large diameter for low frequency measurement and (b) small diameter for mid-high frequency measurement Microphone mounting Layout design for sound absorption impedance tube Technical drawing of the impedance tube Constructed impedance tube Separated sample holder and embedded loudspeaker Diagram of measurement setup using impedance tube to measure sound absorption coefficient Test result of absorption coefficient without measurement sample The autospectrum from each microphone: (a) closest to the loudspeaker and (b) closest to the sample Results of measurement validation using MPP having hole diameter of 0.5 mm and perforation ratio : (a) 0.5% and (b) 1.0% Flow resistivity setup diagram Flow resistivity device Linear regression to obtain flow resistance from the samples Diagram of the measurement setup for the absorption coefficient test. 47 vii

13 3.18 The collected raw materials of paddy fibre. The right side shows the materials cut in small pieces The mould used to construct the absorber sample Examples of fabricated samples from paddy fibers Flow chart of pre-treatment and fabrication processes Horizontal flammability test setup Comparison condition between the sample under the water absorption test and with normal sample Microscopic view of several weight of paddy fiber samples (a) 3 grams (b) 4 grams (c) 5 grams and (d) 6 grams Measured absorption coefficient of samples with the same fiber weight of 2 grams: t =10mm and t =20mm Measured absorption coefficient of samples with the same thickness, t = 20 mm: 2 grams and 4 4 grams Measured absorption coefficient of samples with the same density, bulk = 234 kg/m 3 : t =10mm; 2 grams and 4 t =20mm; 4 grams Measured absorption coefficient of 20 mm thick samples with different fiber weight: 2 grams, B 3 grams, 4 4 grams, 5 grams, 6 grams Measured absorption coefficient of 2 gram samples with thickness of (a) 10 mm and (b) 20 mm with different backed air layer thicknesses: without air layer, D =10mm and O D =20mm Sample of the paddy fiber attached with polyester fabric Measured absorption coefficient of sample (t = 20 mm, 2 grams) with polyester fabric: without, H on front surface, on back surface and on front and back surfaces Comparison of absorption coefficient of the paddy fiber sample (. ; t =20 mm, 3 grams) with that from the commercial glass wool ( ) Sample of paddy fiber with commercial glasswool. 66 viii

14 LIST OF ABBREVIATIONS DAS dpf EPS FFT GWP IRM khz NF NWC Pa SF TLF WCC Data Acquisition System denier per filament Expanded PolyStyrene Fast Fourier Transform Global Warming Potential Inverted Research Microscope kilo Hertz Natural Fiber Non Woven Cloth Pascal Synthetic Fiber Tea Leaf Fiber Woven Cotton Cloth ix

15 LIST OF SYMBOLS A Cross-sectional area c o d E i E r E t f f l f u G 11 G 12 H 12 Speed of sound Diameter of the tube Incident energy Reflected energy Transmitted energy Frequency Lower frequency range of the tube Upper frequency range of the tube Auto-spectrum Cross-spectrum Transfer function between microphone-1 and microphone-2 j = p 1 Imaginary unit k o M m R R s r s t V v W Z tot Z D z f Acoustic wavenumber Acoustic reactance mass per unit area of the panel sample Acoustic resistance Specific flow resistance Reflection coefficient Spacing between microphones Thickness of panel Volume Particle velocity Weight of the sample Total of impedance Impedance of air gap impedance of air x

16 q v b Volumetric airflow rate Sound absorption coefficient Porosity of porous material Acoustic wavelength Density of air Density of sample! Angular frequency Coefficient of viscosity of air xi

17 LIST OF PUBLICATIONS Journal Articles A. Putra, Y. Abdullah, W.M.F.W. Mohamad and N.L. Salleh, Biomass from paddy waste fibers as sustainable acoustic material. Advances in Acoustics and Vibration, Vol. 2013, Article ID , 7 pages (2013), doi: /2013/ A. Putra, Y. Abdullah, H. Efendy, W.M.F.W. Mohamad, M.R. Ayob and M.S. Py, Utilizing sugarcane wasted fibers as sustainable acoustic absorber, Procedia Engineering, Vol. 52, pp (2013) Y. Abdullah, A. Putra, H. Efendy, W.M.F.W. Mohamad and M.R. Ayob, Investigation on sound absorption coefficient of natural paddy fibers, International Journal of Renewable Energy Resources (IJRER), Vol. 3 (1), pp (2013). Proceedings Y. Abdullah, A. Putra, H. Efendy, W.M.F.W Mohamad and M.R. Ayob, The effect of binder on the acoustical performance of the paddy straw green sound absorber. Proceedings of 3rd International Conference on Engineering and ICT (ICEI), Melaka, Malaysia, Y. Abdullah, A. Putra, H. Effendy and W.M.F.W. Mohamad, Investigation on natural waste fibers from dried paddy straw as a sustainable acoustic absorber. IEEE First Conference on Clean Energy and Technology CET, Kuala Lumpur, Malaysia, Y. Abdullah, A. Putra, H. Efendy, W.M.F.W Mohamad and M.R. Ayob, Dried Paddy Straw Fibers as an Acoustic Absorber: A Preliminary Study. Proceedings of Hari Penyelidikan 2011 Fakulti Kejuruteraan Mekanikal, UTeM, Melaka, Malaysia, xii

18 CHAPTER 1 INTRODUCTION 1.1 Background The issue of conserving environmental condition and its relation with global warming has attracted attention of researchers for new technologies which are more environmentally friendly. Besides finding alternative energy to limit the use of fossil fuels and deforestation, attemps are also directed to create products from re-cycleable and sustainable materials. The synthetic materials especially those made from minerals have been known to have issues concerning their pollution with regards to their disposal. For application in building acoustics for example, where sound quality in a room such as the theatre hall, music studio, lecture room, teleconferencing room, cinema as well as the meeting room, classical abrasive and porous acoustic materials are still widely used. Demands of acoustic quality in factory and warehouse should also be taken seriously to control the noise level problem. To increase the sound absorption, the walls in buildings are usually covered by absortive layers using glass wools or acoustic foams made from synthetic chemical substances as seen in Figure 1.1. The room ceiling usually uses the commercial gypsum boards, made by high technology chemical process. Moreover, the production also gives huge contribution to CO 2 pollution to the atmosphere. It is commonly known that these conventional synthetic absorbers can be harmful for human health if inhaled during handling and can cause skin and eyes irritation (Asdrubali, 2006). Most of the absorbers from synthetics fibers such as foamglass, EPS as well as the

19 (a) (b) Figure 1.1 (a) Practical noise insulations in a building (Hometheaterfan, 2011) and (b) glass fiber; synthetic fibrous material common used as sound absorber (Anonymous, 2011). glass fiber are huge contributors to earth global warming. The Global Warming Potential (GWP) chart of sound absorber panels made of natural and synthetic materials as shown in Figure 1.2 represents the equivalent contributions of CO2 into the atmosphere from the production of an absorber panel from cradle to grave (Desarnaulds et. al., 2005). It can be seen that the synthetic-based fibers for example foamglass, contributes high GWP if compared to natural-based fibers for example coconut fibers. Therefore, instead of using the synthetic mineral fibers, researches are directed to find natural fibers as an alternative choice to be developed as sound absorbers. The natural fibers offer some advantages including renewable, biodegradable and cause much less harm to human health. Table 1.1 summarises the advantages of natural fiber compared with the synthetic fibers (Wambua et. al., 2003). 1.2 Problem Statement Asian countries are mainly agriculture-based economy. Over the year, tonnes of nat- ural wastes including the paddy fibers are disposed and are usually burned which leads to 2

20 NRE Non Renewable Energy Mj/Kg Natural cautchuc (6.4 Kg/m3) Coconut fibres (50 Kg/m3) Flax fibres roll (25 Kg/m3) Sheep wool (30 Kg/m3) Cellulose flocks (35-70 Kg/m3) EPS (30 Kg/m3) Foamglass (130 Kg/m3) Glass fiber (34 Kg/m3) Mineral wool (56-60 Kg/m3) 0,0 0,0 0,2-0,3 1,2 2,1 2,4 2,3 3,7 GWP Global Warming Potential Kg CO2 eq. Figure 1.2 Assessment on Global Warming Potential (Desarnaulds et. al., 2005) contribution of CO 2 release in the atmosphere. The abundance biomass source of this natural fiber is potential to be employed as raw materials for sound absorber panels. Investigation on the ability of the paddy fiber as an acoustic absorber material is therefore of interest. 1.3 Objectives This study embarks on the following objectives: 1. To fabricate impedance tube and flow resistivity device. 2. To fabricate samples of acoustic absorber from paddy fiber. 3. To determine the acoustic properties of paddy fiber through experiment. 4. To measure the physical properties of paddy fiber. 1.4 Scope This study is emphasized on the characteristic of the acoustic properties of paddy fibers as sound absorbers. Physical properties are therefore limited, but it was designed so that the 3

21 Table 1.1 Comparison between natural and man-made fibers (Wambua et. al., 2003). Parameter Natural fiber Synthetic fiber Density Low Higher than NF Cost Low Slightly higher than NF Renewability Yes No Recyclability Yes No Energy Consumption Low High Health risk when inhaled No Yes Disposal Biodegradable Non-biodegradable Environment impact No Yes Greenhouse gas emission Low High trend of the absorption coefficient can be concluded for other properties. This study therefore limits to the following scopes: 1. Samples of the absorber were made for thickness of 10 mm and 20 mm and were limited to weight of 2 grams until 6 grams. 2. Experiment of absorption coefficient was done using impedance tube and thus represents only the absorption performance for normal incidence of sound. 3. The physical test includes the density, porosity, microscopic, water absorption and flammability test. The strength test is not included in this study. 4

22 1.5 Thesis Layout This thesis consists of five chapters. Chapter 1 discusses the problem definition, justification for carrying out the research (background study), objective and the scope of the project. Chapter 2 briefs a description of fundamental theories of sound absorption. General review on natural fiber properties and some of the previous researches on the natural waste fibers are presented. Natural fiber properties and characteristic of paddy are also reviewed. Chapter 3 are the details explanation of the methodology of the research. Development and fabrication of instruments used for acoustic properties measurement, namely impedance tube and flow resistivity instrument are presented in this chapter. This also includes the physical property tests, i.e. the density, porosity, water absorption tests as well as the flammability and microscopic tests. Chapter 4 discusses the results and analysis in details which are the core part of this thesis, particularly for the measured absorption coefficent. The conclusion is written in Chapter 5 followed by the recommendations for the future works. 5

23 CHAPTER 2 LITERATURE REVIEW In this chapter, brief principle of sound absorption and porous absorbers are explained. The properties of general fibers are also described. Established works on sound absorbers from natural materials are reviewed followed by paddy fibers history. 2.1 Sound Absorption Consider an acoustic material which is uniform and unbounded immersed in air and is impinged by a sound wave. Besides reflected and absorbed, the energy is also transmitted to other side of the material as illustrated in Figure 2.1. Incident, E i Absorbed, E a Reflected, E r acoustic materials Transmitted, E t Figure 2.1 Reflection, absorption and transmission of sound energy The energy balance can be written as

24 E i = E r + E a + E t (2.1) where E i is the incident energy, E r is the reflected energy, E a is the absorbed energy and E t is the transmitted energy. The sound absorption coefficient simply indicates the portion of the sound energy absorbed by the material from the total energy of the incoming wave expressed by E r = E i =1 E i E r E i =1 r (2.2) where r is the power reflection coefficient. From Eq.(2.1), E i - E r = E a + E t i.e. the sound energy absorbed by the system (seen from incident field) includes the transmission into the other side of the material. If the material is attached on to a rigid surface, then E t = 0. Whenever the material impedance is equal to the characteristic impedance of the air (medium), maximum sound absorption occurs. Therefore, the amount of the energy being absorbed depends on the material impedance which is determined by the acoustic properties of the material such as porosity, tortuosity and flow resistivity. The absorption varies with frequency as well as with angle of incidence of the sound waves (Everest and Shaw, 2001). To optimise the acoustics in a rooms, among other techniques is to interrupt the paths of sound propagation towards listener as seen in Figure 2.2. Apart from direct sound, sound is transmitted by reflections from the walls and the ceiling. Depending on the sound absorption coefficient of the ceiling and the walls, part of the incident sound always reverberates resulting in a repercussion of the emitted sound by reflection or scattering. The sound barrier should have a certain mass per unit area, and their surface should be 7