Rk Rajput Thermal Engineering Solutions Pdf
Shanta Plansinis
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The growing concern over environmental challenges posed by the usage of non-renewable materials in various industries has spurred a shift towards renewable and sustainable alternatives. As the demand for materials continues to rise, there is a pressing need to explore efficient and eco-friendly solutions that can mitigate the adverse impacts of industrial processes1. While non-renewable resources still have substantial global reserves, the environmental consequences associated with their production and processing are becoming increasingly alarming, necessitating a focus on material efficiency and sustainability2. In response to these challenges, there has been a renewed interest in harnessing renewable resources3,4,5, with bamboo emerging as a promising nature-based solution (NbS). Bamboo offers several advantages over traditional wood and herbaceous biomass, such as rapid biomass accumulation, high photosynthesis rates, and exceptional carbon fixation capacity6,7,8. Additionally, lignocellulosic biomass from bamboo holds great promise, particularly in the development of nanocomposites, structural materials, and renewable energy applications9,10. The potential of bamboo as a superior renewable material has garnered attention, and several studies have focused on its composition and suitability for various applications. Notably, the bamboo species, with approximately 1700 reported species, has exhibited remarkable mechanical properties owing to its lignocellulosic fibre content, positioning it as a potential alternative to solid wood and synthetic fibres in commercial sectors11. Despite the significant potential, many bamboo species remain underexplored.
Bambusa balcooa20 shown in Fig. 3 is a remarkable drought resistant bamboo species with a unique ability to thrive in regions with low rainfall. This exceptional bamboo has the potential to yield over 100 metric tons per hectare, making it a valuable resource for sustainable cultivation and economic purposes. Originally native to the Indian subcontinent and Indo-China, Bambusa balcooa Roxb is a clumping bamboo known for its impressive height, reaching up to 25 m, and substantial wall thickness, measuring 15 cm. Figure 3a shows Bambusa balcooa culms and Fig. 2b shows longitudinal section of culm between the nodes Its ability to grow in arid conditions and its remarkable yield potential make it an essential species for conservation efforts and a promising option for various industries and applications. Figure 3c and d shows the top view of the cross section of culm detailing the fibre orientation Bambusa balcooa.
As we traverse from the inner to the outer region of the bamboo stem, a consistent pattern of increasing tensile strength in the bamboo fibres becomes evident. Moreover, there is a noticeable rise in the tensile elastic modulus, while the strain to failure decreases. The fibres closer to the inner part exhibit a brittle fracture behaviour, while those nearer to the outer part demonstrate characteristics similar to ductile fracture25. In this particular study, the focus was on extracting fibres from the outer sheath of the bamboo stem. Three common methods for bamboo fibre extraction are available: mechanical, chemical, and a combination of both26. For this research, the mechanical extraction method called mechanical retting was employed. The process involved obtaining fresh internode billets from carefully selected bamboo plants and cutting them into 200 mm sections. Each section was further divided into six equally sized strips along the grain. These strips were soaked in water for approximately three days to facilitate the extraction process. Subsequently, the researchers manually scraped the bamboo fibre bundles from the soaked strips using a sharp knife. Although the fibres broke along their length during this process, they were found to be of strong and good quality. Only fibre bundles longer than 80 mm, possessing even thickness and a smooth surface, were selected to create tensile specimens. A total of 150 specimens were prepared, divided into six groups, each comprising 25 specimens. To ensure consistent moisture content and avoid any potential moisture-related variability in results, all the specimens were placed in a constant temperature and humidity box set at 20 C and 65% relative humidity for moisture equilibration. This meticulous preparation and extraction process aimed to obtain reliable and standardized tensile specimens for further testing and analysis. The mechanical retting method was chosen due to its effectiveness in preserving the integrity and strength of the extracted fibres. By employing such carefully controlled procedures, the researchers sought to explore the mechanical properties of the bamboo fibres comprehensively, providing valuable insights into their potential applications in various industries, including construction, textiles, and engineering. Additionally, understanding the varying mechanical behaviour of the fibres along the stem could shed light on the structural design and engineering applications of bamboo-based materials, which are increasingly recognized for their sustainability and eco-friendliness.
The cellulose, hemicellulose, and lignin content of the samples were determined29. First, the sample was refluxed with ethanol four times, with each reflux lasting for 15 min. It was then washed with distilled water and dried in an oven at 40 C overnight to estimate the dry weight (A). Then the sample was treated with 24% KOH (Potassium hydroxide) for 4 h at 25 C. Afterwards, it was thoroughly washed with distilled water and dried in an oven at 80 C overnight, and the dry weight (B) was measured. The sample was treated with 72% H2SO4 (Sulphuric acid) for 3 h to hydrolyse the cellulose, and then refluxed with 5% H2SO4 for 2 h. The samples were washed with distilled water and dried in an oven at 80 C overnight, and the dry weight (C) was measured. By following this method, the cellulose, hemicellulose, and lignin content of the samples could be determined accurately as follows.
The series of treatments allowed for the isolation and quantification of each component separately. Cellulose is the main component responsible for the structural strength of plant cell walls, while hemicellulose contributes to the amorphous regions of the cell wall and plays a role in bonding cellulose fibres together. Lignin, on the other hand, provides rigidity and resistance to degradation. Understanding the content of these components is crucial for assessing the quality and potential applications of the plant materials being studied.
Strictly adhering to ASTM D 2495 standards, the moisture content percentage of the specimens was measured by using the oven drying method30. The moisture content in the Bamboo fibres was determined by equation31, 32.
An adaptation of the ASTM D570-98 standard was employed to assess water absorption in the test specimens. In this modified approach, the specimens were submerged in distilled water maintained at 21.5 C for varying time spans, with a maximum of 60 min. The samples were retrieved from the water at specific intervals: 1, 3, 5, 10, 15, 20, 25, 30, and 60 min. Once removed, the samples were rapidly rid of any surface dampness and then weighed with precision to the nearest 0.0001 g. The difference in weight post-immersion was used to quantify the absorbed water volume. This methodology offers insights into the material's water uptake kinetics and sheds light on how it responds to prolonged exposure to water under controlled conditions.
The surface morphology of the three sample fibres was examined using scanning electron microscopy at an operating voltage of 10 kV using JEOL JSM-IT510 instrument. To enhance the conductivity of the fibre before the experiment, the samples were coated with gold in a vacuum environment.
Energy dispersive X-ray spectroscopy or EDX is a popular technique for identifying the elemental components of natural fibre like Carbon, Oxygen, and Nitrogen. The elemental composition of bamboo fibres was determined with EDX JEOL JSM-IT510 instrument associated with the SEM.
Tests were performed using a Computerized Universal Testing Machine, specifically the KALPAK UTM, Model No. KIC-2-1000-C, with a maximum load capacity of 100 kN and a 0.1 kN load cell, to determine the tensile strength of individual bamboo fibres. The tests followed the ASTM D3822-07 standard, treating bamboo fibres similarly to natural and textile fibres. Various fibre lengths were examined during the experiments to obtain comprehensive data on their tensile properties.
The physical characterization of bamboo fibres was done by thickness/diameter and density measurements. Like any other natural fibre, the bamboo fibres are of uneven thickness hence the diameter measurement was carried out at different lengths of the fibres shown in Fig. 6. The analysis using optical microscope indicated that all the bamboo fibres individually measured, the diameter varied from 0.3 to 0.4 mm and the mean diameter was found to be 0.35 mm. Figure 6 shows the diameter measurement and microscopic view of a fibre. The density value of the Bamboo fibres ranged from 1.08 to 1.24 g/cc. The species Pseudoxytenanthera ritchie showed the highest value for density measurement. Density measurements are always an important factor in assessing the mechanical property since there fibres are of natural origin6. The density of the bamboo fibre is comparable to the other economically important fibres36. The diameter and density values were given in Table 1.
The cellulose, hemicellulose and lignin content of the samples were determined using the method mentioned earlier. The two varieties BR and BS possessed very high cellulose content of 75.05% and 72.93% respectively compared to the common variety BB (60.98%). It is considered that the high cellulose content in plant fibres increases the tensile strength, stability, stiffness and hydrolysis resistance which are the important parameters in commercialization of the fibres37. The high cellulose content of the samples in present study is the best indication of the superior quality of these two varieties. The hemicellulose content varies from 3.1 to 23% which also attributes to the high tensile strength of the fibres. The lignin content of the two varieties were 21.85% (BR) and 18.82% (BS). A previous study on different bamboo varieties shows that lignin content varies from 16 to 25%38. The values were tabulated in Table 1.