2. Thesis and Dissertations
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Item Development of Solar Cooker With Temperature Controlled Thermal Energy Storage Units(National Institute Of Technology Karnataka Surathkal, 2023) B C, Anil Kumar; M, Ranjith; SS, AnishSolar cookers (SCs) have been a research focus worldwide because of their numerous advantages, such as no running costs, non-polluting nature, and ample availability of solar energy. Different sensible and latent heat storage materials are used to extend the usability of SCs in the late evening hours. Recently, the latent heat of phase change materials (PCMs) used as thermal energy storage (TES) medium has become remarkable because of its high energy density and constant temperature operating characteristics. In light of this, the main objective of the present study is to design, optimize, fabricate, and perform an experimental investigation of solar box cooker (SBC) with constant temperature heat storage unit incorporating PCM. Prediction models are also developed to forecast the component temperatures of SBC. As a preliminary work, three geometries of SBCs are developed and tested to familiarize the test procedures and performance assessment. A rectangular-shaped SBC (RSBC) is fabricated by incorporating an optimum mixture of sensible heat storage materials below the absorber plate. The optimum cooker surface area is estimated with analytical heat loss and design equations solved through an iterative procedure implemented in MATLAB. Next, a cylindrical-shaped SBC (CSBC) is designed and fabricated using the minimum entropy generation (MEG) method and iterative design procedure. The experimental investigation is carried out to check the effectiveness of the frustum of a decahedron-shaped reflector on the performance of CSBC. Through experiments, it is observed that the absorber plate attains peak temperature of about 138oC-150oC. Finally, the performance of trapezoidal shaped SBC (TSBC) fitted with four outer reflectors is assessed using water and glycerol as cooking load. The TSBC shows maximum absorber plate temperature of 171°C, making this an A-grade SBC. Comparing standardized cooking power and energy efficiency, TSBC fitted with four outer reflectors performs more than CSBC equipped with decahedron-shaped reflectors. The analysis of annualized life cycle cost and pay-back period show that TSBC is more economically feasible than CSBC. viii The next stage study focuses on developing prediction model for SBCs through computational and machine learning (ML) approaches. The objective is to forecast the component temperatures of SBC through ML techniques such as random forest (RF), k-Nearest Neighbor (k-NN), linear regression, and decision tree. A numerical model based on thermal balance is used to generate the data set for the ML algorithm. Heat transfer model is developed by considering all the components of SBC such as absorber plate, glazing cover, cooking pot, lid, air cavity, and cooking load. The total heat loss from the SBC to the surroundings is estimated by considering heat loss from the absorber plate to the ambient through all faces of the cooker. The absorber plate receives solar irradiance through the double-glazing covers. Among this, some heat energy is absorbed, and the rest is rejected via convection heat transfer to inner air cavity, radiation heat transfer to second glass, and conductive heat loss through bottom of absorber plate via insulation and casing. Experiments on the TSBC are conducted to validate the numerical model. The temperatures of different components obtained through numerical modeling agree with experimental values with less than 7% maximum error. The RF model outperformed the other models and has great accuracy in predicting the thermal parameters of SBC. The third stage study focuses on the design optimization of PCM based TES unit for SBC. A computational procedure is developed to estimate the optimum mass of PCM and dimensions of the TES unit. MATLAB code is written to implement the iterative procedure, simplifying exhaustive calculations required for optimizing and designing the TES unit. The computational procedure is validated by the present experimental study and also compared with previous works. A modified TES unit containing PCM as heat storage medium surrounding cooking vessel is designed and fabricated with the iterative procedure. The TES units developed in this study have the provisions for filling the PCM on all sides, including the lid, enhancing the heat storage. The present work also aims to design, fabricate and test different geometries of TES units using paraffin wax as the PCM. After six hours of the test, the cooking load temperature in all geometries of TES units reached the melting point of PCM. TES units with cylindrical shapes perform best among hexagon and square designs. ix The selection of optimum PCM is also important for effective heat storage in SCs. Therefore, the present work aims to select the optimum PCM among the alternatives for the TES unit incorporated in SBC. Based on the melting temperature, the PCMs are pre-screened among the alternatives used in earlier works. The optimum PCM is selected with multi-criteria decision-making (MCDM) techniques like TOPSIS, EDAS, and MOORA. The criteria weights required for the optimization algorithm are found by using AHP, ENTROPY, and CRITIC methods. All MCDM techniques show that erythritol is the best alternative for the TES medium incorporated in the SBC. The iterative solution procedure also selects erythritol as the best alternative since it requires less quantity than other PCMs. In the last stage, the performance of optimized TES units is experimentally assessed using SBC. The performance parameters of the RSBC having iron grits, sand, brick powder, and charcoal powder in the optimum ratio (mass) of 1:2:2:3 respectively as heat storage material is investigated. It is found that water temperature in the developed TES incorporated RSBC is maintained above 70oC till 6 PM in a day. The performance test on CSBC is carried out with the optimized cooking vessel surrounded by the TES unit filled with paraffin wax as the PCM. The results show that the TES maintains water temperature between 55oC-60oC during evening hours. Finally, the optimized TES unit containing erythritol as PCM is tested with TSBC using glycerol and water as cooking load. Glycerol and water show more than 115oC and 90oC, respectively, during night hours by absorbing latent heat energy from the TES unit. As a summary, this study focused on the design, fabrication, and experimental assessment of the performance of a novel solar box cooker with thermal energy storage unit using phase change material. It includes optimum design of solar box cooker and thermal energy storage unit, computational, and machine learning approaches for the prediction model development. The optimum phase change material is selected based on the multi criteria decision making techniques and computational procedure. As per literature study no other work incorporates x computational, experimental, and machine learning aspects of solar cooker assessment. Researchers can predict solar cooker performance through the study without requiring elaborate experiments, which saves both time and money. This study will inspire researchers to explore the possibilities of optimization, numerical and machine learning approaches for solar thermal conversion applications.Item Design and Development of Magnetorheological Fluid Damper to Suppress the Tool Vibration In Hard Turning Operation(National Institute Of Technology Karnataka Surathkal, 2023) Aralikatti, Suhas S.; Kumar, HemanthaThe state of the cutting tool determines the quality of the surface finish produced on the machined parts. A faulty tool produces poor surface and inaccurate geometry leading to the rejection of parts. It is necessary to monitor tool conditions to have consistent quality and economic production. Condition monitoring is ineffective without the implementation of a real-time corrective strategy. In the present study, fault classification of single-point cutting tools for hard turning has been carried out by employing signal processing and machine learning technique using cutting force signals and vibration signals. A comparison of the performance of classifiers was made between cutting force and vibration signal to choose the best signal acquisition method in classifying the tool fault conditions using the machine learning technique. A set of four tool conditions, namely healthy, worn flank, broken insert and extended tool overhang, have been considered for the study. These faulty tools produce undesired vibration that reduces machine quality and production rate. The adverse effect of tool vibration leads to loss of geometric tolerance, accelerated tool wear, poor surface finish and machine instability. The author designed a current- controlled compact magnetorheological fluid (MRF) damper consisting of an electromagnetic coil in the piston as a corrective measure. The damper is fitted onto the lathe machine with the optimal fluid composition to evaluate its performance in controlling the tool vibration. The optimal composition of MRF is identified by a genetic algorithm through the central composite design of the experiment. To cross- verify the algorithm's output values, a validation study is done. A comparison between optimal in-house MR fluid and commercial MR fluid is conducted. The comparison demonstrates that in-house prepared MR fluid performs equally well compared to commercial fluid. The MR damper effectively damps high-amplitude vibration at aggressive cutting conditions. The L9 Taguchi design of the experiment opted to arrive at minimal machining parameters to evaluate the performance of the damper in machining two workpiece materials, namely oil-hardened nickel steel (OHNS) and high carbon high chromium (HCHCR) die steel. The surface roughness and tool vibration iiiare reduced with the damper. It is noted that in-house MR fluid performed equally well as commercial MR fluid. The tool wear study is also carried out to monitor the influence of external damping over tool life. The stability lobe diagram is obtained analytically with experimental validation to mark the stability limit of the machining condition. The stability boundary increases with the damper enabling aggressive cutting conditions. The designed MR damper is controlled by a real-time controller considering the vibration-limiting feedback approach. The Bouc-Wen model is used to estimate the damping force based on the vibration feedback of the tool. The tool wear, surface roughness, and amplitude of tool vibration are evaluated with and without a semi-active MR damper. The above-developed MR damper forms an external adaptor to control the tool vibration that can be installed on the lathe. To improve the design configuration of the MR damper, an internally damped novel tool holder is designed that houses MR fluid in its axial hollow section. The MR fluid is activated by the internal electromagnet coil wound around the inverse beam supported at the inner wall of the hollow portion. The developed MR tool damper reduces the tool vibration with the electric current supply.Item Phonology Analysis From Childrens' Speech(National Institute of Technology Karnataka, Surathkal, 2022) Bhaskar, Ramteke Pravin; Koolagudi, Shashidhar G.Human vocal tract can produce various sounds. The speech sounds are relatively a very small set of such sounds that appears uniquely quali ed to be used in the production of speech. It includes positions of the parts of the body necessary for producing spoken words and the e ect of air rushing from lungs as it passes through the larynx, pharynx, vocal cords, nasal passages and mouth. Phonetic sounds (phones) are the actual speech sounds classi ed by the manner and place of articulation (i.e. the way in which air is forced through the mouth and shaped by the tongue, teeth, palate, lips and in some languages by the uvula). Children begin language acquisition with their rst meaningful word. Further, they acquire language by mimicking the adult pronunciation. This development mainly depends on the development of vocal tract, neuro-motor control and in uence from the language of people surrounding them. Signi cant di erence can be observed in the vocal tract of the child and adult where the vocal tract in children is underdeveloped and short in comparison with the adult vocal tract. Along with these, other oral cavity parameters such as tongue, larynx, epiglottis, vocal cords are also underdeveloped. Due to this, children face di culty in producing speech sounds, where the pronunciations are simpli ed by substituting the di cult speech sounds with other simple one. This results in signi cant deviations and replacements in the pronunciation of phonemes in children leading to mispronunciation or pronunciation errors. These processes are referred to as phonological processes. The phonological processes appear in the children represents the agewise speech learning ability. The analysis helps the Speech Language Pathologists (SLPs) in studying language learning ability of the children. The manual process of phonology analysis involves lot of human e ort and time. Literature reports that the phonological processes are properly studied in the children speaking English as native language. Indian languages are syllabic in nature and di er from English which is phonemic in nature. Hence, the observations made in the case of English children may not be directly applicable to the study of phonological developments observed in the case of Indian children. In general, the appearance of phonological processes in the case of Indian children is not well studied i and documented. The appearance of these processes beyond certain age may indicate the presence of the phonological disorder. It helps the SLPs to automatically identify the processes and analyse the language learning pattern along with disorders present if processes are observed beyond certain age. In this work, we aim to develop the systems for automatic identi cation of phonological processes in Kannada language. Applications of this research work include evaluation of language learning ability, identi cation of speech and motor disorder, gender based analysis of phonological processes, etc. Some of the important issues in this research area are, large number of non-standardized phonological processes; lack of detailed studies in Indian languages; availability of children's speech databases in the required age range from 31 2 to 61 2 years; di culties in adapting existing systems of mispronunciation identi cation due to huge di erence in the speech production parameters of the adults and children for the proposed age range; need of identifying features characterizing each phonological process in comparison based algorithms. We recorded Kannada language speech dataset from children between age 3 1 2 to 61 2 years and named it as NITK Kids' Speech Corpus. It is collected in three age groups with an interval of one year in each age group. For each age range, the data is recorded from 40 children (20 male and 20 female). This work provides, the detailed analysis of the phonological processes that appear in children from age 3 1 2 years to 6 1 2 years speaking Kannada as native language. Based on the pattern of disappearance of the phonological process, the age-wise analysis of the acquisition of phonemes is provided. A detailed comparison of language learning ability of the children speaking English language and Kannada language is also performed. Based on the e ectiveness of the comparison based algorithms in identi cation of phonological processes in smaller age range, it is considered for the analysis. Commonly observed phonological processes that are considered for our study are: aspiration, nasal- ization & nasal assimilation, palatal fricative fronting, nal consonant deletion, voicing assimilation and vowel deviations. Spectral, prosodic and excitation source features ef- cient in discriminating the correct pronunciation of a phoneme and its mispronounced counterpart are identi ed and exploited for the identi cation of phonological processes. Two case studies are considered for the evaluation. Based on the availability of the dataset for phonological disorder, 'rhotacism' is considered for the analysis. The spec- tral and prosodic features e cient in characterization of the phonological disorder are explored. During the processes of phonological process identi cation, we came across ii interesting problem of children gender identi cation. The task of gender identi cation from children's speech is di cult compared to adult gender identi cation. The gender identi cation from adult speech is also performed to analyze the di culties in the task of children gender identi cation in comparison with the adult speech. The role of spec- tral, prosodic, excitation source features have been proposed gender identi cation in both implementations using suitable machine learning algorithms. Detailed experimental eval- uation is carried out to compare the performance of each of the proposed approaches against baseline and state-of-the-art systems.