1. Ph.D Theses
Permanent URI for this collectionhttps://idr.nitk.ac.in/handle/1/11
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Item Nanofluid Mediated Gas- Liquid Mass Transfer Enhancement In Pulsed Plate Column(National Institute of Technology Karnataka, Surathkal, 2023) Shet, Amruta S; K, Vidya ShettyOxygen transfer limitations result in poor performance in bioreactors and reduced efficiency in catalytic and photocatalytic reaction systems where oxygen transfer is involved. Adequate oxygen transfer can be achieved by increasing the volumetric oxygen transfer coefficient (kLa). Several investigations have shown that the enhancement of kLa can be achieved in the presence of nanofluid which is a colloidal suspension of nanoparticles in any base fluid. Nanoparticles may be intentionally added to the reactor fluid or may be inherently present in the reactor to form a nanofluid. Pulsed plate column (PPC) is widely used as an aerobic bioreactor and gas-liquid contactor for various applications. In the present study, the influence of TiO2, SiO2, and α-Fe2O3 nanofluids with water as the base fluid on kLa was studied in PPC. The effect of nanofluid parameters such as nanofluid type in terms of nanoparticles used, their size and loading along with the column parameters such as frequency (f) and amplitude (A) of pulsation, pulsing velocity (A×f) and gas velocity (Ug) was studied. The use of nanofluids led to kLa enhancement. It was found that kLa increased as the nanoparticle loading increased, attained a maximum at the critical loading, and then reduced as the loading was further increased. The critical loading depended on the nanofluid. kLa was found to increase with the increase in A, f, and Ug. The nanoparticle loading and A×f showed an interacting effect on kLa resulting in one or more hydrodynamic regimes depending upon the type of nanofluids, size, and loading of the nanoparticles. Nanofluids with lower-size nanoparticles showed higher kLa compared to those with larger sizes. TiO2 nanofluid provided a better kLa enhancement than SiO2 and α-Fe2O3 nanofluid. The maximum enhancement factors were obtained with TiO2, SiO2, and α-Fe2O3 nanofluids at the critical loading conditions. The order of magnitude analysis implied that the convective currents caused by the Brownian movement of the nanoparticles in the fluid can be the possible reason for mass transfer enhancement in PPC. Pseudo-homogeneous model was tested and it was found to accurately predict the enhancement only till the critical loading conditions. The developed dimensionless correlations and artificial neural network models could accurately predict kLa and thus may find potential applications in the design of pulsed plate column when used as gas-liquid mass transfer contactors, bioreactors, or photocatalytic reactors. The results of this study indicate that the pulsing conditions required to achieve the desired mass transfer characteristics can be reduced by using a nanofluid instead of the base fluid, thus potentially leading to tremendous saving of energy.Item Investigations on Machinability Characteristics of EN47 Spring Steel using Optimization Techniques(National Institute of Technology Karnataka, Surathkal, 2019) Vasu, M.; Nayaka, H Shivananda.Challenge of any manufacturing industry to give a better quality of products to society with minimum manufacturing cost, low manufacturing time and less consumption of raw material. Manufacturing involves various processes to convert raw material into finished products and hence meet demands with high-quality products. Selection of process parameters plays a significant role to satisfy all demands to ensure the quality of the product, increased production rate, and reduced operating cost. For such cases, optimization is essential to represent manufacturing process. Process parameters have been optimized by chosen best possible optimization techniques. Before conducting any experiments, selection of workpiece and tools it is necessary, to explore the literature to know, what has happened in earlier days. A literature survey has been done thoroughly existing statistical techniques are understood and implemented to optimize speed, feed, and depth of cut. EN47 spring steel has been chosen as work material which has a hardness of 45-48HRC. Hard turning process eliminates grinding process, and EN47 steel possesses low thermal conductivity and suitably oil hardened and tempered. Hardened spring steel offers excellent toughness and shock resistance, and are considered as suitable material for automobile applications. Other applications involve such as manufacturing of die, leaf spring for a heavy vehicle, crankshaft, spindles, pumps and steering knuckles and many general engineering applications. Experiments were performed using two different techniques, namely, one factor at a time (OFAT) approach and Design of Experiments (DOE). Cutting tool inserts are commercially available in the form of PVD coated TiAlN German make and are used during machining. Cutting forces, surface roughness, tool tip temperature, and material removal rate are estimated experimentally. From the experimental work, it is known that with an increase in nose radius, cutting forces, tool tip temperature, and material removal rate are increased, but surface roughness is decreased. Further, a tool with 0.8mm nose radius exhibits nominal performance in all output performances. 0.8mm nose radius tools are used to work in three different cutting environments, namely dry, wet and cryogenic. From the analysis, cryogenic machining showed better quality of the machined surface, tool wear also reduced and tool tip temperature decreased.viii Experiments were performed and analyzed using design of experiments (DOE) technique L27 full factorial design. A second order regression model was developed to know the interaction effect of output responses. Tool wear was analyzed by confocal microscope and SEM, with varying cutting time. ANOVA was used to identify the significant factor and percentage contribution for a particular output. Results from machining reveal that cutting force is mainly influenced by feed rate and depth of cut. Surface roughness was influenced by cutting speed and feed rate. Tool tip temperature was influenced by cutting speed and depth of cut. Material removal rate was influenced by speed, feed, and depth of cut. 3D response surface plots show interaction effect on each output response. Main effects plots show optimum condition for each output performance. Normal probability plots showed that the developed models are adequate by observing normal error distribution. Determination coefficient (R2) value should be in between 1 or 100% in the model. Multi-objective optimization was identified by Desirability Approach (DA) and Particle Swarm Optimization (PSO). Also, Artificial Neural Network (ANN) is used to predict experimental results and compared with RSM model, as well as, experimental value. Statistical analysis was done by Minitab and Design Expert Software. Validation was performed by ANN. MATLAB is used to develop artificial neural network model, as well as; codes are developed for PSO. From the experimental analysis, the developed model showed a significant and good agreement between the experimental value and predicted value.Item Buckling and Dynamic Behavior of Non-Uniformly Heated Cylindrical Panels(National Institute of Technology Karnataka, Surathkal, 2018) Bhagat, Vinod; Jeyaraj, P.; Murigendrappa, S. M.Today, curved panels especially cylindrical and conical are considered as a backbone of numerous engineering structures. Knowledge of buckling and dynamic behavior of structures over a range of temperature is essential for their better design. Most of the studies carried out on heated panels are based on uniform temperature distribution assumption. However, in real life application, the cylindrical panels employed in structures are exposed to non-uniform temperature variation due to the location of the heating source and thermal boundary conditions. In the present study, the thermal buckling strength of the non-uniformly heated metallic panel predicted numerically is validated experimentally using in-house developed experimental set-up. Further studies are extended to investigate the effect of non-uniform temperature variation on buckling strength and free vibration characteristics of metallic, laminated composite, and functionally graded carbon nanotube (FGCNT) reinforced polymer composite, cylindrical panels using the finite element method. Finally, the optimization of a non-uniformly heated laminated cylindrical panel against thermal buckling strength and fundamental natural frequency is also carried out. Typical variation of temperature-deflection plot for different temperature fields is obtained experimentally and further, inflection point method is used to predict the critical buckling temperature from temperature-deflection plot. Experimental studies are further extended to analyze the influence of geometrical parameters and structural boundary constraints on critical buckling temperature. Experimentation results reveal that the location of the heat source and resulting non-uniform ivtemperature field influences the thermal buckling strength significantly. Among three cases examined in experimentation for the position of heat source, minimal buckling strength is observed when the heater is located at the center of the panel while maximum buckling strength is observed when the heater is located at the forefront curved edge. It is also found that aspect ratio and structural boundary constraints play a major role in deciding the buckling strength of the panel. From the numerical studies carried out on non-uniformly heated panels, a relation known as magnification factor is established to evaluate the buckling strength of non-uniformly heated cylindrical panels knowing the buckling strength of uniformly heated panels. Among five cases investigated for the position of heat source, the highest magnification factor is observed for a panel with the heat source located at the forefront curved edge. It is observed that the free vibration mode shapes of the panel change significantly with increase in elevated temperature. The changes are observed in terms switching of modes with a significant change in modal indices. With the rise in temperature, nodal and anti-nodal positions of a particular free vibration mode shape are shifting towards the location where the intensity of the heat source is high and structural stiffness is low. It is found that for a stiffer panel, the buckling strength of the laminated and FG-CNT composite panels with temperature-dependent elastic properties is significantly lesser than that of the panels with temperature independent elastic properties. Panel with maximum area exposed to a peak temperature of particular non-uniform temperature fields shows lowest buckling strength. Functional grading of CNTs with more amount of CNTs located close to top and bottom of the panel (FG-X) results in higher buckling strength and free vibration frequencies compared to those panel with maximum CNTs distribution near the mid-plane. Free vibration frequencies of non-uniformly heated FG-CNT panel with temperature dependent properties is observed to decrease drastically with elevated temperature compared to the panel with temperature independent properties. Variation vin frequencies observed in a pre-stressed panel with temperature dependent and independent properties is more significant in stiffer panels. Irrespective of temperature dependent and independent properties, shifting of nodal and anti-nodal lines and change of modal indices are also observed at elevated temperature. Well-known and generally acknowledged optimization technique, particle swarm optimization is employed for the optimization of thermal buckling strength of laminated composite panels exposed to five different temperature fields. Two different optimization approach like single objective optimization approach and multiobjective optimization approach are employed. In single objective optimization, the panel is exposed known temperature field whereas, in multi-objective optimization, the panel is exposed to unknown temperature fields when in-service. It is found from the analysis that the variation in the optimum buckling strength of non-uniformly heated panels is more significant at lower curvature ratio. Whereas, variation in the optimum fiber orientation under different temperature fields is significant at higher curvature ratio. Multi-objective optimization approach has proved to be superior to that of single objective optimization approach when panels are exposed to the unpredictable thermal environment. Further, studies are carried out on optimization of both thermal buckling strength and fundamental free vibration frequency of heated panels using particle swarm optimization in conjunction with the artificial neural network. Multiobjective design index (MODI) has been derived for the panel considering buckling strength and fundamental frequency as objectives for optimization. It is found that MODI of the cylindrical panels under thermal load is complex and significantly influenced by the temperature fields, lamination scheme, in-plane boundary constraints, elevated temperature and geometric parameters. It is also observed that the MODI of the panel can be maximized by optimizing laminate orientations. Further, it is observed that panel with lamination scheme of (θ°/–θ°/θ°/–θ°)S gives higher value of MODI compared to other lamination schemes considered.