http://localhost:8081/jspui/handle/123456789/34 2026-05-07T21:18:17Z http://localhost:8081/jspui/handle/123456789/20501 Title: PERFORMANCE STUDIES OF COATED TOOL INSERTS DURING HARD MACHINING Authors: Tamta, Rajneesh Raghav Abstract: The progress in manufacturing technologies has driven the need for enhanced cutting tool materials and coatings, capable of meeting the challenges of high-speed and high-precision machining of hard materials. This research aims to improve the performance and sustainability of cutting tools used in hard machining applications by developing, characterizing, and applying magnetron sputtered PVD coatings on ceramic cutting tool inserts. The primary objectives are to enhance the hardness, adhesion, and tribological properties of these coatings by strategically doping them with different elements, and to thoroughly assess the cutting performance of both coated and uncoated tools across various cutting parameters. Ceramic cutting tools are highly valued for their exceptional hardness and thermal stability. However, their performance can be greatly improved by applying advanced coatings. In this study, TiN and CrN thin films were deposited onto ceramic inserts using magnetron sputtering, a versatile physical vapor deposition (PVD) technique known for producing uniform and strongly adherent coatings. These coatings were then doped with specific elements to optimize their mechanical and tribological properties. TiN coating was doped with vanadium (V) to form TiVN coating and CrN coating was doped with titanium (Ti) to develop CrTiN coating onto SiAlON ceramic cutting tool inserts. The hardness and adhesion of the coatings were evaluated using nanoindentation and scratch tests, respectively, while Field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) were used to analyze the coating’s microstructure and phase composition. Furthermore, Energy dispersive X-ray spectroscopy (EDS) was utilized to validate the elemental composition of the coating present on the substrate. 2024-06-01T00:00:00Z http://localhost:8081/jspui/handle/123456789/20500 Title: INVESTIGATIONS ON SOLIDIFICATION DURING IN-SITU MICROWAVE CASTING OF METALLIC MATERIALS Authors: Parvej Abstract: Tailoring microstructures in metallic materials is crucial as it directly influences their mechanical properties, durability, and performance. Fine-tuning of microstructures allows enhanced strength, ductility, corrosion resistance, etc. Components with specially oriented microstructure, in general, exhibit better thermo-mechanical and physical properties at elevated temperatures, for example, creep resistance, fatigue resistance, tensile strength, ductility, elasticity, and thermal shock resistance capability. Further, functionally graded materials (FGMs) exhibit gradual variations in composition and structure, enhancing their performance in terms of thermal resistance, mechanical strength, corrosion resistance, etc. Such tailoring of microstructure in metallic materials can be achieved through a process known as directional solidification (DS). In DS, heat is extracted in a specific direction from the molten charge to establish a temperature gradient that aligns the structure in a preferred orientation. In addition, application of an external magnetic field can cause further transitions in microstructure and fabrication of functionally graded materials. Many techniques were employed to achieve directional solidification, aligning with the specific material requirements and applications. In these techniques, various types of heating sources were used, such as induction heating, resistance heating, arc melting, and radio frequency heating. High initial and operational costs, inefficient heat transfer between source and target material, and higher energy requirements are some of the drawbacks of the existing methods that call for innovative approaches. 2024-10-01T00:00:00Z http://localhost:8081/jspui/handle/123456789/20499 Title: Performance assessment of passive enhancement methods during in-tube condensation and heat pipe applications Authors: Kumar, Anil Abstract: To understand the fundamental of flow condensation phenomenon and enhance its performance, a thorough study on the liquid-vapor phase change heat transfer is targeted by means of macroscale level experiments and numerical simulations. An application-based investigation to understand the interfacial physics which relates with the thermal performance during micro pulsating heat pipe operations is also targeted in the present work. At first, a proposal for enhancement of flow condensation is made by developing tube with discrete internal structure. Mass flux from 75 to 215 kg m-2s-1, vapor quality from 0.1 to 0.9 and condensing temperature from 35 °C to 40 °C has been considered as the experimental range using R134a refrigerant in an in-house experimental set up. The heat transfer characteristics of the newly developed tubes with internal micropillar (MP) tube are compared with the two different commercially available microfin (MF1 and MF2) tubes and smooth (SM) tube. The overall performance is calculated using performance evaluation factor (PEF) which is defined to evaluate the thermal-hydraulic performance of the tubes. Using the same, it has been observed that the newly developed MP tube has a PEF value greater than unity which suggest augmentation of heat transfer coefficient at the expense of lesser pressure drop penalty. Comparison of the flow patterns of the refrigerant inside the newly developed tube has been made to confirm the fluidic facts behind enhancement. With a target of understanding the interfacial dynamics in flow condensation, Volume of Fluid (VOF) based three dimensional numerical simulations have been performed with R134a refrigerant flowing inside horizontal smooth and enhanced tubes. At first, the hemispherical rib structure on the circumferential surface of the tube with square pitch variations of 2.5 mm, 4 mm and 5 mm is simulated and compared with the smooth tube. Liquid vapor interfaces at different axial and longitudinal locations for both smooth and hemispherical rib tube are presented to better understand the condensation process. The results indicate that the vapor quality and liquid film thickness inside structured tube are lower than the same observed inside smooth tube. Also, the average heat transfer coefficient and pressure drop for both smooth and enhanced tubes are reported and interestingly, the tube with a 2.5 mm square pitch has shown twice the heat transfer coefficient with minimal increase in the pressure drop when compared with the smooth tube. Further, considering the optimum pitch as 2.5 mm, the numerical simulation has also been performed to investigate the effect of various structures on the thermo-fluidic characteristics during the flow condensation of representative R134a refrigerant. Along with a perfectly smooth surface, four different surface structures, i.e., hemispherical ribs, conical fins, axial, and circumferential continuous protrusions (tunnels and huddles) on the inner surface of the tube are tried to understand the heat transfer enhancement mechanism. The effect of structures on the flow behaviour is analysed, and the presence of directional condensate drainage near the protrusions is observed. The qualitative and quantitative examinations of interfacial structures at different axial and longitudinal sections are also presented to better understand the distinctive condensation phenomenon for smooth and enhanced tubes. The spatial and time-averaged vapor fraction and liquid film thickness show lower values in the case of enhanced tubes compared to the smooth surface for all tested operating conditions. Furthermore, the hemispherical rib structure showed the highest heat transfer coefficient among the tested structures, whereas a tube with circumferential protrusions (huddles) results in maximum pressure drop during flow condensation. The benefits of heat transfer enhancement appear to be more than the pressure drop penalty for tubes with a conical fin structure and axial tunnels. 2024-06-01T00:00:00Z http://localhost:8081/jspui/handle/123456789/20431 Title: ENHANCEMENT OF HEAT TRANSFER DURING FILM CONDENSATION OF R32 VAPOUR OVER SINGLE HORIZONTAL INTEGRAL-FIN TUBES Authors: Mohammed, Ibrahim Mustefa Abstract: The demand for energy conservation and environmental issues have become a critical global concern, which mandates deep investigation and improvement in engineering and technology appliances. Global energy consumption has grown in a century from the 1900s with only 1 TWh to an energy consumption of 17 TWh in 2011. As the world population grows faster, energy consumption has climbed by approximately 4-6 TWh. It is also expected to rise in the same trend in the upcoming years. Various researchers have tried to bring about new technologies that comply with energy conservation and environmentally friendly technologies to combat these issues. The improvement of heat transfer devices, such as shell and tube condensers, makes a substantial contribution to energy conservation, system performance efficiencies, and device compactness. A chiller unit is one of the devices found as a central component in air-conditioning systems, marine propulsion, process industries, and oil refineries. A shell-and-tube heat exchanger is a chiller unit employed for extracting heat energy from the vapor form of fluid, through which the vapor changes its phase into liquid form. Researchers have been developing different external surface structures to achieve augmented values of the coefficient of condensation heat transfer, such as two-dimensional and three-dimensional integral finned tubes, dimpled surfaces, petal-shaped fins, and serrated surfaces. In fact, unless optimal retrofit design considerations are taken on the augmented surface, structured tubes increase the pressure drop, which would cost extra pumping power and reduce the overall performance of the chiller unit. The advancements in manufacturing technology can help with the flexible development of three-dimensional fin profiles from the optimum two-dimensional finned tubes. However, condenser tubes with various three-dimensional surfaces, which exhibit superior enhancement factors in single condenser tests, have a stronger bundle effect in the full set condenser than the common two-dimensional integrally finned tubes. The continuous fins of integral fin tubes may operate as dams to avoid the axial diffusion of film condensate, which would explain the favorable row effect. Although increasing the active surface area for condensation heat transfer is the primary goal of low-finned integrated fin tubes, determining the ideal fin spacing for a particular refrigerant becomes crucial. Since the surface tension effect increases, the condensation heat transfer coefficient decreases as the fin spacing decreases. During film condensation over the outer surface, 2024-03-01T00:00:00Z