DSpace Collection:

Role of flow development, turbulence intensity, and pulsation on jet impingement heat transfer

2026-06-20T00:00:00Z

Title: Role of flow development, turbulence intensity, and pulsation on jet impingement heat transfer Authors: Bhati, Kuldhir Singh Abstract: In this dissertation, we discuss the effects of pipe length and inlet turbulence intensity, 𝑇𝑢, on the heat transfer enhancement. We found that shorter pipe lengths with developing flow at the pipe exit exhibit a significant increase in heat transfer. This is particularly useful in gas turbine blade cooling, where, due to space limitations, the nozzle connecting the coolant chamber to the core chamber is short. The Analysis System (ANSYS) Fluent Computational fluid dynamics (CFD) package is used to determine the dependence of the hydrodynamic entry length on inlet turbulence intensity, thereby determining the prevailing flow regime at the pipe exit. Simulations are also performed to obtain the dependence of the Nusselt number on the pipe length and inlet turbulence intensity for the steady jet impinging on the flat surface. These are validated using an in-house experimental facility. The entry length first decreases with increasing intensity and exhibits a local minimum around 5 %. The entry length at Reynolds number, 𝑅𝑒 = 10000 and 𝑇𝑢 = 2 % is more than 80 times the pipe diameter. It is also observed that the reduction in entry length with increasing turbulence intensity is not linear. Increasing turbulence intensity from 2 % to 4 % reduces the entry length by more than 40 % for Reynolds numbers of 5000 and 10000. Results at 𝑅𝑒 = 10000 show that a higher average Nusselt number, 𝑁𝑢𝑎𝑣𝑔, can be obtained at a pipe length shorter than 40𝐷 and 𝑇𝑢 < 6 %. A distinct high-performance region is identified, extending from approximately 𝐿/𝐷 = 20 at higher turbulence intensity (𝑇𝑢 ≈ 6 %) to 𝐿/𝐷 = 60 at lower turbulence intensity (𝑇𝑢 ≈ 2 %), where significantly enhanced heat transfer is achieved. The turbulence kinetic energy contours for the 𝐿/𝐷 = 20, 𝑅𝑒 = 10,000, and 𝑇𝑢 = 6 %, show a high level of turbulence intensity in the wall jet region at low nozzle-to-surface (stand-off) distances. This increased turbulence enhances mixing and promotes the transport of thermal energy from the jet core to the wall, thereby augmenting heat transfer. Experiments with a hot-wire anemometer confirmed that at 𝑅𝑒 = 10000, the velocity profile at the nozzle exit is not fully developed for 𝐿/𝐷 = 80. Experiments using infrared imaging show that, for 𝐿/𝐷 = 10, the average Nusselt number is at least 8.2 % higher than that for a pipe with longer lengths. At 𝐻/𝐷 = 3, the average Nusselt number for 𝐿/𝐷 = 10 is 16.5 % higher than that for 𝐿/𝐷 = 80, indicating that the average Nusselt number under developing flow conditions is higher than that for fully developed flow, and that higher heat transfer rates can be achieved with shorter pipe lengths.

Experimental and numerical investigations on dissimilar material joining via magnetic pulse crimping: a joint integrity and performance [RESTRICTED THESIS-01 Year]

2026-05-27T00:00:00Z

Title: Experimental and numerical investigations on dissimilar material joining via magnetic pulse crimping: a joint integrity and performance [RESTRICTED THESIS-01 Year] Authors: Singh, Ummed Abstract: [Abstract is restricted for 01 Year, due to IPR related issue]

Exploring the pyrocatalysis performance of 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 compositions for degradation of organic pollutants [RESTRICTED THESIS-02 Years]

2026-05-08T00:00:00Z

Title: Exploring the pyrocatalysis performance of 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 compositions for degradation of organic pollutants [RESTRICTED THESIS-02 Years] Authors: Gaur, Aditya Abstract: [Abstract is restricted for 02 Years, due to IPR related issue]

Investigations on laser direct writing and laser micro-3D printing of metals and ceramics towards MEMS structures printing for functional applications [RESTRICTED THESIS-03 Months]

2026-04-07T00:00:00Z

Title: Investigations on laser direct writing and laser micro-3D printing of metals and ceramics towards MEMS structures printing for functional applications [RESTRICTED THESIS-03 Months] Authors: Singh, Arpit Kumar Abstract: The growing demand for high-performance Microelectromechanical Systems (MEMS) in fields such as biomedical devices, energy harvesting, and flexible electronics necessitates advanced micromanufacturing techniques capable of processing multifunctional materials with sub-micron precision. This thesis investigates two laser-based fabrication methodologies-Laser Direct Writing (LDW) and Laser Micro-3D Printing-to develop metallic and ceramic microstructures tailored for MEMS applications. LDW, employing a 10.6 μm CO₂ laser, is utilized for direct synthesis of porous laser-induced graphene (LIG) on polyimide substrates. Optimized parameters (4.5 W laser power, 15 mm/s scan speed) produced uniform graphene structures exhibiting high conductivity and porous morphology, confirmed by Raman spectroscopy with characteristic D (~1350 cm⁻¹), G (~1580 cm⁻¹), and 2D (~2700 cm⁻¹) peaks. The fabricated LIG-based strain sensors demonstrated excellent mechanical resilience, surviving over 1250 bending cycles without degradation.