Title: Numerical investigations of transient heat flux-based pool boiling.

Abstract: Researchers have extensively studied the heat transfer ability of boiling under steady heating conditions. However, critical thermal failures in industries often involve a sudden and rapid increase in heat flux over a very short duration. This presentation is to study the effect of transient (periodic) heating on nucleate boiling by comparing steady heat-flux-based pool boiling with that of exponential heat flux. This presentation looks at vertical coalescence patterns formed during periodic heating, as single-bubble coalescence is viewed as a precursor to critical heat flux (CHF). An in-house CFD code based on the Sharp Interface Level Set Method was used to study coalescence patterns under a periodic exponential heat flux of varying excursion rates (ethanol as working fluid). Simulations reveal that while no coalescence is observed in steady heating, various vertical coalescence regimes are identified for transient heating (upon reduction of excursion time): uncoalesced, periodic, chaotic, and chain. An increase in bubble frequency and vertical bubble coalescence is observed with reduced excursion time, while the departure diameter remains nearly constant. The simulations also reveal that for periodic coalescence, the sooner the first heat flux cycle is completed after the departure of the preceding bubble (at the nucleating cavity), the more likely it is for coalescence to occur. For Chaotic and Chain coalescence, the formation and dampening of oscillations at the interface of a coalescing bubble governs the frequency of coalescence. It is also observed that an increase in surface contact angle results in coalescence occurring at higher excursion rates. 

Bio: Nipun Kothare completed his B.E (Hons.) in Mechanical Engineering from BITS Pilani, Pilani campus in 2013. After working for 2.5 years as a Technical Engineer at Tata Motors Ltd, he continued his higher degree studies at Coventry University, UK; receiving his Masters in Automotive Engineering in 2018. After a brief stint at a startup working on CFD analysis of flowmeters, Nipun joined the PhD program at IIT Bombay in Jan 2020. Nipun's key areas of interest are in CFD analysis, Multiphase Flow and Pool Boiling, with a special focus on Transient heat flux-based pool boiling.

Speaker 2: Ravi Raj

Title: Finite Element Modelling of In-situ Rolling assisted Directed Energy Deposition

Abstract: The talk will present the development of a fully coupled thermo-mechanical finite element model for in-situ micro-rolling in Directed Energy Deposition (DED), a novel hybrid metal additive manufacturing process designed to enhance part quality through localized plastic deformation. The model integrates heat transfer and mechanical analysis to accurately capture how the rolling tool interacts with the material during layer-by-layer printing. It includes temperature- and strain-dependent material behaviour, implemented using custom Fortran code in Abaqus, allowing for a more realistic simulation of plastic deformation and remelting. Python scripts are used to automate the simulation setup and run parametric studies efficiently. The model is validated through experiments using a specially designed DED system with in-situ rolling. This work offers a predictive computational tool for designing and controlling in-situ rolling strategies, providing detailed insights into the underlying thermo-mechanical phenomena. It also sets the stage for future research into metallurgical changes observed during printing to better control part quality and link process conditions to material properties.

Brief Bio: Ravi Raj is a doctoral researcher jointly enrolled at IIT Bombay (under the supervision of Prof. Deepak Marla) and Monash University (under the supervision of Prof. Aijun Huang). His research focuses on thermo-mechanical modelling of a hybrid metal additive manufacturing process. He holds integrated B.Tech–M.Tech degrees in Mechanical Engineering from IIT Kanpur. His broader research interests lie in the computational modelling of advanced manufacturing processes.