Defect and Diffusion Forum Vol. 433

Abstract: Understanding heat transfer phenomena is crucial in high-power amplifiers to keep components within safe operating temperatures. This article investigates the GaN Power Amplifier (PA) thermal analysis for the optimum design of the heatsink. GaN PAs are roughly separated into junction, package, and heat sink layers to calculate the junction’s transient thermal response. It has been proven that allowing individual components to operate at temperatures over their maximum rated junction temperatures significantly reduces the system's operational reliability as a whole. This analysis investigates two different heat sinks for the optimum case temperature (T_case) for these different PAs. These PAs are operating S-band (2-3.4 GHz) and C-Ku-band (5-18 GHz) with drain efficiency of 60-65% and 9-22%, respectively. The design analysis of the heat sink for optimal performance is explored in this work.

Abstract: The escalating global demand for fossil fuels, coupled with geopolitical uncertainties, underscores the imperative for alternative fuels in internal combustion engines. Simultaneously, the pressing issue of plastic waste disposal necessitates sustainable solutions. This research delves into the impact of hydrogen enrichment on a CRDI-diesel engine using diesel and waste plastic oil, varying fuel injection timing (23, 25, and 27) °CA bTDC at 400 bar fuel injection pressure. The addition of hydrogen at 4 lpm improves Brake Thermal Efficiency (BTE) and lowers Brake Specific Fuel Consumption (BSFC), resulting in reduced hydrocarbons (HC) and carbon monoxide (CO) emissions, though Exhaust Gas Temperature (EGT) and NOx emissions increase. The WPO10+4H₂ blend at 25 °CA bTDC demonstrates an 8.7% BTE increase, a 10.5% BSFC reduction at full load, and substantial decreases in HC and CO emissions compared to diesel. Despite these advantages, NOx emissions increase by 8% compared to pure diesel. Hydrogen integration in CRDI engines enhances performance and addresses sustainability, while waste plastic oil in diesel engines repurposes plastic waste, reduces fossil fuel dependency, and supports a circular economy with energy recovery.

Abstract: New opportunities for applications in areas including photothermal therapy (PTT), biomedical imaging, and energy conversion have been made possible by advancements in nanoparticle technology. Understanding the thermal and fluidic behavior of these nanoparticles is crucial for their effective utilization. In this computational study, numerical simulations are used to examine the convective velocities connected to various gold nanoparticle (AuNP) morphologies, including nanorods, nanoshells, and nanodiscs. Our findings clearly demonstrate that nanorods have the maximum convective velocity of 91 µm/s, making them the most attractive choice for applications needing excellent thermal and fluidic performance. Additionally, we investigate the relationship between bubble diameter and convective velocity in the vicinity of gold nanorods and nanoshells. Our findings indicate that as the bubble diameter expands to 10 μm, there is a noticeable surge in convective velocity, which eventually plateaus. Furthermore, we explore the impact of shell thickness and core radius on convective velocity. A decrease in shell thickness and an increase in core radius were found to significantly enhance convective velocity, with an optimal core radius of 38 nm identified for peak performance. These findings provide vital information for the design optimization of AuNPs, notably for PTT and photoacoustic (PA) imaging, two fields where precise control of thermal and fluidic processes is essential.

Abstract: Deep learning has achieved great progress in image recognition, segmentation, semantic recognition, and game theory. It also shows potential to solve scientific computing such as simulation problems in engineering. On the other hand, the numerical simulation method requires constitutive modelling, involves a huge computation volume and takes a long time. In this paper, two mirror U-Net models were proposed for the simulation of the heat transfer during the casting process. These models include an upper U-Net branch for the treatment of the geometries of casting, mold, and chill, and a lower U-Net branch for the treatment of the initial temperature field. Their difference is whether the bottoms of upper and lower U-Nets are shared. These two branches tackle the problems involving the input of a geometrical model which consists of three types of materials and the input of an initial or current temperature field image. These models were trained and validated with a big database with hundreds of casting shapes. The prediction results show that the average accuracy reaches 98.8%.

Abstract: The study aims to investigate convective heat transfer in multi-story buildings in Metro Manila and its impact on residents' thermal comfort. The increasing demand for residential construction in Metro Manila has resulted in a higher concentration of buildings and paved surfaces, which exacerbate the city's hot and humid climate. This study aims to identify factors that contribute to convective heat transfer, such as building design, insulation, and ventilation, and assess their impact on energy consumption and indoor air quality. The research will provide insights into effective strategies for reducing energy consumption and improving indoor temperature conditions, resulting in more comfortable and sustainable living environments for residents.