Emir Yilmaz

The global rise in carbon emissions presents a rising challenge for current and future generations. In the pursuit of zero carbon emissions, ammonia (NH3) has emerged as an attractive alternative energy source. Ammonia offers a carbon-free fuel option with a higher energy density than liquid hydrogen while maintaining ease of transport and storage. However, ammonia still has its drawbacks, such as a high autoignition temperature, slow burning velocity, and low heating value, that demand further investigation of its combustion characteristics. This experiment was done to study the effect of nozzle shape and equivalence ratio (ɸ) on the combustion of an ammonia/oxygen/argon mixture using a constant volume combustor equipped with a sub-chamber. The fuels were premixed for 10 minutes and conditioned to an initial pressure of 0.2 MPa and an initial mixture temperature of 423 K. The results show that the different nozzle shapes each have their advantages in terms of pressure and jet speed. Overall, the lean mixtures (ɸ0.6 and ɸ0.8) consistently performed better compared to the stoichiometric mixtures (ɸ1.0) in all categories investigated in this study. The round nozzle generates higher pressure, while the special shape nozzle enhances jet speed, highlighting trade-offs between the two.

<jats:p>This study examines the feasibility of utilizing the press forming method on multi-layer, multi-orientation continuous CFRP preform produced by the additive manufacturing (AM) technique. The 5-layer preforms with fiber orientations of 45° and -45° impregnated in Nylon-6 resin layers were made by a 3D printer, and press-formed in varying temperatures and pressures. Optimal forming outcomes were determined by qualitative evaluations of the surface finish, fiber impregnation, resin flow, and quantitative observations on shape variations by comparison with the mold dimensions. Experimental results showed that the molding temperature of 220°C and pressure between 0.5MPa - 1MPa could produce preforms with optimal surface conditions. There was almost no void of bubble defects, no excess resin flow, and a smooth transition was established between the carbon fiber and the matrix resin layers while allowing the full mechanical strength properties to be realized. The formed preform evaluations confirmed that the press molding method is feasible on multi-layer, multi-orientation continuous CFRP with optimal surface conditions.</jats:p>

Abstract Aquifer thermal energy storage is a versatile method for regulating building temperatures, utilizing groundwater as a medium for both summer cooling and winter heating. Water has high thermal conductivity and specific heat but is corrosive, creating a mineral build-up that causes scaling. Additionally, its high freezing point presents operational challenges. Vegetable oils emerge as a promising alternative, owing to their lower freezing points. In light of environmental concerns, researchers are exploring vegetable oils as substitutes for petroleum-derived mineral oils. This paper is intended as an initial study using vegetable oils, i.e. coconut and sunflower oil, as the heat-transfer medium in aquifer thermal energy storage. The experiments assess the heat-transfer coefficient of coconut, sunflower, mineral, and synthetic oils when exposed to the same heat source. The study also evaluates the impact of introducing micro-carbon (graphite and charcoal) to the oils. Results indicate that sunflower oil has the highest heat-transfer coefficient of 374.4 W/m2 K among the oils, making it suitable for aquifer thermal energy storage applications. Furthermore, augmenting sunflower oil with charcoal powder enhances its performance by increasing the heat-transfer coefficient to 474.9 W/m2 K, or a 27% increase. In contrast, coconut oil proves unsuitable for aquifer thermal energy storage deployment because of its low heat-transfer coefficient of 293.7 W/m2 K. The heat-transfer coefficient of synthetic oil increases with graphite powder but decreases with charcoal powder introduction.