Defect and Diffusion Forum Vol. 390

Abstract: In this study, a plunger and injection nozzle were designed to improve the injector used in multi-point injection NGV engines. The purpose of this study is to analyze the pressure and velocity characteristics of the injector plunger and show mass flow rate trends for the gas injected from the nozzle. Using the ANSYS program, a new injector was modeled according to applicable design variables, and the gas flow into the plunger was visualized. In addition, methane fuel was used in the simulation, and the inlet and outlet of the injector were applied with 8 bars pressure and opening conditions. As a result, in the model with a 1.2 mm inner diameter plunger valve, the mass flow rate of gas injected from the injection nozzle was stable from 0.075 mm to 0.2 mm, and it was possible to reduce the velocity variation and pressure generated inside the plunger.

Abstract: The study investigates the impact of a nanofluid suspended in carbonated water (CW) on the CO₂ mass transfer into hydrocarbon in a carbonated water/hydrocarbon system. Furthermore the study addresses into the influence of the nanofluid assisted CO₂ mass transfer on the viscosity and density of hydrocarbon and its relevance to enhanced oil recovery (EOR). The experiments were carried out at 10-70 bar at 25°C and 45°C using an axisymmetric drop shape analysis (ADSA) for three concentrations of silica nanofluid (0, 0.05, 0.5, and 1.0 g/l). A pressure decay method was used to estimate the change in CO₂ solubility in water in the presence of the nanofluid. A mathematical model coupled with experimental input was used to quantify the mass of CO₂ transferred into the hydrocarbon from the CW. Although this work does not address the EOR process, it indicates its applicability for EOR. The results showed that the dispersed nanofluid in CW enhanced the CO₂ mass transfer into the hydrocarbon, and reduced the hydrocarbon viscosity and density. The pressure decay experiments indicated that the nanofluid increases the mass of CO₂ in water by 17% compared to that without nanofluid. Compared to CW, CNF (CW+nanofluid) increased the CO₂ mass transfer into the hydrocarbon drop by approximately 2% at 10 bar and 45% at 60 bar, this leads to an increment in volume of the pendant drop by approximately 3% at 10 bar and 48% at 60 bar at 25°C. A similar observation was made at 45°C. The nanofluid through CO₂ mass transfer was responsible for approximately 40% and 29% reduction in the viscosity and density respectively, when compared with CW. Compared to CO₂/hydrocarbon the CNF/hydrocarbon lead to a 17.3% volume increase at 30 bar to 91.2% at 50 bar. The increase in the drop volume is unlikely to be due to the migration of nanofluid across the interface into the hydrocarbon drop as indicated by analysis done using UV spectrophotometry and may be due to increase in the CO₂ concentration gradient across the interface due to increase in the CO₂ solubility in CW.

Abstract: The existing heat pipe applied to a LED headlamp has a large size although it has only small area of contact. Therefore, it is difficult to achieve a harmonious radiation of heat along with the difficulty in attaching the LED due to its large volume. This study proposed a plate heat pipe to solve the aforementioned problems. Through the study, the effects of the thickness and acetone filling rate on the heat radiation effects of a plate heat pipe at room temperature and vehicle driving environment were confirmed along with comparison with the heat radiation effects of the existing copper heat pipe. The heat radiation effects were checked by attaching a thermocouple to the evaporator, adiabatic section and condenser of the LED. As the results of the experiment, it was found that a temperature below 120oC, which is the allowable temperature to guarantee the performance of the LED, is maintained. In addition, as the results of comparison of radiation of heat, it was confirmed that the plate heat pipe with a thickness of 2 mm and 20% filled with acetone has a better performance than the existing copper heat pipe.

Abstract: The purpose of this work is to model turbulent Taylor-Couette-Poiseuille flows submitted to a temperature gradient. These flows are relevant in many industrial applications including rotating machineries and more especially for the effective cooling of electric motors. Several turbulence closures (k-ω SST, RSM and LES) are first compared in the isothermal case and validated against the reliable experimental data of Escudier and Gouldson [1]. A detailed analysis of the coherent structures within the boundary layers is proposed. The model offering the best compromise between computational cost and accuracy is then used to perform more computations in the configuration with a temperature gradient considered by Kuosa et al. [2]. In their system, the air flow enters the rotor-stator cavity radially. Correlations for the average Nusselt numbers along the rotor and stator as a function of the control parameters (rotation rate, air flow rate, Prandtl number) are provided and compared with data available in the literature [3].

Abstract: The main topic of this paper is the development of a mathematical model, based on the Lattice Boltzmann equations (LBE), which is proposed for the simulation of the complex convective flow, held in an electrically conducting melt, driven by the combined action of buoyancy, surface-tension, and electromagnetic forces. The lattice Boltzmann method (LBM) is relatively novel and contrasts with the usual well-known methods to physical modeling in the domain of computational fluid dynamics (CFD). Indeed, the LBM describes the fluid (i.e. lattice fluid) at a microscopic level (molecular) and proposes models for the collision between molecules. The full continuum-level physics (i.e. the macroscopic hydrodynamic fields) is implicitly contained in the LB model. Indeed those macroscopic quantities are defined as moments of the so-called particle distribution functions. In the present work, a two-dimensions (2D) LBE-based model is developed to the simulation of convection melt flow driven by the combination of natural buoyancy, surface tension, and electromagnetic forces. The model is applied to numerical modeling of the problems of buoyancy, surface-tension, and electromagnetic driven convection melt flow in an enclosure. The melt system used has a low Prandtl number, which is appropriate to crystal growth melts.

Abstract: This paper shows the methodology used for the evaluation of the structural integrity of a boiling water reactor (BWR-5). This evaluation is relevant, because this vessel is the coolant pressure boundary for cooling the nuclear core. In the case of this paper, an axial crack is postulated in the adjacent internal wall of a vessel to the core, which is denominated beltline. Such a crack is subjected to an internal pressure and neutron irradiation. Additionally, a crack on the inlet nozzle of the low-pressure coolant injection (LPCI) was also considered. The analysis presented in this paper, evaluated the transient conditions which take place during the start-up and shutdown of a BWR 5. The neutronic irradiation damage at the beltline was also incorporated to the analysis. It induces an embrittlement. Linear elastic fracture mechanics was applied with the requirements established at the Appendix G of ASME Code Section XI. The finite element method was used to simulate the transient conditions of the components considering the critical parameter, such as the service temperature, thickness, stresses and the material properties.

Abstract: Large amount of crude oil remains in the reservoir due to the poor sweep and displacement efficiency after displacing fluid injection. To remediate this effect, a thicker displacing fluid is used to reduce viscous fingering for a more stable flood front. A ferrofluid is a suitable candidate due to the tunable viscosity profile when subjected to a magnetic field [1]. In this work, the ability of cobalt substituted magnetite ferrofluid to improve incremental recovery after waterflooding has been investigated via sand pack flooding. Prior to sand pack flooding, structural and magnetic properties of cobalt substituted magnetite nanoparticles were characterized via XRD, FESEM and VSM. Viscosity tests with field strength variation from 0 to 66.88 mT have shown a significant dependency of the ferrofluid’s viscosity on the applied field strength. 6-fold increment of viscosity was recorded when magnetic field strength changes from 19.5 to 66.88 mT. During sand pack flooding, 7.20% of incremental oil was obtained with the ferrofluid injection, even without the presence of a magnetic field. When subjected to a magnetic field, 12.93% and 15.83% of the incremental oil was obtained at 19.5 and 66.88 mT, respectively. It is proven that increase of ferrofluid viscosity with magnetic field strength results in higher incremental recovery. Improved sweep and displacement efficiency has been achieved by injecting the ferrofluid into the oil reservoir.

Abstract: Literature has indicated that, experimentally, solvent fronts in hybrid solvent recovery processes progress more rapidly than what can be predicted using current approximations and more rapidly than thermal processes alone. Research using finite differences to model the nonlinear advection, diffusion and dispersion (ADD) equation suggests that nonlinear mass transfer effects are important in predicting the rate of solvent advance. Nonlinearities can be ascribed to both diffusion and flow velocity functionality. Earlier work using linear concentration dependent diffusion and log-linear velocity behaviour confirmed the importance of nonlinear effects when compared to linear theory that uses constant diffusion, dispersion and velocity coefficients. The mathematical nature of the nonlinear ADD equation further suggests that the shape of concentration dependent diffusion and flow velocity will affect the shape of the solvent concentration profiles, and influence the rate of propagation of the solvent front. This research focuses on results obtained using finite differences to explore the effects of various diffusion and velocity functionalities that affect the solvent rate propagation using a nonlinear ADD equation. The results obtained from this analysis indicate that these functionalities determine the shape of the solvent concentration profile. The concentration dependent diffusion and velocity functions were chosen according to recent literature which proposes experimentally obtained functions to more accurately model solvent penetration in the media. Preliminary results from this study suggest that the velocity functionality has more influence on the process at both the lab and field scales for the parameters considered in this study. The shapes of the concentration profiles are affected by both diffusion functionality and velocity functionality.

Abstract: This paper aims a numerical investigation about the fluid dynamic behavior of an oscillating water column (OWC) wave energy converter (WEC) into electrical energy. Constructal design is employed to perform a geometric evaluation of an OWC WEC submitted a Pierson-Moskowitz wave spectrum. The objective function is to maximize the energy conversion. The hydropneumatic chamber volume (V_HC) and the total OWC volume (V_T) are adopted as geometric constraints. In the first stage, the values are constant during the maximization process. However, in a second stage they are changed according to the constraint variation (C_V). One of the goals is to analyze the influence of the choice of this geometric constraints value on the OWC performance in relation to the wave spectrum. For this purpose, are considered three different scenarios: 1) V_Hyd is equal to the minimum incident wavelength (λ_min), that is relative to the maximum frequency of the wave spectrum times the significant wave height (H_S); 2) V_Hyd is equal to the peak incident wavelength (λ_peak), that is relative to peak frequency of the wave spectrum times the significant wave height (H_S); and 3)V_Hyd is equal to the maximum incident wavelength (λ_max), that is relative to minimum frequency of the wave spectrum times the significant wave height (H_S). To do so, constructal design is employed varying the degree of freedom (DOF) H₁/L (ratio between the height and length of OWC chamber), while the others DOF’s H₂/l (ratio between height and length of chimney) and H₃ (lip submergence), are kept fixed. It is employed a Pierson-Moskowitz wave spectrum with significant period (T_S) equal to 7.5 s and significant wave height (H_S) equal to 1.5 m. For the numerical solution it is used the computational fluid dynamic (CFD) code, based on the finite volume method (FVM). The multiphase volume of fluid (VOF) model is applied to tackle with the water-air interaction. The computational domain is represented by the OWC WEC coupled with the wave tank. The results showed that when C_V = 2.25 for λ_max and (H₁/L)_O = 0.2152 the highest average for power was obtained, nearly 18,000 W. While for λ_min and (H₁/L)_O = 0.2193 it was smaller than 1,000 W. Besides, it was obtained a theoretical recommendation about the geometric constraints employed for the constructal design application, aiming the maximization of the OWC energy conversion from the incident wave spectrum.