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Go to Editorial ManagerThe hydraulic characteristics of dams can be predicted with high precision and reliability of physical and numerical models depending on accurate hydraulic data. The model is operated and simulated to get a more efficient, optimized utilization of the dam. This research included a comprehensive overview and literature examination of the Makhool Dam which is considered one of the most important dams under construction in Iraq. Previous studies of the dam focused on different topics in the operation of the dam and analyses of its properties, part of which focused on the dam ability to manage flood and how it works best with other dams in critical times, and another part studied the properties of the stilling basin, velocity in the dam reservoir, pressure, seepage and other characteristics that affect the operating the dam. Despite this research and the variety of topics discussed, there is no well-established research on the operation of the bottom and emergency spillway of the dam by using computational fluid dynamics (CFD) simulation software. CFD is considered an essential tech because it has an important influence in determining the hydraulic properties of a spillway and studying its effectiveness under different operating conditions. Because the spillway is an important element in the dam body, the research highlighted the necessity of performing a simulation using appropriate CFD software for this part. This research has also reviewed previous research on CFD software and their ability to simulate previously constructed or under-construction dams to analysis of its hydraulic properties.
The solar vortex engine (SVE) has been investigated to generate power using renewable energy. The SVE was constructed from a vortex generation engine (VGE) and solar air collector (SAC). The SVE system primarily utilizes vertical air movement. However, the airflow entering the VGE experiences an obstruction. The purpose of this paper is to propose a new design for the VGE that creates a swirling updraft capable of overcoming air obstruction and reducing energy losses. A 3D numerical model of VGE was developed to visualize vortex generation. The modeling of the VGE is carried using SOLIDWORKS software and ANSYS-FLUENT 18. The improved VGE has six vertical twisted convergence blades connected to six guide vanes to direct updraft air in an anticlockwise swirl. All blades and vanes are housed in a VGE cylinder with a diameter of 20cm and a height of 30cm. The simulation results were validated by comparing with the results obtained from the present experimental model. The simulation results match with a mean difference of less than 5% with the experimental measurements. The results of the current CFD investigation indicate that there is a gradient in air temperature and pressure within the VGE, ranging from the highest values of 314 K and 3.85 Pa to the lowest values of 308 K and 2.42 Pa, respectively. The CFD visualization shows a threefold increase in axial velocity and a fivefold increase in tangential velocity within an artificial vortex. Therefore, it can be concluded that the new VGE construction is highly efficient in generating a vortex.
The hydrodynamics of stirred tanks and bubble breakup are crucial in gas-liquid flows, yet this system has not been well characterized for different operating conditions. In this work, the numerical method was used to investigate the hydrodynamics of six- flat blades impeller (Rushton turbine) and the results were employed to understand the bubble breakup behavior in the stirred tank. Simulation results of predicted flow pattern, power number, and the distribution of turbulence energy generated were performed with COMSOL Multiphysics. Numerical results showed good agreement with the experimental literature. The effect of rotational speed on bubble breakup behavior, such as breakage probability, the average number of daughter bubbles, and the breakage time was investigated using the high-speed imaging method. The main finding is that the breakage process occurs in the high energy area of high turbulence intensity, which is located within a distance equal to the blade width of a radius of (15-35 mm). The breakage probability (Bp) was found to be increased by 12.61 percent for a mother bubble of 4 mm at 340 rpm, with an average fragmentation of up to 22 fragments. Furthermore, the bubble breakage time was found to decrease with increasing impeller rotational speed, with an average value of 19.8 ms.
The heavy metals are considered dangerous pollutants which harm health and environment. The adsorption process is the cost effective process to get-rid of heavy metal efficiently. In this study, the adsorption bed of Nickel is simulated by using COMSOL Multiphysics to find the effect of different operating parameters namely; flow rate, temperature and pollutant concentration on adsorption bed efficiency. The modeling of non-isothermal adsorption bed based on experimental isotherms kinetic of previous work is developed too. The results showed that the optimal conditions to generate maximum removal efficiency of heavy metal were at 50?C inlet temperature, 0.1 M inlet concentration, and 80 ml/min flow rate to achieve removal values higher than 50 % of long operation period time.
Improvements in the thermo-physical properties of Phase Change Materials (PCM) caused by nanoparticle dissipation are critical for a wide range of technologies. The current study describes numerically the investigation of the charging and discharging process of paraffin wax dispersed with different concentrations (1%, 3%, 5%, 7%, and 10% ) of Alumina nanoparticles (Al2O3), in a Single Thermal Energy Storage (STES) system. For this study, a time-dependent, two-dimensional simulation of the solidification and melting process was performed numerically for different velocities. The study is realized using the CFD ANSYS FLUENT software package (Version 18) that employs the phase-change phenomenon using the enthalpy technique. The results show that adding alumina nanoparticles to paraffin wax reduces the melting and solidification process, and raising nanoparticle concentration accelerated the melting and solidification process even more when compared to pure paraffin wax. The greatest improvement was obtained with the maximum concentration of nanoparticles with total time saving between (12% - 11.76% ) in the charging process and between ( 15.71% - 19.60% ) in the discharging process depending on velocity. Furthermore, other important findings were that the presence of nanoparticles makes a little effect in the early stages of the solidification and melting processes, but as time passes, the rate of solidification and melting rises. Comparison with previous works gave good agreement of about 34%.
The improvement in solar chimneys' thermal performance and thermal behavior that can be achieved by adding metal foam has been tested in computational work. The flow and heat transfer governing equations for solar chimney models were solved using computational fluid dynamics (CFD). It was solved using the control volume numerical method in ANSYS FLUENT 14.5. It is used to construct a finite volume modeling technique for solving the governing equations and the radiation heat transfer equations. With standard flat absorber plates, the results showed that heat transmission was increased by the inclusion of metal foam (10 PPI), leading to an increase in air velocity at the solar chimney of around 13.3%. The highest average air velocity with 10 PPI drops by 54.4% as the height of the absorber plate changes from 5 cm to 25 cm respectively.
A numerical study was performed of natural laminar convective heat transfer to its concentrated triangular enclosure around a horizontal circular cylinder. The air-filled enclosure kept the inner and outer cylinders at uniform temperatures. The Boussinesq density approximation to the momentum problem and the control volume approach iteratively resolved the governing equations to explain buoyancy. CFD results show that the velocity behavior increases by increasing Ra, so the stream lines becomes more sluggish and less uniform behavior and vortices gets less circulated pattern. The rotation angle ? has significant effect on vortices, at 90o gives the higher range of velocity zones of free convection with higher range. The thermal boundary layer seems to be larger in rr=0.455 as compared with rr=0.345 and decreases by increasing ?. The larger variation of isotherms and thermal boundary layer appears at lower ? because the higher heat transfer rate occurs at higher ? and becomes maximum at 90o. Eight correlations of average Nusselt number have been deduced as a function of Rayleigh number for the taken values of aspect ratio and enclosure angles of rotation and inclination.