Papers by Keyword: Flow Pattern

Abstract: The current research paper presents an investigation into the behavior of two-phase flow of liquid-vapour R134a within vertical circular channels with a 1 mm diameter, utilizing the Volume of Fluid (VOF) method. The main objective of these simulations was to create a numerical flow regime map to delineate the boundaries of different flow patterns for liquid-gas R134a. The injection of vapor was performed through an annular (concentric) nozzle configuration. To optimize computational efficiency, a two-dimensional axisymmetric assumption was made. The results of this study led to the identification of four fundamental flow patterns: bubbly flow/confined bubble flow, slug flow, churn flow, and annular flow. The accuracy of these findings was confirmed by comparing them with experimental flow visualization results, demonstrating a strong agreement. This study highlights the effectiveness of Computational Fluid Dynamics in establishing a reliable two-phase flow pattern map.

Abstract: The purpose of this research is to better understand the characteristics of two-phase flow in a rectangular bubble column. Computational Fluid Dynamics (CFD) (ANSYS-FLUENT R15.0®) has been used to conduct numerical studies of the flow pattern. Furthermore, the experimental data is used to verify the accuracy of the numerical data. This unique CFD simulation research included a 3D system, Reynolds-Average, Navier-Stokes equations (RANS), k-turbulence model, and total interphase forces. Bulk flow patterns were revealed through CFD analysis. Total contact force, both constant and non-steady, is also analyzed for its impact. The data show liquid upflow in the column's bulk section and liquid downflow near the wall. In the gas phase, bubbles rose in the middle area and departed the bed. In addition, bubbles without enough velocity to leave the bed circulate towards the wall with liquid and follow a similar pattern. The results show that the phenomenon of the central peak can only be captured by using a single bubble and no drag forces. The correlation between simulation and experimental findings is excellent. Within the higher, middle, and nearby gas distributor height ranges, the outcome agrees extremely well with the experiment. In addition, the results of the experiments show that the level of turbulence has played a crucial role in dynamic behavior. The CFD model described qualitative and quantitative flow performance, producing excellent results. The results also gave a framework for comparing and evaluating future designs and gave insights into the fluid dynamics of the bubble column reactor. Efforts were made to compare and contrast the main operating modes of different reactor designs. Keywords: Two phase, Ansys, Bubble column, CFD, Drag force, Flow Pattern.

Abstract: Two-phase flow has been used in so many industrial processes, such as boilers, reactors, heat exchangers, geothermal and others. Some parameters which need to be studied include flow patterns, void fractions, and pressure changes. Research on void fractions aims to determine the composition of the gas and liquid phases that will affect the nature and value of the flow property. The purpose of this study is to find out the characteristics of the void fraction of various patterns that occurs and to determine the characteristics of the velocity, length, and frequency of bubbly and plug. Data acquisition was used to convert the data from analog to digital so that it can be recorded, stored, processed, and analyzed. High-speed camera Nikon type J4 was used to record the flow. The condition of the study was adiabatic with variation of superficial gas velocity (J_G), superficial fluid velocity (J_L), and also working fluid. To determine the void fraction by using the digital image processing method. The results of the study found that the flow patterns which occurred in this study were bubbly, plug, annular, slug-annular and churn flows. It also showed that the void fraction value is determined by the superficial velocity of the liquid and air. The higher the superficial velocity of the air, the lower the void fraction value.

Abstract: The gas, oil and water co-current flow in pipes either flow in separate layers or in the form of a mixture. Other than gas, the liquid mixtures are common during the transportation of oil. In liquid mixtures, one liquid acts as a continuous phase and the other liquid dispersed in it. The phase inversion in three-phase flow majorly depends on the superficial velocity of individual phases, the volume fraction of liquid phases in total liquid and the internal diameter of the pipe. Pipe bends and fittings are commonly used in pipe networks for the diversion and distribution of flow. The 90° elbow bends are commonly used in such systems, where they change the flow direction from horizontal to vertical and vice versa. For the case of horizontal to upward vertical flow, the bend offers restriction to the flow compared to the straight pipe. Therefore, the process of phase inversion gets effected upstream 90° bend. In the current work, the phase inversion process during three-phase horizontal flow upstream 90° bend has been studied. The internal diameter of the pipe was 0.1524 m and the bend radius to diameter ratio (r/d) was 1. The range of superficial velocities are 0.5-5, 0.08-0.4, and 0.08-0.4 for oil-gas and water respectively. The continuous liquid phase and its effect on pressure drop have been studied at various oil to liquid volume ratios (f_o). The results show the different oil-water relationships and the liquid holdup occurred due to the bend.

Abstract: Flow patterns and temperature distributions of buoyancy–Marangoni convection in a liquid were analyzed both experimentally and theoretically. We focused on two-dimensional natural convection in a horizontal liquid layer. In the experiment, silicone oil (with a viscosity of 1 × 10⁻⁵ m²/s) was used as a test liquid and the temperature and velocity fields were visualized using liquid crystal capsules. The visualization experiment included cases of both steady flow and oscillatory flow. In the case of a deep liquid layer, an oscillatory flow with repeated acceleration and deceleration occurred due to the interaction of the buoyancy convection and the Marangoni convection; however, this did not occur when the liquid layer was shallow. In the numerical calculation, the governing equations of buoyancy–Marangoni convection were solved using a finite difference method. The numerical calculation results demonstrate that the position of the downward flow due to buoyancy convection was changed by the Marangoni convection, which agreed with the experimental result.

Abstract: Air flow pattern in urban environment are radically influenced by the sophisticated topography of buildings. Although in general the wind velocity is less than that in rural areas there are many critical points where the air movement accelerates. Such phenomenon can be observed in narrow streets, around the corners and below arcades.Vegetation can not only decrease the wind velocity but accelerate it. Trees can redirect air flow downward, whilst shrubs do upward. Around the corners of buildings high wind velocity and turbulence can develop which itself may lead to discomfort, in case of gust even the chance of accidents cannot be excluded. Together with low air temperature the wind-chill index may result in thermal discomfort.From the point of view of pedestrians the air flow up to the 2 meter height is to be investigated. The question is how the whirling air flow around the building corners can be tempered by vegetation in this band. The height of shrubs may be estimated as 1 meter while the canopy of trees hinders the air flow from about 3 meter height. Different combinations of shrubs and trees may contribute to wind discomfort as well as prevent it. In this paper the suitable arrangement of vegetation is analysed in function of street layout and wind direction.

Abstract: In this work, supersonic biplanes of the Busemann concept have been analysed, focusing on the unsteady aerodynamic characteristic due to flow disturbance using Computational Fluid Dynamics (CFD) codes in viscous flow. Flow disturbance is modelled by sinusoidal pitch motion simulated by mesh morphing using radial basis functions (RBF) method. The results suggest that there are two flow patterns of the Busemann biplane: oblique wave sequences flow (Pattern A) and choke-flow (Pattern B) with higher wave drag. Unsteady aerodynamic disturbance represented by pitch motion may cause flow pattern transformation. We have also obtained that Pattern B is more stable than Pattern A and choke-flow cannot be eliminated even after returning to the initial flight attitude. Moreover, amplitudes and frequencies of sinusoidal pitch motion play important roles in flow pattern transformation and there exist critical amplitudes and frequencies.

Abstract: Spool valves are the main elements in electro-hydro servo valves. Hydraulic measurement is an important method for spool valve’s null cutting measuring process. Because of the flow pattern transition, the discharge coefficient is a variable. This phenomenon causes errors if we assume the discharge coefficient is a constant as we always do. In this paper, the variable discharge coefficient is considered to the submerged discharge equation, and the flow pattern error is defined. For improving the precision of overlap values measurements, a compensation method of flow pattern error is presented in this paper.

Abstract: In recent years, minimum quantity lubrication (MQL) machining is regarded as a promising method for reducing machining cost and cutting fluid, while improving cutting performance. However the effectiveness and the working principle of MQL are still questionable with very few explanations provided. The aim of this study is to determine the optimum distance between the nozzle and tool tip and appropriate flow pattern of the mist flow for minimum quantity lubricant using Particle Image Velocimetry (PIV) and Computer Fluid Dynamic (CFD) for optimizing the spraying conditions thus reducing the lubricant consumption. The spray from the nozzle with outlet diameter of 2.5mm is analysed using Particle Image Velocimetry (PIV) to measure the mist flow velocity and identify the flow pattern. The input pressure of 0.2, 0.3 and 0.4MPa will be discharged throughout the experiment. Higher pressure produce more mass flow rate which helps in reducing the cutting force and cutting temperature efficiently and prolong tool life. Thus the appropriate distance can reduce lubricant consumption and increase the cooling and lubricating ability with best nozzle position. The applied distance increases the efficiencies of MQL applied during machining process.

Abstract: Experimental and numerical simulation of heat transfer and flow regimes for vertical flow across horizontal tubes are presented for mass flow rate in the range 0.03 – 0.17 kg/s and heat fluxes in the range 1.07–1.35 kW/m². The tubes had a diameter of 9.75 mm and a pitch to diameter ratio of 1.85. The CFX version 14.0 from ANSYS was used to predict the flow regimes and the temperature distribution in the tube bundles. These data and the predictions from numerical simulation were compared with the data available in the literature. It is found that the circulation zone in the shell becomes bigger as the mass flow rate is increases. The flow patterns identified in this experiment are bubbly, intermittent and annular flow. These data agrees well with the published data.