In pipeline-riser systems, pressure fluctuations which result from the formation of large liquid Slugs and gas surges due to operational changes or low mass flow rate from production wells and the profile of pipeline-riser systems often lead to trips at the inlet of the separator; and thereby, the problem causes a a loss of the production. In this study, on a sample deep-water oil field off the coast of West Africa is focused. The field lies in water depths greater than 1000 m. Moreover, the wells are connected via a pipeline-riser system to the topside. The Slug suppression system (S3) was changed as a control structure on the field case study. S3 comprises of a mini separator coupled with dynamically controlled valves at the liquid and gas outlets. This control structure was modeled on OLGA, a one-dimensional, and two-fluid equations based commercial multiphase flow simulation tool. In implementing the S3, it was transformed into a parallel configuration of two proportional-integral (PI) controllers (the separator level and pressure controllers) which controls the total volumetric flow and liquid flow respectively by subsequent opening of the valves at the outlets while stabilizing the riser base pressure. In addition, separator sizing was based on the volume of multiphase fluid at the riser-top. Also, controller-tuning parameters were obtained from parametric studies with pressure and liquid level set point at 20. 5 bar and 0. 5 m. Finally, it is found out that S3 is able to stabilize the riser base pressure and flow rate at the outlet of the mini-separator. Moreover, the comparison of production rates before and after the implementation of the control structure indicated an increase of 12. 5% in the production rate.

Semi-solid metal (SSM) processing has been used to produce of the engineering components with the suitable proper-ties and at the closet form of the final part. Thixoforging is one of SSM processes that in this process the forming opera-tion is performed on materials with the solid fraction of less than 55%. The purpose of this paper is to discuss on the Temperature (mold and specimen Temperature and holding time) for the producing of a relatively complex piece. The characteristics of the microstructures and mechanical properties of thixoforged Al-A356 alloy were studied. For this aim, some experimental tests were done. Also the results of these tests are compared with the results of simulations. The results showed that by increasing mold Temperature, causes more inhomogeneous microstructure and therefore the hardness and forming force decreased %12. 5 and %20. 6 respectively. Also the results showed that increasing the spec-imen Temperature and holding time, the grain size of primary α – al phase increased. For example in holding time of 5 min, by increasing the Temperature from 570° C to 600° C, the grain size of primary α – al increased 3. 5 percent. Also in the Temperature from 570° C, by increasing holding time of 5 min to 30 min, the grain size of primary α – al increased 73. 9 percent. In this work, the T6 heat treatment process was used for improving the hardness. The hardness was in-creased %17. 3, because of changing in primary α – al phase and produced the homogeneous microstructure.

In this paper, the effect of gas and liquid inlet superficial velocities and distance from upstream on Slug frequency is studied experimentally. Empirical correlations are also presented based on the obtained results. The tests are conducted for liquid holdup al=0.75 and three distances from inlet in a long horizontal channel made of Plexiglas with dimensions of 5x10cm2 and 36m length in Multiphase Flow Lab. of Tarbiat Modares University. The superficial liquid and air velocities rated as to 0.11-0.56m/s and 1.88-13m/s, respectively. The obtained results show that Slug frequency is dependent to superficial liquid velocity directly. Slug frequency decreases with slip ratio increase. Slug frequency has strong dependency on superficial liquid velocity and increases monotonically with it. However, superficial gas velocity has damping effect on Slug frequency. As Slug moves towards downstream, Slug frequency will be decreased but Slug velocity will be increased.

One of the important issues in the production of concrete is environmental variability that affects the concrete and elements constructed from this material. Due to the importance of different characteristics of concrete in short- and long-term conditions, this article aims to investigate the influence of initial Temperature conditions of self-compacting concrete on its long-term characteristics and determine the initial optimal Temperature of concrete. For these purposes, several experiments under three Temperature conditions of 5, 20, and 40 degree-of-Celsius were conducted to evaluate the rheology and mechanical properties of fresh concrete in the range of 7 and 28 days. In these experiments, alternative mineral admixtures of cement such as micro-silica, fly ash, and zeolite were used to build the concrete specimens. Results demonstrate that the mechanical properties of the specimens increase with increasing initial Temperature in the short term, while such properties significantly decrease in the long term compared to the specimens constructed under lower initial Temperature. Moreover, the fluidity of self-compacting concrete increases with increasing initial Temperature.

This paper presents a methodology for calculation of a Slug, two-phase flow hold-up in a horizontal pipe. The advantage of this method is that the Slug unit hold up can be calculated directly from the solutions of flow field equations with no need to use correlations. An experimental apparatus to measure air-water hold up was setup. The flow pattern and liquid holdup in horizontal and inclined pipes, from angles 5o to 40o, for air-water two-phase flow, are experimentally observed. The test section, with an inside diameter of 30 mm and 3 m in length, was made of plexy-glass to permit visual observations of the flow patterns. The proposed model was tested extensively against experimentally collected data. Furthermore, other data sources for Slug flow in horizontal pipes, for air-water and air-oil systems, were also used for comparison. The presented methodology was compared against four recently developed models of a two phase, Slug flow holdup in horizontal pipes. Not only does the presented model demonstrate good agreement, with less than 6.8% error, compared to the experimental data, but also has less error compared to other models. These results substantiate the general validity of the model.

In this paper, direct numerical simulation of two-phase incompressible gas-liquid flow for simulation of bubble motion in a microtube is presented. Microtube radius is 10 mm. The interface is tracked using volume of fluid (VOF) method with continuous surface force (CSF) model. The flow is solved using a finite volume scheme, based on PISO algorithm. Numerical simulation is performed on a axisymmetric mesh with cyclic boundary condition for different values of pressure gradient, void fraction, and bubble period. The mean pressure gradient is fixed for each simulation and the superficial Reynolds numbers of gas and liquid are 0.3 – 7 and 5 – 210, respectively. The numerical results are coincident with Serizawa regime map and there is a linear relation between void fraction and gas flow ratio. Pressure drop and liquid film thickness are compared with different empirical correlations. The computed liquid film thickness is closer to Irandoust correlation.

In this paper, numerical investigation of upward two phase flow of air-water has been studied. Different conditions of flow regimes including annular, wispy annular, Slug, churn and bubbly are simulated based on Hewitt and Roberts map, and a good agreement between the experimental data of the map and the numerical simulation has been observed. Accordingly, a proper CFD model in CFD software of Fluent with the required User Defined Function (UDF) has been obtained to simulate two phase flows of fluids with large density ratio in vertical tubes. The simulation is carried out with the volume of fluid (VOF) method and piecewise interface calculation (PLIC) algorithm for tracking the interface for the annular, wispy annular, churn and Slug flow regimes and drift flux model for bubbly with proper selection of computational cell and time step sizes. Furthermore, water and air momentum fluxes have been changed and the changes to the flow patterns are studied.

In many explored gas reservoirs in the word, which are considered as gas-gas condensate reservoirs, many surface facilities receive the gas as well as hydrocarbon condensates and water. Condensates cause Slugs in a pipeline. The Slugs, which are an aggregate of fluids, cause many problems in multiphase pipelines. Therefore, in order to separate condensates, Slug catchers are normally used. A Slug catcher is necessary equipment at the entry of a multi-phase flow processing factory. The specific performance of a Slug catcher is the separation of gas and liquid phases and temporary storage of the liquids. In this paper, we recommend a method for designing finger type Slug catchers, based on two phase flow in principles. Then, using the proposed method, we design a Slug catcher for the two present phases in the South Pars gas field. At the end, by considering condensate recovery and economical investigation of the suggested Slug catchers, we choose the optimum Slug catcher for these two phases. Among the most important results of this investigation, we can mention an efficient pattern for designing finger type Slug catchers and the selection of the optimum one. Using this pattern is recommended for a proper design and reduction of time and costs.

Slug flow is one the most complicated flow regimes in industrial processes that is seen for a wide range of fluid flow. However, there are always a lot of differences between experimental and numerical studies on Slug flow. Following the previous attempt on the selection of the best turbulent model for numerical simulation, the Slug flow is solved two-dimensionaly with implicit VOF method and k-e RNG turbulent model using FLUENT solver to extract the Slug flow parameters behavior accurately.The differences of numerical simulation of Slug flow with and without turbulent model are also presented. To overcome this procedure, a new user defined function code is developed. This UDF computes and predicts Slug parameters from FLUENT solver result without increasing the computational cost. The important Slug parametrs are presented which are: liquid Slug body velocity, liquid film velocity, Slug front and tail velocity, Slug center position and length, Slug front and tail positions, pressure difference across Slug, wall shear stress, Slug mixture velocity, Slug initiation time and position from the duct inlet. These parameters are discussed in detail, then validated.

Two-phase gas-liquid flows occur in a wide variety of situations, e.g., in chemical processing, power generation, water supply systems, and petroleum industry. The study of two-phase fluid flows is of great importance in hydraulic engineering. This type of flow typically occurs in pressurized flow tunnels, culverts, siphons, and bends in which the gas trapped in water pipelines releases from the water as the pressure reduces. The relative discharge rate of fluids and the pipe slope produce a wide variety of flow patterns including stratified, wavy, and Slug flows. In this paper, the unstable two-phase air-water flow is experimentally investigated. The image processing technique is applied for estimating the fluctuations of such parameters as void fraction and length, period and celerity of Slug waves. It is shown that the pipe inclination and air flow rate have significant effects on flow characteristics. Also, the relative wave length (L/D, D is the pipe diameter) in a Slug flow varies from 10 to 85, while air bubble length varies from 1/3 to 1/2 of wave length.