On Deriving High Pressure Empirical Multiphase Forcing Functions From CFD Analysis

New empirical PVT correlations for estimating bubblepoint pressure, solution gas-oil ratio, bubblepoint oil formation volume factor and undersaturated isothermal oil compressibility have been developed as a function of commonly available field data. Results show that these PVT properties can be predicted with average absolute errors ranging from 0.64% for bubblepoint oil formation volume factor to 6.66% for undersaturated isothermal oil compressibility.

In high pressure Hydro-processing Units high pressure equipment and piping are provided with weld neck ring & tongue joint (WN-RTJ) type flanges for ensuring leak free joints. Most of these flanges are made of austenitic stainless steels types, 321SS or 347SS. However, equipment flanges may be of low alloy steel base metal with weld overlay (WO) of type 347SS. RTJ grooves of these solid stainless steel or overlaid flanges may develop cracks in operation and if not detected and repaired in time may eventually leak. Cracking usually takes place due to various factors e.g. high stress concentration in the RTJ groove, stress corrosion cracking (SCC) due to polythionic acids or presence of chlorides and long term reduction in ductility of low alloy steel flange base metal due to exposure to high temperature hydrogen resulting in SS WO cracking. This paper describes the systematic inspection of these RTJ flanges in various planned shutdowns in a residue desulphurizer unit in one refinery where, extensive cracking was observed in high pressure fixed bed reactor inlet nozzle flange RTJ groove which was successfully repaired in-situ. Also many other stainless steel flanges / spacers in high pressure piping were found with extensive cracking in RTJ groove. Some of these were replaced in kind where as others were repaired successfully. Refinery Inspection has established a systematic inspection program of periodically checking these flanges and repairing / replacing as required.

The research in this paper is a sequel of an earlier work by the author in which experimental and CFD results were compared for an absorber plate made of iron with and without fins for two flow rates. The research yielded a good comparative result between the experimental and computational process for an optimized flow rate and the effect of the fins. The objective of this paper is to verify the effect of the overlay composite absorber plate material on a solar air heater through experimental and computational fluid dynamics. The experimental setup consists of an absorber plate as an overlay composite of aluminum and copper for enhanced heat transfer. Experiments and CFD analysis were done in three configurations. In configuration one, only the aluminum absorber plate with fins was considered. In configuration two, the overlay composite was considered with copper on the top and aluminum at the bottom as fins, and in configuration three, the overlay composite was considered with aluminum at the top and copper at the bottom as fins. A transient 8 hours CFD analysis was carried out using these configurations. While validating the results it was found that the overlay absorber plate Cu-Al was capable of generating a high outlet temperature Max of 88 °C and capable of generating 83 °C air for 5 hours and had good thermal efficiency when compared to the other materials in the other two configuration. It was found that experimental and computational analysis were in very close agreement, and the margin of error between the experimental and computational processes was less than 8 %.

Three different morphological variations of monodispersed Zn-Al-containing layered double hydroxide (ZnAl-LDH) microspheres were synthesized, with varying degrees of spacing between the nanosheets. The ZnAl-LDH materials were calcined into Zn-Al-containing layered double oxide (ZnAl-LDO) microspheres and loaded with Cu to be used as catalyst candidates for CO2 hydrogenation to methanol under high pressure and constant flow. Two different low-cost facile Cu loading methods were also employed, namely, wet impregnation and ion exchange. The different morphological variations were then evaluated and compared by computational fluid dynamics (CFD) simulation (ANSYS Fluent) as well as the hydrogenation reaction of CO2 to methanol with the purpose of exploring the effect of nanosheet spacing on catalyst performance in terms of the overall catalytic activity and methanol selectivity. The different metal loading methods have also led to different stability results, where there is a slight drop in performance of the incipient wet-impregnated catalyst, while the ion-exchanged catalyst retains much better performance over the same period of 40 h. Based on our simple CFD modeling, an increase in the nanosheet spacing improves convection-driven vortices within the wider channels of the LDH assemblage, with the vortices reaching deeper into the interior core of the microsphere. The simulated vortex phenomena explain the higher catalytic activities observed in our experimental results. This work indicates that catalysts with intricate morphological structure engineering would significantly enhance their catalytic activities.

Multiphase flow phenomena are widespread in nature and production process. The study of the flow mechanism and characteristics are a very important in the multiphase pipe flow. The establishment of multiphase flow experimental devices and systems is necessary in the study. In order to multi-phase pipe flow simulation, the small-scale physical experimental system based on the PLC control, and the experimental simulation system of based on Configuration software design are achieved. The physical experimental system can be achieved signals acquisition and control. Bubble flow, stratified flow, wavy flow, slug flow and other flow patterns can be formed in the experimental pipeline by changing the oil-gas-water flow rate. The virtual experimental system consists of the control interface and virtual physical interface. The simulation experiments of the multiphase flow generation can be achieved through the data exchange by two computers. This system meets the requirements for multiphase flow experiment.

In this paper, in order to improve temperature prediction, 2D axisymmetric CFD analysis has been implemented to determine the cavity flow network in Finite Difference Method (FDM) thermal analysis model. With this work process, for example, the complex recirculation of cavity flow can be considered in FDM thermal analysis. In the beginning, the rig test of simplified cavity with rotating disk and PIV measurement are carried out to investigate the flow structure in the cavity and to validate CFD analysis. CFD result has matched well with the measurement data of PIV, and it has been found that SST k-ω turbulent model provides the most reliable result by the sensitivity study. The study result also helps to choose the most suitable scheme of discretization and the method of pressure correction. Then, the modeling of the cavity flow network based on CFD analysis result has been applied to the thermal analysis for the aero-engine. Compared with the measured data, the result with this modeling shows that temperature prediction has been well improved.

The simplest devices are jet ejectors between all compressors and vacuum pumps. There are no moving parts, lubricants, or seals and are therefore considered to be the most reliable devices with low supporting costs. Factors affecting the performance of a jet ejector are molecular fluid weight, feed rate, tube length mixing, tube area, throat size, fluid speed, pressure rating, and temperature range. In this work, the optimization of jet ejector using CFD was carried out by creating a model and analyzing the multi-phase flow model of steam and water and the consequence of possible borderline environment on the clone answers using a commercial software of Ansys Academic 2021. The results show a 14.66% increase in the entrainment ratio of the fluids. The CFD results were compared to analytical model, and the deviation was calculated which was in the acceptable range, thus conforming to the reliability of CFD models. Lastly, a two-inlet nozzle was studied which gave an appreciable amount of entrainment ratio.KeywordsSteam jet ejectorComputational fluid dynamics (CFD)Mass transferNozzle

Numerical study on the condensation flow and heat transfer characteristics of hydrocarbon mixtures inside the tubes of liquefied natural gas coil-wound heat exchangers

Previous multiphase pipe flow tests have mainly been conducted in horizontal and vertical pipes, with few tests conducted on multiphase pipe flow under different inclined angles. In this study, in light of mid–high yield and highly deviated wells in the Middle East and on the basis of existent multiphase flow pressure research on well bores, multiphase pipe flow tests were conducted under different inclined angles, liquid rates, and gas rates. A pressure prediction model based on Mukherjee model, but with new coefficients and higher accuracy for well bores in the study block, was obtained. It was verified that the newly built pressure drawdown prediction model tallies better with experimental data, with an error of only 11.3%. The effect of inclination, output, and gas rate on the flow pattern, liquid holdup, and friction in the course of multiphase flow were analyzed comprehensively, and six kinds of classical flow regime maps were verified with this model. The results showed that for annular and slug flow, the Mukherjee flow pattern map had a higher accuracy of 100% and 80–100%, respectively. For transition flow, Duns and Ros flow pattern map had a higher accuracy of 46–66%.

Generation-IV SuperCritical Water-cooled Reactors (SCWRs) are expected to have high thermal efficiencies within the range of 45–50% owing to the reactor’s high pressures and outlet temperatures. The behavior of supercritical water however, is not well understood and most of the methods available to predict the effects of the heat transfer phenomena within the pseudocritical region are based on empirical one-directional correlations which do not capture the multi-dimensional effects and do not provide accurate results in regions such as the deteriorated heat transfer regime. Computational Fluid Dynamics (CFD) is a numerical approach to model fluids in multidimensional space using the Navier-Stokes equations and databases of fluid properties to arrive at a full simulation of a fluid dynamics and heat transfer system. In this work, the CFD code, FLUENT-12, is used with associated software such as Gambit and NIST REFPROP to predict the Heat Transfer Coefficients at the wall and corresponding wall temperature profiles inside vertical bare tubes with SuperCritical Water (SCW) as the cooling medium. The numerical results are compared with experimental data and 1-D models represented by existing empirical correlations. Analysis of the individual heat-transfer regimes is conducted using an axisymmetric 2-D model of tubes of various lengths and composed of different nodalizations along the heated length. Wall temperatures and heat transfer coefficients were analyzed to select the best model for each region (below, at and above the pseudocritical region). Two turbulent models were used in the process: k-ε and k-ω, with variations in the sub-model parameters such as viscous heating, thermal effects, and low-Reynolds number correction. Results of the analysis show a fit of ±10% for the wall temperatures using the SST k-ω model in the deteriorated heat transfer regime and less than ±5% for the normal heat transfer regime. The accuracy of the model is higher than any empirical correlation tested in the mentioned regimes, and provides additional information about the multidimensional effects between the bulk-fluid and wall temperatures.

In this paper are presented the results of the CFD analysis evaluations performed by the authors to determine the erosion rate in pipe bends used in technological installations that circulate fluids together with a small percentage of solid particles under the form of sand. The pipe bends that were analysed have different curvatures and diameters and the same wall thickness. The CFD analysis is focused on determining the areas where the erosion occurs together with the erosion rate values. The main area where erosion occurs is at the pipe bend extrados. The differences that have been noticed are influenced by the pipe bend type, as the maximum erosion rate increases as the bend curvature increases. The research will continue with designing an experimental test rig for erosion testing to compare the CFD and experimental program results.

A model for the combined spectral radiative and convective heat transfer analysis of solar chimneys is developed. The radiation part of this model is based on the spectral distribution of the solar heat flux and spectral radiative properties solar chimney components. Two methods are used for the convective part of this model, empirical correlations and a CFD analysis. The empirical correlations consist of stack effect correlation for air flow motion and convective heat transfer correlation for heat transfer coefficient calculations. The empirical correlations were used to obtain an initial estimation of surface temperatures which were then used in a CFD model to determine an improved estimation of the heat transfer coefficients and flow rates. By iterating between the spectral radiative and CFD models a converged value for the solar chimney flow rate and its thermal characteristics is obtained. The model is used to predict the volume flow rate of air moved for various configurations of solar chimneys (slopes and air gap distance).

This study presents the results of a Computational Fluid Dynamics (CFD) simulation of two-phase medium viscosity oil-air flow in a 50.8 mm internal diameter horizontal pipe. Void fraction and pressure gradient predictions were validated using experimental data for four different oil viscosities (0.039, 0.06, 0.108 and 0.166 Pa s) and different flow rates varying from 0.1 to 2.9 m/s for the gas phase and from 0.01 to 2.95 m/s for the liquid phase, where four flow patterns were predicted (stratified, dispersed bubble, bubble elongated and slug flow). The obtained results of void fraction and pressure gradient presented a mean relative error of 30.04 and 21.38%, respectively. Furthermore, the CFD results were compared against 66 empirical correlations and predictions from OLGA. It was found that between the three studied methods (CFD, OLGA and empirical correlations) the CFD model outperformed the other two methods regarding the predicted flow patterns, pressure gradients and void fractions on most cases.

CFD simulation of combustible solid waste pyrolysis in a fluidized bed reactor

The main purpose of this work is to simulate the flow of air and solid particles over a wildfire and to investigate the single and multiphase flow over the surface of a custom-designed wing with an Eppler-420 airfoil including an appendant custom-designed blended winglet. The wing is the result of a conceptual and preliminary design of a small-scale unmanned aerial vehicle (UAV) designed to assist in firefighting. The fire embers will be simulated in the Ansys Fluent commercial code as solid particles injected in the continuous phase, in an Euler–Lagrange approach. Primarily studied were the response of the model in air and air–solid flows, as well as the impact on aerodynamic efficiency due to the existence of the second phase. Moreover, the effects of unstructured, structured and mosaic poly-hexcore meshes are investigated and compared. The computational fluid dynamics (CFD) simulations, were implemented using a pressure-based solver, spatial discretization was conducted with a second-order upwind scheme, and the k-omega SST (k-ω SST) turbulence model was applied. Meanwhile, the two-phase flow was simulated using the Discrete Phase Model with reflect boundary condition on the surface of the wing and two-way coupling between continuous and discrete phase. To validate the results, experiments were conducted in a subsonic wind tunnel using a 3D printed model of the wing. The results show good agreement between simulations and experiments, with the structured mesh coming closer to reality, followed by the mosaic and unstructured meshes, respectively. Finally, a reduction in the aerodynamic efficiency of the wing section is observed, due to the presence of solid particles.