A CFD study on hydrocarbon mean residence time in a horizontal oil–water separator

This study presents computational fluid dynamics analyses on oil–water flow characteristics in a horizontal separator. The performance of these vessels are inferred from mean residence time and cumulative residence time distribution of the hydrocarbon phase inside the separator. The authors model a separator used by previous researchers and evaluate mean residence time of the hydrocarbon phase in a two-phase mixture of oil and water. Three different water-cuts of 21%, 32%, and 57% are used. Additional analyses are done to assess how certain geometric features of the separator influence hydrocarbon mean residence time. The results show that the addition of a second perforated baffle plate does not improve the hydrocarbon mean residence time significantly. However, introducing a downward slanting throat section between the primary zone and the gravity separation zone improves the hydrocarbon mean residence time at 21% and 32% water-cuts. The results suggest oil–water separators with a throat section may be more efficient than regular horizontal separators without the throat section at low water-cuts.

A Wet Gas Metering System Based on the Extended-Throat Venturi Tube

Although the use of a classical Venturi tube for wet gas metering has been extensively studied in the literature, the use of an extended-throat Venturi (ETV) tube has rarely been reported since its first proposal by J. R. Fincke in 1999. The structure of an ETV is very simple, but due to the complexity of multiphase flow, its theoretical model has not been fully established yet. Therefore, in this paper theoretical models have been developed for the convergent and throat sections of an ETV, and the gradients of front and rear differential pressures are derived analytically. Several flowrate algorithms have been proposed and compared with the existing ones. Among them, the iteration algorithm is found to be the best. A reasonable explanation is provided for its performance. The relationship between the differential pressure gradient and the flowrate relative error is also studied, such that the relative error distributions varying with ETV measured flowrates can be derived. The gas flowrate error of ETV increases with the liquid content whilst the liquid flowrate error of ETV decreases with the liquid content, and the relative errors of liquid flowrate are generally 2 to 3 times larger than that of the gas flowrate. Finally, the ETV tends to be more accurate than the classical Venturi tube. The ETV can be designed more compact under the same signal intensity due to its significantly higher velocity in the throat section.

Investigation on the Effect of Structural Parameters on Cavitation Characteristics for the Venturi Tube Using the CFD Method

The venturi tube is a special kind of pipe which has been widely applied in many fields. Cavitation is one of the most important research issues for the Venturi tube. Hence, three key structural parameters (contraction angle, diffusion angle and contraction ratio) were selected to investigate the influence of different factors on cavitation characteristics, using the computational fluid dynamics (CFD) method. A series of experiments for measuring the relationship between differential pressure and flow rate were carried out to verify the accuracy of the simulation method. Results showed that the simulation results had a high accuracy and the numerical method was feasible. The average vapor volume fraction of cross-section from the throat in the axial direction increased with increasing contraction angle. The cavity length increased with increasing contraction angle. The average volume fraction in the diffusion section rapidly decreased with increasing diffusion angle. The diffusion angle had no significant effect on the cavitation characteristics in the throat section and had a significant influence in the diffusion section. The average vapor volume fraction increased with decreasing contraction ratio. The contraction ratio had no significant effect on the cavity length under the same differential pressure. The average vapor volume fraction increased with decreasing contraction ratio. However, the variation in the throat section was less than the diffusion section. Under the same inlet and outlet pressure, the cavity lengths for different contraction ratios were basically the same, which indicated that the contraction ratio had no significant effect on the cavity length.

Influence of a recessed step at the throat section of a supersonic nozzle

ABSTRACTThe geometry of a planar converging-diverging nozzle operating with dry air in dilute gas conditions is modified by the introduction of a small recessed step at the throat section. Pressure measurements along the nozzle axis, schlieren visualisations and numerical simulations are performed to investigate the influence of the recessed step on the supersonic flow-field. In the experiments, the height of the recessed step is 0.1 mm and the nozzle height at the throat is 10 mm. Numerical simulations examine also 0.05 mm and 0.2 mm step heights. From the numerical simulations, the flow Mach number at the step location is 1.04 and the Reynolds number computed using the sonic conditions and the throat half-height is Re = 3.73 × 105. A perturbation wave pattern originates from the step, which results in a perturbation of the measured pressure profile close to the throat section. In the diverging portion, sufficiently far from the throat section, the pressure profile of the recessed-step nozzle matches the one measured in the clean configuration.

Rapid design method and new contours for a class of three dimensional supersonic nozzle of arbitrary exit cross section

The aim of this work is to develop a new and rapid numerical method for designing a new contour of the supersonic nozzle with arbitrary exit cross sections as a class of three dimensional nozzle extracted from the calculation of stationary flow solutions in axisymmetric nozzle. The application is made for nozzle giving a uniform and parallel flow at the exit section. The determination of the points of the axisymmetric nozzle contours in a non-dimensional manner with respect to the arbitrary throat radius is necessary. The exit section of the nozzle must be discretized at several points. The radii of the points of the throat section are determined by equalizing the ratio of the axisymmetric critical sections corresponding to each selected point of the exit section. Each point passes a contour of the nozzle to the throat where their position is determined by the multiplication of the non-dimensional positions of the axisymmetric nozzle point by the throat radius of this contour. A uniform portion is added at the end of each contour to compensate the decrease in its length. Longitudinal discretization of the nozzle is necessary. The flow properties of each point are the same as those of the points of the axisymmetric nozzle. The temperature and the deviation of the flow at each point of any section are determined by their interpolations between two successive points of each contour. The Mach number, the pressure and the density are determined accordingly. The application is made for air at high temperature lower than the dissociation threshold of the molecules.

Research on Structural Optimization for Regenerative-Cooling Thrust Chamber

A regenerative-cooling liquid rocket engine chamber is applied as the study object, and the heat transfer models are established to get the distributions of chamber parameters. A thermal-fatigue simulation is carried out go get the strain of the throat section with the thermal field and pressure field applied as the boundary conditions of a two-dimensional finite-element model. A usage factor is used for the life estimation of chamber, and the structural parameters of cooling channels are optimized aiming for a smallest usage factor which means a longest life. The influence of parameter changes is researched in this paper respectively. Three methods, linear search method, conjugate gradient method and gradient free method are respectively applied for the structural parametric optimization of cooling channels. The result of the research shows that the optimized structures have a longer life than the initial one has.

CFD Simulation of Throat Pressure in Venturi Scrubber

In nuclear power plant (NPP), particulate matter and gaseous pollutant release into the environment in severe accidents. To prevent from this disaster, filtered vented containment system (FVCS) containing venturi scrubber is being installed. The present work herein is the CFD simulation of throat pressure in venturi scrubber. A commercial software ANSYS CFX tool has been selected for this research. Euler-Euler regime is used to get the picture of behavior of fluid dynamics inside the venturi scrubber. Gas and liquid interact with each other in throat section of venturi scrubber. The pressure at the throat is one of the important factors to analyze the performance of venturi scrubber. In order to verify the results, mesh independency is checked. CFX and experimental results show good agreement with each other. The results obtained from CFX simulation are useful to improve the venturi design.

Research on Mechanism of Two Phase Flow Lifting Pressure Equipment and Output Regulation

Taking into account the process and mechanism of lifting pressure were complex due to the condensation and shock wave, a one-dimensional theory model based on direct contact condensation is presented to analyze the lifting pressure character of steam-water two phase flow injector, and some key issues, such as inter-phase mass transfer computed by the average condensation heat transfer coefficient and phase volume fraction determined by steam plume, are discussed in detail. The regulations of discharge mass flow and output temperature are decoupling control according to the theory model, and the inlet water mass flow is to determine the output temperature, the variable throat section of steam nozzle is to determine the discharge mass flow.

Simulation of a Gas Turbine Engine With Performance Degradation Modeling

A simulation of performance degradation for an aeronautical gas turbine engine (Honeywell T55 L712) is presented. The effects of turbine (low and high pressure stages) erosion on the engine performance have been investigated in some detail. The behavior of the engine has been simulated using a dynamic model implemented in Matlab-Simulink. Using a throughflow code the LPT and HPT have been simulated and their performance maps have been obtained with a high level of accuracy. In order to understand the effects of turbine erosion nine degradation levels have been introduced and the LPT and HPT performance have been computed using the abovementioned throughflow code. The degradation levels have been based on stator erosion effects (increase of throat section and blade thickness reduction) only according to the experimental evidence from the engine tests from Piaggio Aero Industries. The introduction of the modified turbine characteristics into the Matlab-Simulink model has allowed the degradation effects on the overall engine performance to be tested and discussed. Finally, using experimental data from the industrial maintenance database, the link of each level of degradation with the number of the engine operational time (hours) has been obtained.

A Study on Back Flow Structure in a 2-Bladed Helical Inducer at a Partial Flow Rate

The attachment of inducer upstream of main impeller is an effective method to improve the suction performance of turbopump. However, various types of cavitation instabilities are known to occur even at the designed flow rate as well as in the partial flow rate region. The cavitation surge occurring at partial flow rates is known to be strongly associated with the inlet back flow. In the present study, in order to understand the detailed structure of internal flow of inducer, we firstly carried out the experimental and numerical studies of non-cavitating flow, focusing on the flow field near the inlet throat section and inside the blade passage of a two bladed inducer at a partial flow rate. The steady flow simulation with cavitation model was also made to investigate the difference of the flow field between in the cavitating and non-cavitating conditions.