Fluid flow analysis and design of flow distributor in fluid separator sing Commercial CFD software Pranita Shinde, Dr. Yogesh Bhalerao, Pramod Kothmire Department of Mechanical Engineering MITAOE, Alandi, Pune. Abstract- The aim of study was to investigate the possible use of commercial Computational Fluid dynamic software (CFD) in the design process of distributor which is used in fluid separator. Because of limited computational resources some simplification had to be made in order to contribute the design in reasonable time span. The porous media model (distributor) was used in order to simulate the influence of velocity characteristics at different flow rates further, a combination of CFD analysis and spreadsheet calculations was used. Keywords- CFD, distributor, Flow rates, fluid separator. I. INTRODUCTION The production of oil from reservoir is often associated with salinity produced water, sediments and contaminants. Due to the presence of salty water in oil there are numerous problems arrived such as corrosion, precipitation. Etc. Therefore, Separation of water in crude oil emulsion has been viewed as one of the greatest challenge in industries.
Before sending the oil to refineries, the salty water should be separated from oil. This is done in fluid separator/ desalter plants in which various techniques such as addition of chemical demulsifier, gravity settling, and electrostatic dimulisfication are used. To resolve water in oil emulsion into bulk phases of oil and water can be viewed as a three stages, i) destabilization, ii) coalescence, iii) gravity separation. In short, destabilization involve the upsetting of stabilization effect of natural emulsifiers that form a film surrounding dispersed water droplets. Coalescence occur when film surrounding the water droplet is drained, allowing the contact between droplets that coalesce into large droplet. Gravity separation require sufficient residence time that will allow the coalescence droplets of water separate from oil.
There are problem in design process of fluid separator which can be accompanied by CFD analysis. Fluid flow distribution is one of them. Quite often a uniform flow distribution is design assumption and CFD can be tool to investigate if such assumption is correct and to design an appropriate flow distributor if necessary. CFD calculations can provide sensitivity analysis or extrapolation to operating conditions and corresponding physical properties outside the accessible range of experiments; on the other hand, CFD calculations will still require validation since the development of new closure models. Moreover, hydrodynamic simulations using a two-ﬂuid model could be coupled with chemical species transport and reactive absorption modeling. Such an approach would allow quantifying the impact of hydrodynamic distribution on the packing transfer performance and thus better deﬁnition of design criteria for distribution technologies. It is thus believed that CFD should be a more and more useful tool for R&D chemical engineers who develop new solutions.
The effects of liquid inflow rates and feeding pipe directions upon outflow distribution have been analyzed by modeling different pre-distributors. It was concluded that liquid distributed differently under various flow rates which could induce different outflow characteristics. And the outflow was sensitive to the exact location and orientation of the feeding pipes. The simulation results showed that vertical feeding in the centre was the best feeding way for the pre-distributor. CFD simulation of hydrodynamics of perforated tube has been carried out at different design configuration. Mesh independent study was carried out to ensure a reliable and converged result. Besides, fluid flow at different velocity in the same perforated pipe configuration was carried out. The purpose was to ensure that the designed perforated pipe actually distribute uniform fluid flow at top orifices within a range of inlet velocities. The larger the inlet velocity is, the worse the velocity uniformity will be, as larger ﬂow velocity leads to insuﬃcient time for the velocity proﬁle recovery in the same bifurcation stage The velocity distribution in T-shape distributor can be improved by shrinking the vertical channel width.
In summary, the outlet velocity uniformity is decided by both the channel bifurcation angle and the total ﬂow length at the same inlet velocity, which means more time can be oﬀered for the recovery of asymmetric velocity proﬁle caused by the last bifurcation stage, then the ﬂow rate distributed to next bifurcation stage can obtain better uniformity. Perforated tubes are widely used in industries. An attempt has been made to provide an analytical method to model perforated tubes with mass and momentum balance equation. Equations were solved to get flow behavior of perforated tubes. Effect of changing various non-dimensional parameters on flow pattern is also predicted. Theory is extended to design perforated tube for desired flow behavior. The size of the holes, its pitch etc. can be arrived at to get the required flow profile.With the advent of horizontal drilling technology, flow in long perforated pipe has become and important issue in both environmental remediation and in petroleum industry.
Four pertinent of flow into perforated or porous pipe were reviewed. The condition of this experiments varied widely, but they consistently show two basic features: Perforation causes an increase in pressure losses both with and without inflow through the perforations, and inflow causes larger pressure losses than would occurred without inflow, but not as large as would be expected assuming constant wall shear and considering only the momentum increase induced by increasing velocities. The models for single-phase flow in perforated pipes with influx can be mainly divided into two types based on the number of openings. Models developed based on experiments with one perforation include Asheim model, Yalniz model and Zhou model. The other models including Siwon model, Ouyang model, Yuan model, Wang model and Su model are based on experiments with multiple perforations. The first models has limited applicability and may not be readily utilized to calculate the pressure drop without modification.
The second models may be appropriate for the practical calculations, but all of them are semi-empirical. Siwon model and Yuan model are the most complete and comprehensive models which can be used to account for various factors affecting the pressure drop behaviors such as perforations and influx through the pipe surface. Ouyang model is relatively simple but quite practical. Though the correlation of wall friction factor is established through the method of regression of the experimental data, it seems to have a higher frequency of use and wider application in engineering calculations. The equivalent friction factor due to the perforations on the pipe wall of Su model has a more theoretical foundation and more room for improvement compared to Siwon model. This analysis indicates that more efforts should be made to get a better understanding of the flow mechanism and develop a comprehensive model which is more theoretical and robust.
The formula for flow rate into a perforated drain tube obtained for rectangular perforation but applicable to circular holes as well, is presented. It reduces to previously obtained results when the perforation pattern is that of a drain tile. Circular openings have less entrance resistance to flow than any other shaped openings as observed by Schwab and Kirkham. However', the results of numerical analysis indicate that having many long (in terms of d), narrow slits in the drain tube is preferable to having fewer circular holes, since a much better approximation to a porous drain is obtained. The effect of inlet angle of distributor on flow distribution is significant. The flow maldistribution in lateral and gross flow directions is different. The effect of flow Reynolds number on flow misdistribution is obvious. Greater Reynolds no results in more severe flow maldistribution. It was demonstrate that an improvement in distributor configuration could effectively enhance the performance of plate fin heat exchanger by keeping the non-uniform distribution of flow under control.
The method of segregated production has the advantages of increasing the oil production rate, decreasing the water production rate and improving oil recovery. However, these good results must be treated with caution due to the limitations of the mathematical simulation method used. The most important limitations are:
(a) the inability of model to simulate the oil and water production after the water breakthrough;
(b) a lack of analytical representation of the oil/water transition zone and related effects of water saturation changes.
Flow distribution has been simulated in both conventional and modified inlet header configurations by using FLUENT. The results indicate that the flow maldistribution in the plate-fin heat exchanger increases due to the improper header configuration and is detrimental to heat transfer. The effect of the proposed header configuration on the velocity distribution in the intersection is remarkable. The numerical simulation confirms that CFD should be a suitable tool for predicting the flow distribution and optimizing the design of plate-fin heat exchangers. The results presented should be of great significance to the optimum design of the header configuration and plate-fin heat exchangers in the future. Design of a crude oil dehydrator was performed using CFD calculations. Numerical calculations gave qualitative results that permit to get guide-lines. The challenge was to integrate eelctrocoalescence/centrifugation and separation parts in the same device while considering separately the effects of electro coalescence and centrifugal forces. The technical objective was to facilitate the growth of fine water droplet present in oil by applying an optimized electrical field. Then after droplet diameter increases up to 100µm, centrifugal effect accelerates the droplet and separator inlet in a third part permitted to separate the water from oil.
The applicability and accuracy of a new discrete dividing flow manifold model was investigated. A three-dimensional CFD model was also constructed, and dimensionless volume flow rate distributions along a specified dividing-flow manifold were calculated with the two theoretical models. Experimental investigations were performed, and results of calculations compared favorably with those of own experiments. The measured distributions were accurately reproduced by the CFD and discrete models. The discrete model is flexible and expansively applicable for manifold design. CFD is less suitable for geometry optimization; however, the accuracies of our CFD results are adequate. Experimental investigation is the least flexible approach and unsuitable for design tasks; nevertheless, the available experimental database was extended, and these results can be used as reference data for further validation.
In summary, CFD tools like Fluent may be considered as a useful aid for design and evaluation of performance of packed column internals. Nevertheless, the immense run time associated with CFD simulations may be a disadvantage to potential users. Computational Fluid Dynamics is a powerful way of modeling fluid flow, heat transfer, and related processes for a wide range of important scientific and engineering problems. A fully integrated numerical method for flutter analysis with a coupled fluid structure interaction is presented. The technique replaces a hands-on process guided by experience to yield accurate and reliable low fidelity models. There are problem in design process of fluid separator which can be accompanied by CFD analysis. Fluid flow distribution is one of them. Quite often a uniform flow distribution is design assumption and CFD can be tool to investigate if such assumption is correct and to design an appropriate flow distributor if necessary.