Flow In Coiled Tubes Research Articles

Heat Transfer in Gas-Liquid Taylor Flow in Mini-Scale Coiled Tubes

This paper focuses on heat transfer in gas-liquid Taylor flows in mini-scale coiled tubes. An experimental study is conducted to investigate the effects of liquid slug ratio, radius of curvature, and Prandtl number. Previously, the conducted studies on Taylor flows in straight tubes revealed that heat transfer rates are related to the flow segmentation ratio. Single-phase flows show a higher heat transfer rate in the coiled tubes. In the present study, an experimental setup is assembled using open loop of mini-scale coiled tubes subjected to a constant wall temperature. The Taylor flow data are carefully collected using 0.65, 1 and 3 cSt silicone oils and segmented by gas phase at 0.5 liquid fraction. Three coils of radii, 10, 20, and 40 mm are formed to demonstrate the effect of the secondary flows on the heat transfer rates. The results are presented in the dimensionless forms of the Nusselt number. A new model is proposed to predict Nusselt number of the gas-liquid Taylor flow in coiled tubes. This achievement presents a significant insight on the heat transfer in mini/micro scale channels.

Optimization of carbon dioxide dissolution in an injection tubing for geologic sequestration in aquifers

Dissolution of liquefied carbon dioxide in a turbulent tubing flow for geologic sequestration in aquifers is simulated. The problem is solved by a two-fluid approach in a three dimensional formulation. For accurate calculation of the droplet dissolution rate, an evolution of droplet size distribution along a tubing is modelled by the population balance equation accounting for droplet breakup, coalescence and interphase mass transfer. The dissolution rate in a horizontal tubing is rather slow due to gravity-induced droplet stratification. The dissolution process in a horizontal tubing is compared with that in a coiled tubing wound on a horizontal reel. In a coiled tubing flow, droplet stratification significantly decreases due to the gravity force causing periodical motion of droplets across the tubing. At relatively high flow velocities, CO2 droplets are well-dispersed even across a horizontal tubing. Droplet dissolution is rather fast in this case, and a notable difference in the dissolution rates in straight and coiled tubing is not observed. An effect of the flow rate on the dissolution process at different tubing diameters is illustrated. Thus, numerical studies show that a coiled tubing can be efficiently used for intensification of liquefied carbon dioxide dissolution for relatively low and moderate flow rates. • Dissolution of CO 2 droplets in a tubing flow in 3-D formulation is modelled. • Dissolution rate in horizontal tubing flow is low due to droplet stratification. • Using coiled tubing wound on a reel strongly enhances dissolution rate. • 3-D simulations allow optimal selection of coiled tubing parameters.

A brief review on frictional pressure drop reduction studies for laminar and turbulent flow in helically coiled tubes

This review, summarises the pertinent literature on drag reduction (DR) in laminar and turbulent flow in coiled tubes. Due to their compact design, ease of manufacture and superior fluid mixing properties, helically coiled tubes are widely used in numerous industries. However, flow through coiled tubes yields enhanced frictional pressure drops and thus, drag reduction is desirable as it can: decrease the system energy consumption, increase the flow rate and reduce the pipe and pump size. The main findings and correlations for the friction factor are summarised for drag reduction with the: injection of air bubbles and addition of surfactant and polymer additives. The purpose of this study is to provide researchers in academia and industry with a concise and practical summary of the relevant correlations and supporting theory for the calculation of the frictional pressure drop with drag reducing additives in coiled tubes. A significant scope for future research has also been identified in the fields of: air bubble and polymer drag reduction techniques.

Numerical investigation of heat transfer and entropy generation of laminar flow in helical tubes with various cross sections

This study evaluates heat transfer performance and entropy generation of laminar flow in coiled tubes with various cross-sections geometries i.e. circular, ellipse and square, relatives to the straight tubes of similar cross-sections. A computational fluid dynamics model is developed and validated against empirical correlations. Good agreement is obtained within range of Reynolds and Dean numbers considered. Effect of geometry, wall temperature, Reynolds number and heating/cooling mode were examined. To evaluate the heat transfer performance of the coiled tube configurations, a parameter referred as Figure of Merit (FoM) is defined as the ratio heat transfer rate to the required pumping power. In addition, exergy analysis is carried out to examine the inefficiency of the coiled tube configurations. The results indicate that coiled tubes provide higher heat transfer rate. In addition, it was found to be more efficient as reflected by lower entropy generation as compared to straight tubes. Among the studied cross-section, square cross-section generates the highest entropy, followed by ellipse and circular counterpart. Entropy production from heat transfer contribution is two order-of-magnitude higher than that of entropy contribution from viscous dissipation. Cooling case produces slightly higher entropy than heating counterpart. Finally, this study can provide practical guideline to design more efficient coiled heat exchanger.

Hydrodynamic chromatography using flow of a highly concentrated dextran solution through a coiled tube

Separation of colloidal particles in non-Newtonian fluid is important in food engineering. Using hydrodynamic chromatography, colloidal particles and starch granules originating from corn were individually injected into dextran solutions (Mw 2,000,000g/mol) flowing through a coiled tube for efficient size separation. Rheological properties of dextran solutions ranging from 50 to 250g/L were determined, revealing pseudoplastic fluid behavior. Velocity profiles for dextran solution flow in coiled tubes were obtained from rheological power law parameters. Suspensions of colloidal particles of diameters 1.0 and 20μm were individually injected into the dextran flows, demonstrating that dextran solutions at high concentration separated colloidal particles. Starch granules were separated by size using a dextran solution flow (250g/L). Thus, we expect to obtain efficient separation of colloidal particles in foods using highly concentrated dextran solutions.

Prediction of flow profiles and interfacial phenomena for two-phase flow in coiled tubes

The objective of the present study is to investigate the local variables and interfacial phenomena for two-phase flow in coiled tube. We believe that such information is not reported in the open literature and will be helpful for design purposes. A three-dimensional CFD model using volume of fluid (VOF) approach is presented for predicting the development of velocity fields, local and average friction factor, interfacial friction factor, phase distribution and entry length using a commercial CFD package (FLUENT 6.2). The effect of geometrical parameters (curvature ratio, λ = D c/ d; dimensionless pitch, H = p/2π R c) and operating conditions, Dean number, N De (= N Re ( d/ D c) 0.5) is also presented. The model predictions are in good agreement with the experimental dataset reported in literature [V. Czop, D. Barbier, S. Dong, Pressure in drop, void fraction and shear stress measurements in an adiabatic two-phase flow in a coiled tube, Nucl. Eng. Des. 149 (1994) 323–333; L.S. Yao, S.A. Berger, Entry flow in a coiled pipe, J. Fluid Mech. 67 (1975) 177–196; L.R. Austin, J.D. Seader, Fully developed viscous flow in coiled circular pipes, AIChE J. 19 (1973) 85–93].

Theoretical Analysis of Turbulent Flow of Power-Law Fluids in Coiled Tubing

Summary A comprehensive theoretical analysis of turbulent flow of a power-law fluid in coiled tubing is conducted with the approach of boundary layer approximation. Equations of momentum integrals for the boundary layer flow are derived and solved numerically. Based on the results of the numerical analysis, a new friction-factor correlation is developed which is applicable to a wide range of flow behavior index of power-law fluid model. The new correlation is verified by comparing it with the published Ito correlation for the special case of Newtonian fluid. For non-Newtonian fluids, there is also a close agreement between the new correlation and the experimental data from recent full-scale coiled tubing flow experiments.

Theoretical analysis of laminar flow of power‐law fluids in coiled tubing

AbstractA comprehensive theoretical study of the flow of power‐law fluid in coiled tubing by using the boundary layer approximation method is presented. First, a boundary layer approximation analysis was applied to the governing equations of continuity and motion of a power law fluid in the curved tubing flow geometry. Momentum integral equations for the boundary layer flow were then derived and solved numerically. The resulting solutions of the velocity field were used to develop a new friction factor correlation in terms of generalized Dean number, coiled tubing curvature ratio, and flow behavior index of the power law fluid model. The new correlation of this study and a previous correlation by Mashelkar and Devarajan were evaluated using experimental data obtained from full‐scale coiled tubing flow experiments. An excellent agreement was found between the new correlation and the experimental results. The Mashelkar and Devarajan correlation did not result in any acceptable agreement with the experimental data, nor did it match the Ito correlation for the limiting case of Newtonian fluids (n = 1). This work extends the range of applicability of the new correlation to fluids with flow behavior indices as low as 0.25, which would cover most fluids used for coiled tubing operations in the oil and gas industry as well as fluids used in other industries. © 2007 American Institute of Chemical Engineers AIChE J, 2007

Drag reduction characteristics in straight and coiled tubing — An experimental study

An excessive friction pressure loss due to the small tubing diameter and curvature (which is believed to cause secondary flow) of Coiled Tubing (CT) often limits the maximum obtainable fluid flow rate in most CT operations. Good drag reduction property becomes a desirable quality for drilling, completion and workover fluids for CT applications. Yet, the drag reduction phenomenon in coiled tubing has not been well understood. This paper presents an experimental study of drag reduction performance of commonly used drag reducing agent, high molecular weight, anionic, AMPS copolymer (Nalco ASP-820) in straight and coiled tubing. The flow loop used consisted of three 1/2-in. OD coiled tubing reels with curvature ratios of 0.01, 0.019, and 0.031. A 1/2-in. OD, 10-ft straight section was also included to compare the drag reduction behavior between straight and coiled tubing. Various concentrations of drag reducing fluid were tested. The optimum concentration was then determined from the results of drag reduction exhibited by the fluid. The differential pressure versus flow rate data were reduced in terms of Fanning friction factor and solvent Reynolds number for estimating drag reduction characteristics. The results show that the drag reduction in coiled tubing are significantly lower than in straight tubing. As curvature ratio increases, the drag reduction decreases. A new drag reduction envelope (which is parallel to the Virk's envelope for drag reduction in straight pipes) is proposed to evaluate the essential characteristics of drag reduction in coiled tubing. The test data plotted on this new envelope clearly show the delayed onset of drag reduction and the effects of curvature and polymer concentration on drag reduction. Presently, the correlations for accurately predicting drag reduction characteristics of a commonly used drag reducing fluid in coiled tubing are non-existent. In this study, new drag reduction correlations are developed that can be used for the engineering design of coiled tubing hydraulics. The correlations are also evaluated using the experimental data from full-scale coiled tubing flow experiments and results showed the good agreement with the predictions from the developed correlations.

Liquid phase residence time distribution for two phase flow in coiled tubes

AbstractThe residence time distribution (RTD) of the liquid phase in air‐water flow through helical coils has been studied. Upward and downward cocurrent flows have been investigated in three coils with curvature ratios ranging from 11 to 60.7. The ranges of the Reynolds numbers for the gas and the liquid varied from 1500 to 3000 and 620 to 3200, respectively. A model has been proposed that describes the liquid phase RTD as combination of two different residence time distributions applicable for turbulent and laminar liquid flows.

Prediction of film inversion in two-phase flow in coiled tubes

Depending on the flow conditions, the liquid film in annular two-phase flow in coiled tubes may be pushed towards the outer or the inner side by the centrifugal force. It is important to understand the mechanism of this ‘film inversion’ in order to develop a predictive model for the film thickness distribution. In this paper, this phenomenon is studied analytically, and a new criterion, based on the secondary flow in the thin liquid film, is proposed to predict its occurrence. The criterion shows good agreement with available experimental data. It is suggested that the analytical model can readily be extended to predict the distribution of the film thickness and film flow rate in coiled tubes.

Flow regimes, hold–up and pressure drop for two phase flowin helical coils

AbstractExperimental results on flow pattern, hold–up and pressure drop are presented for cocurrent upward and downward air water flow in helical coils. A tube of 0.01 m internal diameter was used and the ratio of coil to tube diameter was varied from 11 to 156.5. Water flow rate was varied from 4.9 × 10‐6 m3/s to 92 × 10‐6 m3/s while the range of gas flow rate covered was 83 × 10‐6 m3/s to 610 × 10‐6 m3/s.A new mechanistic approach is proposed to correlate pressure drop data in coils. The proposed model retains the identity of each phase and separately accounts for the effects of curvature and tube inclination resulting from the torsion of the tube. This makes it possible to use a single model to predict pressure drop for both upward and downward two–phase flow in coiled tubes. Required correlations for hold–up, interfacial friction factor and friction factors for individual phases are provided.

EFFECT OF COIL PITCH AND CROSS-SECTIONAL ELLIPTICITY ON RTD FOR DIFFUSION-FREE LAMINAR FLOW IN COILED TUBES

The effect of coil pitch and the cross-sectional ellipticity on residence time distribution (RTD) for diffusion-free laminar flow in helically coiled tubes has been studied. The numerically computed RTDs reveal that the increase in the coil pitch broadens the RTD while the increase in the cross-sectional ellipticity narrows the RTD. The condition under which the effect of coil pitch on RTD can be ignored has been reported.

Friction Pressure Drop and Heat Transfer Coefficient of Two-Phase Flow in Helically Coiled Tube Once-Through Steam Generator for Integrated Type Marine Water Reactor

Two-phase friction pressure drop and heat transfer coefficients in a once-through steam generator with helically coiled tubes were investigated with the model test rig of an integrated type marine water reactor. As the dimensions of the heat transfer tubes and the thermal-fluid conditions are almost the same as those of real reactors, the data applicable directly to the real reactor design were obtained. As to the friction pressure drop, modified Kozeki's prediction which is based on the experimental data by Kozeki for coiled tubes, agreed the best with the experimental data. Modified Martinelli-Nelson's prediction which is based on Martinelli-Nelson's multiplier using Ito's equation for single-phase flow in coiled tube, agreed within 30%. The effect of coiled tube on the average heat transfer coefficients at boiling region were small, and the predictions for straight tube could also be applied to coiled tube. Schrock-Grossman's correlation agreed well with the experimental data at the pressures of lower than 3.5 MPa. It was suggested that dryout should be occurred at the quality of greater than 90% within the conditions of this report.

Friction pressure drop and heat transfer coefficient of two-phase flow in helically coiled tube once-through steam generator for integrated type marine water reactor.

Two-phase friction pressure drop and heat transfer coefficients in a once-through steam generator with helically coiled tubes were investigated with the model test rig of an integrated type marine water reactor. As the dimensions of the heat transfer tubes and the thermal-fluid conditions are almost the same as those of real reactors, the data applicable directly to the real reactor design were obtained. As to the friction pressure drop, modified Kozeki's prediction which is based on the experimental data by Kozeki for coiled tubes, agreed the best with the experimental data. Modified Martinelli-Nelson's prediction which is based on Martinelli-Nelson's multiplier using Ito's equation for single-phase flow in coiled tube, agreed within 30%. The effect of coiled tube on the average heat transfer coefficients at boiling region were small, and the predictions for straight tube could also be applied to coiled tube. Schrock-Grossman's correlation agreed well with the experimental data at the pressures of lower ...