A new heat transfer correlation for flow boiling in helically coiled tubes

Based on the superposition principle of the nucleate boiling and convective heat transfer terms,a new correlation is developed for flow boiling heat transfer characteristics in helically coiled tubes.The effects of the geometric and system parameters on heat transfer characteristics in helically coiled tubes are investigated by collecting large amounts of experimental data and analyzing the heat transfer mechanisms. The existing correlations are divided into two categories,and they are calculated with the experimental data.The Dn factor is introduced to take into account the effect of a complex geometrical structure on flow boiling heat transfer.A new correlation is developed for predicting the flow boiling heat transfer coefficients in the helically coiled tubes,which is validated by the experimental data of R134a flow boiling heat transfer in them;and the average relative error and root mean square error of the new correlation are calculated.The results show that the new correlation agrees well with the experimental data,indicating that the new correlation can be used for predicting flow boiling heat transfer characteristics in the helically coiled tubes.

Fluid flow and heat transfer characteristics of spiral coiled tube: Effects of Reynolds number and curvature ratio

Numerical analysis was performed to investigate flow and heat transfer characteristics in spiral coiled tube heat exchanger. Radius of curvature of the spiral coiled tube was gradually increased as total rotating angle reached 12n. As the varying radius of curvature became a dominant flow parameter, three-dimensional flow analysis was performed to this flow together with different Reynolds numbers while constant wall heat flux condition was set in thermal field. From the analysis, centrifugal force due to curvature effect is found to have significant role in behavior of pressure drop and heat transfer. The centrifugal force enhances pressure drop and heat transfer to have generally higher values in the spiral coiled tube than those in the straight tube. Even then, friction factor and Nusselt number are found to follow the proportionality with square root of the Dean number. Individual effect of flow parameters of Reynolds number and curvature ratio was investigated and effect of Reynolds number is found to be stronger than that of curvature effect.

Efficiency and Effectiveness Thermal Analysis of the Shell and Helical Coil Tube Heat Exchanger Used in an Aqueous Solution of Ammonium Nitrate Solubility (<i>ANSOL</i>) with 20% H₂O and 80% <i>AN</i>

The case study is about obtaining the flow rate and saturation temperature of steam that makes it possible to heat a solution of water and ammonia nitrate (ANSOL) in a shell and helical coil tube heat exchanger, within a time interval, without that the crystallization of the ANSOL solution occurs. The desired production per batch of the solution is 5750 kg in 80 minutes. The analysis uses the concepts of efficiency and effectiveness to determine the heat transfer rate and temperature profiles that satisfy the imposed condition within a certain degree of safety and with the lowest possible cost in steam generation. Intermediate quantities necessary to reach the objective are the Reynolds number, Nusselt number, and global heat transfer coefficient for the shell and helical coil tube heat exchanger. Initially, the water is heated for a specified period and, subsequently, the ammonium nitrate is added to a given flow in a fixed mass flow rate.

Fatigue Life Analysis of Coiled Tubing in Deep Well Jet Plugging Removal

The coiled tubing plugging has become the main means of plugging in gas Wells in Xinjiang. These Wells are deep and have high pressure, which can easily affect the fatigue life of the operating coiled tubing. In order to improve the life of coiled tubing in high-pressure gas Wells, this paper studies the plugging conditions of coiled tubing in high-pressure ultra-deep Wells. Firstly, the cross section deformation of coiled tubing under high internal pressure is analyzed. Secondly, the factors influencing the fatigue life of coiled tubing and the influence of surface damage on the fatigue life of coiled tubing were studied. Finally, the mechanism of furrow damage caused by coiled tubing and the main measures to reduce furrow damage are analyzed. The following suggestions are made to improve the life of coiled tubing: select the right material and the right size coiled tubing;Use appropriate measures to prevent premature coiled tubing failure and reduce operating costs.

Investigations into the coiled tubing partial underbalanced drilling (CT-PUBD)technique for drilling hard formations

To improve the rate of penetration(ROP) in drilling deep and hard formations, this paper proposes a new drilling method called coiled tubing partial underbalanced drilling(CT-PUBD). As a preliminary investigation into the new drilling method, this paper presents predictions of hole cleaning efficiency, drilling speed, cuttings migration and pressure loss in the drilling process with CT-PUBD. Based on numerical simulation and full-scale experimental studies, we conclude that using CT-PUBD, an underbalanced drilling condition can be achieved near the bit while maintaining wellbore safety at the same time. This condition can be achieved using a cuttings discharge device, a rotary packer and a backflow controller.According to the numerical simulations performed in this study, CT-PUBD can achieve high efficiency of hole cleaning.Along the cuttings migration process, the fluid velocities can reach the maximum values in the backflow holes. A full-scale laboratory experimental system was used to test the hydraulic characteristics and obtain the drilling performance of the new technology. The result shows that CT-PUBD significantly improves the ROP compared to the conventional drilling method.

A Statistical Evaluation of the Frictional Pressure Losses Correlations for Slurry Flow

Hydraulic fracturing has increased immensely in recent years. An accurate prediction of frictional pressure losses of fracturing slurries is crucial for successful treatment and avoiding premature screen-out or even treatment failure. Scarce data and lack of theoretical basis of slurry flow, especially in coiled tubing, has led to very limited number of correlations that are available to predict slurry frictional pressure losses. Yet, the accuracy of the available correlations is still questionable. The current paper presents a statistical comparative analysis of the available frictional pressure losses correlations for slurry flow in straight and coiled tubing employing the recently introduced math modeling technique giving weight for the models known as A1C （Akaike information criterion）. With the help of AIC, the authors evaluated the available correlations to examine their accuracy. The results show that none of the available correlations can accurately predict friction pressure losses of slurries. The correlations show some reasonable accuracy within a very limited data range. However, they failed outside this range indicative of their poor applicability. AIC shows how much information is lost when using these correlations which can lead to erroneous results, and even job failure. This fact keeps the gates widely opened for more in-depth experimental, analytical, and theoretical analysis for better understanding of flow behavior with fracturing slurries aiming at developing a more realistic correlation to predict their frictional pressure losses. This paper represents the authors＇ first step toward developing such correlation, with the application of information theory and AIC.

Preliminary build and application of a data analysis platform for coiled tubing steel strips

To solve the problems in the quality control and improvement of coiled tubing steel strips production, such as scattered and inefficient production data, difficult performance fluctuation factor analysis, complex multivariate statistical analysis, and low accuracy and difficulty in mechanical property prediction, an industrial data analysis platform for coiled tubing steel strips production has been preliminarily developed.As the premise and foundation of analysis, industrial data collection, storage, and utilization are realized by using multiple big data technologies.With Django as the agile development framework, data visualization and comprehensive analyses are achieved.The platform has functions including overview survey, stability analysis, comprehensive analysis(such as exploratory data analysis, correlation analysis, and multivariate statistics),precise steel strength prediction, and skin-passing process recommendation.The platform is helpful for production overviewing and prompt responding, laying a foundation for an in-depth understanding of product characteristics and improving product performance stability.

Relationship between the Intensity of Secondary Flow and Convection Heat Transfer in a Helically Coiled Circular Tube with Uniform Wall Temperature

Numerical method is used to investigate fully developed laminar flow in helically coiled circular tube in this paper.The non-dimensional parameter(secondary flow Reynolds number Se)based on absolute vorticity flux along the mainstream is used to indicate the intensity of secondary flow caused by the centrifugal effect in helically coiled circular tube.The relationship between the intensity of secondary flow and the intensity of laminar convective heat transfer is studied.The effects of curvature and torsion on the enhancement of heat transfer are also considered.The results reveal that the absolute vorticity flux along the mainstream can be used to indicate the local or averaged intensity of secondary flow;the non-dimensional parameter of the absolute vortex along the main flow determines the convective heat transfer and friction factor.The relationships of Nusselt number and friction factor with the Se are obtained.The effect of curvature on Nusselt number is obvious,but the effect of torsion on Nusselt number is less obvious.

Experimental Investigation of Forced Convective Boiling Flow Instabilities in Horizontal Helically Coiled Tubes

An experimental investigation is described for the characteristics of convective boiling flow instabilities in horizontally helically coiled tubes using a steam-water two-phase closed circulation test loop at pressure from 0.5 MPa to 3.5 MPa. Three kinds of oscillation are reported: density waves; pressure drop excursions; thermal fluctuations. We describe their dependence on main system parameters such as system pressure, mass flowrate, inlet subcooling, compressible volume and heat flux. Utilizing the experimental data together with conservation constraints, a dimensionless correlation is proposed for the occurrence of density waves.

Turbulent Convective Heat Transfer of Methane at Supercritical Pressure in a Helical Coiled Tube

The heat transfer of methane at supercritical pressure in a helically coiled tube was numerically investigated using the Reynolds Stress Model under constant wall temperature. The effects of mass flux （G）, inlet pressure （Pin） and buoyancy force on the heat transfer behaviors were discussed in detail. Results show that the light fluid with higher temperature appears near the inner wall of the helically coiled tube. When the bulk temperature is less than or approach to the pscudocritical temperature （Tpc）, the combined effects of buoyancy force and centrifugal force make heavy fluid with lower temperature appear near the outer-right of the helically coiled tube. Beyond the Tpc, the heavy fluid with lower temperature moves from the outer-right region to the outer region owing to the centrifugal force. The buoyancy force caused by density variation, which can be characterized by Gr/Re3 and Gr/Re2.7, enhances the heat transfer coefficient （h） when the bulk temperature is less than or near the T~, and the h expe- riences oscillation due to the buoyancy force. The oscillation is reduced progressively with the increase of G. Moreover, h reaches its peak value near the Tpv. Higher G could improve the heat transfer performance in the whole temperature range. The peak value ofh depends on Pin. A new correlation was proposed for methane at su- percritical pressure convective heat transfer in the helical tube, which shows a good agreement with the present simulated results.

Numerical Investigation of Boundary Grid Effect on Heat Transfer Computation of RP-3 at Supercritical Temperature of Helical Tube Wall

To get reliable computational results,the RNG k-ε turbulence model with enhanced wall treatment was validated to solve the heat transfer of supercritical RP-3 in a helically coiled tube,and models of the thermo-physical properties of RP-3 were optimally chosen.Most significantly,the grid independence was validated by two-step procedure,and the effect of boundary grids of the supercritical-temperature wall on the computational accuracy was well studied.Through adjusting boundary-layer girds' size,four regions (increased,pseudo-convergence,decreased and convergence) of the outlet temperature Tout were obtained and analyzed.The results showed that the maximum computation errors of Tout and the pressure differential between the inlet and outlet ΔP reached 20.65% and 98.15%,respectively,indicating that boundary grids have a significant influence on computation of flow and heat transfer.Based on this,a dimensionless distance from the wall-adjacent cell to the wall y+=Prw-1/1.78 (Prw denotes Wall Prandtl number) was recommended as a convergence point.The variation laws of viscous length scale y* were discussed under different structural parameters,operation parameters,and helical lengths.An explicit model of y* was proposed to calculate the height (y) of the first boundary layer grids and refine boundary grids efficiently.A modified model for coefficient of fiiction factor Cf was proposed based on Rogers's,and Nusselt number Nu was proposed based on an analogy of momentum and heat transfer.The above models about y*,Cf and Nu could apply to both the entrance region and the whole tube length,and showed good performance when Reynolds number was extended to above 70 000,or whenever the outlet temperature is below or above the critical point.

CONDENSATION HEAT TRANSFER OF R-134A IN HORIZONTAL STRAIGHT AND HELICALLY COILED TUBE-IN-TUBE HEAT EXCHANGERS

This article presents an experimental investigation on condensation heat transfer of R-134a in horizontal straight and helically coiled tube-in-tube heat exchangers. The experiments were carried out at three saturation temperatures（35 ℃ , 40 ℃ and 45 ℃ ） with the refrigerant mass flux varying from 100 kg/m2 s to 400 kg/m2 s and the vapor quality ranging from 0.1 to 0.8. The effects of vapor quality and mass flux of R-134a on the condensation heat transfer coefficient were investigated. The results indicate that the condensation heat transfer coefficients of the helical section are 4%-13.8% higher than that of the straight section. The experimental results were compared with the data available in literature for helical and straight pipes.

High-Quality Critical Heat Flux in Horizontally Coiled Tubes

An investigation on the high-quality dryout in two electrically heated coiled tubes with horizontally helix axes is reported. The temperature profiles both along the tube and around the circumference are measured, and it is found that the temperature profiles around the circumference are not idelltical for the cross-sections at different parts of the coil. The 'local condition hypothesis' seems applicable under present conditions, and the critical heat flux qcr decreases with increasing critical quality xcr The CHF increases as mass velocity and ratio of tube diameter to coil diameter (d/D) increases, and it seems not to be effected by the system pressure. The CHF is larger with coils than that with straight tubes, and the difference increases with increasing mass velocity and d/D.

THE FRICTIONAL RESISTANCE CHARACTERISTICS OF GAS LIQUID TWO PHASE FLOW IN HELICAL COILED TUBES

This paper deal with the frictional resistance characteristics of gas liquid two phase flow in vertical upward helical coiled tubes under the system pressure 0.1 0.6MPa. By means of dimension analysis and π theorem, the correlation formulas were obtained for calculating the frictional resistance coefficients of gas liquid two phase flow in helical coiled tubes. The calculated results agree well with the experimental results.

Microstructure Control of Non-quenched and Tempered CT80Grade Coiled Tubing Steel

Complex working condition of coiled tube （CT） steel demands high strength and low ratio of yield strength （YS） to tensile strength （TS）. Reasonable microstructure control is a key problem of CT steel. Controlled rolling and controlled cooling experiments were carded out by two kinds of tested steels with different chemical compositions to develop the non-quenched and tempered CT80 steel. Mechanical properties of the tested steels at different processes are all in good agreement with the properties requirement of CT80. Increasing of Mo and Nb contents improves transformation of acicular ferrite and martensite-austenite （M-A） islands. 4 vol% of fine M/A islands increase TS and decreases ratio of YS/ TS, Cooling rate increasing also improves acicular ferrite transformation and enhances TS, but has little effect on ratio of YS/TS. To meet the requirement of high strength and low ratio of YS/TS, optimized complex microstructure of the CT80 steel is composed of acicular ferrite, about 30 vol% of bainite and 4 vol% of M-A islands.

Settling behavior of spherical particles in vertical annulus:Experimental study and model development

Coiled tubing(CT)drilling technology offers significant advantages in terms of cost and efficiency for exploitations of unconventional oil and gas resources.However,the development of CT drilling technol-ogy is restricted by cuttings accumulation in the wellbore due to non-rotation of the drill string and limited circulating capacity.Cuttings cleaning becomes more difficult with the wall resistance of pipe-wellbore annulus on the cutting transport.Accurate description of particle transport process in the pipe-wellbore annulus is,therefore,important for improving the wellbore cleanliness.In this study,high-speed cam-era is used to record and analyze the settling process of particles in the transparent annulus filled with power-law fluids.A total of 540 tests were carried out,involving dimensionless diameters of 0.10-0.95 and particle Reynolds Numbers of 0.01-12.97,revealing the effect of the dimensionless diameter and particle Reynolds number on the annulus wall effect,and the wall factor model with an average relative error of2.75%was established.In addition,a dimensionless parameter,Archimedes number,independent of the settling velocity,was introduced to establish an explicit model of the settling velocity of spherical particles in the vertical annulus,with the average relative error of 7.89%.Finally,a calculation example was provided to show how to use the explicit model of settling velocity in annulus.The results of this study are expected to provide guidance for field engineers to improve the wellbore cleanliness of coiled tubing drilling.

A Least-Squares Solution to Nonlinear Steady-State Multi-Dimensional IHCP

In this paper,the least-squares method is used to solve the Inverse Heat Conduction Problem(IHCP)to determine the space-wise variation of the unknown boundary condition on the inner surface of a helically coiled tube with fluid flow inside,electrical heating and insulation outside.The sensitivity coefficient is analyzed to give a rational distribution of the thermocouples. The results demonstrate that the method effectively extracts information about the unknown boundary condition for the heat conduction problem from the experimental measurements. The results also show that the least-squares method converges very quickly.

Application of a Lumped Multi-Section Model for Analyzing the Thermal Performance of a Small-Scale Biomass Boiler

The stationary lumped-cell model was developed and used to simulate the thermal characteristics of domestic biomass boiler with helically coiled tube heat exchanger(HCHE).The device serves as the heat source for ORC(Organic Rankine Cycle)unit and utilizes the thermal oil as the medium transferring the heat to the unit.Most of studies available in the literature refer to the CFD simulations for water flow in tube coils or in one-or two-turn coil elements.These investigations are basically focused on the determination of Nusselt number.The proposed herein model aims at determining the thermal performance of flue gas-oil HCHE while providing low CPU time.To demonstrate the model possibilities,it was used to predict the flue gas temperatures at the inlet and outlet from the heat exchange zone,based on measurement data regarding the outlet temperature of thermal oil.Six test series were considered.The computation results appeared to be in satisfactory agreement with experimental results(the discrepancies do not exceed 12%).The investigations showed that the used approach may be recommended as an alternative method that allows for fast prediction of thermal parameters for units of complex geometries,in particular the multi-coil heat exchangers.