Helical Coiled Tube Research Articles

An alternative approach using numerical modelling for equivalent ultrasound propagation and its application: Prediction of heat transfer performance of a vertically helical-coiled tube heat exchanger induced by ultrasound

ABSTRACT This research presents an alternative approach using numerical modelling for the prediction of simplified ultrasound distribution in a 3D water flow domain. The simulation was conducted using the Ansys-Fluent CFD commercial program. The results from this approach were compared with those from other researchers, covering an ultrasonic power range of 9.6–400 W and a frequency range of 24 kHz–1.7 MHz based on the parameters of mean axial and average velocity, Nusselt number, and the heat transfer coefficient. The maximum and minimum errors for the range of studies were 25.91% and 1.65%, respectively. Hence, this numerical setup can be utilized to achieve accurate prediction of the fluid flow and heat transfer over a controlled space which provides more realistic results for a whole domain with rapid calculation, especially in the far field region. Furthermore, this approach was applied to predict the augmentation of heat transfer in a vertically helical-coiled tube exchanger using 24 kHz ultrasonic waves. With very low numerical error, the results showed that the maximum thermal performance factor was 19% and 33% when the waves were emitted from one and two ultrasonic transducers at positions UT12 and UT12,9, respectively.

Two-phase flow frictional pressure drop prediction in helical coiled tubes

Based on the construction of different experimental databases, the frictional pressure drop in helical tubes for single-phase and water-steam two-phase flow was analyzed empirically. The aim of the present study is to provide the scientific community with a reliable and simple to use predictive tool for estimating frictional pressure drop in helical tubes covering operating conditions of interest for the design and operation of coiled tube once-through steam generators, as those used in small modular advanced nuclear reactors.The single-phase database contains around 2000 data points from 14 different sources, including data measured with air and water as working fluids, covering Reynolds numbers ranging from 40 to 145,000 and curvatures between 0.0027 and 0.3. The prediction capability of some existing correlations for simple phase flow was analyzed, concluding that Ito correlations for laminar and turbulent regime (1959) are the best ones fitting the experimental data. The average difference between experimental data and Ito correlations was 3.75% for laminar regime and 2.11% for turbulent regime.The two-phase flow database was built with data available from open literature works. Due to the fact no existing correlation was found to successfully predict the available data, a new prediction tool based on the homogeneous equilibrium model was developed for water-steam flows at conditions of interest.The proposed tool, so-called FEMA correlation, converges to the Ito correlations for single phase flow, i.e. for thermodynamic qualities equal to 0 and 1. In addition, the correlation successfully fits the experimental data with an average error of 7.4% which is smaller than any other existing correlation. In addition, the new correlation is recommended for water-steam flow in vertical helical tubes with liquid only Reynolds numbers ranging from 20000 and 124000, pressures between 1 and 8 MPa, curvatures between 0.01 and 0.08, and thermodynamic qualities ranging from 0 to 1.

Calculation method of gas–liquid two-phase boiling heat transfer in helically-coiled tube based on separated phase flow model

Helically-coiled tube has a vital effect on the heat transfer coefficient of the heat exchanger. The limitation of present research is that the correlation of boiling heat transfer in the helically-coiled tube has a certain scope of application. Separated phase flow model was developed to establish a calculation method for gas–liquid two-phase boiling heat transfer in helically-coiled tube. Viscous force, gravity and centrifugal force were used to solve gas-film velocity, gas-film thickness and heat transfer coefficient. Then the calculation model was corrected by considering the influence of the flow pattern and wall superheat. The calculated results were compared with experimental results obtained from opening literature. Results show that the error between the calculated value and the experimental value is in the range of 32% and 41%. The error between the corrected value and the experimental value is located in 9% and 20%. The calculation model shows excellent predictive capability for gas–liquid two-phase boiling heat transfer in helically-coiled tube.

Experimental analysis of R410A flow in helically rib-roughened tubes

In this study, an experimental setup was built to investigate the two-phase flow characteristics of R410A refrigerant fluid inside a horizontal internally micro-fin helical coiled tube made of copper. The experimental measurements are carried out with a fixed refrigerant fluid evaporation with temperature equals to 10˚C for eleven mass fluxes values varied from 0.00635 (kg/s) to 0.02150 (kg/s), and the Reynolds number ranged from 6998 to 23,695 covering turbulent flow regime. The heat flux supplied to the micro finned test section was fixed in 10 (kW/m2) and mixture quality at 30% of the vapor phase. The experimental results were accurately measured under the diabatic condition. Friction factor and heat transfer coefficient were obtained experimentally and compared with available literature correlations for smooth and finned tube configurations. Results showed that the presence of internal helical-rib roughness increased friction factor by 27% when compared with a smooth wall, and 5.3% when compared with finned tubes correlation. New correlation to predict the friction factor of R410A refrigerant fluid inside the micro-fin helical coiled tube was developed based on flow patterns and it agrees with experiment data within the deviation of ±0.4%. The heat transfer coefficient shows a minimum average deviation of 10.5% when compared with literature.

A Novel Application for Parabolic Trough Solar Collector Based on Helical Receiver Tube and Nano-Fluid with a Solar Tracking Mechanism

Novel techniques to enhance thermal performance using a helical coil receiver tube and nano-fluid materials are presented in this paper. Two different applied techniques to enhance thermal performance are used as a new application on parabolic trough solar collector (PTSC). Lots of researches are going on to enhance the heat transfer rate using the helical coil tube and nano-fluid for heat exchanger and dish solar concentrated. So that these combining techniques together combined with the PTSC can be considered as a new application.
 Novel techniques to enhance thermal performance using a helical coil receiver tube and Nano-fluid materials are presented in this paper. Two different applied techniques to enhance thermal performance are used as a new application on parabolic trough solar collector (PTSC). In the present work, PTSC has been fabricated using Dioxide Silicon SiO2 with an average particle size of 40nm by taking volume fraction of SiO2 0.1, 0.2 and 0.3%. Distilled water based Nano-fluid as a working fluid and a helical coil receiver tube were used in this paper. Varying the flow rate of Nano-fluids 100,150 and 200l/h are used, respectively. A solar tracking mechanism experimentally has been used with the PTSC. As per ASHRAE standard, the experimental results showed that at volume fraction 0.3 % and flow rate of 200 l/h, the highest increase in the energy absorbed factor FR(τα) was 14.6 % and energy removal factor FRUL was 29.4 % compared with distilled water...

Parametrization of secondary flow intensity for laminar forced convection in twisted elliptical tube and derivation of loss coefficient and Nusselt number correlations by numerical analysis

The parameters used to specify the intensity of secondary flow in helical coiled tube and tubes with twisted tape insert can be obtained easily without knowing whole detail velocity field. It is found these parameters determine the characteristics of heat transfer and fluid flow. There are no parameters to specify the intensity of secondary flow in a twisted elliptical tube. Thus, this paper tried to find out a parameter that can be obtained easily and can specify the intensity of secondary flow in twisted elliptical tube. The effort was made to establish the correlations between the intensity of secondary flow and the flow friction factor or average Nusselt number. The results show that three types of parameters can be used to describe the intensity of secondary flow in twisted elliptical tube; there exists close relationships between these parameters. Among them a swirl parameter can be obtained without knowing whole detail velocity field. The average Nusselt number of twisted elliptical tube is the summation of Nusselt number of straight elliptical tube and Nusselt number term induced by secondary flow. And friction factor of twist elliptical tube can be divided into the friction factor of straight elliptical tube and a friction factor term caused by secondary flow.

Development of a thermal-hydraulic analysis code for helically coiled once-through steam generator

Helically coiled once-through steam generators being compact in size and most efficient for heat transfer have been widely used in many SMRs (Small and Medium-size Reactor). It is very imperative to study the hydraulic characteristics of the helically coiled once-through steam generator prior to their integration with SMRs. In this study a thermal hydraulics code that uses a two-fluid two-phase flow model with the consideration of thermal non-equilibrium is developed for thermal-hydraulic characteristics analyses of helically coiled steam generators. A pressure-velocity coupling algorithm is applied to solve equations and a set of heat transfer correlations and frictional pressure drop correlations are embedded into the code.Validation of the code is done using experimental data of pressure drop and heat transfer for helical coil tubes. The code is also tested for simulation of the transient as well as steady state thermal-hydraulic characteristics of OTSG (Once-Through Steam Generator) of IRIS (International Reactor Innovative and Secure) and results are compared with the design data and the RELAP5’s result, the simulation results are found in close agreement with these available results.

Tomographic PIV measurements and RANS simulations of secondary flows inside a horizontally positioned helically coiled tube

Helically coiled tubes are widely used in industry to enhance heat and mass transfer in the laminar flow regime, due to their secondary flow pattern. In this study, tomographic particle image velocimetry (tomo-PIV) is used in a horizontally coiled helical tube to systematically acquire 3C-3D velocity fields for Reynolds numbers ranging from 20 to 1400 and Dean numbers from 8 to 567. The velocity field evaluations are performed using two different approaches: time-averaged velocity field calculation from instantaneous velocity fields and velocity field determination by cross-correlation from an ensemble of instantaneous reconstructed volumes. Equivalent velocity field accuracy is achieved in both velocity approaches when the flow can be considered stationary. Moreover, numerical simulations were carried out in the same geometry at the same flow conditions and were validated against the experimental 3C-3D data sets. The simulation results show good agreement with the measured velocities, offering the possibility of parametric studies and design optimization. To the authors’ best knowledge, this is the first systematic experimental investigation of a helical coil flow by means of 3C-3D velocity measurements, which results can now be used for validation of numerical models in computational fluid dynamics.Graphic abstractMeasured time-averaged velocity visualized by vector-magnitude colour at horizontal and vertical slices (left) and Dean vortices detected by 3D Q-criterion (right) from the time-averaged measurements (purple isosurfaces) and from the simulation (red isosurfaces) inside the helically-coiled tube at Re = 220 and De = 89.

Condensation frictional pressure drop characteristic of R-600a inside the horizontal smooth and dimpled helical coiled tube in shell type heat exchanger

In this paper, an experimental study on condensation frictional pressure drop of R-600a inside smooth and dimpled helical coiled tubes were examined. The experiments were performed at saturation temperature of 35 °C, and 45 °C with mass fluxes of 75, 115, 156 and 191 kg m−2s −1. The effect of vapor quality, mass flux and saturation temperature on the frictional pressure drop were inspected. Moreover, the results obtained from smooth and dimpled helical coiled tube were also compared from those smooth straight tube at same operating condition. The results showed that the dimpled helical coiled tube offers higher frictional pressure drop compared to the smooth straight tube and smooth helically coiled tube. Finally, the correlations have been proposed to predict the frictional pressure drop during condensation of R-600a inside smooth and dimpled helically coil tube that predict the data within ±20%.

Heat Transfer Characteristics of Inclined Helical Coil Tube by Forced and Free Convection : A Review

Aim of this review work is to examine the relative advantage of using an inclined helical coil tube heat exchanger for high-pressure syngas under various industries application. It observed that the heat transfer in the helical coil tube is higher as compared to the straight tube due to their shape. Inclined helical coil tube heat exchanger offers advantageous over straight tubes due to their compactness and increased heat transfer coefficient. The increased heat transfer coefficients are a consequence of the curvature of the coil, which induces centrifugal forces to act on the moving syngas. Due to the curvature effect, the fluid streams in the outer side of the pipe moves faster than the syngas streams on the inner side of the tube. Heat transfer augmentation techniques refer to various methods used to increase the heat transfer rate without changing much the overall performance of the system. The arrangements are useful in a variety of applications where more heat transfer rates desired. Some of the claims involved in heat exchanger used in Thermal Power plants, process industries, air-conditioning equipment, heating and cooling in evaporators, radiators for space vehicles, automobiles, refrigerators. These techniques broadly of three types viz. passive, active, compound heat transfer augmentation techniques. The present paper reviews the experimental investigation of free and forced convection heat transfer from different helical coiled tubes.

Numerical Investigation of Subcooled Boiling Heat Transfer in Helically-Coiled Tube

Subcooled boiling heat transfer in helically-coiled tubes offers better heat transfer performance than any other types of boiling processes due to its ability to capture high heat flux with a relatively low wall superheat. This study investigates turbulent subcooled forced convection boiling performances of water-vapour in a helically-coiled tube with various operating conditions i.e. operating pressure, heat, and mass flux. Developed CFD model is validated against previously published experimental results using the RPI model. The model is developed based on the Eulerian-Eulerian framework coupled with k-ε RNG turbulence model and Standard Wall-Function. A good agreement is found between numerical prediction and experimental counterpart for the bulk fluid temperature and non-dimensional length. The result indicates that the subcooled boiling heat transfer in a helically-coiled tube tends to improve heat transfer coefficient and pressure drop in the domain. Subcooled boiling starts at the inner side of the helically-coiled tube (f=9900) due to the existence of secondary flow that comes from the coil curvature. Heat transfer coefficient and pressure drop increased with increasing heat flux and decreasing mass flux, and operating pressure. This is caused by the bubble movement and convective heat transfer phenomena in a helically-coiled tube. Finally, this study can provide a guideline for future research of the subcooled boiling in a helically-coiled tube.

EFFECT OF DEAN NUMBER ON THE HEAT TRANSFER CHARACTERISTICS OF A HELICAL COIL TUBE WITH VARIABLE VELOCITY & PRESSURE INLET

The heat transfer, friction factor, pressure difference, Nusselt number of a helical coil tube using variable pressure and velocity during inlet for various values of Dean number [ratio of coil diameter (D) to tube diameter (d)] has been studied using commercially available computational tool. A validation is performed using the computational tool through the experimental data and it was observed that the results are in good agreement. The helical coil of 0.3 m diameter with four (4) turns of inner diameter 0.01 m with length 3.77 has been modelled, meshed and analyzed for both laminar and turbulent flows of constant wall temperature and heat flux. A grid independence test is also performed. The results show that increase in Dean number increases the heat transfer of the helical tube. The increases in pressure have less effect on heat transfer during laminar flow while adverse effect can be observed during turbulent flow.

Energy and Exergy Analysis of Shell and Coil Heat Exchanger Using Water Based Al2O3 Nanofluid Including Diverse Coil Geometries: An Experimental Study

The aim of this research is to investigate experimentally the characteristics of the convective heat transfer and exergy analysis of pure water and water based Al2O3 nanofluid through helical coiled tubes (HCTs) and conical coiled tubes (CCTs) inside shell and coil heat exchangers. HCT and CCT fabricated with different coil torsions (λ) ranges from 0.0202 to 0.052 with different two angles (0° and 45°) while have the same curvature ratio (δ = 0.0564). The effects of mean coil torsion, the cone angle and nanoparticles volume concentration on the thermal performance were investigated. Results indicated that the overall heat transfer coefficient (Uov), convection heat transfer coefficient (ht), the tube side Nusselt number (Nut), effectiveness (ɛ) and exergy efficiency (ηex) of nanofluids are higher than those of the pure water at same flow condition, and this increase goes up with the increase in particle volume concentration (ϕ). The results also showed that Uov, ht, Nut, ɛ and ηex increases by decreasing the coil torsion from 0.052 to 0.0202. Correlations for Nut as a function of the investigated parameters are obtained.

Forced convection boiling heat transfer inside helically-coiled heat exchanger

For decades, forced convection boiling heat transfer has been considered as one of the most efficient type in the heat transfer mechanism. It has been widely utilized in heat transfer equipment of various industries. Meanwhile, helically-coiled heat exchanger has been commonly utilized in numerous industrial applications. Thus, there is an interest to utilize forced convection boiling heat transfer in helically-coiled heat exchanger. Boiling phenomenon inside helically-coiled tube is more complex as compared to the straight tube due to the secondary flow induced by centrifugal force. This study investigates flow boiling heat transfer performance of water-vapor inside helically-coiled tube by using computational fluid dynamic approach. A Eulerian-Eulerian two-fluid model is used to capture interphase exchange forces and heat transfer between liquid and vapor phase. Wall boiling model is adopted to take into account the boiling condition in the vicinity of the wall. The developed model is then validated against the previously published experimental data. Good agreement for the outlet vapor quality and pressure drop between numerical study and experimental measured value is achieved. The result reveals that the boiling starts at the inner wall of the tube (φ=450°) due to the presence of secondary flow induced by coil curvature. The relationship between HTC and vapor quality along the helically-coiled tube are discussed and evaluated. This study serves as a guideline for future study on forced convection boiling heat transfer in the helically-coiled tube.

Numerical investigation of helical coil tube bundle in turbulent cross flow using large eddy simulation

A realistic five-layered helical coil tube bundle in turbulent cross flow is numerically investigated using large eddy simulation (LES). The geometry of the helical coil tube bundle, which is a 1/45 sector of a helical coil steam generator design for an advanced small modular reactor, has three counterclockwise helical layers and two clockwise helical layers stacked in alternating fashion in the radial direction. A Reynolds number of 21,800 is considered based on the mean gap velocity, diameter of the coil tube, and kinematic viscosity of the working fluid. The WALE sub-grid scale model is employed for LES to resolve scale smaller than the grid size. Additionally, LES for an ideal five-layered coil bundle model without a helical geometry is utilized to generate comparison data. Instantaneous flow fields are explored by analyzing velocity magnitude, vorticity, static pressure, and vortical structures. The detachments of vortical structures from the coil tube surface are observed by visualizing vortical structures and wall shear stress distributions simultaneously. Various turbulent statistics at multiple monitoring locations are presented with an emphasis on feature difference between realistic and ideal coil bundle models. The results of spectral analyses, including the power spectral density and continuous wavelet transform analyses, are addressed from the perspective of flow-induced vibration. The key feature of this paper is the discussion of three-dimensional effects based on the helical geometry of a coil bundle.

One-dimensional design approach to integrated steam generator with helical-coil tube bundles for a sodium-cooled fast reactor

A potential of a sodium-water reaction in a steam generator (SG) has been known to result in a drastic increase of the capital cost of a sodium-cooled fast reactor (SFR). This is mainly because an essential risk of potential sodium-water reaction (SWR) at the pressure boundary between water/steam and liquid sodium in the SG unit of an SFR. To prevent the SWR event during the whole plant lifetime, the novel design of an integrated steam generator (ISG) concept was proposed and its creative thermal-hydraulic design approach was developed as well. The ISG design for an SFR is based on the concept of combined SG unit with an intermediate heat exchanger (IHX) to make the chance to contact of water vapor with liquid sodium very few. However, it requires far more heat transfer area than that of an existing design with both IHX and SG unit due to the lower thermal conductivity of an alternative intermediate heat transfer medium. In order to minimize the heat transfer area of ISG, its thermal-sizing analyses using three representative design parameters, such as the number of tubes, tube bundle arrangement, and tube inclination angle, were conducted by a one-dimensional analysis code. In this study, the optimal design condition of the integrated steam generator for the reference plant of KALIMER-600 was obtained and the required heat transfer area of the ISG unit was compared to that of the existing SG unit and IHX unit in KALIMER-600. It was found that the proposed ISG design requires 2.25 times of heat transfer area to transport the same amount of heat as the conventional two heat exchanger system.

Local measurement of bubbly flow in helically coiled tubes using double-sensor conductivity probe

ABSTRACTThe two-phase flow in helically coiled tubes (HCTs) is rather important in many industries, such as the heat exchange facility in nuclear power plant. In this work, a double-sensor conductivity probe was used to study the air/water bubbly flow in HCTs. The cross-sectional distribution profile of the interfacial parameters (void fraction, interfacial area concentration, bubble size, etc.) of air–water bubbly flow were systematically studied. Through carefully processing the raw data collected by the double-sensor conductivity probe, the distribution of the void fraction, interfacial area concentration, the bubbles number frequency over the cross-section are demonstrated, as well as the bubble velocities and sizes vertically in the dense region. Some statistical parameters of cross-sectional-averaged quantities, coefficients of variation, and bubble aggregation core coordinates are defined to quantitatively describe the distribution characteristics of interfacial parameters. The measured data are helpful for improving the understanding of two-phase flow characteristics in HCTs.

Laminar convective heat transfer in helical tube with twisted tape insert

Tape insert has been commonly adopted as heat transfer enhancement method in a thermal system. Most studies dealing with tape insert have been focused on straight tube. Helical coil tube, on the other hand, has been proven to have higher heat transfer than straight tube. It is of interest to combine both enhancement methods and obtain the optimum heat transfer enhancement. The main objective of this study is, therefore, to numerically investigate flow behaviour and the corresponding heat transfer in helical tube with twisted tape insert subjected to constant wall temperature. A three-dimensional computational model is developed based on conservation equations of mass, momentum, and energy, and is validated against the established empirical correlations. Good agreement is achieved between the numerical prediction and the empirical correlation calculation within the considered range of Reynolds (Re=100−2000) and Dean Numbers (De=25−1200). The effects of twist ratio, inlet Reynolds number and wall temperature are evaluated and discussed in the light of numerical result. It is found that adding twisted tape insert in helical heat exchanger can enhance heat transfer performance by up to four times as compared to conventional straight tube heat exchanger, at a cost of higher frictional pressure drop. Lower twisting ratio gives rise to a higher heat transfer enhancement as it promotes higher secondary flow. At low Pr (air), heat transfer enhancement ratio increases as Re is increased; however, at high Pr (water), heat transfer enhancement ratio is higher at Re 500–1000. Finally, Nu and f correlations are developed to predict heat transfer and pressure drop for practical applications.

Code improvement, separate-effect validation, and benchmark calculation for thermal-hydraulic analysis of helical coil once-through steam generator

Helical coil once-through steam generators (HCOTSGs) have been widely used in the design of small modular reactor (SMR) during the past several decades. As the widely accepted system analysis code, RELAP5 underestimates the heat transfer capability and pressure drop of helical coil tube steam generators using the original geometrical parameters of HCOTSG, because the built-in thermal-hydraulic empirical correlations are only suitable for straight tubes. In this study, thermal-hydraulic models for helical coil tubes and tube bundles are implemented in RELAP5 while the original functions of the code are not affected. A new flag for helical component is proposed and heat transfer boundaries for tube side and shell side are developed. The separate-effect validations of friction factor and heat transfer in helical coil tube are carried out based on experimental data and code-to-code verification. Then, the original RELAP5 and developed RELAP5-HCOTSG are used to simulate helical coil tube steam generators of two SMRs. One is the integral reactor IRIS, and the other is MRX. The calculated results are compared to the design parameters. It shows that the HCOTSG module developed in this study can improve the capability of RELAP5 to predict the thermal-hydraulic characteristics in SMR once-through steam generators with helical coil tubes.

On the relevance of turbulent structures resolution for cross-flow in a helical-coil tube bundle

Helical-coil steam generators are being adopted in a number of advanced nuclear reactor designs because of their increased heat transfer efficiency and compactness. Due to the limited operational experience and the expected high cost of dedicated experiments, it is imperative to demonstrate the modeling capability. Computational fluid dynamics is ideally suited for this problem, due to its high resolution and accuracy. However, traditional low-cost URANS turbulence models have shown limited applicability for cross-flow in helical tube bundles. On the other hand, LES methods provide high-accuracy and high-fidelity data with prohibitively high computational cost for design use. In this work, the recently proposed hybrid second-generation model STRUCT is compared to classic URANS turbulence formulations against high-fidelity LES simulations. The STRUCT model produces accurate predictions for all relevant quantities, demonstrating high potential for reproducing helical-coil tube bundle flow phenomena accurately, at an affordable computational cost.