Helical Pipe Research Articles

Experimental and numerical investigations on the heat transfer and flow characteristics of a helical coil heat exchanger

Experimental and numerical investigations have been carried out on a helical coil double pipe heat exchanger to study its heat transfer and flow characteristics. Two major parameters are identified to affect convective heat transfer, namely the Dean number and torsion. Overall heat transfer coefficients are calculated and the heat transfer coefficients are determined using Wilson plot. The numerical scheme is validated with the experimental results obtained from present study also with that reported in literature. The results showed that use of helical coil heat exchanger instead of straight tube type leads to an enhancement in the Nusselt number. However the friction factor is high in helical coil. The Nusselt number in the inner tube and annulus increase with Dean number and the effect of Dean number on Nusselt number is more significant in the annulus. The overall heat transfer coefficient varies with pitch and there exists an optimum value of pitch. A correlation is proposed to estimate Nusselt number in terms of Dean number, Prandtl number and dimensionless pitch.

Experimental investigation on mitigation of severe slugging in pipeline-riser system by quasi-plane helical pipe device

Efficient mitigation of severe slugging in pipeline-riser system can promote a higher level of flow assurance in offshore petroleum exploitation. However, for passive methods, challenges lie in developing a simple and efficient device which is convenient for both underwater installation and pigging operation. In this work, a quasi-plane helical pipe device without hampering both underwater installation and pigging operation was proposed for mitigating severe slugging in pipeline-riser system. The effect of the quasi-plane helical pipe device on severe slugging was illustrated through detailed comparisons between the conditions with and without the quasi-plane helical device on aspects of flow pattern, differential pressure, and liquid production. The experimental results proved the feasibility of the quasi-plane helical pipe device. The velocity ranges of typical severe slugging and of unstable flow on the flow pattern map have been shrunken dramatically with the device, i.e. smaller maximum liquid and gas velocities for the occurrence of severe slugging and unstable flow; and the occurrence of large-amplitude pressure fluctuation in the pipeline and the intermittency of liquid outflow has also been reduced.

Study of a toroidal-helical pipe as an innovative static mixer in laminar flows

In this paper we present the design of a novel, passive mixer, to enhance mixing and residence time distribution for promoting transport and reaction mechanisms in such devices. The goal is to understand and optimize the flow patterns for enhancing mixing in laminar flows through toroidal helical pipes, inspired by the coiled flow inverter (CFI) (Saxena and Nigam, 1984). A toroidal helix is a smooth analytical curve winding around a torus. It is characterized by three parameters: the radius of the torus’ centerline, the radius of the torus’ cross-section, and the number of turns it winds around the torus. Unlike the torus or the straight helix which have constant curvatures, the toroidal helix has a spatially oscillating curvature. We found that this causes the otherwise separated pair of Dean vortices to couple together, periodically re-orient, shrink and grow within each turn of the pipe. The resultant complex streamlines span the entire cross-section and enhances mixing via advective means. By constraining the total pipe length, a meaningful comparison of mixing efficiency within a given volume of pipe can be assessed as the torus’s cross-section radius and the number of helix turns are systematically varied. Reynolds number of up to 400 is explored with the number of turns of 3, 5, 7 and 8. The optimization study shows that the best mixing performance is achieved using a moderate number of turns. Apart from flow pattern and mixing efficiency, we also studied the pressure drop to monitor increased energy consumption and residence time distribution of the flow to monitor degree of mixing.

Experimental research on the thermal performance of PEX helical coil pipes for heating the biogas digester

To verify the feasibility of cross-linked polyethylene (PEX) pipe as a biogas digester heat exchanger and to study its thermal performance, a PEX helical coil pipe heat exchanger was designed, and a field experimental system was implemented at Shaanxi, China. The fermentation slurry temperature, inlet and outlet temperatures of the coil pipe, and the flow rate of the heat medium were all monitored to determine the efficiency of the system. The effects of the inlet temperature, flow rate, coil pipe length and total solid concentration of the slurry on the thermal performance of the coil pipe were all determined. The results indicate that the thermal conductivity of the PEX pipe is low, but the slurry temperature could still be raised to mesophilic temperature fermentation level over a short time period. Increasing the inlet temperature and coil pipe length was more effective for increasing the amount of heat transfer and shortening the preheating time. The total solid concentration of the slurry has an important effect on the heat performance of the coil pipe and the slurry temperature distribution. The results of the experiment can provide a basis for the design and application of biogas digester heating system in cold areas.

Developing Helical Grooved Drill Pipe for Increased Drive and Mud Pump Efficiency

Grooved drilled pipe is a type of drill pipe design, which can be a solution to some of major problems faced by drilling industry and increase overall efficiency of drilling as well. The problem in reference is differential drill pipe sticking. Simply put, grooved pipe is a type of drill pipe with spiral grooves on outer side (as used for experiments and calculations in this paper). This paper gives a comparative analysis between conventional and grooved drill pipes. Analysis is made on basis of theoretical formulas and working model using control scenarios to prove efficiency of grooved pipe over conventional drill pipe. Physical scale model was carefully fabricated to simulate conditions of a wellbore (in the best possible way for a scale model), carefully considering all the aspects of a conventional well. Theoretical formulas are also used to further support advantages of grooved pipe. Fabrication of model and experiment performed is meticulously explained in the paper. Almost everything comes with its own set of advantages and disadvantages. I have also listed a number of possible shortcomings of this idea. Even though results of experiment were better than anticipated andefficiency of grooved pipe over conventional pipe is quite significant, even for a scale model, the practicality of this project depends on whether advantages will outweigh disadvantages or not, in a real scenario. Further this paper aims to have an idea about future development studies and upcoming possibilities.

Optimal Reynolds number for liquid-liquid mixing in helical pipes

A computational study has been performed to determine the mixing behaviour of two miscible liquids in helical pipes with different geometrical dimensions. To evaluate the mixing efficiency between the two liquids, the scalar transport technique has been employed. The main objectives are to investigate the influence of the geometrical parameters on the mixing behaviour and to find the optimal values of Reynolds number (Re) corresponding to the highest possible mixing efficiencies, while keeping acceptable pressure drop. The Reynolds number has been varied broadly from Re = 5 to Re = 4000, corresponding to Dean numbers from De = 1 to De = 1500, covering a wide range of laminar flows relevant for practical applications. Three main geometrical parameters of the helical pipe have been considered; the coil pitch, the pipe diameter, and the coil diameter were varied in the ranges of 16–60 mm, 5–15 mm, and 70–150 mm, respectively. The results show that an increase in coil pitch results generally in lower mixing efficiencies, negligibly higher pressure drops, and lower values of optimal Reynolds numbers. Increasing the pipe diameter leads to lower mixing efficiencies but significantly lower pressure drops. Finally, as the coil diameter is increased, the mixing efficiency and the pressure drop are slightly reduced, while the optimal Reynolds number is moderately shifted to higher values. Furthermore, two optimal values of Reynolds number could be obtained for all configurations, leading systematically to high mixing performance, Re ≈ 40 and Re ≈ 750. The pressure drop for the lower value of the Reynolds number is considerably lower than that of the second optimal value, while mixing efficiency is comparable. Therefore, it is recommended to operate liquid-liquid mixing in helical reactors at Re ≈ 40. This value corresponds to the Dean number range of 7 ⩽ De ⩽ 15 for all the considered geometries.

Experimental studies on local and average heat transfer characteristics in helical pipes with single phase flow

In order to investigate the effects of centrifugal force and buoyancy on the local and average convective heat transfer characteristics of single phase, experiments were carried out on uniformly heated helical pipes. The local wall temperature is measured along the length of coil as well as in the circumferential direction using eight thermocouples at each cross section, which is made of INCONEL alloy 625 tubes with an inner diameter of 15.26 mm and a thickness of 1.8 mm. The ratio of the pipe diameter to coil diameter is 0.0436 and coil pitch is 194 mm. It is shown that the circumferentially local heat transfer coefficient vary drastically between different regions at cross section in helical coil tubes. A non-dimensional number which represents the ratio of centrifugal force and buoyancy could predict heat transfer characteristic in helical coil tubes well. It is also demonstrated that experimental data of the average Nusselt number agrees well with existing correlations. However, the local circumferential average Nusselt number is not well predicted by existing correlation.

Studies of Resistances of Natural Liquid Flow in Helical and Curved Pipes

Abstract The main aim of this research was to determine in three ways, i.e. experimentally, analytically and by means of numerical modelling, the resistances of the flow of a natural liquid in a helical pipe and in curved pipes. The analyses were carried out for three pipes: one helical pipe and two curved pipes. Each of the pipes was 2 m long and its inside diameter was 4 mm. The experiment was carried out on a test stand making it possible to measure the rate of the flow of the liquid, the temperature at the pipe’s inlet and outlet and the pressure at the pipe’s inlet and outlet. The resistances of the flow of the liquid were calculated from analytical or empirical formulas found in the literature on the subject. Moreover, numerical modelling was performed using the finite volume element method.

Direct numerical simulation of transitional flow in a finite length curved pipe

ABSTRACTTransition to turbulent flow in a curved pipe has been well studied through experiments and numerical simulations. Numerical simulations often use a helical pipe with an infinite length such that the inlet and outlet boundary conditions can be modelled as periodic which greatly reduces computational time. In this study, we examined a finite length curved pipe with Poiseuille flow imposed at the inlet and a stress-free boundary condition at the outlet. Direct numerical simulation of the Navier-Stokes equations for rigid walls and a Newtonian fluid was performed using nek5000. Straight extensions were added to the inlet and outlet such to diminish the impact of boundary conditions on the flow field in the region with curvature. The examined model has a pipe radius of curvature that is three times the pipe radius. The model has ∼355 million nodes and required an order of magnitude greater computational time when compared with an infinite length curved pipe. Results show that the critical Reynolds number, the lowest value with instabilities present in the flow, is much greater than that of a straight pipe and occurs near Re=5000–5200. This is larger than the critical Reynolds number typically reported for an infinite length curved pipe (Re=4200–4300).

Thermal Design of the High-Temperature Steam Generator for the Nuclear Power Plant GT-MGR with Helical (Coil-in-Box) Pipe Bundles

Thermal Design of the High-Temperature Steam Generator for the Nuclear Power Plant GT-MGR with Helical (Coil-in-Box) Pipe Bundles

Numerical investigation of turbulent forced convection flow of nano fluid in curved and helical pipe using four-equation model

Using nano fluid and curved pipes are two efficient methods for improving heat transfer rate. In the present research, turbulent flow in curved tube and helically coiled tubes is numerically investigated in developing flow. In addition, convective heat transfer is investigated in helically coils under constant wall heat flux. Heat transfer in Nano fluids is solved using homogeneous model or two-phase model. In the present study, the four-equation model is applied, considering slip mechanisms between two phases. This model is simplified in comparison with two-phase model; it can be used as an efficient model for numerical solution of nanofluid heat transfer. Governing equations are solved in OpenFOAM. Three turbulent models, komegaSST, SAS and LES are used. The results illustrate a better agreement of these models with experimental data, in comparison with homogeneous model.

CFD-Based Numerical Simulation for Helical Heating Pipes

For helical pipes, author builds their three-dimensional models, identifies their boundary conditions and makes CFD-based simulating calculation for their heat transfer in this paper. Therefore, related theoretical guidance could be made for the design and application of helical heat exchanger by referring to the temperature-distribution and heat-transferring laws elicited from both contrastive analysis and calculation for internal/external flow and temperature distribution in helical heating pipes with different inner diameters and screw pitches.

Optimization of Process Parameters of Helical Grooved Heat pipe Using Response Surface Methodology

Heat pipe is a special type of heat exchanger that transfers large amount of heat due to the effect of capillary action and phase change heat transfer principle .In this paper Empirical relationship was developed to predict the thermal performance of helical grooved heat pipe with DI water as a working fluid,in terms of heat transfer coefficient by incorporating process parameters i.e mass flow rates(m) of coolant(water),inclination angles(θ) of heat pipe and heat inputs to the heat pipe(Q). The process parameters were optimized by using Response Surface Methodology(RSM) in Design Expert software to attain maximum thermal performance .The maximum heat transfer coefficient of 6874.48 W/m2K was obtained under the optimized conditions of 0.03 kg/s of mass flow rate, 67.5o of inclination angle and 213 W of heat input.

Numerical Evaluation of Heat Transfer and Entropy Generation of Helical Tubes with Various Cross-sections under Constant Heat Flux Condition

The presence of curvature-induced secondary flow in helical pipe which create complex transport phenomena and higher transfer rate has attracted significant attention from both academic and industry. Flow behavior and transport processes in helical tube have been intensively investigated. Nevertheless, most studies were focused on the performance based on first law of thermodynamics with limited studies concerning the performance based on second law of thermodynamics. The objective of this study is to investigate the heat transfer performance of helical tube according to both first and second law. The heat transfer rate and entropy generation of helical tubes with various cross-sections, i.e. circular, ellipse and square, subjected to constant wall heat flux conditions are numerically evaluated by utilizing computational fluid dynamics (CFD) approach. Their performances are compared to those of straight tube with identical cross-section. The results indicate that helical tube provides higher heat transfer at the cost of higher pressure. Moreover, it was found that entropy generation in helical tubes is considerably lower as compared to that in straight tube. Among the studied cross-sections, square has the highest heat transfer albeit having the highest pressure drop and entropy generation for both straight and helical tubes.

Asymptotic solution for the Darcy-Brinkman-Boussinesq flow in a pipe with helicoidal shape

We study the fluid flow and heat transfer in a helical pipe filled with a sparsely packed porous medium. Motivated by the engineering applications, pipe?s thickness and the distance between two coils of the helix have the same small order of magnitude, whereas the fluid inside the pipe is assumed to be cooled (or heated) by the exterior medium. After writing the dimensionless Darcy?Brinkman?Boussinesq system in curvilinear coordinates, we employ the multi-scale expansion technique to formally derive the effective model valid for small Brinkman?Darcy number. The obtained asymptotic solution is given in the explicit form which is important with regards to numerical simulations. Comparison with our previous results on the straight-pipe flow is also provided.

Gas propagation following a sudden loss of vacuum in a pipe cooled by He I and He II.

Many cryogenic systems around the world are concerned with the sudden catastrophic loss of vacuum for cost, preventative damage, safety or other reasons. The experiments in this paper were designed to simulate the sudden vacuum break in the beam-line pipe of a liquid helium cooled superconducting particle accelerator. This paper expands previous research conducted at the National High Magnetic Field Laboratory and evaluates the differences between normal helium (He I) and superfluid helium (He II). For the experiments, a straight pipe and was evacuated and immersed in liquid helium at 4.2 K and below 2.17 K. Vacuum loss was simulated by opening a solenoid valve on a buffer tank filled nitrogen gas. Gas front arrival was observed by a temperature rise of the tube. Preliminary results suggested that the speed of the gas front through the experiment decreased exponentially along the tube for both normal liquid helium and super-fluid helium. The system was modified to a helical pipe system to increase propagation length. Testing and analysis on these two systems revealed there was minor difference between He I and He II despite the difference between the two distinct helium phases heat transfer mechanisms: convection vs thermal counterflow. Furthermore, the results indicated that the temperature of the tube wall above the LHe bath also plays a significant role in the initial front propagation. More systematic measurements are planned in with the helical tube system to further verify the results.

Numerical study of heat transfer and thermal homogenization in a helical reactor

A fast and accurate control of the flow temperature by heating or cooling through the wall is essential for many chemical applications, in particular to achieve optimal reaction intensification. A numerical study based on computational fluid dynamics (CFD) has been done to investigate thermal homogenization within a horizontally-coiled helical pipe. The main target is to examine and compare the flow and mixing characteristics when heating different axial parts of the coil. The entrance region and two other locations within the fully-developed flow region have been investigated for that purpose; the first, the third and the fifth turn of a ten-turn coil have been heated individually. In each case, temperature field and thermal homogenization were assessed. The performance was quantified in terms of the required axial length for the temperature profile to become uniform again after heating. The investigations were performed for water as a working fluid, and for a wide range of Reynolds numbers between 2000 and 16,000, covering both the laminar range and transition to turbulence in the helical pipe. The thermal mixing performance in the entrance region was found to be noticeably better than that in the fully-developed region, increasingly so at higher Reynolds numbers. Therefore, it is recommended to systematically use the entrance region of a coil reactor for a fast and efficient step rise of the flow temperature.

Design of a Permeator-Against-Vacuum mock-Up for the tritium extraction from PbLi at low speed

The Permeator Against Vacuum (PAV) is one of the candidate Tritium extraction and removal technology from the Lithium-Lead circulating in the breeding blanket currently under consideration for the EU DEMO. In this work the design of a PAV mock-up, dimensioned for the test in the TRIEX facility at ENEA Brasimone, is presented, together with a structural and fluid-dynamic analysis. The mock-up consists of parallel helical vanadium pipes inserted in a vacuum vessel, where the Tritium permeates from the PbLi. The extraction efficiency of the mock-up is computed using an established Tritium permeation model, demonstrating that the mock-up reaches the target 80% efficiency in nominal conditions.

Numerical study of liquid-liquid mixing in helical pipes

The flow characteristics and the mixing performance of two miscible liquids in helical pipes have been studied numerically by computational fluid dynamics (CFD). The scalar transport technique is employed to quantify species mixing between the two fluids. The focus of the present study is set on investigating the optimal mixing behavior as a function of different parameters. The study is carried out for a wide range of relevant Schmidt and Reynolds numbers for laminar flow conditions. The Reynolds number (Re) and Schmidt number (Sc) have been varied from 5 to 104, and from 10 to 105, respectively. The model is first validated against experimental data from the literature. The effect of the inlet configuration is then examined; a vertical liquid interface at the inlet lead to the highest mixing efficiency. For low values of the Reynolds number, the results show that the mixing efficiency is reduced with increasing Schmidt number, until an asymptotic behavior is reached for very high Sc. For high values of the Reynolds number, increasing Schmidt number is observed to have only a minor influence on the mixing coefficient. The Reynolds number is found to have a more complex impact on mixing efficiency. Nevertheless, two optimal values of the Reynolds number can be found that lead to best mixing conditions in the laminar regime for a given length of the helical pipe. Though both values depend on the available length of the helix, they are typically found around Re≈50 and Re≈1000.

Numerical Study of Turbulent Helical Pipe Flow With Comparison to the Experimental Results

Turbulent flow through helical pipes with circular cross section is numerically investigated comparing with the experimental results obtained by our team. Numerical calculations are carried out for two helical circular pipes having different pitches and the same nondimensional curvature δ (=0.1) over a wide range of the Reynolds number from 3000 to 21,000 for torsion parameter β (=torsion /2δ = 0.02 and 0.45). We numerically obtained the secondary flow, the axial flow and the intensity of the turbulent kinetic energy by use of three turbulence models incorporated in OpenFOAM. We found that the change to fully developed turbulence is identified by comparing experimental data with the results of numerical simulations using turbulence models. We also found that renormalization group (RNG) k−ε turbulence model can predict excellently the fully developed turbulent flow with comparison to the experimental data. It is found that the momentum transfer due to turbulence dominates the secondary flow pattern of the turbulent helical pipe flow. It is interesting that torsion effect is more remarkable for turbulent flows than laminar flows.