Coiled Tube Research Articles

Detached-eddy simulation of the flow behavior in the shell-side of the coil tube bundle in turbulent flow

The coil tube bundle of Coil-wound heat exchanger (CWHE) is densely arranged, resulting in a complex flow domain in the shell. And Flow-induced vibration (FIV) is a common phenomenon in working situations where coil tubes are submerged in the oncoming flow. Understanding the flow and FIV characteristics of the shell-side plays a significant key in engineering issues, such as the design of coil tube bundle arrangements and safety verification of heat exchangers. This paper presented a detailed investigation of flow in the shell-side of the three-layer coil tube bundle with Detached eddy simulation (DES), whose validity was verified by comparison with the experimental results. Eight calculated cases of inlet flow rates from 0.01 m3/s to 0.15 m3/s with an interval of 0.02 m3/s were set up to determine that the flow domain of the shell-side is turbulent. The flow was found to form flow channels between adjacent layers, while variable eddy currents appeared around coil tubes. Subsequently, the gap transverse flow velocity was predicted and the calculation correlation was proposed. Furthermore, spectral and wavelet analyses were carried out to investigate the time-frequency data of fluctuating velocities in the flow, to bring to light vortex shedding frequencies and to capture St with respect to this tube bundle arrangement.

Assessing the performance of foams stabilized by anionic/nonionic surfactant mixture under high temperature and pressure conditions

Foam flooding is an effective tertiary recovery method for oil and gas reservoirs. However, foam performance is very sensitive to the reservoir temperature and pressure. In this study, the formation and collapse of a water-based foam stabilized by a mixed ionic and nonionic surfactant system under typical reservoir conditions (up to 150 °C and 50 MPa) were investigated. A multifunctional foam analyzer, an interfacial rheometer, and a coiled tube are used to assess foam microstructure, surface tension and bulk viscosity under 25 – 80 °C and 0.1 – 10 MPa. Results show that the foam comprehensive value is highest under low temperature and high pressure. With increasing temperature, the gas bubbles become larger, fewer in number, and more irregular in shape coupled with a thinner liquid film. Increased pressure, on the other hand, decreases the bubble size, increases the number of bubbles and contributes to a more uniform and dense foam. At constant temperature, the surface tension decreases as the pressure increases, while at constant pressure, a minimum surface tension is observed with increasing temperature, which in turn increased with increasing pressure. Foam viscosity displayed an opposite trend to that of the surface tension. Understanding the variation of foam properties with temperature and pressure is key toward successful application of foam flooding.

Study on thermal performance improvement technology of latent heat thermal energy storage for building heating

Thermal energy storage technology incorporating phase change materials (PCM) is a feasible option to take advantage of off-peak electricity tariff for achieving the function of “peak load shaving” and energy efficiency economically in electric heating systems. However, the low thermal conductivity of phase change materials in these systems limits its application. In this work, a design of non-uniformly distributed fin configuration was proposed, considering the optimization of the non-uniform arrangement and coil structure to enhance heat transfer. A two-dimensional CFD model has been developed and validated with test data. The coil inner diameter, tube pitch, row spacing and fin height were optimized based on the simulated temperature variations and visualizations of the PCM during charging and discharging processes. Results demonstrated that the mass of fully melted PCM is increased by 24.5%, and the outlet water temperature is about 3℃ higher for the optimal non-uniform finned coil structure. Additionally, the influence of the device overall dimensions on the PCM utilization rate is also demonstrated in this study. After optimization, the heat energy discharged-charged ratio can be increased by 39.6% to achieve a better thermal energy discharging efficiency. The results may provide valuable references for appropriate latent thermal energy storage design solutions in practice.

Flow-Induced Vibration and Heat Transfer Analysis for a Novel Hollow Heat Exchanger

A novel hollow shell-and-tube heat exchanger with helical elastic coiled tubes was designed to improve the overall heat transfer performance. Different numbers of helical baffles installed on the hollow helical elastic tubes (HHETs) heat exchanger were compared with the HHET heat exchanger without a baffle. The fluid–solid coupling method was provided to study the effects of the entrance velocity and baffle number on the performances of heat transfer and vibration-enhanced heat transfer. Based on the numerical results, the performances of vibration and heat transfer become more obvious by increasing the entrance velocity. Compared with the HHET heat exchanger without a baffle, adding a baffle or baffles on the HHET heat exchanger can remarkably make the fluid flow more consistent. Whereas a higher number of baffles can weaken the vibration and heat transfer performance of the novel heat exchange, the performance evaluation criteria of the HHET heat exchanger with one baffle, two baffles, and four baffles is improved by 2.04, 4.37, and 2.3%, respectively. It indicates that adding a baffle or baffles to the novel heat exchanger can effectively improve the overall thermal and hydraulic characteristics of the novel heat exchanger.

Forecasting of saturated boiling heat transfer inside smooth helically coiled tubes using conventional and machine learning techniques

This study concerns to model the flow boiling heat transfer coefficient (HTC) in smooth helically coiled tubes. A dataset including 1035 samples was collected from 13 independent studies, enveloping a broad range of geometrical and operating conditions. The predictive capability of the earlier models was assessed for straight and coiled tubes by the analyzed database that they were not precise enough. Accordingly, a new empirical model based on the least square fitting method (LSFM) was constructed using seven input effective dimensionless factors. It was found that LSFM was not able to describe the complex and nonlinear nature of HTC in smooth helically coiled tubes. Furthermore, the intelligent method of genetic programming (GP) was utilized to obtain more accurate explicit correlation for HTC, which produced an acceptable average absolute relative error (AARE) of 17.35%. Finally, the machine learning approaches of multilayer perceptron (MLP), Gaussian process regression (GPR), radial basis function (RBF) was also implemented to model HTC in smooth coiled tubes. Although all intelligent based models provided excellent results, the GPR model outperformed the others with an average absolute relative error (AARE) of 5.93% for the tested dataset. In addition to the proposed models’ performance, the most influential factors in controlling the boiling HTC in coiled tubes were also detected.

Investigation of heat transfer Exergy loss number and its application in optimization for the shell and helically coiled tube heat exchanger

In this study, the Exergy analysis of the shell and helically coiled tube heat exchanger (SHCTHX) were investigated. The heat transfer Exergy loss of the SHCTHX implemented by MATLAB software was developed, where the dimensionless number named heat transfer Exergy loss number (ξHT) was proposed. The effect of parameters (core tube diameter (DC), space between the shell and the core tube (ΔDBC), inner diameter of coiled tube (di), thickness of the coiled tube (dt) and mass flow rate (Mshell)) on the effectiveness (ε), heat transfer Exergy loss number (ξHT) and number of transfer unit (NTU) were investigated. Moreover, the optimization of the SHCTHX was studied. When the design parameters are set as DC, ΔDBC, di, and dt, there is coincidently opposite variation trend for ξHT and ε, the optimization results of which are identical. When the design parameters are set as DC, ΔDBC, di, dt and Mshell, the effectiveness (ε) of optimization results with ξHT is 30% larger than that without ξHT; while the heat transfer area, the overall heat transfer coefficient, the needed mass flow rate and the heat transfer irreversible loss of optimization results with ξHT have reduction of 30%, 15%, 30% and 10% than those without ξHT.

Simulation of Shell and Helical Coil Heat Exchanger for Hot and Cold Fluid Flowing Fe2O3 Nanofluid with Water as Its Base by Using CFD

Abstract: Shell and Helical coils are eminent coiled tubes which have been used in diversity of solicitations e.g. heat recovery, air-conditioning and preservation schemes, chemical reactors and dairy practices. Shell and Helical coil heat exchanger is the recent improvement of heat exchangers, to accomplish the industrial demand. A shell and helical coil are necessary for various heat exchangers, nuclear reactors and in chemical engineering, for of large quantity of heat is conveying in a slight space with high heat transmission rates and slight habitation time distributions even it suffers through a disadvantage of larger pressure drop. The unbiased of this work is to cheered the pressure drop inside a shell and helical coil heat exchanger, heat transfer progression can be improved by increasing secondary flow inside the coil and this can be allow by appropriate blending of the fluid inside the helical coil. For this, my planned work on CFD to scrutinize the helical coil by using ANSYS 15. A 3D design of CAD model of helical coil of tube outer diameter (do) 16 mm, inner diameter of helical coil (di) 12 mm, pitch of 26.3mm, pitch coil dia. 86 mm, tube length of 235 mm, shell diameter is 110 mm and shell length is 215 mm, is generated by using ANSYS fluent 15.

Secondary Flow Effect on Supercritical Kerosene Oxidation Deposition and Heat Transfer in a Coiled Tube.

Deposition in fuel cooling systems remains a challenge to the development of active cooling technologies for air-breathing engines. We experimentally and numerically investigated the influence of the secondary flow and heat-transfer characteristics of supercritical kerosene in a coiled tube on oxidation deposition. A coiled heated tube reactor (3000 mm long, 23 cycles) under constant heat flux and flow rate was applied to simulate the conditions of the fuel side in the heat exchanger of an aero-engine cooling system. The coupling characteristics of coking distribution with the development of secondary flow were studied along the whole pipe. The dynamic pressure, temperature, and velocity were analyzed in two specific circular cross sections located in the bend of the tube. The secondary flows induced in the coiled tube greatly enhance the heat transfer and slightly decrease the deposition rate, resulting in linear wall temperature profiles and a uniform coking distribution along the tube compared to the long straight tube. There is no obvious heat-transfer enhancement or deterioration in the whole coiled tube. The modified heat-transfer correlation of the supercritical RP-3 in the coiled tube was fitted at different flow rates and heat fluxes with an error of ±10%.

A new microsporidian parasite, Microsporidium theragrae n. sp., infecting Alaska pollock Gadus chalcogrammus (Teleostei: Gadidae).

A new microsporidian infecting Gadus chalcogrammus Pallas, 1814 (Gadidae), is described based on morphological, ultrastructural, and molecular studies. This microsporidian parasite develops inside intramuscular spindle-shaped lesions measuring approximately 1-2mm in width and 4-8mm in length. Infected cells encapsulated by a host-produced wall containing a sponge-like acellular zone. Sporogony presumably proceeds via segmentation of sporogonial plasmodium, resulting in a variable number of spores. Sporogonial stages develop in sporophorous vesicles (SVs), abutting a moderately electron-dense thick walled coat of a homogeneous amorphous material. SVs space contains rare granular and tubular inclusions. Neighboring SVs often interconnected by bridges of the host cell cytoplasm that were limited by membrane comparable with SV coat. The elongate-ovoid spores, measuring 4.29 ± 0.38 × 2.51 ± 0.26μm (N 104), possess a bipartite polaroplast and polar tube with 15-16 coils arranged in 2-3 layers. The angle of tilt of the polar tube coils is less than 30°. The sequence analysis of SSU rDNA coding region showed that the studied microsporidians differs from other fish muscle-infecting species at least in 17bp (2.58%) and is closely related to Microsporidium cypselurus Yokoyama et al. (2002) infecting the flying fish from East China Sea. The parasite is provisionally positioned as Microsporidium theragrae sp. n.

Investigation in the Natural Frequency of Wound Tube for Coil-Wound Heat Exchanger

Abstract Wound tube, which is an important component of coil-wound heat exchanger (CWHE), is subjected to cross-flow impacting and thereby vibrating. Owing to investigating flow-induced vibration (FIV) of wound tubes, it is essential to study the vibration characteristics of the tubes. In this paper, the natural vibration characteristics of wound tube, which was divided into curved tube and coil tube based on support conditions, were studied in detail. And experiments, numerical simulations, and calculation methods were carried out. First, the structures of the two tubes were described parametrically. Afterwards, vibration experiments proved the reliability of numerical simulations of the tubes. Furthermore, calculation methods for the fundamental frequencies of the two tubes were proposed, the accuracies of which were further proven by comparison with simulation results. In addition, the first three mode shapes of the curved tube and coil tube were bending vibration modes. Then the influence of structural parameters on the fundamental frequency was discussed and the independence of parameters was demonstrated. The effects of the variables of the layer pitch ratio, a, the same layer pitch ratio, b, and helix angle, α, on the added mass coefficient, Cm, were ultimately investigated. In general, this paper provides a technical basis to evaluate the design and machining for design and supervision staff.

Determination of friction factor and heat transfer rate in laminar flow in an agitated vessel

Helical coils are commonly employed in a variety of process industries due to their superior fluid mixing capabilities, the flexibility of fabrication, and simple design. Frictional pressure losses occur in flow-through helically coiled tubes, affecting the heat transfer rate across the coils. An inquiry is carried out in the current experimental study to discover friction factors and heat transfer rates within the coil tubes of test fluids flowing in the laminar flow area. Non-Newtonian test fluids comprised ichorous solutions of Carboxy Methyl Cellulose (CMC) at concentrations of 0.5 percent, 1 percent, and 2 percent, whereas Newtonian test fluids consisted of water. With the use of an appropriate viscosity expression, Newtonian consonances are demonstrated to apply to several non-Newtonian fluids with certain constraints. In a laminar flow, the shear stress in a helical coil is greater than in a straight conduit. It has been proved that the experimental data can be fruitfully correlated across a broad extent of fluid data and coil radius stretch. The investigated data obtained has been correlated with Standard a deviation of 15.6% with the range 25<D_e < 2000 and 40<P_r < 226.

Anastomotic Leak Rate and Prolonged Postoperative Paralytic Ileus in Patients Undergoing Laparoscopic Surgery for Colo-Rectal Cancer After Placement of No-Coil Endoanal Tube.

Colorectal cancer (CRC) is the second most common gastrointestinal tumor in men and the third in women. Left-hemicolectomy (LC) and low anterior resection (LAR) are considered the gold standard curative treatment. In this retrospective study, we evaluated the presence or absence of post-operative complications, in all patients who underwent Video-laparoscopic (VLS) LAR/LC with No Coil trans-anal tube positioning, and compared the data with the current literature on the topic. Thirty-nine patients diagnosed with CRC of the descending colon, splenic flexure, sigma, and rectum were recruited. LC was performed for sigmoid and descending colon cancers, while LAR was applied for tumors of the upper two-thirds of the rectum. The No Coil trans-anal tube (SapiMed Spa, Alessandria, Italy) was placed in all patients of the study at the end of surgical treatment. Eighteen patients received a LAR-VLS (46%) and 21 patients received a LC-VLS (54%). The average length of hospital stay after surgery was 7days. PPOI occurred in only one in 39 patients (2.6%) who had undergone LAR-VLS. As for complications, in no patient of the study did AL (0%) occur. In patients undergoing LAR-VLS and LC-VLS, we performed colorectal anastomosis and in the same surgical operation we introduced the No-Coil device. Although this is a preliminary study and subject to further investigation, we believe that the No Coil tube positioning may reduce the time of presence of first flatus and feces and the risk of AL.

Numerical analysis on heat transfer enhancement of Al2O3 nanofluid in the flattened conically coiled tubes

AbstractEnhancement in the heat transfer of the working fluid flowing inside the tube is achieved by modification of tubes and changing the direction of fluid flow. For this purpose, the straight tube can be changed into a conical coil tube, thereby, heat transfer is increased due to the centrifugal effect caused by the curvature of the tube. Furthermore, the circular cross‐section of the tube is modified into an oblong shape for more heat transfer enhancement. In this study, the numerical heat transfer and pressure drop characteristics of Al2O3–water nanofluids in the flattened conically coiled tube are studied. The effect of the aspect ratio, cone angle, coil pitch, and solid volume fraction of nanofluids on heat transfer and pressure drop are examined. It is found that the heat transfer coefficient and pressure drop increase with the rise of aspect ratio, Reynolds number, and solid volume fraction of nanofluid, while it decreases with the increment of cone angles and coil pitches of conical coil tube. Furthermore, the effect of aspect ratio on the heat transfer enhancement factor, pressure drop ratio, and thermal performance index for Al2O3–water nanofluid are presented.

Entropy optimization of an additively manufactured heat exchanger with a dual stage Gifford-McMahon cryogenic refrigerator for hydrogen liquefaction

Small-scale hydrogen liquefaction has emerged as an approach to fuel small aircraft powered by fuel cells. However, limited research on the design and optimization of small-scale hydrogen liquefiers, specifically the heat exchangers, is available. This paper describes a minimum entropy design for a heat exchanger mounted on a dual stage Gifford-McMahon cryogenic refrigerator. To minimize entropy generation the heat exchanger utilizes a bifurcating flow structure with varying wall thickness. Numerical optimization indicates that the heat exchanger will generate half of the entropy of a single coiled tube, significantly reducing the required heat exchanger length by 91.4% and the thermal mass by 43.8%. The heat exchanger was 3D printed with an aluminum alloy and the interior coated with a ruthenium-based catalyst for ortho-parahydrogen conversion. Hydrogen entering the heat exchanger near 293 K and 653 kPa is cooled to 28.1 K and full ortho-parahydrogen conversion is assumed before entering the storage dewar. The resulting experimental tests indicate a potential to increase heat exchanger efficiency in a more compact form factor, as well as a promising future for additively manufactured components in cryogenics.

Vibration-Enhanced Heat Transfer of Helical Tube with Different Number of Tubes

Based on a two-way fluid/solid coupling model, the heat transfer enhancement mechanism of a helical elastic coiled tube (HECT) by fluid-induced vibration (FIV) was numerically studied. The field synergy principle was used to compare and analyze the shell-side convective heat transfer of the HECT. The field synergy angle, Nusselt number, and comprehensive enhanced heat transfer performance were quantitatively studied from the overall and local perspectives. The influences of the Reynolds number and the number of tubes on heat transfer performance and vibration-enhanced heat transfer performance were analyzed. Numerical results show that the field synergy level and the oscillation relative velocity near the tube are two important factors for fluid-induced tube vibration to enhance heat transfer. The average Nusselt number of coiled tubes decreases when the number of tubes increases and increases when the Reynolds number increases. The comprehensive heat transfer enhancement capability of the heat exchanger with different numbers of tubes of 2, 4, and 8 gradually decreases as the number of tubes increases, and the average performance evaluation criteria of the heat exchanger are 1.043, 1.023, and 1.004, respectively, for the three typical cases. The tubes on the upper and lower sides have a better heat transfer enhancement effect by the FIV.

Closed-loop aluminium oxide nanofluid cooled photovoltaic thermal collector energy and exergy analysis, an experimental study

PV/T collector cooling was studied experimentally regarding the energy and exergy analysis by Al2O3 nanofluid circulation which is in two different flow patterns. A 20 W polycrystalline PV module was used as a comparison module. Identical PV modules were used for the construction of PV/T collectors, too. PV/T-A collector model was created with the PV module, a copper coil tube was the nanofluid circulated was placed to the backside of it. A PV/T-B collector was made up by placing the Al2O3 nanofluid circulating polyamide channel structure on the backside of the PV module. A 50 W monocrystalline PV module was used to supply power to the circulation pump and heat exchanger fans to provide energy independence from mains electricity. PV/T-A and PV/T-B collectors exposed to 792.83 W/m2 solar radiation equivalent 121.3 W solar power were cooled 28.94% and 48.54% better regarding the PV module. Electrical power outputs are 5.8 W, 8.13 W, 10.34 W for the PV module, PV/T-A, and PV/T-B collectors. Electrical gaining from the PV/T-A and PV/T-B collectors increased 40.17% and 78.27% by cooling. Thermal gaining from PV/T-A and PV/T-B collectors are 42.8 W and 53.39 W. First and second law efficiencies were determined as 4.78%, 42%, 52.52%, and 5.01%, 7.35%, and 9.42% for PV module, PV/T-A, and PV/T-B collectors. Enhancement in solar utilization with PV/T-A and PV/T-B collectors are 45.13 W, and 57.93 W and proportionate equivalents to 37.2% and 47.75%. Enviro-economics size was estimated as 0.094 tCO2/year, and 0.121 tCO2/year carbon reduction and equivalent 1.41$ and 1.81$ carbon trade value.

Numerical investigation of grooves effects on the thermal performance of helically grooved shell and coil tube heat exchanger

Heat exchangers are integral parts of important industrial units such as petrochemicals, medicine and power plants. Due to the importance of systems energy consumption, different modifications have been applied on heat exchangers in terms of size and structure. In this study, a novel heat exchanger with helically grooved annulus shell and helically coiled tube was investigated by numerical simulation. Helically grooves with the same pitch of the helical coil tube and different depth are created on the inner and outer wall of annulus shell to improve the thermal performance of heat exchanger. In the first section, thermal performance of the shell and coil heat exchanger with the helical grooves on its outer shell wall was compared with same but without helical grooves. At the second section, helically grooves created on both outer and inner wall of the annulus shell with different groove depths. The results showed that the heat exchanger with grooves on both inner and outer shell wall has better thermal performance up to 20% compared to the heat exchanger with grooves on only outer shell wall. The highest thermal performance achieves at lower flow rates and higher groove depths whereas the pressure drop did not increase significantly.

Fill dynamics and sample mixing in the AirCore

Abstract. The AirCore is a long coiled tube that acts as a “tape recorder” of the composition of air as it is slowly filled or flushed. When launched by balloon with one end of the tube open and the other closed, the initial fill air flows out during ascent as the outside air pressure drops. During descent atmospheric air flows back in. I describe how we can associate the position of an air parcel in the tube with the altitude it came from by modeling the dynamics of the fill process. The conditions that need to be satisfied for the model to be accurate are derived. The extent of the mixing of air parcels that enter at different times is calculated so that we know how many independent samples are in the tube upon landing and later when the AirCore is analyzed.

Dehydration of gas-phase benzyl amine alcohols studied at atmospheric pressure

Gas-phase ion chemistry is a useful approach for the investigation of physical organic chemistry and the study of reactivity, structure, and thermochemical properties of ionic and neutral organic substrates. Herein, one-step dehydration of gas-phase benzyl amine alcohols to give benzazetidines was discovered without the use of catalysts. Mechanistic investigations of the gas-phase dehydration reactions were explored to study the possible influence of charged microdroplet acceleration during electrospray ionization (ESI) and collisions occurring during ion transfer through the atmospheric pressure interface (API) of the mass spectrometer. The product ion distribution was observed to be less sensitive to droplet effects (spray distance and voltage), and temperature of transfer capillary in the API. However, the product ion distribution exhibit high sensitivity to different S-lens radio frequency (RF) voltage of the API, providing evidence that the dehydration reaction is driven by collisions during ion transfer in the API. With this insight, we developed atmospheric pressure thermal dissociation platform that allowed thermal-induced collisions outside of the mass spectrometer when the benzyl amine alcohols are carried through a heated coiled tube. Up to 98% dissociation efficiency was achieved with the coiled tube heated to a temperature of 200 °C, yielding only the desired benzazetidine product. By performing the atmospheric pressure thermal dissociation experiment outside of the mass spectrometer, we believe it will be straightforward to collect the dehydration product.

Effect of Using A Double Coil Tube with Modified Pitch on The Overall Heat Transfer Rate

The goal of this work was to design a simple and cost-effective technique for improving the performance of heat exchangers, and the emphasis was on the experimental side while not neglecting the necessity of validating our findings with theoretical results using CFD. A new method was used to enhance the heat transfer inside the heat exchanger by using a coil with modified steps, as the published papers did not previously address this method, which proved its effectiveness. For varied coil pitches, the numerical findings were in good agreement with the experimentally obtained results, with an error rate of less than 8%. To compare results and confirm effective correlation between pitch changes, a double coil tube is manufactured with a fixed pitch and a double coil tube with modified pitches, while maintaining the basic design parameters of tube diameter ( ), shell diameter ( ), height of shell ( ), and coil height ( ) in order to try to increase the overall heat transfer coefficient and heat transfer. This new design enhanced heat transfer and total heat transfer coefficient at Reynolds number (400< <2000), with a 22% improvement in overall heat transfer coefficient. The new design of the coil (modified pitch) also gave an improvement in the flow distribution, which generated a higher secondary flow than the traditional pitch coil.