Helical Coiled Tube Research Articles

Experimental and theoretical study on liquid film thickness of upward annular flow in helically coiled tubes

The liquid film thickness is crucial for studying the thermal hydraulic mechanism of the annular flow region in helically coiled tubes (HCTs). This paper introduces a refined experimental study on the liquid film thickness of annular flow in HCTs, utilizing a newly developed liquid film sensor. The experimental results indicate that the smaller coil diameters and pitches result in thinner average liquid film thicknesses. The average liquid film thickness decreases with increasing superficial gas velocity and decreasing superficial liquid velocity. However, the liquid film thickness at different circumferential positions on the cross-section of the tube exhibits varying sensitivities to superficial gas and liquid velocities. The experimental data reveal that the existing typical correlation formula for the average liquid film thickness of annular flow in straight tubes does not apply to HCTs. Consequently, a new prediction model is proposed for the average liquid film thickness of the annular flow region in HCTs, based on the modified Froude number, modified Dean number, Ekman number, and Reynolds number. This model comprehensively incorporates the structural characteristics of HCTs and fluid properties, and its validity is verified through the utilization of available and current data in the literature.

Experimental and numerical investigation of the thermal - hydraulic performance of flow inside helical coil elliptic tubes

Helical coil tubes are essential in a variety of engineering applications due to their improved heat transfer and compact shape. The current study presents an experimental and numerical investigation of geometrical optimization for helical coil elliptic tubes. Four distinct coil pitch values are examined with a constant perimeter for all geometries and three aspect ratio values (1, 0.75, 0.5) utilizing water as the working fluid across varying the volume flow rates. The helical coil has the same surface area as the tube for each coil. The numerical simulation is conducted using the ANSYS FLUENT CFD software (Version 19.2). The experimental and numerical results indicate that the increase in heat transfer due to an increase in mass flow rate is significantly greater than the improvement gained by changing the aspect ratios. Increasing the volume flow rate to 3 L/min significantly improves the average heat transfer coefficient, with a 66.6 % increase found at a maximum coil pitch of 0.08 m and an aspect ratio of 0.5. Furthermore, a helical coil with an aspect ratio of one (circular cross-section) exhibits the best compromise between pressure drop penalty and heat transfer enhancement, resulting in the greatest hydraulic thermal performance parameter.

Hydrothermal behaviour of hybrid nanofluid flow in two types of shell and helical coil tube heat exchangers with a new design. Numerical approach

High-efficiency thermal energy systems are very important in meeting the growing demand for thermal energy. As a result, several heat transfer improvements have been proposed. Some promising methods include flow heat transfer in shell and spiral tube exchangers.In a shell-and-coil heat exchanger, utilizing a meticulously designed coil instead of a basic one significantly boosts heat transfer and overall thermal efficiency. This is due to the enhanced fluid dynamics and increased turbulence facilitated by the advanced coil design, making it ideal for space-constrained applications. Moreover, the helical configuration helps minimize fouling and maintenance, and may also provide self-cleaning benefits. Consequently, helical coils are highly regarded in industrial contexts for their superior performance, maintenance ease, and design adaptability.This study conducts a numerical evaluation of the heat transfer and fluid flow properties of two distinct shell-and-coil heat exchangers with specialized designs. The fluids analyzed include water-based hybrid nanofluids, specifically Water/MgO-TiO2and Ag-HEG/water, with results compared to those obtained using pure water. The investigation spans Reynolds numbers from 500 to 2000 and is divided into two segments.The first segment examines the influence of spiral coil geometry and fluid type on the heat exchanger's endothermic performance, utilizing nanoparticle volume concentrations of φ1 = φ2 = 0.3. In the second segment, the optimal geometric and fluid model is chosen based on the findings from the first part. Following this, the impact of various hybrid nanofluids on thermal performance is assessed, comparing fluids with volume concentrations of φ1 = φ2 = 0.3 to pure water (φ1 = φ2 = 0).The findings reveal that Case [A], featuring a unique geometry with Water/Ag_HEG, achieves the highest thermal performance across all examined Reynolds numbers. At the lowest Reynolds number, the thermal efficiency improvements for Case [A], Case [B], and Case [C] were 137 %, 113 %, and 56 %, respectively, compared to the baseline. Additionally, the second part of the study demonstrates that at the lowest Reynolds number, the thermal efficiencies of Water/MgO-TiO2 and Water/Ag_HEG nanohybrid fluids increased by 76 % and 49 %, respectively.

Effect of air bubble injection on the thermal performance of a vertical helical coiled tube heat exchanger: an experimental study

This study investigates the effect of air bubble injection on the thermal performance of a vertical counter-current coiled tube heat exchanger. A cylindrical PVC shell (height: 500 mm, diameter: 152.4 mm) was constructed to carry a copper coil with 11 regular turns and covered approximately 76% and 75% of the total shell height and diameter, respectively. The key operational parameters involving the shell side flow rate (2–10 L/min), the coil side flow rate (1–2 L/min), the air flow rate (0–10 L/min) and the temperature difference between the hot and cold fluids ((20 °C, 30 °C and 36 °C) were tested to determine the overall heat transfer coefficient (U). Air was injected into the shell side of the heat exchanger as bubbles with an average diameter of approximately 100 μm via a porous sparger. The results showed that air injection significantly enhanced U, with the highest improvement (158%) occurring at an air flow rate of 6 L/min, while the minimum improvement was 34%. Furthermore, the ratio of the overall heat transfer coefficient with air injection to that without air injection had its maximum value at a shell side flow rate of 6 L/min.

Thermo-hydraulic performance of parallel multi-shell and multi-helical coiled tube heat exchanger CFD model with Taguchi-grey relational analysis

This study utilized four distinct shell and helical tube heat exchanger layouts to numerically evaluate the thermal and hydraulic efficiency of each arrangement. The numerical research was conducted using ANSYS FLUENT 2022R1. Currently, there has been no research conducted on the investigation of multiple helical coiled tubes enclosed by multiple shell heat exchangers. This study aimed to optimize various tasks using the Grey Relational Analysis approach in combination with the Taguchi method to maximize thermal efficiency and minimize pressure drop.A parallel configuration was used to connect two to three concentric helical tubes, with each helical tube being enclosed by a shell to control the flow of fluid. The P–P-2M − 36 design, consisting of two helical tubes, has the highest enhancement ratio of Uo = 26.75 %, when compared to the P–P-3M − 36 configuration. Similarly, the P–P-2M − 42 configuration enhances Uo by 38.42 % in comparison to the P–P-3M − 42 configuration. These findings demonstrate that a configuration consisting of two helical tubes exhibits a higher enhancement ratio of Uo compared to a configuration consisting of three helical tubes. The P–P-3M − 36 design, which consists of three helical tubes, exhibits a minimum pressure drop of 39.19 % compared to the P–P-2M − 36 configuration. Similarly, the P–P-3M − 42 configuration reduces pressure drop by 37.76 % compared to the P–P-2M − 42 configuration. The P–P-3M − 36 configuration is designed to simultaneously reduce pressure drop and boost heat transfer rate. The model achieves the optimal values for heat transfer rate and pressure drop at a Reynolds number of 55,000.

Advances in nanofluids for tubular heat exchangers: Thermal performance, environmental effects, economics and outlook

Heat transfer deterioration in thermal systems significantly limits the efficiency and practicality of these systems. This review explores state-of-the-art studies on the use of nanofluids (NFs) in various tubular heat exchangers (HEXs), addressing their influence on overcoming the limitations. It discusses the fundamentals of HEXs and NFs, including design criteria, heat transfer mechanisms and thermal transport properties. This work compiles effective thermal conductivity and viscosity correlations under diverse conditions and evaluates NF performance in reactor, flat and helical coiled tube, twisted tube, U-tube and finned tube-based HEXs. Results revealed substantial improvements in system efficiency, with SiC–MWCNT/water NFs achieving 99.9 % absorbance in solar collectors and Ag–rGO/water and Ag–ZnO/silicon oil NFs enhancing efficiency by 210 % and 240 %, respectively. Water–alumina NFs increased convective heat transfer rates and friction factors in flat tube HEXs by 123.6 % and 210 %, respectively. Helical coil exchangers exhibited a pressure drop of 47.35 % with MWCNT/water NFs and a 69.62 % rise in heat transfer coefficient with polyaniline–water NFs. This review suggests that optimising HEX efficiency depends on the strategic use of NFs and finned-tube designs. It also highlights the significance of selecting suitable source materials for NFs, the corresponding health risks, disposal and waste management. Economic viability depends on using optimal flow parameters, including temperature, concentration of nanoparticles, system compactness and installation and running costs. Finally, this review concludes with insights into existing challenges and prospects in thermohydraulic, environmental and economic aspects, pointing to future developments in engineered fluids and their commercial applications.

Construction of highly stable, monodisperse water-in-water Pickering emulsions with full particle coverage using a composite system of microfluidics and helical coiled tube

Water-in-water (W/W) Pickering emulsions, exhibit considerable potential in the food and pharmaceutical fields owing to their compartmentalization and high biocompatibility. However, constrained by the non-uniform distribution of shear forces during emulsification or the spatial obstruction in polydimethylsiloxane (PDMS) passive microfluidic platform, the existing methods cannot generate monodisperse W/W Pickering emulsions with high particle coverage rate, thereby limiting their applications. Herein, a novel microfluidic system is designed for the preparation of monodisperse and highly particle-covered W/W Pickering emulsions under mild conditions. pH-responsive Polyethylene glycol (PEG)/phosphate aqueous two-phase system (ATPS) is used for the emulsions' preparation. Notably, a coverage rate of 96 ± 3 % is obtained by adjusting the length of the helical coiled tube, as well as the size and contact angle of genipin cross-linked BSA (BSA-GP) particles. Moreover, these W/W Pickering emulsions, with surfaces almost completely covered, can maintain monodisperse (Ncoal = 1.18 ± 0.03) for one day. Furthermore, the results of ranitidine hydrochloride (RH) release demonstrated that the drug release rate of W/W Pickering emulsions in the simulated gastric fluid (SGF) was 10 times faster than that in the neutral solution. We believe that the highly particle-covered monodisperse W/W Pickering emulsions possess great potential applications in bioencapsulation for foods and drug delivery.

Comparison of heat transfer characteristics of a heat exchanger with straight helical tube and a heat exchanger with coiled flow reverser

Vertical shell and coiled tube heat exchangers are an important aspect of numerous industrial processes and are renowned for their high heat transfer efficiency, versatility, compact design, easy manufacturability and maintenance. As a novel technique, a coiled flow reverser was used to enhance the thermal performance of shell and coiled tube heat exchangers. Therefore, the impact of employing a coiled flow reverser on the heat transfer characteristics and pressure drop in a counter-current shell and tube heat exchanger is investigated using both numerical and experimental approaches. The results are compared to a straight helical coiled tube heat exchanger. The numerical simulations were carried out by employing computational fluid dynamics (CFD) techniques, and the SIMPLE scheme was implemented through the second-order upwind discretization method. The laboratory device used for experimentation features a shell with an inner diameter of 15 cm, and the coil pitch and coil diameter of both coiled tubes are set at 3 cm and 12.1 cm, respectively. Results reveal that the overall heat transfer coefficient of the heat exchanger with a coiled flow reverser is 39.5 % to 49.9 % higher than that of the heat exchanger with a straight helical tube. The effectiveness ratio of the heat exchanger with coiled flow reverser to the straight helical tube heat exchanger ranges from 1.254 to 1.379. Optimal results are observed at a cold flow rate of 6 LPM and a hot flow rate of 1 LPM for both heat exchangers. Additionally, the coiled flow reverser enhances heat transfer performance at the cost of increased pressure drop. Numerical results are in good agreement with experimental findings, establishing the reliability of the study.

Experimental study on flow-induced vibration under laminar flow and turbulent flow transition state in helical coiled tube

This study investigates the vibration characteristics induced by single-phase flow at low velocities within helical coiled tube, encompassing laminar and turbulent flow transition regimes. Modal experiments were conducted to ascertain the natural frequencies in the radial and vertical directions within the helical coiled tube. The influence of fluid mass in tube on vibration was considered, revealing the fluid mass has a greater influence on the vibration frequency in the vertical direction. When the coil was filled with water, the radial natural frequency decreased by 0.1 Hz, while the vertical natural frequency decreased by 0.8 Hz.By simplifying the spiral coil into a spring system, the intrinsic causes of the influence of mass on the natural frequency are studied and verified with the experimental data. The results show that the radial natural frequency is only related to the local mass change of the pipe, while the vertical natural frequency is related to the static deformation of the system under the influence of gravity.By conducting single-phase flow induced vibration experiments inside the pipeline, the radial and vertical vibration response characteristics were obtained, and the modal experimental results were analyzed. Findings indicated larger vibration displacements when laminar flow prevailed within the tube, with radial RMS (Root Mean Square) at 10.1 μm and vertical RMS at 14.5 μm. After the transition to turbulent flow, significant reductions in vibration displacements were observed, reducing the radial RMS to 2.3 μm and vertical RMS to 5.5 μm.Based on statistical and frequency-domain analysis methods, the influence mechanism of secondary flow on the vibration of helical coils at low flow rates was revealed, and the importance of friction coupling was clarified. Moreover, this study considered the impact of fluid viscosity on vibration response and experimentally validated the critical role of friction coupling in exciting secondary flows.

Experimental investigation of shell and helical coiled heat exchanger with Al2O3 nano-fluid with wide range of particle concentration

The purpose of this study is to experimentally enhance the heat exchange rate of the shell and helical coil tube heat exchanger by mixing water with aluminum oxide (Al2O3) nanoparticles, as well as to explore the effect of inlet thermal parameters on the performance of the heat exchanger. A test rig was constructed to investigate the influence of particle concentration, and inlet temperatures on the performance of nano-fluid. Parameters such as Nusselt number, pressure drop, performance evaluation criteria (PEC) are considered to rate the performance of the nano-particle with the heat exchanger. In this study a wider range of particle concentration is considered, which varies from 0.0%–0.75%. Experiments with and without nanoparticles are carried out under identical working conditions. By analyzing the experimental data, it was found that nanoparticles significantly improve the coefficient of heat transfer inside the helically coiled tube. From sensitivity analysis, it is obseerved that there is a slight decrease in Nusselt number of the nano-fluid with increase in inlet temperatures of the nano-fluid and the cooling water. Furthermore, it is concluded that an 8.5% increase in PEC value is observed with increase in particle concentration from 0.15% to 0.75%.

Heat transfer analysis of subcooled flow boiling in copper foam helical coiled heat exchanger – A pore-scale numerical study

High performance thermal energy systems are crucial in fulfilling the growing demand of thermal energy. Consequently, numerous heat transfer enhancements have been proposed. Some of the promising methods are boiling flow heat transfer, helical coiled tube and metal foam insert. Although the performance of each strategy has been extensively studied, based on our literature review, the effectiveness of combining these strategies has not been investigated. This missing information may impede further development of efficient heat transfer systems. This study is therefore performed to investigate subcooled flow boiling heat transfer in helical tube with copper foam insert. A high-resolution three-dimensional pore scale model that considers the shape, porosity and pore density of the metal foam is developed and validated against the published experimental results. Using the model, the effect of inlet temperature, mass flux, wall heat flux, porosity, pore density and half-filled metal foam are studied. The results suggest that operating parameters have mild effects on the heat transfer performance. In contrast, porosity and pore density show significant influence in heat transfer coefficient and pressure drop. It has also been found that total heat transfer surface area and base area are better in characterizing heat transfer in pore-scale level than porosity and pore density at pore-scale level. Moreover, implementing metal foam at outer half of the tube is observed to offer slightly better heat transfer than implementing it at the inner side by around 4.8%. Overall, this study indicates that helical metal foam tubes offer the best performance at mass flux of 200 kg/m2∙s with performance index of 0.72, while straight tubes with 0.90 porosity has the highest performance index of 0.66. Empirical correlations to relate dimensionless parameters to the Nusselt number and friction factor is generated. Finally, the model developed in this study can serve to provide guidelines for the upcoming studies in boiling in metal foam structure and assist in designing metal foam heat exchangers.

Thermo-hydraulic performance of metal oxide nanofluid flow through the helical coil tube of a three-fluid heat exchanger: an experimental and optimization study

ABSTRACT The thermo-hydraulic performance of a three-fluid heat exchanger (TFHE) to concurrently transfer heat from a heated nanofluid to ordinary water and air is the subject of investigation in this paper. The fluid flow and heat transfer abilities of the TFHE concerning changes in nanofluid (Al2O3-water, CuO-water, Fe2O3-water) are used to quantify effectiveness and pressure drop. Parametric studies having nanofluid volume fraction (1%, 5%, and 10%), flow rate (100LPH, 150LPH, and 200LPH), and inlet temperature (80°C, 120°C, and 160°C) respectively are considered in the present experimentation. The results of the experiment demonstrate that the use of CuO-water nanofluid at an intake temperature of 160°C and 5% volume percentage led to a considerable improvement in heat transfer effectiveness, with a maximum value of 0.884. At a flow rate of 100 LPH, a volume percentage of 1%, and an inlet temperature of 160°C, the Al2O3-water nanofluid exhibits the least amount of pressure loss. Nine test runs with four control factors are conducted using Taguchi’s experiment design. From Taguchi analysis, it is observed that the nanofluid volume flow rate and nanofluid inlet temperature have the largest and lowest contributions of 68.83%, 3.76%, and 72.05%, 2.03% respectively on heat transfer effectiveness and pressure drop of the TFHE. A multi-response optimization is carried out using the Taguchi-Gray Analysis to determine the least pressure drop and the highest possible heat transfer effectiveness. At 1% volume fraction, 100 LPH volume flow rate, and 160°C intake temperature, Al2O3-water nanofluids show an increase in the total performance of the TFHE of 10.39%.

Experimental investigation of three fluid heat exchangers using roughness on the outer surface of a helical coil

AbstractThe aim of this study is to utilize waste thermal energy from industries into useful heat for water and air heating. In this paper, the thermal modeling and performance of three fluid heat exchangers (TFHE) have been experimentally investigated. The TFHE considered here is an enhanced version of the double‐pipe heat exchanger. A novel TFHE having fin (1 mm thin copper wire of 10 mm pitch) acts as a roughness element, which is wrapped on the helical coil's outer surface for increasing heat transfer (HT) rate and the turbulence effect for normal water, and this outer surface finned helical coil is inserted between two concentric straight tubes. The innermost tube carries atmospheric air, the finned helical coil tube carries waste hot fluid while normal water flows in the inner annulus of the outermost tube. The coiled‐side Reynolds number is varied in the range of 7000–30,000, while the curvature ratio of 0.1315, pitch‐to‐inside diameter ratio of 2.88 and wire‐to‐tube diameter of the helical tube is kept constant. A counterflow arrangement has been made for experimentation. Nusselt number is calculated using the traditional Wilson plot method that is compared and validated with results available in the literature. The overall HT coefficient is found to increase by increasing the volume flow rate of fluids, while effectiveness decreases or increases depending on residence time and capacity ratio. The percentage increment in the Nusselt number, maximum friction factor, overall HT coefficient between waste hot fluid to normal water, effectiveness is found to be 21.10%–23.88%, 90.91%, 3.40%–29.45%, 3.40%–25.33%, respectively, for the coil side. TFHE is thus proposed for heating water and space simultaneously.

INVESTIGATING THE IMPACT OF USING MAGNETIC-TYPE NANOFLUID ON THE THERMAL PERFORMANCE OF A SOLAR WATER COLLECTOR WITH HELICALLY COILED TUBE ABSORBER

In recent years, solar water collectors are commonly preferred for supplying heated water to be utilized in various processes. In the present study, a solar water collector equipped with a helically coiled absorbing surface has been manufactured and experimented under various working conditions to determine its general behavior. The main goal of using a helically coiled absorber is enhancing energy harvest in the collector by ensuring vertical angle between the absorbing area and incident radiation. In addition, for providing greater increase in thermal efficiency, magnetic type nanofluid has been used as a working fluid. In this context, NiFe<sub>2</sub>O<sub>4</sub> nano-sized particles have been mixed with water at the ratio of 2% (wt./wt.). Accordingly, the performance of the collector has been empirically examined using both water and magnetic nanofluid at two different flow rates. The overall results of the present survey exhibited successful use of magnetic type nanofluid in a solar collector equipped with a helically coiled absorbing surface. Utilizing magnetic nanofluid in the collector as circulating fluid raised the thermal efficiency on an average of 20.29% and 23.59% at volumetric flow rates of 0.5 lpm, and 0.9 lpm, respectively. Moreover, utilizing NiFe<sub>2</sub>O<sub>4</sub>/water nanofluid in the water collector enhanced the exergy efficiency on an average of 44.53% and 40.04% at volumetric flow rates of 0.5 lpm and 0.9 lpm, respectively.

Numerical Simulation of Helical Coil Tube in Tube Heat Exchangers with Grooved Internal Tube

Abstract: The goal of this work is to analyse the heat transfer effects of providing inner tube with formed groove in helical coil tube in tube HE. In order to investigate further heat transmission improvements, the groove depth was increased to find the comparative study of Nusselt number in different cases analysed in this work. This was performed by use of Ansys CFD Fluent Software package by configuring and employing a compact 3-D model of a real and complex system to solve for the case studies in this research. The context for the topic is discussed, as well as explanation of process breakthroughs in CFD analysis. In order to improve the computational fluid dynamics simulations, information on proper mesh selection and geometry was generated with respect to theoretical concerns and finite CFD practises of element size, nodes, and shape appropriateness. The hot fluid flows through the annulus region and the cold fluid flows through the inner tube in the examined model with counterflow setup. After simulating fluid flow and performing a heat transfer study for a helical coil tube in tube HE with structural configuration as mentioned, post processing techniques is applied to produce the results as furnished by means of graphical representation. Moreover, upon discussion on the impact of variation of Nusselt number and friction factor were established, the analysed results create recommendations with the purpose of better understanding the impact of helical coil grooved tube heat transfer capacity in tube heat exchangers and future research. As a result, grooved inner tube treatment can significantly improve heat exchanger total heat transfer capacity, and the findings of this research can provide assistance theoretically for the development and design of helically coiled tubes in HEs.

Single-phase heat transfer prediction in helical coiled tubes in turbulent regime

The accurate estimation of thermal–hydraulic parameters is crucial for the design of Small Modular Reactor steam generators, particularly in the case of complex geometries such as helical coiled tubes (HCTs). Reliable design tools are therefore essential for successful design. In this study, we compiled a database of 706 experiments to evaluate the predictive performance of commonly used correlations for heat transfer estimation in turbulent regime HCTs. Despite ranking the correlations according to their predictive performance, none of the existing correlations were able to accurately predict the broad range of experimental data. Therefore, a new correlation called FAMA was derived, which is simple to use, robust and significantly more accurate than any other correlation. Based on the Colburn Analogy, the FAMA correlation achieved a mean absolute difference of 6.21% compared to the experimental database, which represents a 25.7% improvement over the best existing correlation. Furthermore, the FAMA correlation exhibits good asymptotic behavior in straight tubes and is recommended for single-phase flow in HCTs for turbulent Reynolds numbers up to 135,000, curvatures from 0.00963 to 0.2035, and torsions up to 0.81. The Schmidt́s criterion is adopted for determining the critical Reynolds number. Due to its superior performance and wide range of applicability, the FAMA correlation is recommended for modeling and studying helically coiled steam generators as found in novel integral reactors.

Intensification of the rate of heat and mass transfer at the wall of a stirred tank reactor by integrating a helical coil turbulence promoter with the tank wall

ABSTRACT The influence of a helical coil turbulence promoter on liquid-solid mass transfer rates in a stirred tank was investigated using a technique that involved measuring the rate of diffusion-controlled copper dissolution in acidified dichromate. The study examined the effects of helical coil tube diameter (d), helical coil pitch (p), impeller rotation speed, impeller geometry (axial and radial), the presence of baffles, and solution physical properties. The presence of the helical coil near the reactor wall significantly enhanced mass transfer rates, with a factor ranging from 1.01 to 2.48. This improvement was accompanied by a corresponding increase in the volumetric mass transfer coefficient (kA), ranging from 2.68 to 4.55, depending on operating conditions. Further analysis revealed that the average mass transfer coefficient increased with decreasing coil tube diameter, while coil pitch had a minimal impact. Additionally, radial flow turbines demonstrated superior mass transfer performance compared to axial flow turbines. The presence of baffles also promoted higher mass transfer rates compared to unbaffled reactors. The experimental data were successfully correlated using dimensionless correlations, emphasizing the significance of these correlations in scaleup and design optimization of catalytic stirred tank reactors with efficient cooling systems.

Dean number only can not determine characteristics of fluid flow and heat transfer in helically coiled tubes with large curvature

The majority of reported findings indicate that the fluid flow and heat transfer characteristics within helically coiled tubes (HCTs) with small curvature can be determined solely by Dean number. Due to a scarcity of published investigations pertaining to HCTs with large curvature, the extent to which Dean number can ascertain the attributes of HCTs with large curvature remains uncertain. However, the advancement of technology has enabled the production and utilization of HCTs with large curvature. Consequently, there is a significant demand for understanding the fluid flow and heat transfer characteristics of HCTs with large curvature. The present study employs a numerical approach to investigate the characteristics of laminar fluid flow and heat transfer in HCTs with large curvature, where the ratio of coil radius to tube radius (D/d) is less than 5. The findings indicate that the fluid flow and heat transfer characteristics in HCTs cannot be solely determined by Dean number. In addition to the (D/d)0.5 included in Dean number, the fluid flow friction factor is also influenced by (D/d)−0.1902. When considering uniform wall temperature boundary, Nusselt number is mainly determined by Dean number. However, for uniform wall heat flux boundary, Nusselt number is additionally influenced by (D/d)0.1222.

Optimized shape design and thermal characteristics investigation of helically coiled tube type heat exchanger

The effects of the helical coil tube designs on heat transfer characteristics during heating process were conducted by some researchers and confirmed that the conventional helical coil tube was not the ideal shape for important heat transfer. Despite this, there was no published paper that presented the optimal helical coil structure for important heat transfer. Therefore, this work addresses the influence of different helical coil structure designs on heat transfer characteristics and temperature distribution during heating process. The study was performed for three configurations named constant-diameter coil, variable-diameter coil and variable-pitch coil. Based on CFD simulation, the mathematical model was validated with experimental results and show good agreement. The results suggest that the helical coil with variable-pitch gives the best heat transfer performance compared with other helical coil structure. Among all considered designs, the combined properties of the helical coil with variable-pitch were better than that of other helical coil structures. As a result, this work could provide a shortcut method in the selection of the appropriate helical coil immersed or wrapped on the tank which need the high heat transfer.

Impact of Coil Curvature, Pitch, and Orientation on Vapor Hydrodynamics over Helically Coiled Tubes during Saturated Pool Boiling near Critical Pressure

Impact of Coil Curvature, Pitch, and Orientation on Vapor Hydrodynamics over Helically Coiled Tubes during Saturated Pool Boiling near Critical Pressure