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AbstractCFD simulations are reported to compare hydrodynamic/axial dispersion in a classical helical-shaped and planar serpentine-shaped tubular reactor at a millimetric scale (1-5 mm) for the first time. A two-step simulation approach is validated against experimental data on residence time distribution in serpentine coils. The method is then used for parametric analysis to explore the impact of geometric parameters on the coiling factor and axial dispersion coefficient. Dean vortices in the coiling region are visualized. The findings from the parametric analysis are utilized to develop empirical correlations and Artificial Neural Network (ANN) models for estimating coiling factors and axial dispersion coefficients in both serpentine and helical coils. The absolute average relative error (AERR) in predicting the coiling factor is 3.5% for helical coils and 4.6% for serpentine coils. The AERR of the ANN model for predicting the axial dispersion coefficient is 14% for helical coils and 10% for serpentine coils. The study reveals that both axial dispersion coefficient and pressure drop are higher in serpentine coils compared to helical coils. Axial dispersion is found to be relatively unaffected by pitch (helical) or bend diameter (serpentine) and tube diameter but shows significant reduction with a decrease in pitch circle diameter (helical) or gap between bends (serpentine). The developed correlations and ANN models can aid in the precise sizing of tubular reactors designed as helical or serpentine coils. This is exemplified through a case study involving the synthesis of an ionic liquid, where the helical configuration demonstrated a performance advantage of approximately 6% over the serpentine configuration. [ABSTRACT FROM AUTHOR]

Inductive power transfer (IPT) systems often encounter limitations in efficiency and transmission distance due to near-field magnetic coupling characteristics. Increasing the inductance can enhance the transmission distance, but it also raises the system's Q factor, leading to several issues. This study aimed to optimize the magnetic core design of helical coils to enhance magnetic coupling in IPT systems while minimizing the increase in self-inductance. Through finite element analysis, various core placements were evaluated, leading to a proposed core design process that integrates inner and lower cores at optimal angles. The proposed design was compared with conventional cores, and its performance was validated in an IPT system. The results demonstrate that the proposed core design significantly enhances the coupling coefficient (k) and extends power transmission distance compared with conventional planar and U-shaped core structures without substantially increasing self-inductance (L). This design effectively balances the trade-off between increasing inductance and maintaining system stability, thereby improving transmission efficiency while minimizing frequency instability and voltage stress. [ABSTRACT FROM AUTHOR]

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.

Synthesis of bio-based monomers via continuous flow ozonolysis of cardanol using a simple tubular reactor is demonstrated. The direct ozonolysis of cardanol produces unique monomer 8-(3-hydroxyphenyl) octanal (HPOA) and heptanal along with several other oxidation products. Maximum 47% yield of HPOA with 54.3% conversion of cardanol was obtained at 0 °C in 9 s. The complete conversion of cardanol was obtained at the ozone to cardanol molar flow ratios greater than 2 at all temperatures varied in the range of -10 °C to 20 °C. Owing to large gas–liquid ratios, the mass transfer limitation for transfer of ozone from gas to liquid was negligible; however, the extent of axial dispersion in the liquid phase was significant at lower liquid flow rates. The non-ideal behavior was incorporated in the axial dispersion model to predict the conversion of cardanol. Examination of kinetic rates by both ideal plug-flow model and plug-flow with axial dispersion model revealed that the reaction is fast and is least influenced by the axial-dispersion in the reactor at prevailing operating conditions. The findings of the current study show that continuous flow technique enables a simple and safer synthesis of high-value bio-based monomers via ozonolysis of cardanol compared to traditional batch methods. [ABSTRACT FROM AUTHOR]

Embolization of the middle meningeal artery (MMA) is a safe and effective adjunct in the treatment of chronic subdural hematoma. While prior authors describe the use of coils to assist embolization by preventing reflux through eloquent collaterals, we de- scribe the use of coils to further open the MMA, allowing the administration of greater amounts of embolisate for a more robust embolization. The objective of this study was to demonstrate that helical coils can safely open the MMA following the administration of polyvinyl alcohol (PVA) particles. This allows for more embolisate to be administered into the MMA for more effective treatment. A retrospective review was conducted at our institution including intraoperative images and postoperative clinical and radiographic follow up. Failure rates using MMA embolization with PVA and helical coil augmentation were compared to failure rates in the literature of MMA embolization with PVA or ethylene vinyl-alcohol copolymer alone. A total of 8 cases were reviewed in which this technique was implemented. There were no immediate complications after treatment. All patients that underwent helical coil embolization following the administration of PVA had increased amount of embolisate delivered into the MMA. All patients at follow up had resolution of the subdural hematoma on outpatient imaging. Helical coil embolization allows for more embolisate administration into the MMA and provides a technical advantage for patients that fail traditional techniques of embolization. Case series are taking place to further test this hypothesis and identify the ideal patient population that may gain maximal yield from this novel technique.

Enhancement of heat transfer characteristics in helical condenser coils by modifying the coil shape has been reported by many researchers. While the influence of different types of condenser coil designs on the operating performance of refrigeration machines for hot water production unit is available in the literature, there exists no published numerical or experimental analysis of the impact of geometric parameter of immersed helical condenser coil on heat transfer characteristics and water velocity distribution during water heating process, which is the subject of our article. With using CFD methodology, a numerical study was carried out to present the water velocity distribution with varying coil parameters such as pipe diameter, tube pitch, and turns number. After validating the numerical model by the experimental ones, the effect of coil parameters on water velocity distribution was examined. The results confirm that by reducing the coil pitch and increasing the tube diameter, an increase of the water velocity and a higher natural convection is obtained. On the other hand, the results indicate that with reducing the turns number, the water velocity and the heat transfer coefficient is also increasing. Indeed, the average water velocity of condenser coil with N = 11 turns is higher than the other two condenser coil structures, which presents 21.34% and 63.56% higher than that of N = 13 turns and N = 15 turns, respectively. Thus, this investigation could provide some guidance to obtain the optimum condenser coil structure for water heating process. [ABSTRACT FROM AUTHOR]

Helically coiled pipes are widely used in many industrial and engineering applications because of their compactness, larger heat transfer area per unit volume and higher efficiency in heat and mass transfer compared to other pipe geometries. They are commonly encountered in heat exchangers, steam generators in power plants and chemical reactors. The most notable feature of flow in helical pipes is the secondary flow (i.e., the cross-sectional circulatory motion) caused by centrifugal forces due to the curvature. Other important features are the stabilization effects of turbulent flow and the higher Reynolds number at which the transition from a laminar to a turbulent state occurs compared to straight pipes. A survey of the open literature on helical pipe flows shows that a good deal of experimental and theoretical work has been conducted to derive appropriate correlations to predict frictional pressure losses under laminar and turbulent conditions as well as to study the dependence of the flow characteristics and heat transfer capabilities on the Reynolds number, the Nusselt number and the geometrical parameters of the helical pipe. Despite the progress made so far in understanding the flow and heat transfer characteristics of helical pipe flow, there is still much work to be completed to address the more complex problem of multiphase flows and the impact of pipe deformation and corrugation on single- and multiphase flow. The aim of this paper is to provide a review on the state-of-the-art experimental and theoretical research concerning the flow in helically coiled pipes. [ABSTRACT FROM AUTHOR]

In this study, the flow and heat transfer characteristics of microencapsulated phase change material (MPCM) slurry were experimentally investigated using a newly designed helical coil heat transfer device. The conventional helical coil has been structurally modified with passive enhancement features aiming to further promote fluid mixing. Specifically, 360° plastic tubing with or without wire coil inserts was added after each 180° of the main helical loop to enhance fluid mixing and improve the overall thermal performance of the device. Pressure drop and heat transfer experiments with MPCM slurry were conducted under turbulent flow and constant heat flux conditions. A new friction factor and Nusselt number correlations for MPCM slurry in helical coils with reversed loops and wire coil inserts are proposed. Experimental results show that the structural modifications did enhance the heat transfer performance of MPCM slurry. The experimental results revealed that the phase change process of MPCM considerably enhanced the heat transfer rate of MPCM slurry. Furthermore, the use of reversed loops and wire coil inserts led to better fluid mixing within the coil, resulting in improved convective heat transfer of the MPCM slurry. [ABSTRACT FROM AUTHOR]

Inductive power transfer (IPT) systems often encounter limitations in efficiency and transmission distance due to near-field magnetic coupling characteristics. Increasing the inductance can enhance the transmission distance, but it also raises the system’s Q factor, leading to several issues. This study aimed to optimize the magnetic core design of helical coils to enhance magnetic coupling in IPT systems while minimizing the increase in self-inductance. Through finite element analysis, various core placements were evaluated, leading to a proposed core design process that integrates inner and lower cores at optimal angles. The proposed design was compared with conventional cores, and its performance was validated in an IPT system. The results demonstrate that the proposed core design significantly enhances the coupling coefficient (k) and extends power transmission distance compared with conventional planar and U-shaped core structures without substantially increasing self-inductance (L). This design effectively balances the trade-off between increasing inductance and maintaining system stability, thereby improving transmission efficiency while minimizing frequency instability and voltage stress.

Low-temperature stratification, high-volumetric storage capacity, and less-complicated material processing make phase-changing materials (PCMs) very suitable candidates for solar energy storage applications. However, their poor heat diffusivities and suboptimal containment designs severely limit their decent storage capabilities. In these systems, the arrangement of tubes conveying the heat transport fluid (HTF) plays a crucial role in heat communication between the PCM and HTF during phase transition. This study investigates a helical coil tube-and-shell thermal storage system integrated with a novel central return tube to enhance heat transfer effectiveness. Three-dimensional computational fluid dynamics simulations compare the proposed design against a baseline helical coil system without a return tube under equivalent conditions. Outcomes quantify the return tube's efficacy in augmenting heat transfer uniformity and accelerating phase transition. Adding the return tube markedly boosts heat storage and recovery rates, increasing charging by 88% and discharging by 56% versus the baseline. Moreover, total phase transition time reduces by 48% for melting and 36% for solidification with the return tube. The accelerated charging stems from sustained convective heat transfer inside the return tube even as the molten layer thickens. Meanwhile, enhanced solidification results from ongoing cooling of inner regions. Isotherm analysis visualizes the return tube's efficacy in maintaining thermal uniformity throughout the phase transition process. Overall, the return tube significantly improves PCM thermal response, demonstrating a novel but straightforward approach to address heat transfer limitations in latent thermal storage systems.

In this study, a high-efficiency wireless power transfer (WPT) coil that is robust against interoperability and misalignment was developed by applying an inductive power transfer system to a drone. The transmitting coil had a ferrite plate applied to a helical structure that included the receiving part. The receiving coil was a guard-type receiving part applied to the ferrite sheet. To analyze the spiral and helical coils according to the winding method, the z-axis magnetic field vector was analyzed. A suitable WPT model was developed for each drone by analyzing the mutual inductance based on whether the ferrite was attached to the transmitter or receiver and the ferrite sheet’s location. The electrical characteristics of the coil were derived using Ansys Electronics Maxwell, and a comparative analysis was performed using the measured values of the fabricated coil. The mutual inductance change due to misalignment between the coils of the transmitter and receiver of the proposed model was analyzed. It was demonstrated that the magnetic field distribution was uniform according to the misalignment error. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Chongqing University of Technology (Natural Science) is the property of Chongqing University of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Due to the intermittent and hazardous nature of lightning impulse, researchers rely on artificial impulse generators to study it. The Tesla coil is a commonly used device to generate artificial lightning. This paper presents a parametric analysis of the primary side coil of the Tesla transformer. The analysis employs seven key electrical properties: skin depth, current density, voltage distribution, Ohmic loss, electric field strength, charge density, and energy content. These parameters are used to evaluate the response of various coil types to high voltage impulses. The Ansys high-frequency electromagnetic solver is used to perform a comparative analysis of essential parameters. The results can aid lightning researchers and Tesla coil designers in determining the optimal designs for Tesla primary coils in the future. The analyzed data is validated using Tesla coil hardware, which is used as an artificial lightning producer to test the feasibility of a lightning energy harvester.

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

Removal of brilliant yellow azo dye from wastewater by electrocoagulation was carried out using a cell with Al helical coil whose external surface acts as an anode, and its internal surface acts potentially as a cooler to control the cell temperature. This is important in the case of large-scale cells which use high currents and low electrolyte conductivity where accumulated heat decreases the rate of electrocoagulation. The helical coil anode was enclosed between two Al cylindrical screen cathodes. Variables studied were current density, initial dye concentration, solution pH, solution temperature, NaCl concentration, and magnetic stirring rate. Most of the variables were found to have opposing effects on the % dye removal. Under the optimum conditions, a maximum of 92% dye removal was obtained in 90 min using a current density of 3 mA/cm2, pH 5–6, an initial dye concentration ranging from 10 to 75 ppm, and NaCl concentration of 30 g/L. Electrical energy consumption ranged from 3.258 to 313.3 kW∙h/kg of dye removed depending on the operating conditions. [ABSTRACT FROM AUTHOR]

Fuel cells are gaining popularity because of their efficient energy production without causing environmental pollution. Recently, DRDO has developed a fuel cell-based air-independent propulsion (AIP) system. In this system, the hydrogen is produced onboard while oxygen is carried in liquefied form (LOX) from the land in specially designed insulated storage vessels called dewars. Such vessels are needed because LOX has a low boiling point (NBP ~ 90 K) and heat of vaporization (~ 213 kJ/kg), due to which it boils off easily even when there is a small amount of heat inleak from the ambient. A typical dewar consists of two vessels separated by insulation. Support members are used to hold the two vessels together. Heat inleak through the supports and the insulation of the dewar causes the boiling of LOX. The vessels are subjected to dynamic loads during the voyage due to the filling and consumption of LOX. Therefore, the support system should be designed to withstand the dynamic loads experienced by the dewar. While the support system should have enough mechanical strength to withstand the loads it is subjected to, it should also restrict the heat inleak from the ambient to minimize the LOX boil-off. To meet this requirement, we need to optimize the support system design. Design optimization of support systems is especially critical in submarines to reduce the snorkeling frequency. Even though the dewars are available commercially for various applications, their design methodologies are not available in the open literature. Cylindrical rods are generally used as support members. In earlier studies, the authors have shown that helical coils give better thermal performance than tension rods as dewar supports. These two support systems involve different design criteria. It is important to evolve an optimal design of the support system to maximize the mechanical strength of the support while minimizing the heat inleak through the support. In this paper, we present a design methodology for optimizing helical support. We have proposed a modified optimization technique derived from the classical genetic algorithm (GA) for this purpose. The modification has been done by ensuring the design feasibility of the coil at each step of the algorithm. The proposed optimization technique has been tested on a LOX dewar, and an optimal design of the helical coil support has been obtained. [ABSTRACT FROM AUTHOR]

Helically coiled pipes are widely used in many industrial and engineering applications because of their compactness, larger heat transfer area per unit volume and higher efficiency in heat and mass transfer compared to other pipe geometries. They are commonly encountered in heat exchangers, steam generators in power plants and chemical reactors. The most notable feature of flow in helical pipes is the secondary flow (i.e., the cross-sectional circulatory motion) caused by centrifugal forces due to the curvature. Other important features are the stabilization effects of turbulent flow and the higher Reynolds number at which the transition from a laminar to a turbulent state occurs compared to straight pipes. A survey of the open literature on helical pipe flows shows that a good deal of experimental and theoretical work has been conducted to derive appropriate correlations to predict frictional pressure losses under laminar and turbulent conditions as well as to study the dependence of the flow characteristics and heat transfer capabilities on the Reynolds number, the Nusselt number and the geometrical parameters of the helical pipe. Despite the progress made so far in understanding the flow and heat transfer characteristics of helical pipe flow, there is still much work to be completed to address the more complex problem of multiphase flows and the impact of pipe deformation and corrugation on single- and multiphase flow. The aim of this paper is to provide a review on the state-of-the-art experimental and theoretical research concerning the flow in helically coiled pipes.

A modification is made in the existing concentric heat exchanger design to enhance its heat duty. A standard concentric tube heat exchanger is modified by considering two inner tubes with a combination of helical and sinusoidal coils. Numerical studies are performed in this triple fluid heat exchanger to assess its thermal performance by taking into account mass flow rate, fluid temperatures, heat transfer, which are governed by fundamental heat transfer equations. Computational fluid dynamics simulation methodology together with local and element-byelement method is applied with a MatLab computer code. Hot water and milk fluids are used as working fluids in helical and sinusoidal coils, respectively. Cooling water is used as shell side fluid. The attainment of high heat-load-per-unit-area and high surface-area-to-volume ratio is used as optimizing parameter in the simulations. The helical coil provides an increase in heat transfer rate and overall heat transfer coefficient increases by a percentage 13% for varying hot fluid flow rates, when it is compared with the sinusoidal coil. The pressure drop for the helical coil increases, exponentially compared to the sinusoidal coil, thereby it shows a higher pumping power for the helical coil. [ABSTRACT FROM AUTHOR]

Copyright of Atomic Energy Science & Technology is the property of Editorial Board of Atomic Energy Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Latent heat thermal energy storage (LHTES) using phase change materials (PCM) is a promising way to store energy. The primary problem with PCMs is their low heat conductivity, which causes the charge and discharge processes to take a long time. This study presents an experimental study using fins on helical coils to overcome this issue. The effect of different numbers of fin, changing heat transfer fluid (HTF) inlet temperature and flow rate, are investigated in the charging and discharging processes. Temperature variations in different regions are measured by thermocouples and imaged by a thermal camera to illustrate the PCM melting and solidification. Temperature fluctuation, mean temperature response (MTR), Stefan number (STE), thermal imaging, and the discharge process's heat power supply are used as metrics to examine the impact of different parameters. Results indicate that using 15, 25, and 35 fins can decrease the charging by about 11.2, 18.2, and 29.5%, respectively, and the discharging process by about 6.31, 11.9, 20.9%, respectively. Also, An increase in temperature and flow rate of HTF in the charging remarkably increases the full charge time. Nonetheless, a drop in the flow rate and temperature of the HTF intake has lengthened the discharge. [ABSTRACT FROM AUTHOR]

Due to the compact structure, high heat transfer efficiency and strong reliability, helical coil once-through steam generator (HCSG) is widely used in advanced small reactors. In HCSG, the liquid in the tube side is heated by the helical coils so that subcooled water in the tube side is transferred into superheated steam, and the entire heat transfer regime is covered. Moreover, the evolution mechanism of thermalhydraulic behaviors is complex because it is affected by the helical geometry, the centrifugal force and the secondary flow. Hence, the development of advanced HCSG was limited due to the lack of more accurate models of heat transfer and regime transition. With the financial support of the three major nuclear power groups in China, experimental and theoretical research on heat and mass transfer behaviors in helical coils was carried out systematically. Different helical coils were investigated and comprehensive parametric analysis of heat transfer was conducted to provide a better understanding of different heat transfer regimes. According to our research, a fundamental database of heat transfer and flow resistance in helical coils with a wide range of geometric dimensions and thermalhydraulic parameters was established. In addition, the transition pattern of the circumferential nonuniform heat transfer mechanism was clarified. Due to the secondary flow, it consequently leaded to the nonuniform distribution of flow field. The heat transfer and flow resistance characteristics were notably affected by the special behaviors of liquid in the helical coils. Hence, based on mechanism analysis, several models were proposed to construct a high precision library of allregime prediction model, such as a threeregion dryout quality model, a postdryout heat transfer model based on dryness gradient and a widerange model for twophase frictional multiplier factor. For the model of dryout quality, it takes the relative intensity of gravity, buoyancy and centrifugal force into consideration. Since different dominant forces lead to different heat transfer behaviors, a piecewise correlation is established to give more accurate predictions. As for the postdryout heat transfer model, it considers the influence of dryness gradient and achieves a more accurate prediction. For the twophase pressure drop model, the modified frictional multiplier factor is adjusted according to our database. Then, a prediction model was proposed which was also validated by other researchers and had great prediction accuracy in a wide range. In all, this work includes part of our investigation on the heat transfer of helical coils and provides a highprecision prediction in the entire heat transfer regime, which meets the design requirement of HCSG for advanced reactors.

Summary: Conventional heater is limited by the time and energy‐consuming design, showing high energy loss and causing a negative impact to the environment. A novel air heater integrated with microwave heating and activated carbon (AC) as thermal energy storage has been developed in this study to investigate the heat transfer efficiency in a helical coil. Microwave radiation provides volumetric heating to the AC, which acts as a microwave absorbent to absorb and convert microwave energy into heat energy for storage and subsequently heating the helical coil that in turn heats the air indirectly. The helical coil exerted centrifugal force and induced secondary flow to significantly enhance the heat transfer. Microwave radiation induced a high heating rate of 30°C/min to heat the AC. Low heat loss (6.12°C/min) was shown during the cooling down of AC, indicating high heat retention by the AC. Then, the convective heat transfer between helical coil and air with over a range of AC temperatures was examined. The highest overall heat transfer coefficient (U0) and coefficient of performance (COP) with various AC temperatures were recorded at 310.815 W/m2·°C and 3.958, respectively, at 50 L/min of air flow rate. Nusselt number, Reynolds number, and Dean number were increased with higher air flow rate. The experimental results showed good agreement with literature where convective heat transfer in the helical coil is more efficient at the high‐temperature region as well as when higher flow rate was applied. The use of microwave air heater shows a potentially high efficiency of energy‐saving with capacity to generate hot air at 100°C to 250°C in about 26 min after switching on the microwave oven. [ABSTRACT FROM AUTHOR]

The radius of the coil, the number of turns of the windings, and the parasitic resistances of energy-storing elements affect the performances of wireless power transfer systems. We aimed to study the effects of coil parameters on a wireless power transfer system with the capacitor–capacitor–coupling coil (CCL)-based circuit using numerical simulations. The power transfer system topologies, including series–CCL (S–CCL), CCL–S, and CCL–CCL, were studied vis-à-vis coil parameters. The helical coil and the system topologies were modeled using MATLAB, and the performances of the topologies were examined in comparison to the series–series (S–S) topology. The variables used in the simulations included the radius and number of turns, the parasitic resistance that was merged in the impedance, and the reactance of energy-storing elements. Subsequently, the performances of the topologies were estimated by numerical simulations under several circumstances. The simulation results showed that the parasitic resistance of the coupling coil affects the performances of the topologies directly. The coupling coils with smaller geometries are beneficial to power transfer in the wireless power transfer system and may further contribute to miniaturization. [ABSTRACT FROM AUTHOR]

A dimensionally consistent physics-informed neural network, named DimNet, has been developed to predict dryout quality in helical coils. Central to its design is the automated and optimizable dimensionality reduction technique, leveraging the Buckingham Pi theorem, which transforms 11 dimensional physical quantities into 8 dimensionless groups. Rigorous 5-fold cross-validation and cross-fluid testing affirm its performance, with an mean absolute error of 0.0540 and 0.198, respectively. The strategic incorporation of noise during training elucidates pronounced improvements, accentuating the model's adaptability. In comparison to three other neural network architectures, DimNet consistently displays superior accuracy. Ablation experiments have underscored the efficacy of each module within the model's design. Ultimately, while DimNet presents as a promising tool for enhancing thermal efficiency in helical-coiled steam generators, its design principles also shed light on the broader potential and versatility of dimensionally consistent neural architectures. • A novel neural network model with automatic and optimizable dimensional analysis. • Achieves dimensional consistency via Buckingham Pi theorem. • Improves accuracy over conventional methods and other neural networks. • Noise-augmented training enhances model robustness and generalizability. [ABSTRACT FROM AUTHOR]

This paper investigates the cryogenic heat transfer phenomena of nitrogen flowing in helically coiled tubes under the combined effects of pseudocritical conditions, buoyancy, and coil curvature. The ultimate goal was to design optimum heat exchangers for liquid air energy storage. Local heat transfer coefficients were evaluated peripherally across tube cross sections. The pressure, mass flux, and heat flux effects on the heat transfer were examined. The dual effect of buoyancy and coil curvature on heat transfer coefficients was interpreted via a dimensionless number Ψ, which denotes a ratio between the two effects. Results reveal that the heat transfer coefficients increase with increasing mass flux but decreasing pressure and heat flux. The buoyancy effect dominates the heat transfer at fluid temperatures below the pseudocritical temperature (e.g., −146.3 °C at 35 bar), while the coil curvature-induced centrifugal effect dominates at higher temperatures. The heat transfer coefficients for the helical coil were approximately 13% lower compared with those in straight tube at fluid temperatures below the pseudocritical temperature, but their difference shrinks (<±6%) at higher temperatures. The reason is that the benefits of coil curvature and improved turbulent mixing on heat transfer are counteracted by the thermophysical property variation and buoyancy effect. [ABSTRACT FROM AUTHOR]

The main goal of this paper is to study the second law characteristics of carboxymethyl cellulose (CMC)-based non-Newtonian nanofluids with different nanoparticles of aluminum oxide (Al2O3), copper oxide (CuO), and titanium oxide (TiO2) through a helical coil heat exchanger. The present investigation has been carried out for the volume flow rate of non-Newtonian nanofluids ranges from 1 (L⋅min) to 10 (L⋅min). In this study, the effect of nanoparticles, nanoparticle volume fraction, and inlet temperature of hot fluid exergy loss, second law efficiency, and heat transfer effectiveness are investigated. It is observed that on increasing the volume flow rate of nanofluids the exergy losses increase for all the nanofluids. Moreover, with the increase in particle volume fraction from 0.01% to 0.04%, the exergy loss reduced by 33%, 30%, and 14% for CuO, Al2O3, and TiO2 nanofluids, respectively, as compared to base fluid, while the exergy loss increases as the inlet temperature of hot fluid increases. Also, the maximum value for second law efficiency is found to be 67% for base fluid, whereas the second law efficiency has been achieved to 71%, 74%, and 77% for TiO2, Al2O3, and CuO non-Newtonian nanofluids, respectively. Therefore, it is concluded from the present study that the use of non-Newtonian nanofluids in helical coil heat exchanger reduces the exergy loss and improves the second law efficiency. [ABSTRACT FROM AUTHOR]

The forming of helical coils using a rolling process results in geometrical irregularities (wrinkles and ovality) that are likely to influence the hydrodynamic behaviour of the flow field inside the coil in applications such as air generators. In this study, the above behaviour was investigated by experimental and numerical analyses considering the heat exchanger used in dry air generators. In experimental analysis, a three-turn copper helical coil with wrinkles and ovality was investigated to estimate the global hydrodynamic characteristics inside the helical coil. The results were compared with that of the ideal geometry of a coil without wrinkles and ovality. The effect of wrinkles was assessed through friction factor, and the corresponding equivalent surface roughness was found to increase by 5.7 times, owing to the presence of wrinkles in the helical coil. Numerical simulation was conducted to determine the pressure distribution, velocity distribution, and secondary flow inside the helical coil; the results were validated with experimental data. A critical portion of the helical coil with multiple wrinkles was considered for numerical simulation to investigate the localized effects of wrinkles on the flow field behaviour. The analysis in the vicinity of wrinkles revealed negative pressure development during flow, which in turn would cause re-circulation and cavitation that are undesirable. [ABSTRACT FROM AUTHOR]

• Three types of nanofluids TiO 2 /water, ZnO /water and Ag /water through helical coils are experimentally investigated.. • Increasing the coil pitch reduces both Nusselt number and pressure drop. • Nusselt number enhancement up to 28.7 %, 17.8 % and 11.8 % was achieved for TiO 2 /water, ZnO /water and Ag /water respectively. • Pressure drop increasing up to 28.5%, 23.5% and 25.4% was observed for TiO 2 /water, ZnO /water and Ag /water respectively. • Novel correlations are introduced for Nusselt number and pressure drop. Nanofluids are an innovative attractive challenging field suitable for many heat transfer applications. The helical coil is preferred due to compactness and additional curvature flow disturbance. Heat transfer and pressure drop characteristics of Ag, ZnO and TiO 2 water based nanofluids through helical coil tubes under isothermal boundary conditions are experimentally investigated with 0.25% nanoparticles volume concentration Ag /water, ZnO /water and TiO 2 /water nanofluids. Five coils are constructed with different coil pitches of 2, 4, 6, 8 and 10 cm. The flow rate of the nanofluid varies between 1 to 3.5 L/min with inlet temperature from 30 °C to 60 °C. The results showed that increasing the coil pitch reduces Nusselt number and pressure drop. The nanofluids have a positive impact on the enhancement of heat transfer but with a pressure drop penalty. Average Nusselt number enhancement up to 11.8 %, 17.8 % and 28.7 % was achieved at Ag /water, ZnO /water and TiO 2 /water with average pressure drop increasing up to 25.4%, 23.5% and 28.5% respectively. The results showed that an increase in coil pitch decreases hydrothermal performance index (HTPI) and utilizing nanofluids increases HTPI for all types of nanofluids Ag /water, ZnO /water and TiO 2 /water. Novel correlations were developed to predict Nusselt number and pressure drop. Graphical Abstract [Display omitted]. [ABSTRACT FROM AUTHOR]

At present, solenoid (helical) coils are widely used in various researches, especially electromagnetic forming (EMF), due to their advantages of simple manufacture and high magnetic field strength. However, in the study of EMF, there are still some defects in the high precision calculation of solenoid coils in the magnetic field the main reason is that the solenoid coil is of non-axisymmetric structure, which is generally equivalent to the 2-D or 3-D axisymmetric structure in practical research. Not only can it ignore the effect of the pitch effect of the solenoid coil, but also causes a certain deviation in the calculation of the magnetic field. Hence, this paper establishes 5 helical coils and 3-D axisymmetric finite element coils models with different layers for comparative analysis. The simulation results show that the magnetic flux density distribution deviation of helical coil and the 3-D axisymmetric coil is small and can be ignored when the coil layers are 1 or 2 layers. However, the number of linear circles increasing, the deviation between the two increases obviously. Therefore, in the study of EMF, the effect of solenoid coil pitch effect on magnetic field calculation can be ignored when the layers, radius and pitch of helical coils are used less whereas the effect of solenoid coil pitch effect on magnetic field calculation must be considered when the layers, radius and pitch of helical coils are used more.

In this article, six-lobed absorber tube equipped with combined turbulators was investigated. To enhance the productivity of solar unit, hybrid nanoparticles were added in to working fluid. Helical coil and twisted tape have been employed together. For evaluating the thermal behavior and exergy loss, average solar flux were imposed in boundary condition. Also, variable heat flux was applied to evaluate the thermal efficiency including air gap for solar system. Homogeneous model for hybrid nanomaterial was utilized and outputs were presented to analyze the impact of changing operating fluid. Selecting six-lobed tube instead of circular tube leads to better cooling performance and lower exergy loss. When Re = 10000, convective coefficient augments about 3% while exergy drop declines about 5.198% with using six-lobed tube. Insertion of twisted tape for lower Re leads to augmentation of h by 1.666% and reduction of exergy drop about 1.828%.To scrutinize the influence of width ratio and (w ˜) and revolution number (n ˜) for coil insert, exergy drop and friction factor values in form of bar chart were presented. Velocity augments with rise of both factors and impingement of fluid with wall increases which provides higher pressure drop and lower exergy drop. Exergy loss decreases about 8.671% and 6.286% with augment of n ˜ and w ˜ when Re = 5000. Owing to nice attributes of hybrid nanofluid, not only convective flow augments but also exergy loss reduces by adding such particles. Dispersing nanoparticles can enhance the convective flow about 9.096% and 8.438% for circular tube and six-lobed tube with turbulator, respectively. Also, exergy loss for six-lobed tube with turbulator reduces about 8.562% with adding hybrid nanomaterial. Replacing, six-lobed tube with turbulator instead of circular tube leads to reduction of exergy drop about 17.907% while convective coefficient augments about 12.719%. Augmenting solar irradiation enhances the thermal efficiency about 180.24% and outlet temperature rises from 293.2 K to 293.36 K when Re = 5000. • Combination of Helical coil and twisted tape within six-lobed tube was investigated. • To enhance the efficiency of solar collector, hybrid nanoparticles were added. • Convective coefficient augments about 3% with using sinusoidal tube. • Exergy loss decreases about 8.671% with augment of n ˜ when Re = 5000. • Dispersing nanoparticles can enhance the convective flow about 8.438%. [ABSTRACT FROM AUTHOR]

Industry is looking for more efficient ways to use nanomaterials to decrease water consumption. The addition of greater thermal conductivity nanoparticles to the water enhances the fluid's thermal conductivity and, thus, increases the coefficient of heat transfer. In this work, water-based nanofluids were used to perform heat transfer enhancement studies in a shell and helical coil heat exchanger. Natural convection heat transfer using three water-based nanofluids (Al2O3, CuO and TiO2/water) was investigated in shell and helical coil heat exchanger. Experiments were performed at different hot water flow rates through coil (Dean number) and hot water feed temperatures (40, 50 and 60 °C). The use of water-based nanofluid led in a greater coefficient of shell-side heat transfer compared to the use of pure water on the shell side. The Nusselt number improved due to an increase in nanoparticle concentration. It was observed that with a rise in nanofluid concentration, Dean number and greater coil-side fluid feed temperature, the Rayleigh number increased. [ABSTRACT FROM AUTHOR]

The radius of the coil, the number of turns of the windings, and the parasitic resistances of energy-storing elements affect the performances of wireless power transfer systems. We aimed to study the effects of coil parameters on a wireless power transfer system with the capacitor–capacitor–coupling coil (CCL)-based circuit using numerical simulations. The power transfer system topologies, including series–CCL (S–CCL), CCL–S, and CCL–CCL, were studied vis-à-vis coil parameters. The helical coil and the system topologies were modeled using MATLAB, and the performances of the topologies were examined in comparison to the series–series (S–S) topology. The variables used in the simulations included the radius and number of turns, the parasitic resistance that was merged in the impedance, and the reactance of energy-storing elements. Subsequently, the performances of the topologies were estimated by numerical simulations under several circumstances. The simulation results showed that the parasitic resistance of the coupling coil affects the performances of the topologies directly. The coupling coils with smaller geometries are beneficial to power transfer in the wireless power transfer system and may further contribute to miniaturization.

This numerical study analyzes the thermal performance of a helical shell and tube heat exchanger without a fin, with circular fins, and with cut (V-shaped) circular fins (with an angle of 15°) applying on the coil. The obtained results showed that in both simple and circular finned heat exchangers when the fluid velocity (both hot and cold) on the shell side is higher than the fluid velocity (both hot and cold) on the tube side, the heat transfer improves. It is also found that flowing the cold water through the shell increases its velocity and flowing the hot fluid through the coil results in higher heat transfer values. Moreover, the results revealed that the highest heat transfer magnitude designates the circular finned heat exchanger with a cold water velocity of 3 m s−1 entering the shell and a hot water velocity of 1 m s−1 entering the tube. Finally, it is found that the cut circular fins effects on the helical shell and tube heat exchanger efficiency and heat transfer are insignificant in comparison with the circular fins. [ABSTRACT FROM AUTHOR]

This paper investigates the cryogenic heat transfer phenomena of nitrogen flowing in helically coiled tubes under the combined effects of pseudocritical conditions, buoyancy, and coil curvature. The ultimate goal was to design optimum heat exchangers for liquid air energy storage. Local heat transfer coefficients were evaluated peripherally across tube cross sections. The pressure, mass flux, and heat flux effects on the heat transfer were examined. The dual effect of buoyancy and coil curvature on heat transfer coefficients was interpreted via a dimensionless number Ψ, which denotes a ratio between the two effects. Results reveal that the heat transfer coefficients increase with increasing mass flux but decreasing pressure and heat flux. The buoyancy effect dominates the heat transfer at fluid temperatures below the pseudocritical temperature (e.g., −146.3 °C at 35 bar), while the coil curvature-induced centrifugal effect dominates at higher temperatures. The heat transfer coefficients for the helical coil were approximately 13% lower compared with those in straight tube at fluid temperatures below the pseudocritical temperature, but their difference shrinks (

A novel synthetic polymer-plant-precursor carbonization technique was developed. Carbon micro coils were prepared by the carbonization of plant helical vessels coated with polyaniline or poly(acrylonitrile-co-acrylic acid). The helical vessels served as a helical guide, while the synthetic polymers coated on the vessel surface, which consisted of cellulose, were transformed into carbon material while retaining the helical form. The helical carbon material was prepared without the use of an organic gas or solvents through a relatively simple and convenient process. This technique involved the application of natural resources, the synthesis of a conducting polymer, and carbon science. The biocarbon micro coils thus prepared in this study were characterized by infrared absorption, optical microscopy, and scanning electron microscopy. Moreover, the magnetic properties of the helical carbon were examined by electron spin resonance and a superconducting quantum interference device that proved its paramagnetic features. Additionally, the water transport function in the helical vessels was discussed. [ABSTRACT FROM AUTHOR]