Coil Curvature Research Articles

Evaluation of a concentrated solar power-driven system designed for combined production of cooling and hydrogen

The current technique of hydrogen generation and cooling production raises climatic problems, which calls for the investigation of cleaner alternatives. No research has been conducted to propose and analyze a solar thermal power cycle-based water electrolysis for on-site production of hydrogen and the detailed exergy analysis of a series flow double-effect absorption chilling machine employed for large solar cooling. In this regard, a helically coiled tube embedded central receiver is used in the heliostat field for the simultaneous production of solar cooling and green hydrogen to meet the increasing needs of energy and fuel sustainably. The combined system is composed of four sub-systems including a heliostat field, LiBr–H2O operated series-flow double effect absorption refrigeration cycle (DEARC), organic Rankine cycle (ORC), and proton exchange membrane (PEM) electrolyzer. The system was examined from energy and exergy perspectives in the Engineering Equation Solver (EES) using library data of REFPROP for obtaining the thermodynamic properties of working fluids. The results of the thermodynamic model for the combined system are validated. Furthermore, the effect of ambient temperature, solar irradiation, and type of ORC working fluid on the hydrogen and cooling production, and the overall energy and exergy efficiency of the combined system are examined. A computational fluid dynamics simulation applying ANSYS-FLUENT was used to examine how coil curvature ratio and coil torsion affect solar heat transfer fluid (SHTF) pressure and temperature leaving the receiver. The coil curvature ratio affects temperature increase more than coil torsion. Solar heat transfer fluid outlet temperature increases by 36.9 % when the coil curvature ratio increases from 0.063 to 0.095 at direct normal irradiations (DNI) 1200 W/m2, input temperature of 92°C, and coil torsion of 0.032. The response of the cogeneration cycle to varying operating parameters is examined. Application of R141b as the ORC fluid results in a large increase of cooling exergy efficiency from 14.98 % to 63.48 % when the ambient temperature is increased from 15 °C to 45 °C whereas the exergy efficiency of the combined system is marginally improved. The exergy distribution presents for ORC operating on R141b, out of 100 % input solar exergy, 16.42 % is generated as hydrogen exergy and 13.67 % cooling exergy, 66.79 % is the exergy destroyed, and the rest 3.12 % is exergy loss. Exergy analysis is utilized to identify the sources of losses in useful energy within the components of the system considered and provides a more realistic and meaningful assessment than the traditional energy analysis. The results justify a need for the promotion of exergy analysis through policy decisions in the context of the global energy and environment crisis.

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

The High‐Strength, Flexible Organic Solvent Driven Reversible “Deformation‐Recovery‐Reverse Deformation” Responsive g‐PLA/PPC/PVA Film for Contactless Actuation

AbstractThe non‐contact deformation response driven by organic solvent has potential applications in the fields of intelligent devices, soft robots, sensing detection, and biomedical micro‐devices. The modified polyactic acid (g‐PLA)/polypropyl carbonate (PPC)/polyvinyl alcohol (PVA) sandwich with deformation response film is prepared by the asymmetric swelling response mechanism. Specially, the flexible sandwich film achieves the non‐contact driving response of “deformation‐recovery‐reverse deformation”, showing excellent deformation performance. The curvature of sandwich film reaches 13.79 cm−1 within 15 s, and the film recovers to its initial state within 3 s, then the curvature of the reverse coil reaches 18.18 cm−1 within 15 s and finally achieves a stable state. This special phenomenon is caused by the different adsorption swelling and desorption rates of volatile organic solvents in g‐PLA, PPC, and PVA layers. Additionally, the flexible film has high strength, reversible circulation, and stable actuation performance. The application scenarios of the bionic flower actuator, artificial octopus, intelligent protective cover, and transportable objects are successfully implemented. This work will significantly provide substantial guidance for the development of intelligent driving technology in the future.

Heat Transfer of Near Pseudocritical Nitrogen in Helically Coiled Tube for Cryogenic Energy Storage

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.

Design and implementation of combined liquid pump and active–passive mixer for a drug delivery system utilizing two 1-DOF piezoelectric actuated cantilever beams

In a biomedical drug delivery system, liquid medication is provided to the patient through a saline solution, administered in tiny drops. The spread of the medicine in the solution is an essential aspect for the solution to become homogeneous. The present study introduces a combined pump and active–passive mixer arrangement consisting of dual piezoelectrically actuated 1-degree of freedom (DOF) Aluminium cantilever beams. The free end of each beam is attached to a borosilicate glass tube set-up that works as both pump and a mixer. The setup consists of two vertical tubes, connecting channels, a glass bulb, and a coiled tube. When the piezoelectric actuated cantilever beam is excited by an excitation voltage, it deflects and vibrates along with the glass tube arrangement resulting in the vertical tubes pumping liquid from the two separate glass containers due to the mechanical vibratory movement. The connecting channels pass the pumped fluid into the vibrating glass bulb and the coiled tube where these two liquids mix. We tested the mixing executions of four different geometries, G-1 – G-4, based on changed δ (coil curvature ratio), p (pitch), and n (number of windings). Initial pumping was started at 90 VP-P input voltage for all geometries, and the observed flow rate and velocity were 2.91 ml min−1 and 0.9160 mm min−1 for G-1 geometry. A UV–visible spectrophotometer was used to evaluate the mixing execution by measuring the solution's absorbance values before and after mixing.

Constrained stellarator coil curvature optimization with FOCUS

Finding less complicated coils that have adequately low field errors is a crucial step in stellarator development. One coil metric that is of high importance is the maximum curvature of the coil centreline, or coil single filament. Conductors cannot be bent below some threshold minimum radius of curvature. High coil curvatures can cause strains to exceed acceptable levels, especially in superconducting coils. We investigate three ways to optimize coil curvature and find that applying penalty functions to the coil curvature solves for coils that have a constrained maximum curvature and low field error. Penalty functions are implemented in FOCUS and coil solutions optimized for an HSX-like ‘plasma boundary’ are presented.

Simulation study on modified coil configuration used for shrink fitting of semi-built-up crankshaft and parameters influencing the thermal distribution.

Semi-built-up crankshafts are universally manufactured by shrink-fitting process with induction heating device. The configurations of induction coil have a great impact on the distributions of eddy current and temperature of crankthrows. Most induction devices are apt to cause some undesirable phenomena such as uneven temperature distribution and irregular deformation after induction heating. This article proposes a modified configuration of induction heating coil according to the crankthrow geometry. By combining the heat conduction equation and the heat boundary conditions, a three-dimensional finite element model, which takes into account the nonlinearity of the material's electromagnetic and thermal physical properties in the heating process, was developed. The influence of several parameters, such as position and curvature of the arc coil, the current frequency and density, coaxiality of crankweb hole and coil, influencing the temperature distribution inside the crankthrow was also analyzed. The comparison with the numerical simulation results of the original configuration indicates that the modified configuration has better adaptability to the crankthrow. Also, it can help to improve the temperature distribution, and reduce the deformation of the shrink-fitting hole. This exploration provide an effective way for the enterprise to further enhance the shrink-fitting quality of crankshaft.

NFC/RFID Patch Coil Curvature Effect and Shielding for Medical Applications Wirelessly Powered

This paper presents the design of a flexible $4\times 4$ cm2 square coil for a medical wearable NFC/RFID patch. In such application, the coil is connected to an IC which can power supply an embedded medical sensor. This energy harvesting ability is achieved by inductive resonant coupling using NFC technology at 13.56 MHz. As the patch is fixed on human body (arm), the influence of the human tissue, the need of patch flexibility as well as the interest of a shielding must be investigated. This work focuses herein on the influence of the patch curvature on the coil ability to capture magnetic fields and thus on the recovered energy. This influence, related to the mistuning of the coil, is studied with and without shielding, by means of magnetic and conductive material layers. Measurements show the possible recoverable power level using a NFC chip (NXP NT3H) as the dedicated IC.

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

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

Forced convection boiling heat transfer inside helically-coiled heat exchanger

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

Combined Enhancement Techniques on Double Tube Heat Exchanger Using Nanofluid and Helicoid Tube Shape

Abstract The thermofluid characteristics of Al2O3–water nanofluid in the annulus of double-helical coiled tubes were experimentally and numerically carried out. The purpose was to investigate the effect of combined enhancement techniques of nanofluid and helicoid tube shape on the performance of a double tube heat exchanger. The effects of concentration of nanoparticles, Reynolds number, coil curvature ratio, and flow arrangement through the annulus of double-helical coiled tube were the main points of interest. Three coiled tube heat exchangers were manufactured and experimentally tested to study the design parameters on the performance of such a heat exchanger. A three-dimensional numerical computational fluid dynamic (CFD) model was developed to get additional insights on the thermal performance of double helically coiled tubes with nanofluid on a level of details not always available in experiments. It was found that the Al2O3–water nanofluid achieved an enhancement by 32% on the overall heat transfer coefficient. The heat exchanger effectiveness, heat transfer per unit pumping power, and the Nusselt number were also presented for different design parameters.

Performance of helically coiled gas heaters in supercritical CO2 Rankine cycles: A detailed assessment under convective boundary condition

Helical coil has drawn increasingly attention as the gas heater of supercritical Rankine cycles due to its high heat transfer rate and compact structure. This work focused on the thermal performance of supercritical CO2 helically coiled heater at a practical thermal boundary condition (i.e. convective boundary), under which the coil’s performance has been scarcely paid attention. Supercritical flow turbulence was solved by the Shear-Stress Transport k-ω model and heat transfer was dealt with in a solid-to-fluid conjugate manner. Influence of fluid temperature, mass flux, coil curvature and buoyancy was comprehensively analyzed over a wide range. Results reveal a significant self-regulation of local heat input in the region of Tb < Tpc, where heat flux gently varied along the coil axis. The mass flux and inlet temperature of heat source fluid had a strong impact on the local heat flux, the heat transfer coefficient and the thermal inhomogeneity, while coil curvature only had a weak influence. Comparison with results under uniform heat flux boundary shows that at convective boundary the influence of buoyancy on average heat transfer was weakened in the form of reduced affecting region and intensity, and local thermal inhomogeneity caused by buoyancy and centrifugal force was also relieved. Effect of thermal boundary condition is minimal in buoyancy-negligible cases like high mass flux condition. Further evaluation identifies that several Nusselt correlations obtained at uniform heat flux were capable of predicting average heat transfer at convective boundary, with a relative error within ±20%. Local heat transfer was characterized by a dimensionless number Ψ, which has three critical values of 0.1, 1 and 10 to quantitatively identify the relative importance of buoyancy and centrifugal effects. Finally, evaluation on the system design shows that helically coiled gas heater can contribute to improved compactness, reduced investment cost and a more flexible range of operating conditions for supercritical CO2 Rankine cycle.

Heat transfer enhancement and pressure drop by pulsating flow through helically coiled tube: An experimental study

Pulsating flow was applied as an active technique for heat transfer enhancement. Helically coiled tube was employed and convective heat transfer and pressure drop were experimentally investigated. Four helically coiled tubes with the same tube diameter and different coil curvature were fabricated and subjected to uniform wall heat flux. Distilled water was utilized as working fluid and its thermo-physical properties were estimated at mean temperature using available correlations. At first, Darcy friction factor and Nusselt number in steady laminar flow were compared with several correlations in the literature and the most accurate relations were found. Afterward, experiments were extended for pulsating laminar flow over a Womersly number range of 16–38 which corresponds to 2–10 Hz pulsating frequency, Reynolds number of 2000–9500, and Helical number of 350–2300. The results revealed that increment in pressure drop is nearly 3–7% in pulsating flow compared to steady one, while convective heat transfer enhanced up to 39%. Findings indicated that more heat transfer enhancement can be attained at low Reynolds numbers. Improvement in heat transfer rate and thermal performance was evaluated and discussed in detail. Also, a new correlation was proposed for Nusselt number in laminar pulsating flow. Among the four pulsating frequencies were studied in the current work, the optimum pulsating condition for achieving the best thermal performance was Wo ~ 24 (4 Hz).

Numerical Study of Thermofluid Characteristics of a Double Spirally Coiled Tube Heat Exchanger

In this study, the thermofluid characteristics of double spirally coiled tube heat exchanger (DSCTHE) were investigated numerically. A three-dimensional (3D) computational fluid dynamic (CFD) model was developed using ansys 14.5 software package. To investigate the heat transfer and pressure drop characteristics of DSCTHE, the Realize k–ε turbulence viscous model had been applied with enhanced wall treatment for simulating the turbulent thermofluid characteristics. The governing equations were solved by a finite volume discretization method. The effect of coil curvature ratio on DSCTHE was investigated with three various curvature ratios of 0.023–0.031 and 0.045 for inner tube side and 0.024–0.032–0.047 for annular side. The effects of addition of Al2O3 nanoparticle on water flows inside inner tube side or annular side with different volume concentrations of 0.5%, 1%, and 2% were also presented. The numerical results were carried out for Reynolds number with a range from 3500 to 21,500 for inner tube side and from 5000 to 24,000 for annular side, respectively. The obtained results showed that with increasing coil curvature ratio, a significant effect was discovered on enhancing heat transfer in DSCTHE at the expense of increasing pressure drop. The results also showed that the heat transfer enhancement was increased with increasing Al2O3 nanofluid concentration, and the penalty of pressure drop was approximately negligible.

An optimization of heat transfer of nanofluid flow in a helically coiled pipe using Taguchi method

In this research, water–Fe3O4 nanofluid flow and heat transfer factors are optimized in a helically coiled pipe using Taguchi method. Numerical simulations using the ANSYS Fluent 18.2 are obtained first to provide the input data for the Taguchi method. Experiments are also performed to validate the results of the simulations. An experimental setup is constructed and initial experiments with water and water–Fe3O4 nanofluid are executed using various mass flow rates. A single-phase approach is employed as the numerical simulation model. The Taguchi method is selected as a test design method. Three different control factors (mass flow rate, coil curvature ratio and fluid type) with four levels are selected with the Taguchi method. An effective parameter, η, is defined to investigate the influence of different control parameters on heat transfer and fluid flow characteristics. Results show that mass flow rate is the most effective factor on η. Fluid type and the coil curvature ratio are next effective parameters, respectively. Through the course of this study, it is found that the best conditions to achieve the maximum η value are: mass flow rate value of 6.98 g s−1, 1% vol. nanofluid as fluid type and coil curvature ratio of 0.048.

Consideration of Double Discrete Inclined Ribs in Low Curvature Coil for GSHP System

This article presents an investigation of a low curvature coiled tube with double discrete inclined ribs for an application to ground heat exchanger used in ground heat pump systems. Computational fluid dynamics is employed to analyze the heat transfer and fluid flow with several ribs. The analysis performs detailed study involving flow behavior, pressure drop, heat transfer rate, wall heat flux, absolute vorticity flux for a range of ribs height (0.45 mm, 0.75 mm, and 1 mm) and flowrate (ranging from 6 L/min to 10 L/min) on curvature of coil 2.22 m^-1. COP improvement factor, which is a function of heat transfer enhancement and pressure loss increase, is evaluated. The increasing of ribs height can deviate secondary flow, which contributes to heat transfer and pressure drop enhancement. In the case of higher ribs, circumferential heat flux distribution tends to be more fluctuated. The heat flux distribution also becomes smaller with the increasing of axial distance. The COP improvement factor significantly improves with the increase of ribs height. On the other hand, the COP Improvement factor tends to decrease with the increase in flow rate. The application of ribs in a low curvature coil is attractive and has the potential for Slinky-coil ground heat exchangers.

Development of a real‐scale cooling module for a PV power plant

The goal of this study is to develop units of a photovoltaic (PV) cooling system and evaluate its performance, aiming at commercial electricity production, once the increase in electricity output is obtained by cooling down the temperature of the PV module. The methodology covers the description of production procedures, control and verification of three different models of the cooling system, of which two are sheet-and-tube types, with different diameters of coil curvature (85 and 140 mm), and one is a multi-channel type model. Results show that the production of the two sheet-and-tube models presented no issues during their construction and operating phases, while the multiple-channel model presented some complications at the construction phase (e.g. the thickness of the sheets hampered the welding process, leading to leakages during the tightness tests). The empirical control tests showed that the temperature of the PV module with a cooling system applied remains lower than the nominal operating cell temperature, whereas the PV modules without a cooling system presented temperatures higher than 68.1°C. Thus, the authors conclude that the most appropriate model for large-scale production applied at PV systems is the coil one, with 85 mm of the diameter of coil curvature.

Heat transfer deterioration in helically coiled heat exchangers in trans-critical CO2 Rankine cycles

The heat transfer deterioration (HTD) of supercritical CO2 encountered in trans-critical CO2 Rankine cycle is an important issue related the safety of the whole unit. For the purpose, numerical simulations are performed to get a further insight into the mechanism of heat transfer characteristics of supercritical CO2 flow in helically coiled tube (HCT) both in horizontal and vertical orientations with parameters in a range of p = 8 MPa, G = 100–800 kg/m2s and q = 15–140 kW/m2. The Shear-Stress Transport (SST) k–ω turbulence model with enhanced wall treatment method is employed to handle the coupled wall-to-fluid heat transfer. Results show that secondary flow induced by the coil curvature produces a transverse transport of the fluid over the cross section of the pipe and therefore enhances the heat transfer. Additionally, in the vertical oriented HCT, the HTD at supercritical pressure observed in a smooth straight tube (ST) is significantly alleviated. At a higher q/G, the HTD still exists irrespective of coil orientations. But, different from ST, the HTD in HCT is caused by both gravitational and centrifugal buoyancy force. Therefore, the onset of HTD in HCT cannot be predicted by the empirical correlation (q = 0.0002G) derived from analytical and experimental results for ST. Based on numerical calculation, an improved buoyancy parameter is developed to predict buoyancy effect on vertical HCT with an internal upward flow.

Experimental study on condensation heat transfer in vertical helically coiled tubes

In the present experimental study, condensation of steam inside helically coiled tubes was investigated. Three helical coils of coil diameter 110, 135 and 160 mm were tested. The effect of mass flux, coil curvature ratio and temperature difference between steam and tube inner wall on the condensation heat transfer coefficient were analysed. The condensation heat transfer coefficient increases with the increase in the value of mass flux. Temperature difference has substantial effect on the heat transfer coefficient. For the first time, the effect of coil curvature ratio on condensation heat transfer is studied and discussed in the paper. It is found that helical coil having greater coil curvature ratio has high values of condensation heat transfer coefficient in comparison to a low curvature ratio. Experimental results are compared with the work of earlier investigators. A new empirical correlation is developed to predict the condensation heat transfer coefficient.

Experimental study on condensation heat transfer in vertical helically coiled tubes

In the present experimental study, condensation of steam inside helically coiled tubes was investigated. Three helical coils of coil diameter 110, 135 and 160 mm were tested. The effect of mass flux, coil curvature ratio and temperature difference between steam and tube inner wall on the condensation heat transfer coefficient were analysed. The condensation heat transfer coefficient increases with the increase in the value of mass flux. Temperature difference has substantial effect on the heat transfer coefficient. For the first time, the effect of coil curvature ratio on condensation heat transfer is studied and discussed in the paper. It is found that helical coil having greater coil curvature ratio has high values of condensation heat transfer coefficient in comparison to a low curvature ratio. Experimental results are compared with the work of earlier investigators. A new empirical correlation is developed to predict the condensation heat transfer coefficient.