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Droplet size distribution (DSD) is one of the key quality attributes of liquid–liquid emulsions. Various fluidic devices are used to generate emulsions. Most of the currently available models for estimating DSD are complicated to implement and computationally expensive. In this work, we have developed a simplified drop breakage model that is easy to implement and computationally inexpensive. This model approximates DSDs in three droplet populations, each characterised by a mean diameter. The developed drop breakage model was applied to simulate Sauter mean diameters of oil-in-water emulsions generated using three fluidic devices covering a broad range of shear rates and droplet sizes namely: vortex-based cavitation device (VD), helical coil (HC), and fluidic oscillator (FO). The variation of DSD with the number of passes (np) through the emulsion-producing fluidic devices was measured experimentally. The Sauter mean diameter (d32) and number of droplets (n) in each population were estimated from the measured DSD data. The procedure to estimate model parameters is presented. The simplified breakage model presented here was able to simulate the influence of the number of passes and operating conditions on Sauter mean diameter as well as breakage efficiency. VD was found to exhibit the highest drop breakage efficiency. FO was found to be a preferred choice for low (< 20 J/kg) energy consumption, HC for the middle range (20 – 100 J/kg) and VD for the higher (> 100 J/kg) range of energy consumption. The developed approach and model provide a simplified way of simulating the Sauter mean diameters of emulsions for a variety of emulsion-generating devices.

AbstractNuScale Power has completed a series of full-length helical coil steam generator tests at SIET Laboratories in Piacenza, Italy. The test program included an investigation of the onset and evolution of density wave oscillations (DWOs). This paper describes the mechanisms leading to the onset of DWOs. A semi-empirical DWO stability correlation was developed from first principles using data from tests performed in the full-height (2015) TF-2 counterflow test facility. This research supports the concept that the onset of DWOs is caused by liquid bridging inside the boiling length of the tubes. A DWO onset correlation is obtained by performing a steady-state momentum balance on the liquid slug created by liquid bridging in annular flow. This yields a momentum balance equation in terms of a set of dimensionless superficial velocities, a corresponding dimensionless pressure drop term, and an average void fraction. Envelope theory is then used to obtain a critical void fraction, which is substituted into the dimensionless momentum balance to obtain a DWO onset correlation similar to the Wallis countercurrent flooding correlation. Predictions using the DWO stability correlation have been compared to DWO experiments from the (2022) TF-2, TF-1, and Polimi. The predictions for the onset and termination of DWOs show excellent agreement with the data.

A simple but accurate mathematical model is crucial for dynamic simulations and controller design of helical coil once-through steam generator (OTSG). This paper presents a three-region movable boundary dynamic model of the helical coil OTSG. Based on the secondary side fluid conditions, the OTSG is divided into subcooled region (two control volumes), two-phase region (two control volumes) and superheated region (three control volumes) with movable boiling boundaries between each region. The nonlinear dynamic model is derived based on mass, energy and momentum conservation equations. And the linear model is obtained by using the transfer function and state space transformation, which is a 37-order model of five input and three output. Validations are made under full-power steady-state condition and four transient conditions. Results show good agreements among the nonlinear model, linear model and the RELAP5 model, with acceptable errors. This model can be applied to dynamic simulations and controller design of helical coil OTSG with constant primary-side flow rate.

Mathematical modeling of a helical coil thermal oil heater is difficult due to the complex heat transfer interaction between thermal oil and flue gas. The present publication reports the development of a transient model for the study of transient and steady-state behavior of fired helical coil thermal oil heaters. The mathematical model aims to predict the distribution of the flue gas temperature, thermal oil temperature, and tube wall temperature. A model is used for the accurate prediction of flame temperature and tube wall temperature. Prediction and control of the tube wall temperature are critical for the design and operation of a fired thermal oil heater.

Fluidic devices without moving parts are gaining more attention for continuous crystallization as they offer better mixing and number-up/scale-up possibilities. In this study, a loop setup with various combinations of devices, such as a fluidic oscillator, helical coils, and coiled flow inverters, was designed as a continuous crystallizer for seeded antisolvent crystallization of paracetamol in a methanol–water system. Care was taken to avoid particle settling and clogging while providing adequate residence time in the devices under consideration. The particle size distribution (PSD) of produced crystals was measured by offline imaging method using microscopy. The influence of fluidic device configurations, mode of operation, and residence time/batch time on the PSD of paracetamol crystals was investigated. A population balance model (PBM) was developed to interpret experimentally the observed PSD. The standard method of moments and lognormal distribution function with moment-based parameters (σ and μ) were used for simulating the evolution of PSD. Fitted kinetic parameters and developed PBM were able to simulate PSD over a wide operating range. The setup, approach, and model presented in this paper will be useful for understanding and designing continuous antisolvent crystallization using fluidic devices.

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-TiO2and Water/Ag_HEG nanohybrid fluids increased by 76 % and 49 %, respectively.

In the present study, the heat transfer, friction factor, and thermal performance factor (TPF) of the coil side for a helical coil heat exchanger by using non-Newtonian nanofluids for various modified Dean numbers ranging from 10 to 300 with three different curvature ratios δ equal to 0.072, 0.083, and 0.098 were investigated experimentally. The two-step method was adopted for the preparation of non-Newtonian nanofluids. For the same, the carboxymethyl cellulose (CMC) in concentration of 0.4 wt.% was added to distilled water with three different nanoparticles, viz., CuO, Al2O3, and TiO2, for particle concentrations ranges from 0.01 vol.% to 0.04 vol.%. The present investigation reveals that with increasing particle concentration the Nusselt number increases for all the nanofluids, while with increase in the curvature ratio the heat transfer rate decreases. The maximum enhancement in the Nusselt number was found to be 31.8% for CuO-based nanofluids at 0.04% particle concentration for coil 1, while the least enhancement of 21% was reported for TiO2-based nanofluids for coil 3. Moreover, the friction factor was also increased when particle concentration increases. Therefore, the TPF was evaluated and it was found greater than unity for all combinations. The above conclusion ensures that losses by pressure do not overcome the enhanced value of the heat transfer rate. The maximum value of TPF was found to be 1.30 for CuO-based nanofluids at 0.04 vol.% particle concentration.

•Specific thermal–hydraulic model for two-phase flow instability analysis in parallel helical channel system is established and validated.•The distinctive ϟ-shaped stability boundary line is found in in the parallel helical channel system.•The delay effect causing flow instability is more obvious if the void fraction exceeds 0.7.•The distribution of heat flux in the two-phase region of the channel plays a more significant role in the occurrence of flow instability.

This study investigates the effect of initial reactant concentration, residence time, and flow on the particle size and particle size distribution produced by single-phase reactive precipitation between BaCl2and Na2SO4in a helical coil reactor. Helical coils offer enhanced mixing due to the secondary flow generated by the imbalance of centrifugal forces. The particles produced in a helical coil reactor are found to have smaller sizes and narrower size distribution compared to a straight tube reactor under similar process conditions. It is shown that the average particle size in a helical coil reactor decreases with increasing Dean number, and particle size distribution becomes narrower at higher Dean number. For a reactant concentration of 0.5 M with the reactant concentration ratio of one, the average size changed from 580 to 263 nm when Dean number changed from 64 to 370. The initial reactant concentration is defined in terms of supersaturation ratio, and a decreasing trend in size is also observed with increasing supersaturation ratio. The particle size distribution curve also became narrower at higher supersaturation ratio. The residence time is observed to have no visible effects on the particle mean size and particle size distribution for the range of residence time, from 6 to 34 s, studied for the helical coil in this work.

AbstractTo enable the design of a light water small modular reactor, the boiling flow inside a helical coil steam generator has been simulated with the two-fluid model in Nek-2P. Nek-2P is the multiphase branch of the spectral element code Nek5000. Details of the implementation of the two-fluid model and the included closure models are discussed. The presented closure models include interactions for momentum, heat, and mass transfer between phases. Models for the drag, lift, and turbulent dispersion forces are included. The complete model is fully consistent in the limits of both phasic volume fractions approaching zero and is able to simulate flows of dispersed vapor, continuous liquid, dispersed liquid, continuous vapor, or any combination thereof. The closure models and their implementation in Nek-2P have been validated by comparing to experimental data for a boiling flow, demonstrating excellent agreement. Results from the simulation of the helical coil indicate strong phasic separation driven by the effects of buoyancy and inertia. Significant differences were observed in the results compared to simulations performed using Star-CCM+, although these differences were somewhat expected.

Sensible thermal storage tanks with immersed heat exchangers play a pivotal role in energy storage and exchange within a system, particularly when coupled with solar thermal collectors or heat pumps. Therefore, the optimization of the tank-exchanger assembly design and operation via modelling is of utmost importance in enhancing the performance and efficiency of these systems. This paper presents a critical review of one-dimensional modelling approaches for short-term sensible storage tanks equipped with immersed helical coil heat exchangers, primarily focusing on their application in solar thermal and heat pump systems. The purpose of the review is to identify the limitations, gaps, and challenges in the existing modelling methodologies. A comprehensive literature review and comparative analysis were employed to gather information about the topic and to critically evaluate and compare different studies and approaches within the field, considering their methodologies, findings, strengths, and weaknesses. The review is structured into four main sections, starting with an examination of storage-exchanger assembly configurations discussed from a modelling standpoint, followed by an overview of the fundamental principles and limitations of one-dimensional models, a critical review of contemporary methodologies to determine the overall heat transfer coefficient of immersed helical coil heat exchangers, and a comprehensive survey of simulation models that implement these methodologies. The main issue that has been identified is the absence of up-to-date correlations and empirical coefficients for one-dimensional modelling of tank-exchanger assemblies. In conclusion, this critical review highlights the need for further comprehensive research efforts to establish accurate correlations and empirical coefficients that can be used to effectively model storage tanks with immersed helical coil heat exchangers.

In the present work, heat transfer and fluid flow characteristics for both Newtonian and non-Newtonian fluids in tube-in-tube helical coil (TTHC) heat exchangers have been investigated numerically. The various TTHC heat exchanger configurations studied are (1) parallel and (2) counter flow, with and without baffles. The power law index (n) and Dean number (NDe) are varied from 0.5 to 1.25 and 50 to 500, respectively. Further, two different models have been proposed to predict the friction factor (f) and Nusselt number (Nu) in TTHC. It is observed that fand Nuin the TTHC heat exchanger with baffles in the annulus is higher as compared to without baffles. Furthermore, at low Prandtl number the baffles have significant influence on heat transfer, while at high Prandtl number flow configuration has high significance.

This paper discusses the conjoint effect of circular fin turbulators and alumina (Al2O3) nanofluid on the thermal performance of a helically wound coil-in-shell heat exchanger used for waste heat recovery. An experiment was conducted using three different coils: two with circular fin turbulators brazed to the annular coil surface at 45° and 90° orientations and one plain coil without a fin. The coil side fluid was Al2O3 nanofluid (0.05%, 0.1%, and 0.15% by volume concentrations) flowing in the coil under laminar and turbulent (500 ≤ Re ≤ 5500) conditions, while the hot air at different flow velocities from 1 to 3 m/s (i.e., 4500 ≤ Reh ≤ 13,500) was used as the shell-side fluid. The experiment revealed that the Nusselt number increased by 43.96% and 69.66% and the thermal-hydraulic performance increased by 16.92% and 35.71% for the 90° and 45° fin orientations, respectively, at 0.15% concentration of Al2O3 nanofluid and hot air velocity of 3 m/s. Furthermore, the thermal-hydraulic performance showed a nearly two-fold increase with 45° fin orientation/Al2O3 nanofluid combination. Based on the experiment, correlations were developed for the Nusselt number, friction factor, and thermal-hydraulic performance in the laminar and turbulent regimes, which are fairly in agreement with acceptable limits.

The ophthalmic surgical instrument of claim 1, wherein said respective pointed sharp end of said first helical coil structure and said second helical coil structure are configured to grasp and hold firmly and steadily the cataract lens within the human ocular lens capsule during the cataract surgery for reducing human ocular lens movement of said cataract lens within the human ocular lens capsule, for preventing said cataract lens from producing heat during the cataract removal surgery. The ophthalmic surgical instrument includes a pointed sharp end of the helical coil structure for grasping the human ocular lens without producing heat during the cataract removal surgery for avoiding corneal endothelium heat damage during a cataract removal surgery. The ophthalmic surgical instrument further may also include a connection with a phacoemulsification device for performing phacoemulsification of the cataract to break the cataract into smaller pieces, thereby facilitating removal of a cataract from a human ocular lens capsule. The ophthalmic surgical instrument of claim 1, wherein said respective sharp pointed end of said first helical coil structure and said second helical coil structure are configured to grasp the cataract lens for permitting a phacoemulsification cutting device to cut the cataract lens for performing phacoemulsification of a cataract to break the cataract lens into two or more pieces, thereby facilitating removal of said cataract lens from a human ocular lens capsule. [Extracted from the article]

AbstractHelical coil steam generators (HCSGs) are tube and shell heat exchangers under investigation due to their future in nuclear power applications. A model of an HCSG with a transverse pitch ratio of 2.98 and changing lateral pitch ratio was created to study the pressure on the surface of the tubes under low Reynolds number flow. Pressure-sensitive paint was applied to rods of an outer bundle of the test section, and instantaneous and average pressure fields were analyzed for Reynolds numbers 4000 and 6000. A comparative study showed that the pressures along the rods had nonlinear behavior. Previous studies suggested a relationship between tube bundle characteristics and the lateral pitch ratio in heat exchanger designs. Since the transverse pitch ratio is constant, the lateral pitch ratio defines the tube bundle cross section as either staggered or inline depending on the cross-section location. Averaged pressure distributions were compared to lateral pitch ratios at respective locations. The pressure distributions along the staggered cross-section portion of the test section were found to exhibit a linear behavior across the heat exchanger body. While this study focuses on average surface pressure measurements, the differences between the same lateral pitch ratio and surface pressure show disagreement with previous studies focused on constant cross-section tube bundles. Flow phenomena within tube bundles, such as vortex shedding, are suspected to be the cause of this discrepancy but a transient analysis is necessary to determine its source.

AbstractA model helical coil steam generator test section was designed and constructed to visualize the flow between two adjacent tube bundles—inner and outer bundle—that coil in opposite directions to one another. This study focuses on visualizing and characterizing fluid properties on the shell side of the unique tube-and-shell heat exchanger design. Flow within the shell side is characterized by recirculation regions below the tubes, or wake regions, and streamlined flow between tube bundles. The matched refractive index particle image velocimetry (PIV) experimental technique was used to experimentally capture the flow between the adjacent tube bundles. Images for PIV analysis were taken at three cross-sectional planes of the test section at 10 000 frames per second of an area approximately 24.54  23.20 mm. Average vertical and transverse velocity components were analyzed at a distance of r/rr = 1.1 about the tube centers at a specific rod height to observe flow separation and flow characteristics between the tube bundles. Measurements showed the magnitude of the normalized vertical velocity increased through the planes as the flow followed the helical pitch of the tube bundles. The flow was also observed to experience significant flow separation from recirculating eddies and vortex shedding across the rods.

•A helical coil phase change heat exchanger designed for thermal energy storage.•A prototype energy storage unit with paraffin wax was built and experimentally tested.•Charging time reduced by 35% when inlet HTF temperature increased from 70 to 75 °C.•Higher HTF flow rate reduces charging time but not discharging time.•HTF flow direction has no significant effects on charging and discharging times.

AbstractPost-acceleration of protons in helical coil targets driven by intense, ultrashort laser pulses can enhance ion energy by utilizing the transient current from the targets’ self-discharge. The acceleration length of protons can exceed a few millimeters, and the acceleration gradient is of the order of GeV/m. How to ensure the synchronization between the accelerating electric field and the protons is a crucial problem for efficient post-acceleration. In this paper, we study how the electric field mismatch induced by current dispersion affects the synchronous acceleration of protons. We propose a scheme using a two-stage helical coil to control the current dispersion. With optimized parameters, the energy gain of protons is increased by four times. Proton energy is expected to reach 45 MeV using a hundreds-of-terawatts laser, or more than 100 MeV using a petawatt laser, by controlling the current dispersion.

•Thermal performance of horizontal coiled tube LHTS device was experimentally considered.•Both charging and discharging of PCM were investigated.•Effect of initial temperature and flow rate of HTF on PCM in melting and solidification was tested.•Initial temperature of HTF was significantly affected the melting process.•Optimum HTF flow rate for melting was determined and it was 3 L/h.

Helical-coil is a common structure of heat exchanger unit in phase change heat accumulator and usually has the equal coil pitch between adjacent coils. Its thermal performances could be improved by improving the uniformity of the phase change material (PCM) temperature distribution. Thus, a novel non-equidistant helical-coil structure was proposed in this study. Its coil pitch decreased along the flow direction of heat transfer fluid, which made the heat exchange area in unit volume increase to match the decreasing temperature difference between the heat transfer fluid and PCM. The structure was optimized using numerical simulation. An experimental system was developed and the experiment results indicated that the proposed non-equidistant helical-coil heat accumulator was more effective than equidistant helical-coil for latent heat storage. The uniformity of the temperature distribution was also confirmed by simulation results.

Existing permanent helical coil fasteners, although commonly employed for mesh fixation during laparoscopic hernia repair, are associated with peritoneal tissue attachment formation and resultant visceral complications. We evaluated attachment formation, fastener engagement, and mesh/tissue integration associated with laparoscopic fixation using a novel permanent capped helical coil fastener (HC-Capped) compared to permanent non-capped helical coil fasteners (HC-Non-Capped) in a porcine model. Twelve female pigs underwent bilateral laparoscopic intraperitoneal fixation of Composix™ L/P Mesh (10 × 15 cm oval) with HC-Capped or HC-Non-Capped fasteners. Thirty-two fasteners were used to secure each mesh utilizing a “double-crown” technique. Laparoscopy at 30 days was used to evaluate the presence and area coverage of attachments (Diamond Score) and percentage of engaged fasteners. At 90 days, following necropsy, each mesh was evaluated for the presence, percentage, and tenacity (Butler Score) of attachments and fastener engagement. Samples were biomechanically evaluated to assess tissue integration via T-peel testing. HC-Capped fasteners demonstrated a significantly lower attachment area score compared to the HC-Non-Capped group at 30 days (0.92 ± 0.26 vs. 2.50 ± 0.29/3.00, p= 0.002) and 90 days (0.60 ± 0.22 vs. 2.08 ± 0.29/3.00, p= 0.004). At 90 days, the HC-Capped group evidenced significantly lower attachment tenacity score (1.00 ± 0.37 vs. 2.75 ± 0.33/4.00, p= 0.013). Furthermore, at 30 and 90 days, a significantly greater percentage of HC-Capped fasteners remained properly engaged (30 days: 99.7 % vs. 86.5 %, p< 0.001 and 90 days: 99.4 % vs. 74.5 %, p= 0.001). T-peel biomechanical testing demonstrated significantly greater mesh/tissue integration for HC-Capped group (2.16 ± 0.24 vs. 1.16 ± 0.29 N/cm, p= 0.038). In a porcine model, HC-Capped fasteners demonstrated significantly less attachment coverage and tenacity in the early postoperative period. Furthermore, the HC-Capped cohort evidenced significantly greater percentage of properly engaged fasteners and greater mesh/tissue integration. Data suggest that shielding exposed fastener points on the visceral mesh surface with polymer caps may reduce attachment formation and aid in mesh fixation and integration.

AbstractThis study reports the assessment of helical coil-packed bed columns for Zn2+adsorption on bone char. Zn2+adsorption breakthrough curves have been obtained using helical coil columns with different characteristics and a comparison has been conducted with respect to the results of straight fixed-bed columns. Results showed that the helical coil adsorption columns may offer an equivalent removal performance than that obtained for the traditional packed bed columns but using a compact structure. However, the coil diameter, number of turns, and feed flow appear to be crucial parameters for obtaining the best performance in this packed-bed geometry. A mass transfer model for a mobile fluid flowing through a porous media was used for fitting and predicting the Zn2+breakthrough curves in helical coil bed columns. Results of adsorbent physicochemical characterization showed that Zn2+adsorption on bone char can be attributed to an ion-exchange mechanism. In summary, helical coil columns appear to be a feasible configuration for large-scale adsorption systems with high flow rates where a significant reduction on purification system size can be obtained without compromising the adsorbent performance.

This study reports the assessment of helical coil-packed bed columns for Zn2+adsorption on bone char. Zn2+adsorption breakthrough curves have been obtained using helical coil columns with different characteristics and a comparison has been conducted with respect to the results of straight fixed-bed columns. Results showed that the helical coil adsorption columns may offer an equivalent removal performance than that obtained for the traditional packed bed columns but using a compact structure. However, the coil diameter, number of turns, and feed flow appear to be crucial parameters for obtaining the best performance in this packed-bed geometry. A mass transfer model for a mobile fluid flowing through a porous media was used for fitting and predicting the Zn2+breakthrough curves in helical coil bed columns. Results of adsorbent physicochemical characterization showed that Zn2+adsorption on bone char can be attributed to an ion-exchange mechanism. In summary, helical coil columns appear to be a feasible configuration for large-scale adsorption systems with high flow rates where a significant reduction on purification system size can be obtained without compromising the adsorbent performance.

The advantages and challenges of using the gas–liquid–liquid–solid (GLLS) hydrogenation system are discussed in this work using the case of selective hydrogenation of cinnamaldehyde to cinnamyl alcohol (an important ingredient in the perfume and flavoring industry). The four phases in this system include gas (hydrogen)-liquid (organic, reactant + solvent)-liquid (aqueous KOH)-solid (5% Pt/C catalyst). The addition of second liquid phase, i.e., aqueous KOH significantly increases selectivity toward cinnamyl alcohol compared to the conventional three-phase hydrogenation. The four-phase GLLS reactions were carried out and optimized in a continuous helical coil reactor. The role of key aspects such as gas solubility, kinetics, flow hydrodynamics, axial dispersion, and mass transfer on the performance of a continuous GLLS reactor is presented and discussed in this work. The presented results and discussion will be useful for addressing conflicting demands like long residence time, low axial dispersion, and high mass transfer. The experimental studies and results of the developed mathematical model indicate that the continuous GLLS helical coil reactor outperforms the batch operation. The production rates (kg day–1) of cinnamyl alcohol achieved in continuous operation were at least double in comparison to batch operation, with 32% less consumption of precious catalyst (per kg of product). The presented results will open up new opportunities for enhancing selectivity and overall performance of hydrogenations via introducing a second immiscible liquid phase and designing continuous tubular reactors for the same.

Storage tanks based on helical coil heat exchangers are an integral part of solar water heating systems and require optimal design configuration to achieve maximum heat transfer and a longer storage period. This study is focused on thermal analysis of a vertical helical coil-based water storage tank and derivation of inner and outer Nusselt number correlations by considering the storage tank as well as helical coil and catering to both forced and natural convection effects. A fluid-fluid conjugate heat transfer transient state model is validated with experiments performed with 50/50 % water-glycol mixture as heat transfer fluid at flow rates of 2 and 3 L/min in a solar water heating system, while water remains at static flow condition inside the tank. To reduce the computational cost, a symmetrical downsized (50 % of the real storage tank size) model is also designed and validated, which showed a mean absolute percentage error of 3.25 %. In order to derive the mathematical correlations, alterations were made to the validated model by using coils with curvature ratios ranging from 0.09 to 0.184 with HTF flow rates in laminar flow regimes, ranging from 30 to 100 L h−1at temperatures from 40 °C to 80 °C. Furthermore, inner Nusselt number mathematical correlations based on M number, curvature ratio, and Prandtl number showed good agreement with correlations derived by past investigators. Similarly, the outer Nusselt number of the coil was related to Rayleigh's number and the derived relations showed good agreement with the past studies, while Nuo = 0.1996 (Rado0.326) showed the least error of 2.06 %. Finally, thermal stratification analysis helped to understand that coil position and aspect ratio determine the thermocline developed inside the storage tank. Results show that extension of coil inside the tank up to 83.7 % of the tank height, ensured greater thermocline range, and tank with aspect ratio 3 turned to be better for thermal energy storage for longer period.

The use of phase change materials (PCM) for latent heat thermal energy storage (LHTES) is a common method of storing thermal energy in buildings. Because the thermal conductivity of the PCMs is low, so the rate of their energy charge/discharge would be confined. To overcome this issue, a new design is proposed using helical coil to maximize the contact surface between the heat transfer fluid (HTF) and the PCM. Both sides of the helical coil are filled with PCM, while in the inner region, copper metal foams (porosity of 0.9 and density of 12 PPI) are utilized for heat transfer rate enhancement. Effects of various parameters, including the inlet HTF flow rate, its temperature, and use of porous media on thermal energy storage performance in charge and discharge processes are analyzed experimentally. Six thermocouples are placed inside the PCM in different regions and melting and solidification processes are recorded using a thermal imaging camera. Results are presented in terms of temperature variation in different regions, temperature contours, mean temperature response, Stefan number, the charge/discharge time, and the extracted power of discharge. The results reveal that using porous media can remarkably reduce the charge/discharge time up to 57 %, which is depended on the inlet working fluid temperature. The charging time reduction is higher when the inlet HTF temperature increases. When the flow rate of HTF is increased, the charging time can be slightly shortened, while this effect becomes dominant when using porous media. Use of porous media could also accelerate the discharge time, while a faster discharge rate was observed for lower HTF flow rates during discharging the stored energy. Also, a lower initial temperature of the inlet HTF provides faster depletion rate.

The flow regimes and interfacial shear stress in helical coil with air-Newtonian and non-Newtonian liquid has been analyzed by developing a dynamic interaction model. The model equation has been developed based on the flow regimes, drag at interface and the wettability effect of the liquid. Also the intensity factor of friction factor of two-phase flow in the helical coil is analyzed and correlated with the dynamic, geometric and physical variables. The functional form of equation appears to predict the pressure drop and interfacial stress satisfactorily for two-phase flow in helical coil with sodium carboxymethyl cellulose (SCMC) solution of different concentrations. The analysis of the model may be useful for further understanding of the complex flow behavior in multiphase flow unit for industrial installation.

•The overall heat transfer is enhanced by 2.29% at 2.0% vol. of nanofluid.•Exergy efficiency for the 1.0 vol% nanofluid is higher than the base fluid by 21%.•At 2 lit/min, and 2 vol%, the friction factor is increased to 28.08%.•Heat transfer coefficient is increased to 88.95% at 2.0 vol% and 6 lit/min.

This research investigates a 3-D double-pipe helical coil heat exchanger containing Phase-Change Material (PCM) as a thermal storage system in solar water heaters. A concentric double-pipe follows the helical profile upward and creates a heat storage unit. In the unit, water in turbulent mode flows in the inner pipe as a Heat Transfer Fluid (HTF), and RT-50 is considered PCM placed in the annulus. This heat exchanger with all related conditions is modeled in Ansys Fluent 19 software, and we used the k-ε RNG turbulence model to simulate turbulent flow. For evaluating this novel model of thermal storage unit, the impact of some critical geometrical parameters, like helical pitch, inner and outer pipe diameter, and some flow parameters, such as fluid inlet temperature and Reynolds number, have been analyzed. The most important outcomes of the investigation show that inlet temperature and inner and outer pipe diameter are critical factors for the storage system's design. A 1.5 % change in inlet temperature will enhance the melting rate by 27 %. Also, by increasing the inner pipe diameter by 42 %, the melting process was improved by 92 %, while the outer pipe diameter was inversely related to the melting rate. A 20 % increase in this parameter's value showed a 52 % reduction in the melting. Moreover, the change in the helical pitch could not significantly affect the PCM melting process, and for a 300 % increase in pitch size, the melting process increases only by 0.6 %.

The endovascular coiling of very small ruptured aneurysms with difficult geometry presents a significant treatment challenge because of potential dangerous complications, such as intraprocedural ruptures. We report our initial experience with the use of a dual microcatheter technique, combined with new hypersoft helical coils, for the treatment of these difficult lesions. Fourteen very small aneurysms with a maximum diameter of ≤3 mm that presented difficult configurations, such as a wide neck or an important branch vessel arising from the fundus, were identified using digital subtraction angiography. These lesions were successfully treated using a dual microcatheter technique and new hypersoft helical coils. There were no intraprocedural ruptures or procedure-related thromboembolisms. Complete or near-complete occlusions were achieved in all of the lesions. A Raymond score of RS 1 was achieved in eight of the aneurysms (57.1%) and an RS 2 was achieved in six of the aneurysms (42.9%). The mean packing density was 35.5%. At the last post-procedure clinical follow-up, a good clinical outcome (a modified Rankin scale score of 0–2) was observed in 11 of the patients (91.7%). The result of angiographic follow up in 11 cases showed two recanalized aneurysms. The use of the dual microcatheter technique and new hypersoft helical coil allowed for stable coil framing and good packing in geometrically difficult tiny aneurysms and presented a low rate of adverse events related to the procedure. The technique provided an efficient strategy for treating very small aneurysms with difficult configurations and high risks.

•The CFD method was employed to predict the thermohydraulic performance of an HCHX.•Taguchi method coupled with GRA optimized HCHXs’ thermohydraulic performance.•Coil pitch and coil diameter influenced the thermohydraulic performance of HCHXs the most.•Helical tube's outer diameter had a low impact on HCHXs’ thermohydraulic performance.•The optimized HCHX increased the heat transfer rate and reduced pumping work greatly.

Owing to its advantages of high heat transfer efficiency and compactness, the helical coil once-through steam generator (HCOTSG) can be used in floating nuclear power plants and has been widely used in the design of small modular reactors. The helical tubular geometric structure of the HCOTSG allows heat transfer and local flow changes to occur under complex ocean conditions. In this study, theoretical models of ocean conditions are added to the RELAP5/MOD3.3 code and verified. Using the modified RELAP5 code, the thermal–hydraulic characteristics of the HCOTSG under ocean conditions are simulated. The results show that under rolling conditions, the flow oscillation amplitudes of the single liquid-phase, two-phase flow, and single gas-phase regions are different. A circular change in the horizontal position of the helical tube causes the fluctuation of the parameters to change periodically. A phase difference of approximately 3.9 s at a flow rate of 23 kg/s is observed in the flow fluctuation along the axial direction. The driving force, period, and amplitude of rolling significantly affect the flow fluctuation in the HCOTSG. In natural circulation, the flow in the HCOTSG is complex, and the primary-side flow fluctuation can reduce the trough of the flow oscillation at the helical tube by approximately 24.3%.