Coiled Tube Research Articles

Investigation of the impact of utilizing PCM into a coil in a single-pass air heater (experimental study)

This study aims to design, build, and assess the SAH's performance with an integrated enhanced phase-change material (PCM) absorber storage system. Using materials found locally, two single-pass solar air heaters were designed and produced for this study. The first solar heater was made without phase change material (Conventional SAH), and the second included PCM by adding paraffin wax to the coil tube (Improved SAH). In February, March, and April of 2024, real - results were carried out on the air heaters in Mosul city, Iraq. At a mass flow rate of 0.0147 kg/s, the experiments were conducted with and without a PCM system. As opposed to the first case without PCM, the study's findings indicated that the air temperature outside of the heater increased significantly in the second case with (the addition of paraffin wax). The highest recorded outlet temperatures in February, March, and April for both cases were (39.5, 50.7 °C), (49.4,58.9°C), and (57.4,70.6°C). To compare the efficiencies of the SAHs for both instances (Conventional and Improved), the efficiency of the improved SAH is higher than the efficiency of conventional SAH, such as (48.1% and 68.32 %), (58.6% and 72.8%), and (67.1% and 86.47%) in February, March, and April.

Comparative investigation on water fouling characteristics in 5 mm and 7 mm tubes with smooth type and screwed type

Application of copper tubes with the diameter of 5 mm instead of 7 mm in chillers of central air conditioning systems is the development tendency due to the requirement of copper material saving. However, the heat transfer deterioration by water fouling precipitated in 5 mm tubes may be more serious than that in 7 mm tubes. The purpose of this paper is to comparatively investigate the water fouling characteristics on both 5 mm and 7 mm tubes. An accelerated experimental method of water fouling process was designed to quickly evaluate the fouling degree. Four tube types are tested, i.e. a 7 mm smooth tube, a 7 mm screwed tube, a 5 mm smooth tube and a 5 mm screwed tube, and these tubes are fabricated as flexible coiled tubes with total length of 200 cm. The results show that the water fouling process experiences the initiation, growth and stabilization stages in sequence, and the crystal form of fouling is in the vaterite, aragonite and schistosity patterns respectively. The fouling masses in 5 mm smooth tube and 5 mm screwed tube are respectively 42.1% and 16.9% larger than those in 7 mm smooth tube and 7 mm screwed tube, meaning that 5 mm tubes are more prone to form water fouling compared with 7 mm tubes; while the averaged fouling mass in screwed tubes is 2.8% lower than that in smooth tubes since screwed tubes are benefit to destroy the integrality of fouling layer and enhance the removal of deposited particulates.

Impacts of geometric factors on the hydrothermal characteristics in a shell and cone-shaped coil heat exchanger

Cone coils have a larger surface area and produce more turbulence, which enhances the heat exchange rate, making them a more efficient option for improved heat transfer than simple coils in shell-and-coil heat exchangers. In addition to reducing fouling and the requirement for maintenance, the cone shape may also provide the benefit of a self-cleaning action. Ensuring a more even flow distribution maximizes the heat exchanger's surface area use and reduces poor-flow zones. Applications needing compact solutions without compromising performance significantly benefit from this design's versatility, allowing customization to meet unique operational demands. This work evaluates numerically the impact of employing a cone-shaped coil tube in a shell-and-coil tube heat exchanger, considering various configurations and coil pitches. A commercial CFD code is used to perform the numerical simulations based on the finite volume approach. The present study has two sections. In the first part, three different coil configurations were considered. The best case was considered according to the numerical results obtained from the first section. Then, in the second part, the impact of the cone coil pitch on the hydrothermal characteristics was analyzed. The obtained numerical outcomes revealed that the best performance evaluation criteria factor belongs to the cone-shaped coil with divergent configuration by about 64.1 % and 57.45 % more than the cone-shaped coil with convergent configuration at De = 1,000 and De = 2,500, respectively. Moreover, the cone-shaped coil with a divergent configuration displayed higher JF values by approximately 61.54 % and 58.06 % than a cone-shaped coil with a convergent configuration at De = 1,000 and De = 2,500, respectively. Among different evaluated cone coil pitches, the maximum performance evaluation criteria factor belongs to the case with pitch values of 40 mm. Moreover, the JF value increases by approximately 4.76 % and 5.56 %, respectively, at De = 1,000, when the pitch value grows by around 60 % and 100 %. Furthermore, when the pitch value climbs by 60 % and 100 %, at De = 2,500, the JF value rises by roughly 12.16 % and 19.59 %, respectively.

Construction of pyrrolo[3,2-b]pyrrolyl-linked covalent organic polymers to promote continuous overall H2O2 production

Sacrificial agent-free, solar-driven photocatalytic oxygen reduction holds promise for hydrogen peroxide production. However, the rapid recombination of electron–hole pairs in catalysts and the slow diffusion rate of oxygen on the catalyst surfaces significantly hinder the efficiency of hydrogen peroxide production. To address these issues, we developed a novel class of pyrrolo[3,2-b]pyrrolyl-linked covalent organic polymers (COPs) combined with microreactor technology to enhance hydrogen peroxide synthesis. These structurally well-defined polymers feature photoactive pyrrolo[3,2-b]pyrrolyl units were assembled from aldehyde, aniline, and 2,3-butanedione through a one-pot three-component reaction. Integrating pyrrolo[3,2-b]pyrrolyl moieties into the COPs creates donor–acceptor structures that facilitate the separation of photogenerated electrons and holes. Among them, COP-2 achieved the highest H2O2 yield of 5446 μmol g−1 h−1. Furthermore, we designed a coiled tube photomicroreactor to improve mass transfer efficiency in the gas–liquid–solid triphase system, boosting the H2O2 yield to 20285 μmol g−1h−1 without the need for a sacrificial agent. This study offers new insights into integrating polymer photocatalysts with microflow technology, underscoring the potential for future green and continuous H2O2 production.

Nematocyst Types and Characteristics in the Tentacles of Gershwinia thailandensis and Morbakka sp. (Cubozoa: Carybdeida) from the Gulf of Thailand.

Nematocysts, specialized stinging cells in cnidarians, play a crucial role in both defense and prey capture, containing venomous, coiled tubes within a capsule. While box jellyfish are recognized as a medical threat, information on the nematocysts of species like Gershwinia thailandensis and Morbakka sp. from Thai waters remains sparse. This study explores the types and morphology of nematocysts found in the tentacles of these species using light and scanning electron microscopy. We identified three nematocyst types: club-shaped microbasic p-mastigophores, oval isorhizas, and oval microbasic p-rhopaloids. Notably, significant differences in capsule sizes were observed, especially in the microbasic p-mastigophores and isorhizas. The discharge tubules tapered from the proximal to the distal ends, featuring arrow-shaped spines in a helical pattern. A distinct lancet structure was present in both microbasic p-mastigophores and p-rhopaloids. These findings suggest that variations in nematocyst size and morphology may be linked to evolutionary adaptations, functional roles, and venom toxicity. Further research into venom discharge mechanisms could offer valuable insights into the ecological and medical importance of these cnidarians.

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

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

Identifying synthetic variables influencing the reproducible microfluidic synthesis of ZIF nano- and micro-particles

The reproducible synthesis of nano- and -micro particles is a critical step in multiple synthetic and industrial processes. Microfluidic synthesis offers numerous advantages for development of precise, reliable, and industrially useful synthesis protocols. However, the influence of different synthetic variables on reproducibility in microfluidic synthesis is underexplored. In this work, we systematically study the influence of key synthetic parameters on the microfluidic synthesis of four Zeolitic Imidazolate Frameworks (ZIFs): ZIF-7, ZIF-8, ZIF-9, and ZIF-67. Utilizing a coiled tube microfluidic setup, we explore the influence of key synthetic parameters such as reagent concentration, stoichiometry, aging time, and nine modulators (pH-altering agents, surfactants, and polar polymers). Most importantly, we evaluate the impact of these variables in combination with the role of mixing, using the Dean flow model. Lastly, we focus on the reproducibility problems that a coiled reactor presents at specific flowrates and how these problems can be recognized and avoided. Overall, the insights collected from this work inform the design of synthetic protocols and enhance material reproducibility and control in microfluidic nano- and micro-particle synthesis.

Failure analysis in pyrolysis furnaces: Impact of carburization and thermal cycles on tube properties

The dominant failure mechanism in radiation coil tubes in pyrolysis furnaces is the detrimental interaction between carburization and reduced material ductility. This combination results in localized deformations, significant ovalization, and cracking in the tubes. At the same time, a second critical failure mechanism emerges during emergency furnace shutdowns, characterized by brittle fractures that can generate extensive longitudinal cracks in multiple tubes. This work presents a case study on the occurrence of failures that resulted in brittle fracture rupture of several tubes in a pyrolysis furnace that accumulated 43,720 h of operation. This highlights the practical importance of monitoring and managing the integrity of coil tubes. The tube samples were analyzed using optical and scanning electron microscopy, evaluation of carburization through magnetic permeability and NACE Test TM498, identification of carbides by X-ray diffraction (XRD), and dilatometry. Additionally, thermal stress analyses were performed using the finite element method, along with tensile tests at different temperatures. It was found that the tubes of the coil that operated at lower temperatures in their operational cycle did not rupture during the emergency shutdown, unlike other coils whose tubes experienced significant failures. An important contribution from this study is the demonstration of optimized operational cycle management and thermal control are essential in preserving protective oxide layers, minimizing coke formation and the effects of carburization and creep. This can reduce shutdown frequency and maintenance costs, improving the cost-effectiveness of the cracking process.

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

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

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

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

Performance Assessment of Confined Tube Aerators in Parallel Configuration

Aeration plays a major role in the activated-sludge wastewater treatment process. Microbes require an oxygen-enriched environment to digest organic materials and remove nutrients from the wastewater stream. For providing this oxygen, artificial aeration is required, which is responsible for the majority of energy use in treatment plants. Typically, this is accomplished with diffused aerators, where pressurized air is forced through a porous medium at the bottom of deep basins, and bubbles float up through the water column transferring oxygen in the process. This is a relatively energy-intensive process, which is prone to fouling at the porous media. In this study, a Confined Tube Aeration (CTA) system is proposed, where a pump forces water through a Venturi injector, where air is naturally drawn in. At the Venturi discharge, the flow is diverted to a coiled tube in which oxygen transfer occurs. This study analyzes the effect of parallelizing the CTA system with multiple injectors and at varying pump speeds (flow rates). Using experimental and analytical means, the maximum standard aeration efficiency was found to be with three injectors in parallel, at maximum pump speed, and utilizing a CTA with diameter 31.75 mm and length 3.048 m. This value was found to be 0.542 kg O2/kWh, and represents a 25% increase over the single-injector case. Although the analyses herein utilize a relatively small (0.746 kW) pump, these results indicate that CTA systems may scale well to larger pump sizes necessary for full-scale municipal wastewater treatment.

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

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

Determining of the thermo-hydraulic characteristics and exergy analysis of a triple helical tube with inner twisted tube

An innovative technique to enhance heat transfer as a passive method was investigated. The combination of the twisted tube and helical coil to increase the swirl intensity is presented. The current investigation showed experimentally and numerically the exergy and thermal performance analysis of a new design of a triple tube design called a triple helical tube with inner twisted tube, THTITT. The new design is a modified design of a double helical tube with inner twisted tube, DHTITT which is created by twisting the inner tube. Besides the benefits of adding the third fluid to DHTITT that achieve extra contact surface area per unit length between the intermediate tube and the new passage in the outer tube. In which expected to enhance the temperature gradient between the three fluids and consequently, the thermal characteristics augment occurred. The twisted tube increased the intensity of the swirl flow and more intense disturbance of the fluid in the tube occurred. A 3d CFD model was established to get more insight at a level of detail not always available in the experiment. The effects of twisted pitch ratio, ξ hydraulic diameter, ω, helical coil torsion, α, helical coil inclination angle, φ, as well as Dean number, NDn, h were explored. Four groups of test specimens include various ξ of 5.32, 7.97, and ∞, various ω of 3.8, 6.8, and 9.9 mm, various α of 0.068, 0.095, and 0.121, and various φ of 0°, 45°, and 90° were established, manufactured and examined in this investigation. The investigation covered Reynolds number, NRe,h, for a range of 2450:29300 corresponding to Dean number, NDn, h, for a range of 570:4800. The results showed a higher Nusselt number, NNu, h, of THTITT compared to DHTITT by 61.8 %%, while the increase in fh is approximately negligible. Also, by decreasing ξ from ∞ to 5.32 increases NNu, h by 33.4 %, with an increase in friction factor, fh by 57.6 %. Furthermore, with a decreasing ω from 9.9 mm to 3.8 mm, a significant increase in NNu, h occurs by 20.6 %, at the expense of increasing fh by 36.4 %. In addition, with decreasing α from 0.121 to 0.068, a significant increase in NNu, h occurs by 27.6 %, at the expense of increasing fh by 17.1 %. Finally, the THTITT decreases the heat loss (exergy destruction) between the hot and cold fluids. New correlations to predict NNu,h, and fh are presented.

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

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

Continuous flow hydrothermal synthesis of MoVNbTeOx in micro-coil tubular reactor for oxidative dehydrogenation of ethane

MoVNbTeOx is the most promising catalyst for the oxidative dehydrogenation of ethane (ODHE) process, which is usually prepared by hydrothermal methods. However, the synthesis of MoVNbTeOx is time-consuming and sensitive to the homogeneity of the synthesis environment, which limits its preparation reproducibility and large-scale accessibility. In this work, a continuous flow hydrothermal synthesis (CFHTS) process for the preparation of MoVNbTeOx catalysts was developed and the synthesis parameters were screened using a tubular reactor. Using a micro coil tube as a reactor, MoVNbTeOx catalysts can be synthesized rapidly at 300 °C and 10 MPa. Meanwhile, the catalytic performance of MoVNbTeOx synthesized by CFHTS method was also significantly improved, with the activity nearly doubled compared to the samples prepared by the conventional method. Compared with the conventional method, the preparation time of CFHTS method can be shortened from 48 h in the batch mode to 10 min in the continuous mode, and the capacity per unit volume of the reactor has been increased by orders of magnitude, which provides the possibility of industrial scale-up of MoVNbTeOx catalysts.

Hydrothermal analysis of hybrid nanofluid flow inside a shell and double coil heat exchanger; Numerical examination

In a shell-and-coil heat exchanger, employing a double coil instead of a simple coil causes more heat transfer compared to a simple coil because the double coil improves heat exchange through enhanced fluid flow and turbulence, enabling a longer tube length in constrained locations.. In addition to reducing fouling and the requirement for maintenance, the helical shape may also provide the benefit of a self-cleaning action. Ensuring a more even flow distribution also maximizes the heat exchanger's surface area use and reduces low flow zones. Applications needing compact solutions without compromising performance especially benefit from this design's versatility, allowing customization to meet unique operational demands. In numerous industrial applications, helical coils offer substantial benefits in terms of effectiveness, upkeep, and design freedom.In the present work, heat transfer and fluid flow in a shell-and-coil tube heat exchanger equipped with a double helical coil are evaluated numerically. The employed heat transfer fluids are water-based hybrid nanofluids, including TiO2-Mgi/water and AG-HEG/Water. The obtained outcomes are compared with the results of pure water. The range of considered Reynolds numbers is 500 – 2000. This work consists of two sections. In the first part, the impact of the type of hybrid nanofluid on the hydrothermal behaviour of the proposed heat exchanger is analysed. The volume concentration of the nanoparticles here is ϕ1 = ϕ2 = 0.3. In the second section, the best hybrid nanofluid is selected according to the results of the first section; then, the impact of the nanoparticles' volume concentration on the thermal performance of the proposed heat exchanger is evaluated. Three various nanoparticle volume concentrations, including ϕ1 = ϕ2 = 0.1, ϕ1 = ϕ2 = 0.3, and ϕ1 = ϕ2 = 0.5, are considered, and the results are compared with those of the pure water case (ϕ1 = ϕ2 = 0).The obtained results show that amongst the different heat transfer fluids considered, the Water/MgO-TiO2 model shows the most outstanding value of thermal performance in all the studied Reynolds numbers. Also, the obtained numerical results show that the use of the proposed double coil tube leads to an increase in the heat transfer rate.

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

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

Study of Buffeting Excitation Acting on Coil Tube Bundles in Cross Flow

Abstract The amplitudes induced by random excitation forces on the tubes bring continuous friction between the tube and supports, which results in gradual failure of the tubes due to fretting wear. Therefore, it is very important to determine the envelope lines of the random excitation force spectrum for the coil tube. To the authors' knowledge, there are no published studies on the normalized force spectrum of coil tubes. In this paper, a simplified three-layer experimental model was established. The robustness of the numerical method was demonstrated by comparing the experimental and simulated results, including the vibration response and the fluid excitation force spectrum. Then, a semi-empirical equation for predicting the dominant frequency of turbulent buffeting was constructed by employing the threshold envelope method. Through the observation of time-history and root-mean-square (RMS) data, it was found that the pitch diameter ratio between adjacent tube layers, a, had the greatest influence on the force coefficients. The smaller a is, the larger the force coefficients are. The pitch diameter ratio in the same layer, b, and helix angle, α, had little effect on the force coefficients. With the increase of α, the flow instability in the shell-side flow enhanced and the fluctuation of force coefficients became larger. Finally, the mechanisms of the tube position, Reynolds number (Re), and bundle structure on the normalized force spectrum were studied. The normalized envelope force spectrum for coil tubes was proposed as the guidelines to predict and evaluate the random excitation force acting on the tubes.

Oil wear debris sensor with temperature compensation

In this paper, in response to the problem that oil temperature changes will affect the detection results of the inductive wear debris sensor, a Wheatstone bridge-type oil wear debris sensor was designed using two two-wire helical tube coils, precision potentiometers, precision resistors, and a conditioning circuit with differential, phase-locked, and amplification functions were designed. Through practical tests, 72–400 μm iron particles were detected under the water bath's heating condition from 20℃ to 70℃. It proves that the designed Wheatstone bridge sensor and conditioning circuit can detect ferromagnetic particles in multiple temperature oil. The de-signed sensor and conditioning circuit effectively solves the problem of temperature drift of the detected signal under high-temperature conditions, improving the signal-to-noise ratio of wear debris detection under multiple temperatures. The sensor is suitable for lubricant detection systems with varying or constant high oil temperatures. The work presented in this paper provides significant reference value for the practical operation of oil sensors in real-world environments.

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

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