Side Of Coil Research Articles

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.

Atomic Force Microscopy Study of the Long-Term Effect of the Glycerol Flow, Stopped in a Coiled Heat Exchanger, on Horseradish Peroxidase.

Glycerol is employed as a functional component of heat-transfer fluids, which are of use in both bioreactors and various biosensor devices. At the same time, flowing glycerol was reported to cause considerable triboelectric effects. Herein, by using atomic force microscopy (AFM), we have revealed the long-term effect of glycerol flow, stopped in a ground-shielded coiled heat exchanger, on horseradish peroxidase (HRP) adsorption on mica. Namely, the solution of HRP was incubated in the vicinity of the side of the cylindrical coil with stopped glycerol flow, and then HRP was adsorbed from this solution onto a mica substrate. This incubation has been found to markedly increase the content of aggregated enzyme on mica-as compared with the control enzyme sample. We explain the phenomenon observed by the influence of triboelectrically induced electromagnetic fields of non-trivial topology. The results reported should be further considered in the development of flow-based heat exchangers of biosensors and bioreactors intended for operation with enzymes.

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

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

Analytical Modeling of Slotless Axial Flux Permanent Magnet Motor With Equidirectional Toroidal Winding

This study proposes a two-dimensional (2D) analytical model (AM) of slotless axial flux permanent magnet (AFPM) motor, which includes two submodels of armature winding (AW) and permanent magnet (PM) magnetic fields. It can reveal the operating mechanism of equidirectional toroidal winding (ETW) armature magnetic field in the theory and quantitatively analyze its AW and PM magnetic fields. The proposed AM is characterized in that AW magnetic field submodel is established only based on the current density distribution of the effective conductors on one side of a single toroidal coil considering its width and thickness. First, based on the proposed equivalence principle, the analytical submodels of AW and PM magnetic fields of AFPM motor with ETW are established separately, and the formulas of back EMF and torque of the motor are derived. Second, the electromagnetic performance of a slotless AFPM motor with ETW is studied by the proposed 2D AM, including the waveforms of AW and PM magnetic fields, phase back EMF and torque, which are verified by the finite element model. Finally, a prototype of AFPM motor with ETW is manufactured and tested in open-circuit and on-load conditions, which verifies the accuracy of the proposed AM.

Innovative method for heat transfer enhancement through shell and coil side fluid flow in shell and helical coil heat exchanger

Innovative method for heat transfer enhancement through shell and coil side fluid flow in shell and helical coil heat exchanger

Performance characteristics of shell and helically coiled tube heat exchanger under different tube cross-sections, inclination angles and nanofluids

The current research deals with an experimental and numerical inspection of the shell and helically coiled tube heat exchanger (SHCTHE) under various circular, elliptic, and square tube cross-sections. The research study strives to ameliorate the thermal-hydraulic performance with single nanofluids of Al2O3/H2O, MgO/H2O, and TiO2/H2O. Various factors were inspected to consider the heat exchanger performance under parameters, SHCTHE inclination angle, HCT diameter ratio, flow direction, the cross-section geometry shape, nanomaterials type, and nanomaterials concentration. The modeling engaging a numerical code tool of ANSYS-FLUENT 19 was accomplished with a 3D (RNG)/k–ϵ model. The mass flow rate and working fluid temperatures through the coil and shell sides were (0.05:0.2 kg/s at 80 °C and 0.05–0.2 kg/s at 10 °C, respectively. One of the most important results was that the SHCTHE with a circular tube cross-section gave the highest Nusselt number with an approximate percentage of 62.5%. The SHCTHE effectiveness and the number of transfer units were enhanced by around 19.35% and 30.78%, respectively, by the greater HCT diameter ratio and Al2O3 nanomaterials. Nusselt number, friction factor, and SHCTHE effectiveness were correlated through equations (52:55) with dimensionless factors and their limitations.

A Reverse Electromagnetic Force Suppression Circuit and Its Control Method for Reluctance Coil-Gun

To realize high-speed launch of reluctance coil-gun (RCG) requires the suppression of reverse electromagnetic (EM) force, when the center of the coil coincides with the center of the projectile to disconnect the coil power supply to quickly reduce the current is an effective means. In this study, the problems in the existing researches are explained in terms of circuit theory, and two technical difficulties are pointed out. One is to find the exact coincide time, which is basically estimated by the finite element method (FEM) at present, there are problems of slow calculation speed, and the results are affected by the accuracy of the input electrical parameters. Second, a sudden shutdown of a charged IGBT will create a large inductive electric potential and may be damaged. In this study, the treatment methods are proposed for these two points, respectively. On the one hand, an algorithm model is proposed to quickly estimate the coincide time based on the measured current data in the coil; compared with the FEM, it has the advantages of no need to know the electrical parameters and fast calculation speed. On the other hand, a new circuit topology is proposed, in which the IGBT is moved to the coil branch for current breaking at any time and a resistor–capacitor ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RC</i> ) absorption circuit is connected in parallel to the coil side to protect the IGBT. The comparison of experimental and simulation results proves that the method proposed in this study is feasible, and it avoids both the tedious operation of testing component parameters and the errors caused by inaccurate parameter input, showing the convenience in application.

Experimental Study of Double Pipe Helical Coil Heat Exchangers in the Laminar to Transitional Flow Regime

This study experimentally investigates various heat transfer characteristics, pressure drop, friction factor, Nusselt number, and Dean Number in a double-pipe helical coil heat exchanger. The study examines the hot water mass flow rates ranging from 0.02 to 0.12 kg/s and the cold-water mass flow rates ranging from 0.055 to 0.15 kg/s. The cold-water inlet temperature was maintained at 29°C, while the hot water inlet temperature varied between 65-75°C. Based on the hydraulic diameter of the annular space between the two tubes, the Reynolds number ranged from 1000-6000. All required parameters, such as the inlet and outlet temperatures of the inner coil and annulus fluids and the flow rate of fluids, were measured using appropriate instruments. Seventy-two test runs were conducted, from which the heat transfer coefficients of the inner coil side and annulus side were calculated. The calculated heat transfer coefficients of the inner coil were compared with available correlations from the literature, and a reasonable agreement was found.

A Comprehensive Analysis of Metamaterial-Coupled WPT Systems for Low Electromagnetic Field Leakage

In this article, electromagnetic metamaterials with mu-near-zero (MNZ-MM) have been presented to explain the shielding effect in the wireless power transfer systems. First, the optimized design of the metamaterials unit cell has been carried on to achieve the near-zero permeability at the working frequency of 13.56 MHz. The equivalent circuit model of the MNZ-MM unit cell has been derived, which illustrates metamaterials with near-zero permeability have the great electromagnetic field (EMF) shielding effect. Additionally, the self- and mutual inductances associated with the resonance coils and MNZ-MM unit cells are deduced in detail. Moreover, the simplified human head model is established to investigate the magnetic field cancellation by MNZ-MM on the coil side. To evaluate the performance of the proposed MNZ-MM, the magnetic field strengths of the receiving terminal with different shielding materials have been compared in simulation. Finally, a series of experiments in real-environment are implemented to discuss the shielding effect of the MNZ-MM. The measurement results show the MNZ-MM has better performance in the swine brain sample than the ferrite and aluminum plate on the whole. With the proposed MNZ-MM, we demonstrate a maximum reduction of 17.52 dB in the leakage EMF and basically no effect on transfer efficiency.

Selecting superior fin geometry among four suggested geometries for shell and helically coiled finned tube heat exchangers with numerical simulation and experimental validation

In this paper, the authors investigated the shell and helically coiled finned tube heat exchanger numerically and experimentally. At first they investigated the shell and helically coiled finned tube heat exchanger with simple annular fins for the first time. They considered nine cases for experimental investigation, in which three different fluid flow rates are considered for each side. Then they studied the geometry numerically using Ansys Fluent 18.2 software. After validating the numerical model, the authors suggested four new fin geometries. They studied all the geometries numerically and selected the stepped fin geometry as the superior geometry. The fluid flow inside the tube in this work is in the turbulent flow range and the realizable k−ε turbulence model is used. The authors proposed correlations using the response surface methodology and Taguchi method to predict the mean Nusselt number on the shell and tube sides. The presented correlations have good accuracy for calculating the Nusselt numbers (maximum 10% error). The results show that the mean Nusselt number of the coil side is the same in all geometries, and the Reynolds number of each side has almost no effect on the mean Nusselt number of the other side, and with increasing the fin pitch, the mean Nusselt number of the shell side decreases. The mean Nusselt number of the shell side is 80.79% higher for the stepped fin geometry (superior geometry) compared to the simple annular fin at best.

A Dual-Frequency WPT Based on Multilayer Self-Decoupled Compact Coil and Dual CLCL Hybrid Compensation Topology

This article proposes a dual-frequency wireless power transfer (WPT) with dual <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CLCL</i> hybrid compensation topology and multilayer self-decoupled compact coils (MLSDCCs). It extends the transmission distance corresponding to stable high transmission power and efficiency. Based on the parameter constraints of compensation capacitances and inductances, <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CLCL</i> hybrid compensation topology realizes simultaneous resonance at fundamental and third harmonic frequencies. A typical inverter can meet the requirements of dual-frequency WPT without complex control or more number and improve the utilization rate of square voltage. According to interleaving and rotary stacking of unipolar and bipolar coils in MLSDCCs, the couplings between layers and unnecessary couplings of magnetic coupling mechanism (MCM) are eliminated. Only the main couplings for power transmission are retained and the volume of MCM is reduced. Finally, a 1 kW experimental platform is built. Compared with the typical single-frequency WPT, the maximum transmission power is increased by 2.8%, while the maximum transmission efficiency is only reduced by 0.53%. The main advantage is that the transmission distance corresponding to continuous high-power transmission (in the range of 95%–100% maximum receiving power) is increased by 2.75 times. When the lateral offset distance of the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Y</i> -axis is one-sixth of the coil side length, the transmission efficiency decreases by only 1.47%.

Heat transfer and exergy efficiency analysis of 60% water and 40% ethylene glycol mixture diamond nanofluids flow through a shell and helical coil heat exchanger

The thermodynamic, heat transfer and thermal performance factor were analyzed experimentally at different particle volume loadings of water + ethylene glycol mixture based nanodiamond (ND) nanofluids flow in a shell and helical coiled tube heat exchanger. Chemical treatment was used to make ND nanoparticles with an average size of 5.42 nm. The stable ND nanofluids were prepared by considering 60:40% water + ethylene glycol (weight percentage) mixture as base fluid and the experiments were performed at particle loadings ranging from 0.2% to 1.0% and the Reynolds number ranging from 900 to 4800, respectively. In the heat exchanger, the hot fluid passes through the shell side and the cold fluid (nanofluid) passes through the helical coil side. The Wilson plot method is used to analyze the helical coil side heat transfer coefficients. The hot fluid volume flow rate was fixed to 1 lit/min, whereas, the cold fluid (nanofluid) volume flow rate was varied from 2 to 6 lit/min. Results show, at 1.0 vol% and the Reynolds number of 2702, the heat transfer coefficient and Nusselt number is increased by 36.05%, and 27.47%, respectively, over the base fluid. However, the penalty in friction factor and pressure drop is 17.28% and 14.24% under the same Reynolds number and 1.0 vol% nanofluid over the base fluid. Similarly, at 1.0 vol% and Reynolds number of 2702, the thermal entropy generation is dropped by 38.12%, frictional entropy generation is raised by 12.86%, exergy efficiency is enhanced by 36.48% and thermal performance factor is augmented by 1.2094 times over the base fluid.

무선전력전송 시스템의 송신 코일의 전압 전류 위상차 분석을 통한 수신측 공진주파수 추출

This study proposes a method of identifying the resonant frequency of the receiving side in a wireless power transfer (WPT) system, adopting a double-sided LCC topology. The resonant frequency of the receiving side must match the system’s operating frequency. However, in many cases, determining the resonant frequency of the receiving side from the inverter at the transmitting side is challenging. The method proposed in this study changes the operating frequency of the inverter at the transmitting side, and by observing the phase difference between the voltage and current at the transmitting coil side, the resonant frequency of the receiving side can be identified. Therefore, the WPT system adopting the proposed method does not require additional communication systems at the transmitting and receiving sides. The proposed method was analyzed using equations and validated through simulations and experiments. The proposed method can accurately extract the resonant frequency of the receiving side with an error of less than 0.4 %.

Experimental investigation of heat dispatch controllability through simultaneous charging-discharging and stand-alone discharging operations in vertical cylindrical sensible heat storage tank

Using a vertical cylindrical thermal energy storage (TES) tank with helical discharging coil fitted inside, the present study experimentally investigates the scarcely studied simultaneous charging and discharging (SCAD) mode, as well as the discharging-alone operation following a substantial stand-alone period. The temperature distributions within the tank, coil outlet temperature and primary thermocline thickness serve as the key performance trackers for the storage tank. The primary thermocline thickness increases with increasing coil side flow rate during the SCAD operation. The SCAD operation exhibited the splitting of the primary thermocline, leading to the formation of a secondary thermocline in the lower half of the tank. The sustenance of secondary thermocline, thermal gradients across the tank height, and the discharging efficiency are found to decrease with increasing charging flow rate, whereas the coil outlet temperature and the primary thermocline thickness increase. The highest average discharging efficiency of 80.1 % is observed for the TES charging at 0.5 L/min at 70 °C, accompanied by the 2 L/min discharging flow rate. The average thermal energy stored is the maximum (1758 kJ) for the TES charging at 1.25 L/min at 70 °C, with discharging rate of 0.5 L/min. The stand-alone period prior to the discharging-alone operation exhibits the heat content retention capability of the storage and allows for the thermocline formation. The time required for thermal stratification is more with the higher initial charging temperature. The time required for the complete discharging of the TES storage tank decreases with increasing coil-side flow rate. These modes provide ample operational flexibility and heat content dispatch controllability, resulting in the versatility of the system.

Structuroscopy of Coils after High-Temperature Mechanical Treatment on the Basis of Measurements of Rayleigh Waves Velocity

For the manufacture of spring springs of rolling stock (wagons, locomotives, cars), bars made of spring steels are used. With high-temperature machining, when winding springs and quenching them, there is a difference in the cooling rates of the inner and outer sides of the spring coils, which leads to a difference in the structural state and affects the durability of the springs. The aim of the work is to study the effect of structural changes in the outer and inner surfaces of spring steel coils after winding and high–temperature machining operations on the measured characteristics of Rayleigh acoustic waves.The propagation velocities of Rayleigh waves in spring-spring steel 60C2A after winding and hightemperature machining operations are investigated. The shadow method and the autocirculation method with piezoelectric converters CTS-19 with a frequency of 5 MHz with a special block design were used for research. The converters provide input and reception of the Rayleigh wave along the inner and outer forming surface of the spring. It is shown that the method of comparing the results of measuring the velocity of Rayleigh waves on a fi base by the coil generator on the inner and outer surfaces of the spring is sensitive to disturbances in the structure of the material and the appearance of defects. An unambiguous relationship of the structural states on the outer and inner sides of the spring with the velocity of the Rayleigh wave is found.As a result of the measurements, a conclusion was made about the significant sensitivity of Rayleigh waves to the structural state of the steel under study. An increase in the wave velocity was detected on the inner surface of the coil in the contact zone with the mandrel relative to the outer side of the coil, signaling incomplete hardening of steel in this zone during high-temperature machining. The relative speed difference in different spring samples is approximately up to 1 % (≈ 30 m/s), which is a significant value for assessing the quality of high-temperature machining.

Performance Investigation of a Three Fluid Heat Exchanger Used in Domestic Heating Applications

Recent work analytically investigates the heat transfer characteristics of a three fluid heat exchanger used for domestic heating applications with respect to different design parameters, i.e. flow rate, inlet temperature, tube diameter, coil diameter, and coil pitch. The present and previous results are compared with the literature. Overall agreement among these results are observed with little variation. Afterwards, the present temperature data was verified with prior experimental data and little deviation observed in these results vary from -4.28 % to +6.68 % and -6.17% to +5.92% in parallel and counter flow configuration, respectively. It is ensued that the coil side Nusselt number increases with the rise in coil side fluid flow rate and inlet temperature, coil outside fluid inlet temperature and coil diameter respectively. The increment in coil side flow rate and inlet temperature are identified as the major contributors, with 297% and 39.5% contributions. Similarly, growth in coil outside Nusselt number is observed with the rise in coil side fluid inlet temperature and flow rate, coil outside fluid flow rate and inlet temperature, and coil pitch respectively. The coil pitch and flow rate at the coil outside are identified as major contributors with 36% and 28.5% contribution repsectively. Distinct correlations for heat transfer in the present HEx are proposed for coil inside and outside fluid flow in a turbulent flow regime. The developed correlations results are compared with the present result, and reasonable agreement is observed within the data range of +13% to -14% and +10% to -11% for coil inside and outside Nusselt number, respectively.

Evaluation of Thermal Performance of Conically Shaped Micro Helical Tubes Using Non-Newtonian Nanofluids–A Numerical Study

Abstract Nowadays, the cooling and heating of micro-thermal devices have received a growing interest. To improve the thermal management of these micro-thermal devices, various efforts are being made by the researchers. In the present study, conically shaped micro helical tubes are used to investigate the coil side heat transfer rate and friction factor of non-Newtonian nanofluids under laminar flow conditions. For the numerical analysis, single-phase approach with commercial software ansys-fluent-19 has been utilized. Investigations encompass generalized Reynold numbers ranging from 306 to 2159 and four different curvature ratios (0.066, 0.076, 0.088, and 0.1) of conically shaped micro helical tubes. The inner diameter of the helical tube is 2 mm and contains 20 turns. Al2O3-based non-Newtonian nanofluids with volume concentrations of 0.0%, 0.1%, and 0.2% having base fluid of aqueous solution of carboxymethyl-cellulose (CMC) are used as the working fluid (hot) for the coil side, while in the shell side cold water is used. The results from numerical investigation are validated and found in good agreement with earlier experimental results. The results show that with the increase in the curvature ratio of conically coiled tubes both heat transfer rate and friction factor increase by 46% and 98% respectively, for base fluid at a curvature ratio of 0.1. Also, the present study reveals that adding nanoparticles to the base fluid enhances the heat transfer rate to a maximum value of 40%. Moreover, the maximum value of thermal performance factor (TPF) is found to be 1.52.

Experimental and numerical analysis of vibration-based hybrid energy harvesting from non-classical beam structures

It is known that the displacement and stress on beams will directly affect the energy harvesting performance. For this purpose, structural changes are made on the beam elements. Behaviours of these beam structures are investigated by designing different non-classical beam geometries. This study examines vibration-based electromagnetic and piezoelectric energy harvesting from the non-classical beam structures under various conditions. Before analysing the non-classical beam structure, studies are performed for a classical beam for electromagnetic and piezoelectric energy harvesting studies. In the electromagnetic energy harvesting analysis, the effects of magnitude of magnetic field and the distance between the coil and the permanent magnet on the harvesting performance are studied by free vibration experiments. In this regard, a neodymium permanent magnet is attached to the vibrating aluminium beam endpoint. During the free vibration period, the coil and the magnet interact closely. As a result, a voltage output is obtained by inducing an electric field on the coil side. Secondly, voltage outputs of piezoelectric energy harvesting structures are experimentally evaluated for a classical beam and used for the verification of numerical simulations. Using the verified numerical simulations, new types of beam structures so-called non-classical beams are designed to obtain higher voltage outputs. Finally, by introducing the phenomenon of continuous vibration with the effect of air, the hybrid energy performance is analyzed for the proposed structure. The continuous vibration is created by the air-flow on the square galloping geometry.

Continuously Variable Valve Mechanism for Spark Ignition Engines Using Linear Actuator

In order to achieve higher performance in spark-ignition engines, it is required to control the intake and exhaust valves in stepless manner according to the engine speed. Our research group has been continuously studying the electromagnetic drive valve system using a linear actuator. In this report, we have designed a linear actuator with a dual Halbach array of permanent magnets in the stator to further increase the thrust of the linear actuator. The thrust characteristics of the proposed model were investigated using electromagnetic field analysis based on the finite element method. The analysis confirmed that the Halbach array concentrates the magnetic flux on the coil side, which generates Lorentz force.

Actual measurement and analysis of winter thermal environment of a graduate student studio in Shenyang based on Airpak numerical simulation

This paper takes a graduate workshop in shenyang as the research object, and uses Airpak software to conduct numerical simulation analysis on the air distribution and thermal comfort of the fan coil side air supply mode in winter. The measured air supply temperature is 25°C, air supply speed in the x direction for 0.8m / s, 1.5m / s and 2.3m / s three gears, from east to west up to back air supply 3mode. With the increase of air supply speed, the temperature of the working area gradually increases, and the wind speed increases. PMV index and PPD index were used to evaluate the indoor comfort under the three air supply speeds. The air sup 3ply speeds of 1.5m/s and 2.3m/s can meet the requirements of indoor comfort. According to the distribution of personnel, 18 measuring points were set for measurement. The comparison between the simulation results and the measured results showed a consistent trend, which verified the feasibility and accuracy of Airpak for indoor thermal environment comfort analysis.