Coil Inserts Research Articles

Modeling of active shimming of metallic needles for interventional MRI.

Artifacts caused by large magnetic susceptibility differences between metallic needles and tissue are a persistent problem in many interventional MRI applications. The signal void caused by the needle can hide procedure targets and prevent accurate image-based monitoring. In this paper, a solution to this problemis presented in the form of an active shim insert inspired from degaussing coils used in naval vessels, that isdesignedto correct the field disturbance (ΔB0 ) caused by the needle. The ΔB0 induced by a 10 gauge hollow single-beveled titanium needle at 3T is modeled in different orientations. A set of 63 orthogonal coil pairs with unique tip paths are evaluated for shimming performance, and an optimal coil pair is chosen. Shimming performance and current demands are evaluated over a range of needle orientations. Robust correction of the titanium needle induced ΔB0 is predicted using a flat no-loop coil combined with an orthogonal 1½ turn loop coil angled at the bevel angle for most orientations, with currents well below 1 amp per coil. Reductions in ΔB0 standard deviations with shimming ranged from ~49% to ~10% depending on needle orientation, with performance worsening as the needle is aligned more along B0 . Simulations predict that it is possible to minimize metallic probe induced ΔB0 and signal losses using externally supplied direct current shim coil inserts in arbitrary orientations for potential benefits in many interventional MRI applications.

Experimental investigation of heat transfer and pressure drop inside elliptic tube with inserted helical coils

The paper deals with an experimental study of the influence of varying helical coil cross section diameter and pitches of helical coil on heat transfer and friction characteristics in an elliptical tube. The present work studies the effects of copper helical coils of circular cross section formed with different diameters of 2 and 6 mm at varying pitches (20, 45, 135 and 225 mm) inside elliptic tube. In the experiments, cold air at ambient condition is passed through the uniform heat flux circular tube for Reynolds numbers in a range of 11000 to 37500. The experimental results demonstrate that the use of helical coil inserts in elliptic tube leads to a higher heat transfer rate than that of the plain surface tube. Also, increasing helical coil cross section diameter and decreasing pitches of the helical yield a better heat transfer than the plain tube. The enhancement efficiencies of the helical coil cross section 6 mm over wire cross section 2 mm diameter at a pitch of 20 mm is 2.3% at Re=11000. The results are also correlated in the form of Nusselt number, friction factor and enhance efficiency as a function of Reynolds number, pitches and diameter of helical coil

A comprehensive thermo-hydraulic analysis and optimization of turbulent TiO2/W-EG nano-fluid flow inside double-pipe heat exchangers with helical coil inserts

The main aim in current work is to optimize TiO2/W-EG nano-fluid (with 60 vol% of water and 40 vol% of ethylene glycol) flow within the inner tube of the double-pipe heat exchangers with helical coil inserts. The entropy generation is selected as the target function and is to be minimized. To reach this goal, at the first step, a comprehensive sensitivity analysis is carried out taking into account all of the nano-fluid flow conditions (including nanoparticle volume fraction $$\phi$$ , Reynolds number Re and Prandtl number Pr) and geometric parameters of the helical coil inserts (including thepitch-to-diameter ratio of coil $$\Pi$$ ). Afterward, the genetic algorithm (GA) is utilized in the optimization process. The results of sensitivity analysis reveal that $$\phi$$ and $$\Pi$$ , respectively, have the highest and lowest impact on the thermodynamics characteristics. Also, the addition of up to 0.02 vol% nanoparticles leads to a maximum of 13.93% improvement in dimensionless entropy generation ( $${\text{DEG}}$$ ). The outputs of the GA are $$\phi_{\text{opt}}$$ = 0.0198%, $${\text{Re}}_{\text{opt}}$$ = 8421.173, $${ \Pr }_{\text{opt}}$$ = 32.833, $$\Pi_{\text{opt}}$$ = 2.437 and $${\text{DEG}}_{\text{opt}}$$ = 0.005086. Furthermore, based on the optimization results, a useful correlation is proposed to find the optimum geometry of the helical coil based on the nano-fluid flow conditions.

Enhancing the overall thermal performance of a large aperture parabolic trough solar collector using wire coil inserts

With the use of large apertures (higher concentration ratios) in parabolic trough solar collectors, increased temperature gradients, increased heat losses and increased heat transfer irreversibilities become inevitable. As such, means of reducing the magnitude of these operating parameters to enhance the overall thermal and thermodynamic performances become crucial. In this study, the use of wire coil inserts in the receiver’s absorber tube to improve the parabolic trough solar collector’s performance and to lessen the associated temperature gradients is presented. The parabolic trough solar collector having an aperture width of 9 m and a rim angle of 80° was modeled. Using Monte-Carlo ray tracing, the realistic heat flux profile on the receiver’s absorber tube was obtained. The resulting non-uniform heat flux profile was later coupled to a finite volume based computational fluid dynamics model. The working fluid properties were considered to be temperature-dependent. The wire coil inserts with a pitch of 0.076, 0.114 and 0.152 m and widths of 0.03, 0.033 and 0.036 m were examined in this study. The wire coil has a triangular cross-section of 0.0076 m in size. Results show significant improvements in receiver thermal performance with the use of wire coil inserts owing to the improved fluid mixing, disruption of the thermal boundary layer and reduction in the absorber tube temperatures. The heat transfer performance is increased up to 183% whereas the thermal efficiency improves between 0.4 and 1.4% when the flow rate is below 13 m3/h.

Improving hydrothermal performance of hybrid nanofluid in double tube heat exchanger using tapered wire coil turbulator

Tapered wire coil insert is proposed as a novel enhancer in the double tube heat exchanger and experimental studies on Al2O3 + MgO hybrid nanofluid flowing under the turbulent condition are performed to investigate the hydrothermal characteristics. Effects of using tapered wire coil turbulator and hybrid nanofluid on the hydrothermal behaviors are examined for different coil configurations (Converging (C) type, Diverging (D) type and Conversing-Diverging (C-D) type) and hybrid nanofluid inlet temperatures and volume flow rates. Results show that D-type wire coil insert promotes better hydrothermal performance as compared to C-type and C-D type. Nusselt number and friction factor of hybrid nanofluid using D-type, C-D type and C-type wire coil inserts enhance up to 84%, 71% and 47%, and 68%, 57% and 46%, respectively than that of water in tube without insert. The entropy generation of hybrid nanofluid is lower than that of base fluid in all cases. The thermal performance factor for hybrid nanofluid is found more than one with all inserts. The thermal performance factor is observed a maximum of 1.69 for D-type coil. The study reveals that the hybrid nanofluid and tapered wire coil combination is promising option for improving the hydrothermal characteristics of double pipe heat exchanger.

Experimental and numerical analysis for thermal-hydraulic characteristics in circular tubes with twisted tape and wire coil inserts

Thermal-hydraulic characteristics in circular tubes with twisted tape (Y=4.762, 7.143 and 9.524) and wire coil (p=20mm, e=2mm) inserts were studied experimentally and numerically. It was found from experimental analysis that Nusselt number and friction factor in tubes with twisted tape inserts were 38%-57% and 148%-202%, respectively, higher than those of plain tubes .When wire coil was inserted in plain tubes, the Nusselt number and friction factor grew by 75%-94% and 685%-792%, respectively. In particular, Nusselt number and friction factor in tubes with twisted tape and wire coil inserts were 113%-139% and 836%-874%, respectively, greater than those of plain tubes. Furthermore,PECvalue of tubes with the twisted tape and wire coil inserts was larger than all others. Numerical analysis shows that a large tangential velocity can be generated after inserting a twisted band or coil in the tube. The angle between the temperature gradient vector and velocity vector was significantly less than 90°. So collaborative degree between temperature field and velocity field was improved.

Study of Effects of Dimensionless Parameters on Thermal Efficiency of Enhanced Solar Liquid Collector with Coiled Wire Inserts

Solar liquid collectors are good candidate of heat transfer enhancement. The efficiency of a solar liquid collector can be improved by augmenting tube side heat transfer using enhanced techniques used in heat exchangers. Various types of heat transfer enhancement techniques has been used in heat exchangers which are mainly classified in two types, active and passive techniques. Solar liquid collectors can also be enhanced by these active and passive devices. Passive techniques, mainly swirl flow devices are more popular enhancement techniques in solar liquid collectors as they do not require any external source of power and also they do not affect the mechanical strength of tube material. Initially twisted tape inserts and conical inserts were popular passive devices used in enhanced solar liquid collectors mainly because of availability of established correlations. Wire coil inserts are relatively less experimented passive technique. This study is focused on tube side heat transfer augmentation of a solar flat plate liquid collector by wire coil inserts and effect of various dimensionless parameters on thermal efficiency of solar collector.

Thermal-Hydraulic Performance of an Annular Pipe with Square Wire Coil Inserts Using Computational Fluid Dynamics

The development of high-thermal-performance heat exchangers is a demand of the recent era for efficient utilization of energy sources. The present work deals with the computational fluid dynamics (...

Thermal performance of helical coils with reversed loops and wire coil inserts

Flow and heat transfer characteristics of water in a newly designed helical coil heat transfer device were investigated in this experimental study. The conventional helical coil configuration was structurally modified aiming to improve its heat transfer performance. Specifically, 360° plastic tubing with or without wire coil inserts was added after each 180° of the main helical coil loop to enhance fluid mixing and redistribute the flow, which should have a direct effect on the thermal performance of the helical coil heat transfer device. Experimental results show that the structural modifications of the conventional helical coil configuration led to enhanced heat transfer in the test section while the pressure drop penalty increased slightly. Furthermore, the heat transfer performance of the overall test section improved by using wire coil inserts in the plastic tubing after every 180° of the main helical coil loop. The results reveal that the modified helical coil section offers a good trade-off between heat transfer enhancement and pressure drop penalty.

Pressure loss and performance assessment of horizontal spiral coil inserted pipes during forced convective evaporation of R-600a

The impacts of spiral coil inserts on the pressure loss of environment-friendly refrigerant R-600a are experimentally evaluated during forced convective evaporation within horizontal copper pipes. Then, by considering the current pressure drop and previous heat transfer results and calculating the performance factor, the overall effectiveness of the inserts is determined. Experiments are carried out for smooth and rough tubes. Five spiral coils with various coil pitches and wire diameters are utilized. Also, vapor qualities between 0.08 and 0.7 and mass fluxes between 109.2 and 505 kg m−2 s−1 are considered for tests. Generally, it is observed that inserts augment the pressure loss in the range of 90–958% over the smooth pipe. However, as the wire diameter decreases and the coil pitch increases, less pressure losses are imposed to the system. Depending on the operational conditions and inserts type, the performance factor was obtained between 0.13 and 1.40. The coiled wire “CW5” with the wire diameter of 1 mm and coil pitch of 30 mm performed superior compared to the other inserts by maximum performance factor of 1.4. Finally, by using the current data a new correlation is proposed in order to predict the evaporative pressure loss of R-600a within spiral coil inserted pipes.

Heat transfer performance of TiO2–SiO2 nanofluids in a tube with wire coil inserts

The compound technique that combines nanofluids with wire coil inserts has proven itself in achieving double augmentation in heat transfer. This paper presents the thermal hydraulic performance of TiO2-SiO2 nanofluids with wire coil inserts. The experiments were conducted for Reynolds number from 2300 to 12,000 to determine the heat transfer performance and friction factor of TiO2-SiO2 nanofluids with wire coil inserts. The TiO2-SiO2 nanofluids were prepared by using the two-step method for volume concentrations of 0.5–3.0%. The wire coil inserts are designed at various ratios of pitch over diameter (P/D) in the range of 0.83–4.17. The heat transfer performance of nanofluids was enhanced for a maximum of 254.4%, while the friction factor was obtained in the range of 1.76–6.38 times higher than water/EG in a plain tube. The thermal performance factor (TPF), η for the nanofluids with wire coil inserts at all volume concentrations was observed greater than 1.0. The optimum performance of TiO2-SiO2 nanofluids with wire coil occurred at 2.5% volume concentration and 1.50 pitch ratio. At this condition, the TiO2-SiO2 nanofluids with wire coil inserts provide the highest TPF and represent the best condition for cooling system applications.

Numerical investigation for turbulent heat transfer of TiO2–SiO2 nanofluids with wire coil inserts

A numerical model has been developed for turbulent flow of hybrid nanofluids in a tube with wire coil inserts. The model was developed from van Driest eddy diffusivity equation. The model can be implemented with the consideration of new variables in eddy diffusivity of momentum and heat by using the coefficient, K and Prandtl index, ζ, respectively. The numerical analysis are undertaken for wide range of Reynolds number, different volume concentration, ϕ and various pitch ratio, P/D of wire coil. The numerical results were validated with the experimental data of TiO2–SiO2 nanofluids undertaken for wide range of Reynolds number and volume concentration. The final regression models of coefficient K and Prandtl index ζ were developed as a function of Reynolds number, Re or dimensionless radius, R+, volume concentration, ϕ and pitch ratio, P/D. A good agreement between the experimental data and numerical model indicating the validity of the numerical model for hybrid nanofluids with wire coil inserts. The numerical analysis was proved that the hybrid nanofluids contributes to higher Nusselt number and thus have better heat transfer performance compared to single nanofluids.

A Modified Bridge Switch-Type Flux-Coupling Nonsuperconducting Fault Current Limiter for Suppression of Fault Transients

This paper proposes a modified bridge switch-type flux-coupling nonsuperconducting fault current limiter (BSFC-NSFCL) for suppressing the fault current and voltage sag. A flux-coupling reactor and a bidirectional bridge switch are combined to perform the functions of steady-state line current sharing and fault current suppression. The modified BSFC-NSFCL mainly utilizes the magnetic flux cancellation effect to make the limiter behave as a short circuit on the circuit during normal operation. Hence, there is almost no impact on the power system when the limiter is used. When a fault event occurs, the bridge switch turns off immediately, and then, the magnetic flux cancellation effect disappears. Thus, the impedance of primary coil inserts into the circuit to restrict the fault current and voltage sag phenomena. Once the fault is removed, the bridge switch turns on again, and the BSFC-NSFCL recovers to the normal operation. The modified NSFCL is more cost-effective and easy to be implemented than the flux-coupling superconducting fault current limiter. Theoretical analysis for the BSFC-NSFCL has been fully developed and proven by MATLAB software. Finally, the analytical, simulated, and experimental results have been carried out to verify the feasibility and performance of the proposed BSFC-NSFCL.

Enhancement in Heat Transfer by Using Wire Coil Inserts in Tubular Heat Exchanger

Enhancement in Heat Transfer by Using Wire Coil Inserts in Tubular Heat Exchanger

Combination of nanofluid and inserts for heat transfer enhancement

Improving heat transfer is a critical subject for energy conservation systems which directly affects economic efficiency of these systems. There are active and passive methods which can be employed to enhance the rate of heat transfer without reducing the general efficiency of the energy conservation systems. Among these methods, passive techniques are more cost-effective and reliable in comparison with active ones as they have no moving parts. To achieve further improvements in heat transfer performances, some researchers combined passive techniques. This article performs a review of the literature on the area of heat transfer improvement employing a combination of nanofluid and inserts. Inserts are baffles, twisted tape, vortex generators, and wire coil inserts. The progress made and the current challenges for each combined system are discussed, and some conclusions and suggestions are made for future research.

Computational fluid dynamics (CFD) technique to study the effects of helical wire inserts on heat transfer and pressure drop in a double pipe heat exchanger

In this communication, the computational fluid dynamics (CFD) technique has been employed to study the influence of coiled wire inserts on the Nusselt number, friction coefficient and overall efficiency in double pipe heat-exchangers. For this purpose, some wire coil inserts fitted inside heat-exchangers were meshed and simulated at various Reynolds numbers by using the CFD softwares of Gambit and Fluent. To fulfill reliable and validated results, a big effort was made to generate structural hexahedral meshes over all of the heat-exchanger geometries. The validated models, then, made clear the object and the conditions which could exactly facilitate heat transfer throughout double pipe heat-exchangers. The outcome of this work indicates that taking the advantage of proper wire coils could improve the Nusselt values to 1.77 times. Following the numerical simulation, proper friction coefficient and Nusselt number correlations for various coiled wire inserts with different geometry arrangements under the laminar flow were proposed. Unlike the preceding relations, the correlations of this work are based on the occupied spaces where helical wires take up inside tubes; therefore, the two modified correlations can both be used for non-uniform helical wire insert geometries.

Heat Transfer Enhancement in Pipe Flow using Wire Coil Inserts in Forced Convection

Heat Transfer Enhancement in Pipe Flow using Wire Coil Inserts in Forced Convection

Heat transfer enhancement of Al2O3-EG nanofluid in a car radiator with wire coil inserts

In this experimental study, Aluminums Oxide (Al2O3) in Ethylene Glycol (EG) as nanofluid was used for heat transfer enhancement in car radiator together with wire coil inserts. Two wire coils inserts with different geometry and nanofluids with volume concentrations of 0.08%, 0.5% and 1% were investigated. The results indicated that the use of coils inserts enhanced heat transfer rates up to 9%. In addition, the simultaneous use of the coils inserts with the nanofluid with concentration of 0.08%, 0.5% and 1% resulted the thermal performance enhancement up to 5% as compared to the use of coils inserts alone.

Experimental heat transfer, friction factor and effectiveness analysis of Fe3O4 nanofluid flow in a horizontal plain tube with return bend and wire coil inserts

The paper reports on the convective heat transfer, friction factor, effectiveness and number of transfer units (NTU) of Fe3O4/water nanofluids flow in a double pipe U-bend heat exchanger with and without wire coil inserts under turbulent flow conditions. The heat transfer and friction factor experiments were conducted at different Reynolds numbers (16,000–30,000), different particle concentrations (0.005–0.06%) and different wire coil inserts of coil pitch to tube inside diameter (p/d) ratios (1, 1.34 and 1.79). The experimental results indicate that, Nusselt number increases with increasing Reynolds number and particle concentrations, and decreasing p/d ratio of wire coil inserts. The Nusselt number enhancement for 0.06% volume concentration of nanofluid is 14.7% and it further increases to 32.03% for the same 0.06% nanofluid with wire coil inserts of p/d=1 with a friction penalty of 1.162-times at the Reynolds number of 28,954 compared to water data. The experimental data was fitted using regression analysis to estimate the Nusselt number and friction factor of nanofluid as a function of the Reynolds number, Prandtl number, volume concentration, and wire coil helix ratio. The effectiveness of heat exchanger is formulated in terms of number of transfer units (NTU) for the base fluid and nanofluids.

Numerical investigation on laminar flow and heat transfer in rectangular microchannel heat sink with wire coil inserts

A numerical investigation is carried out to study the laminar liquid flow and coupled heat transfer performance in rectangular microchannel heat sink (MCHS) equipped with wire coil inserts. Distilled water with temperature-dependent thermophysical properties is employed to perform this simulation. The effects of the length and arrangement of wire coil inserts on flow and heat transfer characteristics, and the mechanism of heat transfer enhancement in wire coil inserted MCHSs were analyzed using the first and second law of thermodynamics. This study is also to propose the frication factor and heat transfer correlations for MCHSs with wire coils. The results show that the heat transfer performance in the MCHS is enhanced effectively due to the longitudinal vortexes caused by the wire coils, but the flow resistance is increased simultaneously. The MCHS with long wire coil placed at the center line of microchannel shows the best heat transfer performance with enhancement factor of 1.4–1.8 at a heat flux 400kW/m2. Its overall performance is the best among five configurations using the principle of entropy generation minimization, but using the performance evaluation criteria (PEC), the best performance is only limited to the low Reynolds number. The best overall performance using PEC at the high Reynolds is the MCHS with three segments of short wire coil placed at the center line of microchannel.