Helical Coil Research Articles

Experimental Analysis of the Thermal Performance Enhancement of a Vertical Helical Coil Heat Exchanger Using Copper Oxide-Graphene (80-20%) Hybrid Nanofluid

The thermal performance enhancement of a vertical helical coil heat exchanger using distilled water-based copper oxide-graphene hybrid nanofluid has been analyzed experimentally. Accordingly, the focus of this study is the preparation of CuO-Gp (80-20%) hybrid nanoparticles-based suspensions with various mass fractions (0% ≤ wt ≤ 1%). The volume flow rate is ranged from 0.5 L·min−1 to 1.5 L·min−1 to keep the laminar flow regime (768 ≤ Re ≤ 1843) and the supplied hot fluid’s temperature was chosen to equal 50 °C. To ensure the dispersion and avoid agglomeration an ultrasound sonicator is used and the thermal conductivity is evaluated via KD2 Pro Thermal Properties Analyzer. It has been found that the increment in nanoparticles mass fraction enhances considerably the thermal conductivity and the thermal energy exchange rate. In fact, an enhancement of 23.65% in the heat transfer coefficient is obtained with wt = 0.2%, while it is as high as 79.68% for wt = 1%. Moreover, increasing Reynolds number results in a considerable augmentation of the heat transfer coefficient.

Tailoring coil geometry for secondary heating of substrate towards the development of induction heating-based wire additive manufacturing

Induction heating (IH), a clean energy source, is potentially used to develop wire additive manufacturing (AM) system. The optimised parameters that simultaneously melt the mild steel wire and raise the substrate temperature is established. A fully coupled thermal-electromagnetic model of AM system is developed to perform numerical experiments on temperature development. The proposed hybrid helical-pancake coil with circular cross-section melt the metallic wire and raise the substrate temperature to 1490 K. The hybrid coil provides rapid heating to the wire (2819 K) and substrate together by enhancing magnetic field strength. The experiments using high-frequency IH system (550 A and 353 kHz) with a 3-turn helical coil is validated with model results for 2 mm mild steel wire.

Investigation of Heat and Mass Transfer in Helical Coil and All-regime Prediction Model

Investigation of Heat and Mass Transfer in Helical Coil and All-regime Prediction Model

Development of Three-dimensional Thermal-hydraulic Analysis Code HeTAF for Helical Coil Steam Generator

Development of Three-dimensional Thermal-hydraulic Analysis Code HeTAF for Helical Coil Steam Generator

Evaluation of quality parameters of orange juice stabilized by two thermal treatments (helical heat exchanger and ohmic heating) and non-thermal (high-pressure processing)

This work aims to compare the impact of three thermal (helical coil heat exchanger HCHE, ohmic heating OH, and mild pasteurization MP) and one non-thermal (high-pressure processing HPP) treatments on orange juice by using industrial plants. Nutritional (total phenolic content (TPC), ascorbic acid (AA) and total antioxidant capacity (TAC)), physical (viscosity, colour, browning index (BI) and suspended pulp (SP)), sensory (Triangle test and QDA) as well as chemical (1H NMR spectroscopy) aspects were analyzed. Results revealed a significant (p < 0.05) increase in viscosity for HPP (+20%) compared to untreated samples while the opposite effect was observed for all thermal treatments (−22%). The lowest a* values were observed in HPP and HCHE samples. Total phenolic content decreased significantly only in HCHE (−14%), while the highest ascorbic acid content was observed in HPP samples and it resulted not significantly different from untreated. Regarding the chemical profile, treated samples (except for MP) led to a significant (p < 0.05) decrease of all selected marker peaks, mainly including sugars (alpha- and beta-glucose, beta-fructose, and sucrose) and amino acids compared to untreated ones. HPP samples showed a similar sensory profile if compared with the untreated sample, showing only a significant difference (p < 0.05) in terms of orange aroma; on the contrary, OH, HCHE, MP rated the lowest acceptances due to, among all considered descriptors, orange aroma, cooked aroma, sweetness, cooked taste.

Geometrical Parameter Effects on Solidification/Melting Processes Using Twin Concentric Helical Coil: Experimental Investigations

Moving the load peak to consume electrical power is valuable in air conditioning systems. Consequently, the current study presents an experimental thermal investigation of an ice storage system. For this purpose, a twin concentric helical coil (TCHC) is utilized. The coil is submerged in distilled water in an insulated tank. The main aim is to explore the effect of geometrical/operating conditions for the TCHC on percentage energy stored/regained, solidified/melted mass fraction, and average charging/discharging rate. The main parameters are twin coil pitch and tube diameter while keeping the cold heat transfer fluid (HTF) inlet conditions at −12 °C and 10 L/min. The results disclosed that the discharge time increases by about 79% for total energy gained as the coil pitch rises from 30 to 50 mm at a smaller tube diameter of 9.52 mm. At the same time, the discharge time is doubled when the tube diameter is 15.88 mm. Furthermore, the complete solidification needs half the time (time reduced to 50%) to be achieved as the tube diameter increases from 9.52 mm to 15.88 mm (68% increases in diameter) for lower pitch (P = 30 mm).

Analysis of Heat Transfer and Flow Characteristics of a Helically Coiled Tube with Twisted Elliptical in a Low Reynolds Number Flow

In this paper, the heat transfer and flow characteristics of a helically coiled tube with twisted elliptical in a low Reynolds number (Re = 500–3000) flow were investigated numerically. The working fluid flowed in a laminar regime. Numerical results were compared with empirical correlations in the existing literature, demonstrating the accuracy of the analysis in this study. Firstly, we investigated the effects of geometric parameters and Reynolds number on the heat transfer and flow characteristics. The results showed that lower twist pitch length and semi-major axis length could induce sufficient fluid mixing and a larger temperature gradient near the tube wall, enhancing the heat exchange and producing larger friction resistance. Overall, the heat transfer performances were improved by about 1.04–1.21 times and 1.02–1.23 times for different semi-major axis lengths and different twist pitch lengths, respectively, compared to the smooth helical coil. Secondly, by changing the working fluid, it was found that the Nu when oil was chosen as the working fluid was all 6–6.8 times higher than that of water. Moreover, the effect of using Al2O3 nanofluids with a concentration of 0.10 wt.%, 0.25 wt.% and 0.50 wt.% was discussed. It can be seen that the heat transfer capacity of nanofluids increased by approximately 2–18% compared to the reference model with water as the working fluid, and the nanofluid solution with higher concentration has better heat transfer performance. Finally, Nu and f correlations are given to predict the heat transfer and pressure drop in practical applications.

Energy, exergy, environmental and economic (4E) analysis of evacuated tube solar collector with helical coils

Energy, exergy, environmental and economic (4E) analysis of evacuated tube solar collector with helical coils

A three-region movable-boundary helical coil once-through steam generator model for dynamic simulation and controller design

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.

The kinematics and static equilibria of a Slinky

A Slinky is a loose helical coil spring and is a well-known educational toy. In this paper a model for a Slinky is presented. The Slinky is represented as a sequence of rigid half coils connected by torsional springs. A range of Slinky configurations in static equilibrium are calculated. Where possible the torsion spring model is compared with the much simpler point mass model of a Slinky, and a more sophisticated model that includes axial and shear deformation. The torsional spring model is shown for the most part to produce similar qualitative behaviour as the more complex model. The simplicity of the torsional spring model makes it a candidate for a discrete stair walking dynamic model of a Slinky, The point mass model is straightforward to derive and solve and makes it possible for an undergraduate engineering student in the early part of their degree course to understand. The torsional spring model is a useful tool for showing what can be done in a more advanced mechanics course to model a system that most students would have previous experience of.

Multi-objective optimization of fuel–air tube-in-tube helical coil heat exchangers for cooled cooling air system applied in aeroengines

In fuel–air heat exchangers used in cooled cooling air (CCA) systems, the power-to-weight ratio (G) has to be as high as possible and the air-side pressure drop (Δpair) as low as possible. In this study, a numerical model of a fuel–air tube-in-tube helical coil heat exchanger used in CCA systems was developed. Multi-objective optimization of the heat exchanger was performed to resolve the conflict between G and Δpair by combining response surface methodology and multi-objective genetic algorithm. Finally, an optimal combination of structural parameters was selected using the Pareto-optimal points captured by Non-dominated Sorting Genetic Algorithm-II. The results indicate that the realizable k−ε turbulence model makes the best prediction of thermal and hydraulic characteristics of the heat exchanger. The analysis of variance showed that the most significant parameter affecting G as well as Δpair was the hydraulic diameter of the heat exchanger annulus side (dh), followed by the inner diameter of the heat exchanger inner tube (di,i). The optimized structural parameters were di,i = 1 mm, dh = 2.3 mm, and number of turns = 4.5, and the corresponding values of G and Δpair were 27.6 kW/kg and 255.7 kPa, respectively. In the optimized heat exchanger, G had increased by 5.34% and Δpair reduced by 50.8%.

Development and validation of Nusselt number correlations for a helical coil based energy storage integrated with solar water heating system

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−1 at 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.

Vibrational characteristics of a helical antenna for L-Band satellite communications

Helical coils serve many functions in mechanical systems and are often subjected to a variety of impulsive forces. In this talk we examine the dynamics of a helix modeled after an L-Band helical antenna used for satellite communications in low Earth orbit (LEO). Since the components of a deployed satellite are not accessible, it is critical to understand the dynamics of the antenna given its position outside of the main body. The intent of this work is to identify the frequencies, shapes and Q-values of the vibrational modes of the helix subject to impulsive stimuli and evaluate changes due to environmental exposures and structural modifications. We report on coil-by-coil measurements of the spectra using eight distinct stimulus-response polarizations. Two specific studies are emphasized in this talk. To gauge the sensitivity of the element to thermal variations under (LEO) conditions, we report on the impact of thermal cycling on the vibrational spectra of the helix. We also report on changes in the dynamic response of the helix due to the addition of structural support elements.

Thermal hydraulic characteristics of helical coil once-through steam generator under ocean conditions

Thermal hydraulic characteristics of helical coil once-through steam generator under ocean conditions

Continuous Antisolvent Crystallization Using Fluidic Devices: Fluidic Oscillator, Helical Coil, and Coiled Flow Inverter

Continuous Antisolvent Crystallization Using Fluidic Devices: Fluidic Oscillator, Helical Coil, and Coiled Flow Inverter

Experimental analysis to improve charge/discharge of thermal energy storage in phase change materials using helical coil and porous metal foam

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.

Numerically analysis of a Phase-change Material in concentric double-pipe helical coil with turbulent flow as thermal storage unit in solar water heaters

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 %.

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.

Influence of coil shapes on temperature distribution in induction heating process

Induction heating technology has been widely applied in industrial applications like preheating, brazing, and melting furnaces. In induction heating, eddy currents are induced internally in the workpiece, restriction in these eddy currents due to resistance of material dissipates energy and generates heat into the workpiece. In these processes, obtaining desired temperature profile for homogenized processing of the workpiece can be a very challenging task, here coil geometry can play a significant role in the resulting temperature distribution obtained on the workpiece. This paper provides an improved knowledge of the induction heating process through numerical simulation as well as helps in understanding the relationship between magnetic flux density distribution and resulting heating patterns. Four different shapes of the helical coil including classical, conical, square, and oval are analyzed. Their resulting magnetic fields and temperature control profiles are computed using the finite element method. Results obtained show that different shapes of coil produce different heat patterns. These results can be further applied to predict the heating zones and assist in designing induction heating coils for the induction heating applications like thixoforming, in order to achieve desired temperature profiles.

A recent state of art review on heat transfer enhanced characteristics and material selection of SCTHX

The shell and coil tube heat exchangers (SCTHX) are widely used to transfer heat energy from one medium to another effecting medium, such as refrigeration and air conditioning system, chemical reactor, solar heater and steam power plant. The helical tubes are one of the passive heat transfer enhancement technique in heat exchanger, which are adopted in industries due to higher rate of heat transfer and simplicity in manufacturing. It has been widely employed that heat transfer coefficient in helical coils are higher compare to straight pipe by several researchers. The reason is behind that the formation of secondary flow of nano fluid. It is leading by dean vortex which is imposed to primary flow. Furthermore research on segmental and helical baffle geometry can improve the heat transfer rate in helical coil tube heat exchanger. This study is concerned with the enhancement of convective heat transfer interaction between fluid and solid surface of helical coil. The detailed descriptions of material selection, nano fluid flow physics and heat transfer enhancement inside helical coil tube are very less in open literature. A state of art review indicates that further research work can be carried out by modifying the geometry of SCTHX and enhance factors of fluid property. The heat transfer can also be enhanced by polymer additives added in nano fluids, effect of super hydrophobic surfaces and fluid bubbles generation from roughened heating surface. Finally new ideas are presented in this paper to improve the heat transfer rate and material selection for low cost manufacturing with minimum size.