Helical Coiled Tube Research Articles

Numerical simulation of the heat transfer process of a coiled tube for viscous fluids

This study presents the results of a numerical simulation in a helical coiled tube for Newtonian and non-Newtonian fluids in laminar regime. As a practical contribution, the numerical simulations use non-Newtonian fluids, the rheological properties of which are experimentally measured. In both non-Newtonian fluids, at the helical section, the heat transfer rate was higher than that at the straight section. For the fruit juice, the heat transfer coefficient ( h w ) reached values of 1000 and 1350 W/m 2 K at the coil, which were 73% and 126% higher than in the straight section, for an Re g of 255 and 634, respectively. For the carboxyl methyl cellulose solution, these differences ranged between 76% ( Re g = 255) and 210% ( Re g = 634), reaching h w values at the coil of 1950 and 2700 W/m 2 K. In all non-Newtonian cases, fluid mixing was improved at the coil section. This influenced the viscosity variability along the coil, especially for the fruit juice, with a pronounced pseudoplastic behaviour (flow behaviour index of 0.5). This viscosity variation was more influenced by the strain rate than the viscosity change with temperature, as the fruit juice showed a moderate energy activation (8.2 kJ/mol). • High computational cost model used for helical coiled tube. • Numerical simulation of Newtonian fluids validated with experimental setup. • Good agreement obtained between numerical and experimental results. • Local Nusselt number increased at the coiled section up to 210%.

Flow-Induced Vibration and Heat Transfer Analysis for a Novel Hollow Heat Exchanger

A novel hollow shell-and-tube heat exchanger with helical elastic coiled tubes was designed to improve the overall heat transfer performance. Different numbers of helical baffles installed on the hollow helical elastic tubes (HHETs) heat exchanger were compared with the HHET heat exchanger without a baffle. The fluid–solid coupling method was provided to study the effects of the entrance velocity and baffle number on the performances of heat transfer and vibration-enhanced heat transfer. Based on the numerical results, the performances of vibration and heat transfer become more obvious by increasing the entrance velocity. Compared with the HHET heat exchanger without a baffle, adding a baffle or baffles on the HHET heat exchanger can remarkably make the fluid flow more consistent. Whereas a higher number of baffles can weaken the vibration and heat transfer performance of the novel heat exchange, the performance evaluation criteria of the HHET heat exchanger with one baffle, two baffles, and four baffles is improved by 2.04, 4.37, and 2.3%, respectively. It indicates that adding a baffle or baffles to the novel heat exchanger can effectively improve the overall thermal and hydraulic characteristics of the novel heat exchanger.

Recognition of gas-liquid flow regimes in helically coiled tube using wire-mesh sensor and KNN algorithm

• Flow patterns in helically coiled tube are classified by visual observation. • Void fraction for entire cross-section is measured by wire-mesh sensor. • k -Nearest Neighbors algorithm is utilized to identify flow patterns objectively. • Influence of centrifugal force and secondary flow on phase distribution and flow transition is revealed. Helically coiled tube (HCT) is used extensively in compact types of heat exchangers. Complete knowledge of gas-liquid flow behavior in HCT is essential in designing the heat transfer equipment involving phase change. Although the gas-liquid flow patterns in straight tubes have been widely studied, investigations on flow pattern recognition in HCT are still scarce. In this paper, based on the backlight imaging tomography and self-designed wire-mesh sensor, air-water experiments are carried out to study the characteristics of gas-liquid flow in a transparent HCT. Bubble, plug, slug, wavy and annular flow are observed, and their void fraction at the cross-section of the tube are measured and analyzed using the statistic parameters of time-trace, PDF and CPDF. Owing to the simplicity of implementation, the void fraction data are subsequently utilized along with the k -Nearest Neighbors algorithm (KNN algorithm) to identify the flow patterns objectively. Finally, a flow regime map is proposed and compared with the previous straight flow map and HCT map in the literatures. Accordingly, the influence of curvature-induced centrifugal force and secondary flow on the phase distribution and flow-regime transition is revealed in the present study.

Optimization and application of the concentric conductance probes in liquid film thickness measurement in a helically coiled tube

The liquid film distribution in the helically coiled tube (HCT) is affected by curvature-induced centrifugal force and gravity force, showing more complex characteristics than straight tubes. However, due to the limitation of the measurement technology, the relevant data on liquid film in HCT are still rare. In this paper, based on the time-multiplexed excitation-probing scheme, a type of non-intrusive concentric conductance probes (CCPs) is developed at first. After reporting the operation principle of CCPs, the numerical simulation of potential field distribution in CCPs is conducted, and the effects of electrode structure parameters and liquid film thickness on the performance of CCPs are then analyzed in detail. It is found that in a certain range, the larger the inner electrode and outer electrode diameter, the greater the signal penetration depth (i.e. the larger the measurement range of liquid film thickness). Finally, the spatio-temporal distribution of liquid film on the wall of the HCT is experimentally studied using the optimized CCPs. The results indicate that this probe can realize the high-frequency accurate capture of liquid film flow details such as the occurrence and evolution process of liquid film inversion and the fluctuation characteristics of liquid film in HCT. The wave frequency of the liquid film is demonstrated to be not consistent along the circumferential direction. Using Strouhal number and Lockhart–Martinelli parameter, the wave frequency correlation at the maximum film thickness in the state of film inversion in HCT is obtained.

Vibration-Enhanced Heat Transfer of Helical Tube with Different Number of Tubes

Based on a two-way fluid/solid coupling model, the heat transfer enhancement mechanism of a helical elastic coiled tube (HECT) by fluid-induced vibration (FIV) was numerically studied. The field synergy principle was used to compare and analyze the shell-side convective heat transfer of the HECT. The field synergy angle, Nusselt number, and comprehensive enhanced heat transfer performance were quantitatively studied from the overall and local perspectives. The influences of the Reynolds number and the number of tubes on heat transfer performance and vibration-enhanced heat transfer performance were analyzed. Numerical results show that the field synergy level and the oscillation relative velocity near the tube are two important factors for fluid-induced tube vibration to enhance heat transfer. The average Nusselt number of coiled tubes decreases when the number of tubes increases and increases when the Reynolds number increases. The comprehensive heat transfer enhancement capability of the heat exchanger with different numbers of tubes of 2, 4, and 8 gradually decreases as the number of tubes increases, and the average performance evaluation criteria of the heat exchanger are 1.043, 1.023, and 1.004, respectively, for the three typical cases. The tubes on the upper and lower sides have a better heat transfer enhancement effect by the FIV.

Numerical investigation of grooves effects on the thermal performance of helically grooved shell and coil tube heat exchanger

Heat exchangers are integral parts of important industrial units such as petrochemicals, medicine and power plants. Due to the importance of systems energy consumption, different modifications have been applied on heat exchangers in terms of size and structure. In this study, a novel heat exchanger with helically grooved annulus shell and helically coiled tube was investigated by numerical simulation. Helically grooves with the same pitch of the helical coil tube and different depth are created on the inner and outer wall of annulus shell to improve the thermal performance of heat exchanger. In the first section, thermal performance of the shell and coil heat exchanger with the helical grooves on its outer shell wall was compared with same but without helical grooves. At the second section, helically grooves created on both outer and inner wall of the annulus shell with different groove depths. The results showed that the heat exchanger with grooves on both inner and outer shell wall has better thermal performance up to 20% compared to the heat exchanger with grooves on only outer shell wall. The highest thermal performance achieves at lower flow rates and higher groove depths whereas the pressure drop did not increase significantly.

Numerical investigation of heat-transfer enhancement in helically coiled spiral grooved tube heat exchanger

Passive enhanced heat transfer technology considerably influences helically coiled tube (HCT) heat exchangers (HEs), which are typically used in nuclear power plants. Numerical investigations were performed to study the effects of various grooving methods and depths on the heat transfer characteristics of HCT HEs. The results revealed that grooving on the plain tube could enhance the comprehensive heat transfer performance and simultaneously increase the pressure drop of the fluid. The performance evaluation criterion (PEC) value of the helically coiled spiral grooved tube (HCSGT) HEs was 25% higher than the helically coiled plain tube (HCPT) HEs, whereas the PEC value of a helically coiled parallel grooved tube (HCPGT) HEs was 20% better than that of the HCPT HEs. Furthermore, the HCSGT HEs exhibited superior heat transfer enhancement ability. A comparison of the influences of various grooving depths on the heat transfer enhancement of HCSGT HEs revealed that the increase in the groove depth first increased the Nusselt number (Nu) and friction factor (f), followed by a subsequent decrease. The PEC value of the HCSGT HEs with 0.5 mm groove depth was observed to be maximal. Thus, grooved treatment can effectively improve the comprehensive heat transfer capacity of HEs.

Economic-effectiveness analysis of micro-fins helically coiled tube heat exchanger and optimization based on multi-objective differential evolution algorithm

In this study, the heat transfer characteristics and hydrodynamics of a new type of micro-fin helically coiled tube (MF-HCT) are modelled and compared with those of typical smooth helically coiled tubes (HCTs). Calculation models are developed and compared for both helically coiled tube heat exchangers (HCTHEXs) and micro-fin helically coiled tube heat exchangers (MF-HCTHEXs). The total cost and effectiveness are selected as the objective functions, and five independent structural parameters are selected for each type of HCTHEX. Subsequently, an adaptive multi-objective optimization differential evolution algorithm is implemented for both of them, and the results are compared. The results indicate that, for Reynolds numbers smaller than 22,000, the MF-HCT performs better than the HCT, and the total cost of the MF-HCTHEX is lower than that of the HCTHEX under the same effectiveness. The difference between their total cost increases with their effectiveness and can be up to 79,000 €. For both the HCTHEX and MF-HCTHEX, when the effectiveness is less than 0.9, it is more appropriate to select a larger winding angle, layer spacing, and tube spacing.

An Empirical Analysis of Heat Expulsion and Pressure Drop Attribute in Helical Coil Tube Using Nanomaterials

Water nanofluids were examined in a horizontal helical coil tube with constant temperature limitations for Dean values between 1000 and 10,000 to determine the rate of thermal radiation transmission and pressure drop characteristics. When conducting the tests, a variety of Al2O3 water nanofluid requirements were used, including varying mass flows, heat exchange rates for various nanoparticle volume concentrations, and changes in coil‐side drop in pressure versus coil‐side Dean number. Since nanoparticles have enhanced heat capacity, nanoparticles are developing as a transitional beginning of heat transfer fluids with significant potential in thermal management applications. Many applications require nanofluids to be used as heat transfer fluids; thus, scientists are concentrating their efforts on these fluids. The Reynolds values on the coil and shell were in the 1000 to 7000 range on either side of the wire. This paper discusses the impact of particle volume density on shell‐side flow temperatures, heat expulsion rate, and thermal conduction. The result shows that the average heat transfer rises by 13% and 17% when nanoparticle volume fraction percentage density is 0.1%, 0.2%, and 0.3 percent. The results demonstrate that reducing the mass flow by an increase in particle volume density, pipe diameter, and coil radius improves heat exchanger performance. The efficiency of the model is enhanced by increasing the diameter of the tube while simultaneously decreasing the diameter of the coil.

Plant system study of France–Japan common concept on Sodium-cooled Fast Reactor

This paper provides an overview of plant system studies to establish a common technical view for Sodium-cooled Fast Reactor (SFR) concept (the common SFR concept) between France and Japan based on ASTRID 600 and the new concept with downsized output (ASTRID150). One of important issues on a reactor structure design is to enhance seismic resistance to be tolerable against strong earthquake such that postulated in Japan. A concept of High Frequency Design (HFD) is shared, in which the natural frequency of the reactor structure should be higher than that of peak acceleration of vertical floor seismic response with a horizontal seismic isolation system. The design options related to HFD have been examined and design recommendations are established. ASTRID 600 adopted a gas power conversion system to strictly eliminate the chemical reaction risks due to the proximity of sodium and water in the steam generator units. On the other hand, a steam generator (SG) is thought to be a concept with high technical readiness level and is a reference option in Japan and a backup option in France. Then, design comparison of the SG with single-walled helical coil tubes was mainly conducted in this study from the viewpoint of safety and so on. A common concept of a decay heat removal system is discussed to achieve practical elimination of loss of decay heat removal function. A fuel handling system studies are performed to eliminate and ex-vessel storage of spent fuels in sodium to reduce a construction cost. An adequate confinement system is investigated to achieve practical mitigation of large radiological release to the environment even under the condition of core destructive accident.

Experimental Investigation on Heat Transfer and Pressure Drops Characteristics of the Helically Coiled Tubes Heat Exchanger with Grooves

Experimental Investigation on Heat Transfer and Pressure Drops Characteristics of the Helically Coiled Tubes Heat Exchanger with Grooves

Experimental analysis of copper coated helical coiled tube heat exchanger using nanofluid and water

Many studies focused on improving heat transfer by increasing the electrical, industrial, and transportation processes that are required to achieve a higher heat transfer rate. In general, there are two types of heat transfer enhancement techniques: active and passive. External power inputs such as pulse flow, vibratory force, and a magnetic field are used in the active approach. The heat transfer rate is increased upto 20 % in the passive technique by adding more devices or changing the heat transfer surface. The nanoparticle suspension is a heat transfer improvement approach in this study. An experimental investigation used Al2O3-water nanofluid in the counter flow heat exchanger to improve heat transfer in the range of 20 %. Experiments with varied volume concentrations 0.1 and 0.15 and mass flow rates of nanofluid were carried out. The arrangements are utilized to assess the situation. The temperature fluctuations were measured using the setups and the acquired values are compared to prior nanofluid performance results, and the result demonstrates that the heat transfer rate has risen upto 20 %. It also shows that the Al2O3-water nanofluid performed better than water.

Influence of Helix Angle on Flow and Heat Transfer Characteristics of Lead-Bismuth Flow in Helical-Coiled Tube Bundles

Influence of Helix Angle on Flow and Heat Transfer Characteristics of Lead-Bismuth Flow in Helical-Coiled Tube Bundles

Numerical investigation of hydraulic and heat transfer characteristics of two-phase ice slurry in helically coiled tubes

The helically coiled tubes (HCT) with ice slurry as the cooling medium plays an essential role in reducing the energy consumption of heating, ventilation, air-conditioning, and refrigeration (HVAC&R) systems. However, the hydraulic and heat transfer behavior of ice slurry in HCT has not been fully understood. Therefore, the thermo-fluidic characteristics of ice slurry in HCT are numerically investigated in this study based on Eulerian-Eulerian model. The research revealed that the velocity near the outer wall is larger than that near the inner wall due to the presence of secondary flow, and the high ice concentration region shifts towards the inner wall. As increasing the inlet ice volume fraction and velocity, the ice concentration distribution in vertical radius direction of the cross-section gradually tends to be uniform. The pressure drop increases with increase of the coil radius, while the coil pitch has little influence on the pressure drop. During heat transfer process, the secondary flow causes the ice volume fraction near the inner wall to decline faster than that near the outer wall. At the entrance section, the local heat transfer coefficient decreases sharply from 9320.05 W/(m2·K) to 3002.11 W/(m2·K) and then increases slowly along the flow direction. With increasing Reynolds number, the local heat transfer coefficient enhances linearly. The increase of ice particle diameter and coil radius leads to the enhanced local heat transfer coefficient. In contrast, increasing coil pitch does not bring a significant change of local heat transfer coefficient. In addition, the correlation of local Nusselt number and flow resistance coefficient is proposed.

Experimental investigation on laminar heat transfer performances of RP-3 at supercritical pressure in the helical coiled tube

The laminar heat transfer characteristics of RP-3 in the liquid phase and supercritical phase were experimentally studied at 5 MPa in the helical coiled tubes. The influences of secondary flow and buoyancy on heat transfer were analyzed under different heat fluxes, mass flow rates and helical diameters. The Nu increased with the increase of curvature. When the heat flux was 150 kW/m2, the mass flow rate was 1 g/s, and the wall temperature was higher than the critical temperature, the Re, Nu, and centrifugal Richardson number increased exponentially along the tube length. By introducing the combined parameters of density, specific heat and Grashof number, the correlations of RP-3 were established in the helical coiled tube under supercritical laminar mixed convection. In addition, the experimental data under different fuels, helical diameters and tube diameters were used to verify the above correlation.

Multi-objective optimization of micro-fin helical coil tubes based on the prediction of artificial neural networks and entropy generation theory

The heat transfer, flow resistance and entropy generation characteristics of micro-fin helical coil tubes (MFHCTs) are investigated numerically. MFHCT with different fin numbers (2≤N≤6), coil pitches (150mm≤P≤450mm), coil diameters (600mm≤D≤1200mm) and Reynolds numbers (10945≤Re≤30845) are examined. The effects of these geometric parameters on the Nusselt number (Nu), friction factor (f) and improved entropy generation number (Ns′) are discussed. The performance of MFHCT is then compared to that of a smooth helical coil tube (SHCT). The results show that MFCHT always performs better than SHCT, especially in the lower Reynolds number region. Moreover, artificial neural networks (ANNs) are established to predict Nu, f and Ns′, which are trained by simulation data. This model fits the simulation results better than the multiple linear regression, and the maximum error is no greater than 8%. With the prediction of the network, the micro-fin helical coil tubes are optimized by the entropy minimization method and NSGA-III algorithm. Through optimization, the distribution of design variables is examined. The results demonstrate that a higher Reynolds number and a larger coil diameter and coil pitch lead to a better performance. Additionally, the optimal Pareto points can be utilized to guide the design and operation conditions of micro-fin helical coil tubes.

Implementation of novel triangular fins at a helical coil heat exchanger

Various techniques have been utilized to improve the performance of heat exchangers. In this study, multiple passive enhancement techniques have been applied. Triangular fins have been fabricated on the outside surface of the longitudinal helical heat exchanger. The performance of the new heat exchanger has been investigated experimentally and mathematically. In counterflow, hot water flowed inside the helical tube at 60 ᵒC while cold water entered the shell at 30 ᵒC. A triangle copper fin with 1 cm height, 2 cm base length, and 0.3 cm thickness with 4 cm pitch distance was welded at the external surface of the helical Copper coil tube. Along the helically coiled tube, 123 fins have been welded on the outside surface with 25 overall coil turns heat exchangers.The results showed a good enhancement ratio compared to the unfinned helical heat exchanger. The thermal performance factor showed an improvement of more than 10% compared to plain tube coils with an increase in the effectiveness of 11%. The improvement in the Nusselt number was 16.5%. These results confirmed that the fins addition on the helical coil heat exchanger modified and improved the helical heat exchanger and supported the industrial design with better performance.

Estimation of local heat flux with CFD and enhanced conjugate gradient method for laminar and turbulent flow in a helical coil tube heat exchanger

Estimation of local heat flux with CFD and enhanced conjugate gradient method for laminar and turbulent flow in a helical coil tube heat exchanger

Estimation of local heat flux for turbulent flow in a helical coil tube by conjugate gradient method

Estimation of local heat flux is challenging in a helical coil tube heat exchanger due to the complex flow field developed by tube curvature. The heat flux has uneven distribution in the angular direction of the tube cross-section. The current research aims to estimate the local heat flux at the fluid-solid interface for the turbulent flow of water in a helical coil tube by solving the inverse heat conduction problem (IHCP). Conjugate gradient method (CGM) with an adjoint problem is used as an inverse algorithm. First, the commercial CFD software ANSYS FLUENT is used for solving the governing equations of continuity, momentum, and energy for turbulent flow to obtain the heat flux at the fluid-solid interface. This heat flux is used to determine the temperature distribution at the outer surface of the tube. The heat flux is then considered unknown and it is estimated by CGM algorithm with the developed in-house code in MATLAB. The result shows that the estimation of heat flux by CGM is very accurate.

Axial dispersion in curved channels in the presence of pulsating flow

A narrow residence time distribution (RTD) is desirable in several chemical engineering processes. However, in systems operating at low Reynolds number, axial dispersion can be significant. To lower it, we utilised two mixing approaches: secondary flow achieved with curved geometries and oscillatory variation of the flow rate. We investigated their combined effect on axial dispersion in millifluidic channels with three geometries: straight tube, helically coiled tube (HCT) and coiled flow inverter (CFI). We studied the influence on axial dispersion of two key parameters of pulsating flows: amplitude and frequency of pulsation; in dimensionless form, these are expressed via the amplitude ratio and Strouhal number, respectively. For unsteady flow, we performed numerical simulations to characterise mixing. The results indicate that pulsation enhances radial mixing significantly. Our experimental studies show that axial dispersion is lower in the presence of pulsation, and increasing amplitude and/or frequency has a positive effect. For the same amplitude ratio and Strouhal number, axial dispersion decreases more in the CFIs than in the HCTs. Comparing two extremes, the straight capillary with steady flow (no RTD enhancement) and the CFI with pulsation (lowest axial dispersion achieved in our work), we observed a 10-fold reduction in the axial dispersion number.