Helical Tube Research Articles

Experimental and Numerical Investigations on the Heat Transfer of a Helical Coil Heat Exchanger Utilized α-Al2 O3 nanofluid

This study focused on investigating the impact of α-Al2O3 nanoparticles on heat transfer in shell and helical coiled tube heat exchangers. The objective was to analyze the influence of various geometrical characteristics, specifically the coil pitch, on the Nusselt numbers of both sides using a combination of numerical simulations and experimental methods. The working fluid for the hot side was water. The research encompassed an examination of the friction factor for three different coils, exploring the effects of pitch spacing on heat transfer, and assessing the influence of nanoparticles on heat transfer on the inner side of the coil. The findings of the current work indicated significant improvements in heat transfer parameters when employing water-α-Al2O3 nanoparticles as the cold fluid. Comparing this heat exchanger to one without the inclusion of α-Al2O3 nanoparticles revealed a remarkable efficiency enhancement of 7.68 percent. This increase strongly suggests a notable acceleration in the rate of heat transmission within the heat exchanger. Overall, this study provides valuable insights into the utilization of α-Al2O3 nanoparticles in enhancing heat transfer in shell and helical coiled tube heat exchangers. The results highlight the potential benefits of incorporating nanoparticles into such systems, leading to improved performance and more efficient heat exchange processes.

Experimental Study on Heat Transfer Enhancement of Modified CuO Nanofluid in Helical Grooved Tube

This study proposes a novel technology to enhance heat transfer by combining nanofluid and helical grooved tubes. The researchers used a two-step method to obtain a stable modified CuO nanofluid. They then constructed an experimental setup to investigate the single-phase heat transfer of the nanofluid in a helical grooved tube, and compared its performance to traditional methods under varying volume fractions and Reynolds numbers. The experimental results indicate that the use of nanofluid in the helical grooved tube significantly improves the convective heat transfer coefficient. Furthermore, the heat transfer coefficient increases gradually with the addition of nanoparticle volume fraction and Reynolds number. The helical grooved tube’s internal structure causes local turbulence at low Reynolds numbers, intensifying the nano-scale eddies and turbulence inside the nanofluid, enhancing fluid mixing and thermal diffusion rates, and thus improving the heat transfer efficiency.

Numerical investigation and artificial brain structure-based modeling to predict the heat transfer of hybrid Ag/Au nanofluid in a helical tube heat exchanger

In recent years, due to the low thermal coefficients of common fluids and the increase in size and cost of heat exchangers, technologies for improving heat transfer and reducing dimensions have been developed and widely used in industries such as refrigeration, cooling of processing cells, chemical industries, and more. Previously, increasing heat exchange capacity in heat exchangers was achieved by altering parameters such as boundary conditions, flow geometry, heat exchanger geometry, or changing the type of fluid. Additionally, apart from the use of nanofluids, various other operational methods can be employed to improve the thermal performance of heat exchangers. Accordingly, considering the combination of the aforementioned innovative techniques, this study presents the modeling of flow and heat transfer inside helically coiled tube heat exchangers under the flow of nanofluids containing nickel, gold, silver, and gold/silver hybrid nanoparticles using numerical and artificial intelligence methods. In this study, the effect of variations in the inner diameter of the coiled tube and the volume fraction of nanoparticles was examined. The results showed that increasing the inner diameter and volume fraction of nanoparticles leads to an increase in heat transfer coefficient and Nusselt number, while the friction factor decreases with an increase in Reynolds number and increases with an increase in diameter and volume fraction. Finally, the accuracy and validity of the model were evaluated using statistical parameters and experimental results, which showed a 99.9% level of agreement between the predicted and experimental outcomes.

Numerical assessment of the effect of tube geometries on the performance of phase change material (PCM) integrated solar receiver for dish-micro gas turbine systems

The temperature distribution and melting/solidification behavior of the Phase Change Material (PCM) depends largely on the arrangement of working fluid tubes in the PCM volume. A well-designed tube arrangement in the PCM results in more effective heat transfer and thermal storage. The authors previously presented a concept of Phase Change Material (PCM) integrated solar receiver for short-term thermal storage in the dish-micro gas turbine system. This solar receiver has a cylindrical shape structure filled with PCM, twelve tubes of working fluid (air) immersed in the PCM, and a conical cavity on its front surface. For such a compact thermal storage component, energy storage in the PCM and the charging/discharging rate largely depend on the arrangement of working fluid tubes in the PCM volume. The design of tubes should allow the proper distribution and release of heat in the PCM during the charging and discharging phases, respectively. In this study, the melting behavior and heat storage capacity of the PCM integrated solar receiver were analyzed by considering three different arrangements of the working fluid tubes with two cavity structures; a solar receiver with conical shaped cavity and 172° bend tubes, solar receiver with cylindrical shaped cavity and U-shaped tubes and solar receiver with conical shaped cavity with double helical tubes. The 3D numerical analysis were conducted by using Ansys Fluent 2022R1 to evaluate the effect of tube arrangements on the temperature distribution in PCM volume, melting behavior of PCM and the total storage capacity of the component. Temperature distribution on the cavity walls and heat losses were also considered. The transient simulations were performed using k−ε turbulent model with S2S radiation model and ray-tracing model. The results showed a significant effect of tube geometries on the PCM melting behavior inside the solar receiver. It was found that, in the solar receiver with conical shaped cavity and 172° bend tubes, the tubes arrangement is more suitable throughout the PCM volume and represents a more uniform temperature and melting behavior. Moreover, the pressure drop was much higher in the double helical tubes compared to other bend tubes.

Comparative Experimental Study on Effect of Copper Wire Helical Wound Steel Tube with 2.5” Full Length Insert on Performance of Double Pipe Steel Tube Heat Exchanger

Abstract: A comparative experimental study was conducted to explore the hydrothermal behavior of a double tube heat exchanger with copper wire helical wound steel tubes and plane steel tubes with and without twisted tap inserts of pitch length 2.5 inches. In comparison to helical tubes, corrugated tubes, and many other more compact tube type heat exchangers, straight tube heat exchangers offer advantages since the construction of the heat exchanger tubes is easier. In the current work, the fluid-to-fluid heat exchange is considered, with a flow rate ranging from 15 to 75 liters/hour. Constant wall temperature or constant heat flux ideas are used in the majority of investigations on heat transfer coefficients. The efficiency, overall heat transfer coefficient, and impact of hot water flow rate with constant cold water flow rate for straight steel tube and copper wire helical wrapped steel tube heat exchangers in parallel flow and counter flow configurations were investigated and compared. Utilizing a 2.5" full length clockwise twisted tape insert, both layouts were created. The measurements were carried out in a constant state. When the hot water flow rate is increased while maintaining the cold water flow rate constant, the efficiency of the heat exchanger drops for both the straight steel and the copper wire helical wound steel tube. Compared to a plane steel tube heat exchanger, the copper wire helical wound steel tube heat exchanger has a better efficiency. The test findings demonstrate that inserting inserts causes pressure drop. With 2.5" clockwise twisted tape inserts wrapped in helical copper wire, steel tube was able to transmit heat more quickly than other arrangements.

Investigating the effect of together usage of circular depressions and different Nano-particles for thermal performance improvement of coiled tube

Present paper is a numerical simulation which probes the effect of Nano-particles and circular depressions on performance of helical tube. The pitch of depressions and the type and the volume fraction of Nano-particles were considered as variants of the present investigation. Nano particles included, Cu and Al2O3 particles with volume fraction of 2,3 and 4 percent. Flow was considered to be in turbulent regime and the Dean number was within the range of 2600–7000. Tube was put under constant heat flux of 2500 W/m2. Thermal and frictional behavior of helical tube together with performance index of helical tube in case of having circular corrugation and Nano-particles were evaluated. It was found that the application of corrugations changes flow structure and leads in heat transfer augmentation. Furthermore, it was revealed that circular corrugations increase the heat transfer rate by up to 98%. Besides, application of Al2O3 and Cu Nano particles together with corrugations increases heat transfer rate up to 104% and 108%, respectively. It was found that maximum performance index was about 1.17 which was observed for the tube with pure water and circular corrugations. Also, it was found that application of circular corrugation is more beneficial within Dean number of 2600 and 5800.

Numerical Study on Thermo-Hydraulic Performance of Enhanced Tube With Crossed Helical Dimples

Abstract A numerical investigation was performed to study the thermo-hydraulic performance in an enhanced tube with crossed helical dimples. The simulations were carried out in the Reynolds number range of 5000–30,000 in crossed helical dimple tube of a period length with a constant wall temperature of 350 K. The thermal enhancement, friction factor, and performance evaluation criteria (PEC) were the primary focus of the present work. Moreover, geometric parameters such as spiral pitch, transverse length, and dimple depth were investigated for their effects on thermo-hydraulic performance. The results revealed that the shape of crossed helical dimple exerts positive effects on the heat transfer enhancement. This unique shape generated intensive transverse flow and induced a higher transverse velocity, leading to heat transfer enhancement. Therefore, the synthesized heat transfer performance was increased by 150–225% over that of the smooth tube. Furthermore, the heat transfer enhancement and friction factors increased with increasing dimple depth and declining spiral pitch and transverse length. Within the scope of this study, the maximum PEC = 2.25 was observed for Re = 30,000, P = 30 mm, L = 11.064 mm, and H = 3 mm.

Numerical study on circumferential nonuniform characteristics of flow and heat transfer on double-side heating once-through steam generator with helical tubes

In this paper, double-side heating once-through steam generator with helical tubes as the prototype to establish its two-fluid Euler numerical model and verified through the Becker experiment. The results show that the two-phase fluid in the crescent-shaped passage moves spirally, and the two-phase flow velocity fluctuates along the Z-axis with a slip ratio greater than 1.0. The spiral motion results in greater centrifugal strength of the vapor phase than the liquid phase, the high centrifugal strength of the vapor phase results in a higher vapor phase volume fraction on the outer wall, which makes the position of the beginning of dryout and the position of the total dryout of the outer wall is advanced. The liquid phase volume fraction is highest on the narrow side inner wall and lowest on the wide side inner wall, so the inner wall dryout appears first and total dryout last. The circumferential non-uniformity results in a spiral band of vapor content and temperature distribution.

Study on physical prediction model of liquid film development and dry out point in helical tube

Helical tubes are widely used in nuclear plants, heat recovery process, refrigeration technology, etc. It is obtained the helical tubes dry out point prediction model in accordance with the experimental conditions by numerical simulation. The article is based on the physical model of the liquid membrane in the helical tube before dry out happened, establishing the analytical process of liquid film development in helical tube. The physical mechanism, thermo-hydraulic parameters that affect liquid film crushing are analyzed. The dry out point of helical tubes is predicted based on the experimental data. The result shows that the geometrical, thermo-hydraulic parameters of helical tube will affect the occurrence of the dry out point, the development process of liquid film before evaporation of spiral tube is obtained. The prediction model of dry out point is fitted to experimental data and the predicted results of evaporation point can be used to optimize during the engineering design.

Numerical investigation about radius ratio effect of helical tubes in the heat exchanger

Enormous research has been conducted on the efficient flow and heat transfer performance of helical tube. The helical tube with a large radius ratio (ratio of curvature radius to tube radius) could not be installed when the available space is limited, and the differences in their thermal hydraulic characteristics caused by different radius ratios are rarely studied. The present study aims to use a numerical method to quantify and visualize the radius ratio effect and to determine its mechanism. The result shows that the fitness curve of the theoretical flow field and the numerical result are bell-shaped. Helical tubes with lower radius ratio have a significant improvement in flow and heat transfer performance, while higher radius ratio brings lower circumferential nonuniformity and more heat transfer area. The torsional effect or bending effect is the dominant effect when the radius ratio is low or high, respectively. The promotion of vortex generation is the mechanism of the radius ratio effect. The current study could be used as a reference for the engineering applications of helical tubes, as well as to support further research on the basic mechanism of heat and mass transfer in helical tubes.

Two-tube heat exchanger with variable groove angle on the inner pipe surface: Experimental study

Flow patterns in fluids affected by a grooved surface tube are different from a smooth pipe. The importance of a compact and optimal design of heat exchangers has led to extensive studies in the past focused on geometry (circular, square, etc.), depth, and distance between grooves. In terms of novelty, the present work studies the influence of the groove angle of the inner tube surface on fluid flow and thermal performance. The study method was experimental, and Wilson plots were used to determine the heat transfer coefficient. Three test sections, including smooth pipe and helical grooves, were made. Experiments were performed for the base case (smooth pipe) within the Reynolds number range of 9000–18000 and a constant inlet temperature of 20 °C for cold water. The hot water was kept constant in the Reynolds number range of 2700, and the inlet temperature was 50 °C. Heat transfer, friction factor, effectiveness, and the number of thermal units were evaluated as significant features in heat exchanger performance analysis. The results were presented in two arrangements of parallel and counter fluid flow for helical groove tubes, in comparison, with a smooth pipe. In low Reynolds, geometry and groove angle affect heat transfer more than flow rate. Heat transfer enhances as the groove angle becomes more vertical to the flow. Per 30° change in the slope of the spiral groove from parallel to perpendicular to the fluid flow, the Nusselt number and the friction factor increase by 25–32% and 8–9%, respectively.

Experimental investigation, development of machine learning model and optimization studies of a metal hydride reactor with embedded helical cooling tube

Metal hydride hydrogen storage systems are gaining popularity due to their advantages and suitability for various applications in variety of fields. In this study, a metal hydride reactor using LaNi5 as metal hydride and using water as heat transfer fluid flowing through embedded helical tube was fabricated and experimentally studied. The aim of this study is to experimentally investigate the effect of internal heat transfer arrangement on the absorption and desorption of hydrogen in a metal hydride system. The effect of mass flow rate and temperature of heat transfer fluid, effect of hydrogen supply pressure on the rate of hydrogen absorption and desorption was investigated. It was found that the increase in the hydrogen supply pressure, increase in mass flow rate and decrease in the temperature of heat transfer fluid, results in faster hydrogen absorption rate. Similarly, the increase in mass flow rate and the temperature of heat transfer fluid results in faster hydrogen desorption rate. It was also found out that maximum hydrogen absorbed inside metal hydride reactor was around 34.5 g which corresponds to a gravimetric capacity of 1.34 wt%. Further based on the experimental data various machine learning models were developed and tested and then these models were used for performance prediction. It was found that tree-based regression machine learning models are better compared to other models. Such models can thus be used for prediction of rate of hydrogen absorbed or desorbed and metal hydride bed temperature for different parametric values without doing detailed experimental and numerical trial. Finally, the brute force approach is used to optimize the system for three different applications. The optimization techniques help to fix the value of parameters for particular application and hence save multiple experimental run of absorption and desorption. This is a novel work in the field of using machine learning for modelling and optimizing the metal hydride-based reactor. Use of such tools can save lot of computational time, efforts and experimental resources.

Investigation of flow and heat transfer characteristics of supercritical argon in conical Hampson heat exchangers for a J-T cryocooler

The Hampson-type heat exchanger is critical for the rapid cooling of a conical J-T cryocooler, and its internal flow and heat transfer characteristics directly affect the performance of the conical cryocooler. The flow and heat transfer characteristics of supercritical argon are studied using a numerical model of a conical helical tube in this work. The simulated results show that supercritical argon flow in the conical helical tube is mainly influenced by the combined effect of variable thermophysical properties and the secondary flow produced by centrifugal force. The buoyancy has little impact on heat transfer. The heat transfer coefficient reaches its maximum at the pseudo-critical region. A more significant heat transfer coefficient and faster heat exchanger cooling rate can be achieved by increasing the mass flow rate and maintaining the fluid in the tube close to the pseudo-critical region. At a cone angle of 50°, the maximum total heat exchange quantity is observed. With a greater temperature drop per unit length, a stronger heat transfer effect can be achieved close to the outlet of the tube. Based on the numerical analyses, a new correlation for heat transfer is proposed.

Condensation heat transfer and correlation analysis in helical tube of mixed carbon-hydro refrigerant

The heat transfer coefficient of the mixed carbon-hydrogen refrigerant (hmix) in a helically tube has been confirmed as the core parameter related to natural gas liquefaction. Moreover, an experimental system of the two-phase flow in the helical pipe was designed, and a simulation model was built to analyze the changing law of hmix. The effects of operating parameters (operating pressure (2–4 MP), mass flux (200–600 kg/(m2·s), and vapor quality (0–1)) and structural parameters (spiral diameter (1–3 m), helix angle (4–14°), and inner diameter (8–12 mm)) on hmix of methane/ethane/propane in the spiral tube were examined. Subsequently, 11 heat transfer correlations were analyzed and then compared. As indicated by the comparison results, the correlations of Boyko were the most accurate among the above-mentioned correlations, laying a basis for this type of hmix. Furthermore, the mean absolute relative deviation and determination coefficient of Boyko's correlation were obtained as 20.30% and 0.48, respectively.

A comparative study of plain and enhanced helical microfin evaporator tube with drift flux-based entropy generation model for R32 and R410A refrigerants

In the present paper, a comparative study is carried out to assess the relative thermodynamic performance of plain and helical microfin evaporator tubes with two new emergent refrigerants, R32 and R410A. An entropy generation analysis is performed based on the drift flux model for two-phase forced convective boiling flow, and the comparison of the enhanced tube to the plain one is done quantitatively. A critical value of relevant parameters, i.e., mass flux, tube diameter, length, heat flux, inlet quality, and operating pressure, are identified, below or above which the enhanced tube is observed to be thermodynamically more favourable than the plain tube. The study reveals that by increasing the tube diameter from 8 mm to 14 mm, the critical mass flux increases from 335 kg/m2s to 495 kg/m2s for R32 and 394 kg/m2s to 565 kg/m2s for R410A, respectively, below which the enhanced tube performs better. The helical microfin tube exhibits a better performance below a critical mass flux from 412 kg/m2s to 374 kg/m2s for R32 and 492 kg/m2s to 443 kg/m2s for R410A when tube length increases from 1 m to 5 m. The critical inlet quality, below which the enhanced tube is observed to be superior, shifts to a lower value (0.29 to 0.16 for R32 and 0.44 to 0.26 for R410A), increasing the mass flux from 400 kg/m2s to 500 kg/m2s. However, the enhanced tube shows a better performance above a critical operating pressure, which increases from 11.4 bar to 16.9 bar for R32 and 9.3 bar to 13.4 bar for R410A, with increasing the mass flux from 400 kg/m2s to 500 kg/m2s. The enhanced tube performs better below a critical mass flux which increases from 336 kg/m2s to 461 kg/m2s for R32 and 399 kg/m2s to 489 kg/m2s for R410A when the heat flux is increased from 8 kW/m2 to 15 kW/m2. The overall parametric study with two emergent refrigerants enables one for effective selection of the helical microfin evaporator tube for a suitable range of relevant parameters.

In situ Growth Transition Towards Helical Crystals of Achiral Molecules

The synthesis of chiral crystals such as helical crystals is important due to their chirality‐dependent applications in various fields. Since chiral crystals of achiral molecules are getting more attention, it is important to establish synthetic strategies for helical crystals of achiral molecules. Quite surprisingly, there are numerous examples of helical crystals of achiral molecules, although they are mostly obtained without specific synthetic strategies. Herein, it is proposed that Eshelby twist can be applied to noncovalent molecular crystals by introducing screw dislocations and demonstrates a successful synthesis of helical tube crystals of achiral titanyl phthalocyanine by vapor‐phase crystal growth. The dislocations form where interfaces are created via growth transition from wire growth to tube growth upon growth temperature change. The screw dislocation is confirmed by Burgers vector analysis using transmission electron microscopy. The screw dislocation induces crystal twisting along the growth direction to dissipate the strain applied around the dislocation. The diffraction peak broadening of the (200) and (002) planes confirms the nonuniform strain, i.e., twisting force. This work offers a new approach for the synthesis of helical crystals from achiral molecules.

Numerical investigation on the thermal load heterogeneity of multi-assembly helical coil steam generator in high temperature gas-cooled reactor

The thermal load heterogeneity will lead to inhomogeneous local heat flux and thermal stress, extremely detrimental to the operational stability of heat exchangers with multi-assembly structure. In this paper, a full-scale analysis method for the helical coil steam generator in industry was developed and implemented. The validation was performed against flow boiling heat transfer experiment of helical tube. The simulation of single assembly and full-scale helical coil steam generator in high temperature gas-cooled reactor was performed, and the distributions of thermal-hydraulic parameters in heat exchange region were obtained. The results show that the nonuniform helium flow distribution with the inhomogeneous factor Dm value of 34.83% has a significant influence on the heat transfer characteristics. The peak heat transfer power of central assembly increases by 33.76% against design condition, introducing large thermal load heterogeneity with the inhomogeneous factor Dp value of 30.45%, even threating the structural integrity of helical tube in long-term operation circumstances. The structural elements design in the superior compartment should be optimized to increase the helium mass flow rate of the assemblies below the nozzle and behind the helium baffle, improving flow distribution uniformity and reducing the peak value of local heat flux and thermal stress.

Heat transfer evaluation of liquid lead-bismuth eutectic cross flow tube bundle: Experimental part

Helical coil once-through tube steam generator (HCOTSG) is an excellent form of heat exchanger. HCOTSG is adopted in various industries, such as Lead-bismuth Fast Reactor (LFR). The flow and heat transfer in the shell side of HCOTSG are important for its design and optimization. It is of great significance to carry out relevant experiments to obtain empirical correlations. In this paper, experimental study on the lead-bismuth eutectic (LBE) cross flow around the tube bundle is carried out to investigate the thermal-hydraulic characteristics based on geometric approximation of local region. Three test sections with different inclination angles of 0°, 4°, 8° are adopted in the experiments with Peclect number (Pe) up to 350. The experimental sections are uniformly heated with heat flux ranging from 20 to 100 kW/m2. The heat transfer characteristic of LBE cross flow around inclined tube bundle is obtained, considering the effects of inclination angle of the test section. The heat transfer correlation of LBE cross flow around inclined tube bundle is proposed for the first time. By comparing the data of the experiments, the results are all within the error range of 10%. The correlation is appropriate for the program development of LBE HCOTSG. This study can provide essential experimental data for the design and code development of LBE HCOTSG.

Chirality induced spin selectivity: A classical spin-off.

We demonstrate that angular momentum selectivity of particles traversing chiral environments is not limited to the quantum regime and can be realized in classical scenarios also. In our classical variant, the electron spin, which is central to the quantum chirality induced spin selectivity (CISS) effect, is replaced by the self-rotation of a finite-volume body. The latter is coupled to the center of mass orbital motion of the body through a helical tube via wall friction that acts as a dissipative spin-orbit coupling term. As a specific example, we study C60 molecules that are initially spinning in opposite senses and investigate the effect of various external control parameters on their spatial separation when driven through a rigid helical channel. We highlight resemblances and inherent differences between the quantum CISS effect and its classical variant and discuss the potential of the latter to formulate a new paradigm for enantio-separation.

Heat transfer evaluation of liquid lead‑bismuth eutectic cross flow tube bundle: Numerical simulation part

LBE HCOTSG, which combines the benefits of lead‑bismuth eutectic (LBE) and helical coil once-through tube steam generator (HCOTSG), has the potential to be an excellent heat exchanger choice. Given the similarity of the structure, the analysis of cross/oblique bundle flow heat transfer can help reveal the heat transfer characteristics of the HCOTSG shell side. In this paper, a numerical method for LBE in cross/oblique bundle flow is proposed. Based on the validated method, the application range of the correlation on the flow of the LBE cross/oblique bundle obtained from experiments is broadened based on the numerical simulation work. The influence of tube geometric arrangement in the bundle is also taken into account, including the inclination angle (θ), Smin /d, and various staggered arrangements. The difference between numerical simulation results and experimental data is less than 15%. For LBE cross/oblique bundle flow, the extended correlation taking geometric parameters into account also has good applicability. The alternating inclination angle arrangement at an angle of 8° can greatly enhance heat transmission efficacy by up to 33%. The impact of geometric arrangement is estimated in relation to local temperature. This work provides a correlation for the flow of the LBE cross/oblique bundle that is more broadly applicable. Furthermore, this work will significantly benefit the design optimization and program development of LBE HCOTSG or other innovative heat exchangers with cross flow of LBE.